TECHNICAL FIELD

[0001] The present disclosure relates to catalyst compositions for oxidative coupling of methane (OCM), more specifically catalyst compositions for OCM based on oxides of rare earth elements and Mn/Na ₂ WO ₄ , and methods of making and using same.

BACKGROUND

[0002] Hydrocarbons, and specifically olefins such as ethylene, are typically building blocks used to produce a wide range of products, for example, break-resistant containers and packaging materials. Currently, for industrial scale applications, ethylene is produced by heating natural gas condensates and petroleum distillates, which include ethane and higher hydrocarbons, and the produced ethylene is separated from a product mixture by using gas separation processes.

[0003] Oxidative coupling of the methane (OCM) has been the target of intense scientific and commercial interest for more than thirty years due to the tremendous potential of such technology to reduce costs, energy, and environmental emissions in the production of ethylene (C ₂ H ₄ ). As an overall reaction, in the OCM, methane (CH ₄ ) and oxygen (O ₂ ) react exothermically over a catalyst to form C ₂ H ₄ , water (H ₂ O) and heat.

[0004] Ethylene can be produced by OCM as represented by Equations (I) and (II):

2CH O C H 2H O ∆H 67 k l/ l (I)

[0005] Oxidative conversion of methane to ethylene is exothermic. Excess heat produced from these reactions (Equations (I) and (II)) can push conversion of methane to carbon monoxide and carbon dioxide rather than the desired C ₂ hydrocarbon product (e.g., ethylene):

The excess heat from the reacti ons in Equations (III) and (IV) further exasperate this situation, thereby substantially reducing the selectivity of ethylene production when compared with carbon monoxide and carbon dioxide production.

[0006] Additionally, while the overall OCM is exothermic, catalysts are used to overcome the endothermic nature of the C-H bond breakage. The endothermic nature of the bond breakage is due to the chemical stability of methane, which is a chemically stable molecule due to the presence of its four strong tetrahedral C-H bonds (435 kJ/mol). When catalysts are used in the OCM, the exothermic reaction can lead to a large increase in catalyst bed temperature and uncontrolled heat excursions that can lead to catalyst deactivation and a further decrease in ethylene selectivity. Furthermore, the produced ethylene is highly reactive and can form unwanted and thermodynamically favored deep oxidation products. [0007] Generally, in the OCM, CH ₄ is first oxidatively converted into ethane (C ₂ H ₆ ), and then into C ₂ H ₄ . CH ₄ is activated heterogeneously on a catalyst surface, forming methyl free radicals (e.g., CH ₃ ·), which then couple in a gas phase to form C ₂ H ₆ . C ₂ H ₆ subsequently undergoes dehydrogenation to form C ₂ H ₄ . An overall yield of desired C ₂ hydrocarbons is reduced by non-selective reactions of methyl radicals with oxygen on the catalyst surface and/or in the gas phase, which produce (undesirable) carbon monoxide and carbon dioxide. Some of the best reported OCM outcomes encompass a ~20% conversion of methane and ~80% selectivity to desired C ₂ hydrocarbons.

[0008] There are many catalyst systems developed for OCM processes, but such catalyst systems have many shortcomings. For example, conventional catalysts systems for OCM display catalyst performance problems, such as poor stability of catalyst activity over time. For example, conventional OCM catalysts that are based on Mn/Na ₂ WO ₄ leach Na over time, resulting in catalyst deactivation. Thus, there is an ongoing need for the development of catalyst compositions for OCM processes.

BRIEF SUMMARY

[0009] Disclosed herein is an oxidative coupling of methane (OCM) catalyst composition characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states.

[0010] Also disclosed herein is a method of making an oxidative coupling of methane (OCM) catalyst composition comprising (a) forming an OCM catalyst precursor mixture; wherein the OCM catalyst precursor mixture comprises one or more compounds comprising a first rare earth element cation, one or more compounds comprising a second rare earth element cation, one or more compounds comprising a Mn cation, and Na ₂ WO ₄ ; wherein the first rare earth element cation and the second rare earth element cation are different; wherein the OCM catalyst precursor mixture is characterized by a molar ratio of second rare earth element to first rare earth element of b:1; and wherein b is from about 0 to about 10.0, and wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone, and (b) calcining the OCM catalyst precursor mixture at a temperature of equal to or greater than about 700 ^o C to form the OCM catalyst composition.

[0011] Further disclosed herein is a method for producing olefins comprising (a) introducing a reactant mixture to a reactor comprising an oxidative coupling of methane (OCM) catalyst composition; wherein the reactant mixture comprises methane (CH ₄ ) and oxygen (O ₂ ); wherein the OCM catalyst composition is characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states, (b) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising olefins, (c) recovering at least a portion of the product mixture from the reactor, and (d) recovering at least a portion of the olefins from the product mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a detailed description of the preferred aspects of the disclosed methods, reference will now be made to the accompanying drawing in which:

[ _0013] Figures 1 and 2 display graphs of O ₂ conversion in an OCM reaction over time for different catalysts.

DETAILED DESCRIPTION

[0014] Disclosed herein are oxidative coupling of methane (OCM) catalyst compositions and methods of making and using same. In an aspect, an OCM catalyst composition can be characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states.

[0015] A method of making an OCM catalyst composition as disclosed herein can generally comprise the steps of (a) forming an OCM catalyst precursor mixture; wherein the OCM catalyst precursor mixture comprises one or more compounds comprising a first rare earth element cation, one or more compounds comprising a second rare earth element cation, one or more compounds comprising a Mn cation, and Na ₂ WO ₄ ; wherein the first rare earth element cation and the second rare earth element cation are different; and wherein the OCM catalyst precursor mixture is characterized by a molar ratio of second rare earth element to first rare earth element of b:1, wherein b is from about 0 to about 10.0; and (b) calcining the OCM catalyst precursor mixture to form the OCM catalyst composition, wherein the OCM catalyst composition can be characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states. The one or more compounds comprising a first rare earth element cation comprises a first rare earth element nitrate, a first rare earth element oxide, a first rare earth element hydroxide, a first rare earth element chloride, a first rare earth element acetate, a first rare earth element carbonate, and the like, or combinations thereof; the one or more compounds comprising a second rare earth element cation comprises a second rare earth element nitrate, a second rare earth element oxide, a second rare earth element hydroxide, a second rare earth element chloride, a second rare earth element acetate, a second rare earth element carbonate, and the like, or combinations thereof; and the one or more compounds comprising a Mn cation comprises a Mn nitrate, a Mn oxide, a Mn hydroxide, a Mn chloride, a Mn acetate, a Mn carbonate, and the like, or combinations thereof.

[0016] Other than in the operating examples or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as modified in all instances by the term“about.” Various numerical ranges are disclosed herein. Because these ranges are continuous, they include every value between the minimum and maximum values. The endpoints of all ranges reciting the same characteristic or component are independently combinable and inclusive of the recited endpoint. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations. The endpoints of all ranges directed to the same component or property are inclusive of the endpoint and independently combinable. The term“from more than 0 to an amount” means that the named component is present in some amount more than 0, and up to and including the higher named amount.

[0017] The terms“a,”“an,” and“the” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. As used herein the singular forms“a,”“an,” and“the” include plural referents.

[0018] As used herein,“combinations thereof” is inclusive of one or more of the recited elements, optionally together with a like element not recited, e.g., inclusive of a combination of one or more of the named components, optionally with one or more other components not specifically named that have essentially the same function. As used herein, the term“combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0019] Reference throughout the specification to“an aspect,”“another aspect,”“other aspects,”“some aspects,” and so forth, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the aspect is included in at least an aspect described herein, and may or may not be present in other aspects. In addition, it is to be understood that the described element(s) can be combined in any suitable manner in the various aspects.

[0020] As used herein, the terms“inhibiting” or“reducing” or“preventing” or“avoiding” or any variation of these terms, include any measurable decrease or complete inhibition to achieve a desired result.

[0021] As used herein, the term“effective,” means adequate to accomplish a desired, expected, or intended result.

[0022] As used herein, the terms“comprising” (and any form of comprising, such as“comprise” and “comprises”),“having” (and any form of having, such as“have” and“has”),“including” (and any form of including, such as“include” and“includes”) or“containing” (and any form of containing, such as“contain” and“contains”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0023] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art.

[0024] Compounds are described herein using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash (“-”) that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -CHO is attached through the carbon of the carbonyl group.

[0025] In an aspect, a method for producing olefins as disclosed herein can comprise introducing a reactant mixture to a reactor comprising an oxidative coupling of methane (OCM) catalyst composition to form a product mixture comprising olefins, wherein the reactant mixture comprises methane (CH ₄ ) and oxygen (O ₂ ), and wherein the OCM catalyst composition can be characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states.

[0026] The reactant mixture can be a gaseous mixture. The reactant mixture can comprise a hydrocarbon or mixtures of hydrocarbons, and oxygen. In some aspects, the hydrocarbon or mixtures of hydrocarbons can comprise natural gas (e.g., CH ₄ ), liquefied petroleum gas comprising C ₂ -C ₅ hydrocarbons, C _{6 +} heavy hydrocarbons (e.g., C ₆ to C ₂₄ hydrocarbons such as diesel fuel, jet fuel, gasoline, tars, kerosene, etc.), oxygenated hydrocarbons, biodiesel, alcohols, dimethyl ether, and the like, or combinations thereof. In an aspect, the reactant mixture can comprise CH ₄ and O ₂ .

[0027] The O ₂ used in the reactant mixture can be oxygen gas (which may be obtained via a membrane separation process), technical oxygen (which may contain some air), air, oxygen enriched air, and the like, or combinations thereof.

[0028] The reactant mixture can further comprise a diluent. The diluent is inert with respect to the OCM reaction, e.g., the diluent does not participate in the OCM reaction. In an aspect, the diluent can comprise water, nitrogen, inert gases, and the like, or combinations thereof.

[0029] The diluent can provide for heat control of the OCM reaction, e.g., the diluent can act as a heat sink. Generally, an inert compound (e.g., a diluent) can absorb some of the heat produced in the exothermic OCM reaction, without degrading or participating in any reaction (OCM or other reaction), thereby providing for controlling a temperature inside the reactor. [0030] The diluent can be present in the reactant mixture in an amount of from about 0.5% to about 80%, alternatively from about 5% to about 70%, or alternatively from about 10% to about 60%, based on the total volume of the reactant mixture.

[0031] A method for producing olefins can comprise introducing the reactant mixture to a reactor, wherein the reactor comprises the OCM catalyst composition disclosed herein. The reactor can comprise an adiabatic reactor, an autothermal reactor, an isothermal reactor, a tubular reactor, a cooled tubular reactor, a continuous flow reactor, a fixed bed reactor, a fluidized bed reactor, a moving bed reactor, and the like, or combinations thereof. In an aspect, the reactor can comprise an adiabatic reactor. In an aspect, the reactor can comprise a catalyst bed comprising the OCM catalyst composition disclosed herein.

[0032] The reactant mixture can be introduced to the reactor at a temperature of from about 150 ^o C to about 1,000 ^o C, alternatively from about 225 ^o C to about 900 ^o C, or alternatively from about 250 ^o C to about 800 ^o C. As will be appreciated by one of skill in the art, and with the help of this disclosure, while the OCM reaction is exothermic, heat input is necessary for promoting the formation of methyl radicals from CH ₄ , as the C-H bonds of CH ₄ are very stable, and the formation of methyl radicals from CH ₄ is endothermic. In an aspect, the reactant mixture can be introduced to the reactor at a temperature effective to promote an OCM reaction.

[0033] The reactor can be characterized by a temperature of from about 400 ^o C to about 1,200 ^o C, alternatively from about 500 ^o C to about 1,100 ^o C, or alternatively from about 600 ^o C to about 1,000 ^o C.

[0034] The reactor can be characterized by a pressure of from about ambient pressure (e.g., atmospheric pressure) to about 500 psig, alternatively from about ambient pressure to about 200 psig, or alternatively from about ambient pressure to about 150 psig. In an aspect, the method for producing olefins as disclosed herein can be carried out at ambient pressure.

[0035] The reactor can be characterized by a gas hourly space velocity (GHSV) of from about 500 h ^-1 to about 10,000,000 h ^-1 , alternatively from about 500 h ^-1 to about 1,000,000 h ^-1 , alternatively from about 500 h ^-1 to about 500,000 h ^-1 , alternatively from about 1,000 h ^-1 to about 500,000 h ^-1 , alternatively from about 1,500 h ^-1 to about 500,000 h ^-1 , alternatively from about 2,000 h ^-1 to about 500,000 h ^-1 , alternatively from about 5,000 h ^-1 to about 500,000 h ^-1 , alternatively from about 10,000 h ^-1 to about 500,000 h ^-1 , or alternatively from about 50,000 h ^-1 to about 500,000 h ^-1 . Generally, the GHSV relates a reactant (e.g., reactant mixture) gas flow rate to a reactor volume. GHSV is usually measured at standard temperature and pressure.

[0036] The reactor can comprise an OCM catalyst composition as disclosed herein characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0, alternatively from about 0.1 to about 8, or alternatively from about 0.5 to about 5; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states. As will be appreciated by one of the skill in the art, and with the help of this disclosure, each of the E and D can have multiple oxidation states within the OCM catalyst composition (e.g., within a (E _a D _b O _x ) portion of the OCM catalyst composition), and as such x can have any suitable value that allows for the oxygen anions to balance all the E and D cations within the (E _a D _b O _x ) portion of the OCM catalyst composition. Without wishing to be limited by theory, the different metals (E, D, Na, Mn, W) present in the OCM catalyst compositions as disclosed herein can display synergetic effects in terms of stability, conversion and selectivity. Further, and without wishing to be limited by theory, different ion radii and valences of the multiple metals (E, D, Na, Mn, W) present in the OCM catalyst compositions as disclosed herein can generate formation of uncompensated oxygen vacancies, which can lead to further improvement of catalyst performance, for example in terms of conversion, selectivity, stability, etc.

[0037] The OCM catalyst composition can be regarded as a composite comprising a (E _a D _b O _x ) portion or phase and a Mn/Na ₂ WO ₄ portion or phase, wherein the (E _a D _b O _x ) portion and the Mn/Na ₂ WO ₄ portion can be interspersed. In some aspects, the OCM catalyst composition can comprise a continuous phase comprising Mn/Na ₂ WO ₄ ; having a discontinuous phase comprising (E _a D _b O _x ) dispersed therein. In other aspects, the OCM catalyst composition can comprise a continuous phase comprising (E _a D _b O _x ); having a discontinuous phase comprising Mn/Na ₂ WO ₄ dispersed therein. In yet other aspects, the OCM catalyst composition can comprise both a continuous phase comprising Mn/Na ₂ WO ₄ and a continuous phase comprising (E _a D _b O _x ), wherein the phase comprising Mn/Na ₂ WO ₄ and the phase comprising (E _a D _b O _x ) contact each other. In still yet other aspects, the OCM catalyst composition can comprise regions of a phase comprising Mn/Na ₂ WO ₄ and regions of a phase comprising (E _a D _b O _x ), wherein at least a portion the regions of the phase comprising Mn/Na ₂ WO ₄ contact at least a portion of the regions of the phase comprising (E _a D _b O _x ). As will be appreciated by one of skill in the art, and with the help of this disclosure, the amounts of each Mn/Na ₂ WO ₄ and (E _a D _b O _x ) present in the OCM catalyst composition contribute to the distribution of the phase comprising Mn/Na ₂ WO ₄ and the phase comprising (E _a D _b O _x ) within the OCM catalyst composition.

[0038] The OCM catalyst composition as disclosed herein can comprise a first rare earth element (E), and optionally a second rare earth element (D), wherein E and D are different. The first rare earth element (E) and the second rare earth element (D) can each independently be selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), yttrium (Y), and combinations thereof. [0039] In some aspects, the first rare earth element (E) and the second rare earth element (D) can each independently be selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), and combinations thereof.

[0040] In an aspect, the first rare earth element (E), the second rare earth element (D), or both can be basic (e.g., can exhibit some degree of basicity; can have affinity for hydrogen; can exhibit some degree of affinity for hydrogen).

[0041] In some aspects, the first rare earth element (E) is basic. In other aspects, the second rare earth element (D) is basic. In yet other aspects, both the first rare earth element (E) and the second rare earth element (D) are basic. Nonlimiting examples of rare earth elements that can be considered basic for purposes of the disclosure herein include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), yttrium (Y), or combinations thereof. As will be appreciated by one of skill in the art, and with the help of this disclosure, and without wishing to be limited by theory, the OCM reaction is a multi-step reaction, wherein each step of the OCM reaction could benefit from specific OCM catalytic properties. For example, and without wishing to be limited by theory, an OCM catalyst should exhibit some degree of basicity to abstract a hydrogen from CH ₄ to form hydroxyl groups [OH] on the OCM catalyst surface, as well as methyl radicals (CH ₃ ·). Further, and without wishing to be limited by theory, an OCM catalyst should exhibit oxidative properties for the OCM catalyst to convert the hydroxyl groups [OH] from the catalyst surface to water, which can allow for the OCM reaction to continue (e.g., propagate). Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, and without wishing to be limited by theory, an OCM catalyst could also benefit from properties like oxygen ion conductivity and proton conductivity, which properties can be critical for the OCM reaction to proceed at a very high rate (e.g., its highest possible rate). Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, and without wishing to be limited by theory, an OCM catalyst comprising a single metal might not provide all the necessary properties for an optimum OCM reaction (e.g., best OCM reaction outcome) at the best level, and as such conducting an optimum OCM reaction may require an OCM catalyst with tailored composition in terms of metals present, wherein the different metals can have optimum properties for various OCM reaction steps, and wherein the different metals can provide synergistically for achieving the best performance for the OCM catalyst in an OCM reaction.

[0042] As will be appreciated by one of skill in the art, and with the help of this disclosure, Mn/Na ₂ WO ₄ (e.g., a Mn/Na ₂ WO ₄ portion of the OCM catalyst composition) is a catalyst for an OCM reaction in the absence of the (E _a D _b O _x ) (e.g., the (E _a D _b O _x ) portion of the OCM catalyst composition). The Mn/Na ₂ WO ₄ portion of the OCM catalyst composition can display catalytic activity in an OCM reaction by itself (e.g., without the (E _a D _b O _x ) portion). The Mn/Na ₂ WO ₄ portion of the OCM catalyst composition can stand (e.g., act, operate, etc.) by itself (e.g., without the (E _a D _b O _x ) portion) to catalyze an OCM reaction.

[0043] In an aspect, (E _a D _b O _x ) (e.g., the (E _a D _b O _x ) portion of the OCM catalyst composition) is a catalyst for an OCM reaction in the absence of Mn/Na ₂ WO ₄ (e.g., the Mn/Na ₂ WO ₄ portion of the OCM catalyst composition). The (E _a D _b O _x ) portion of the OCM catalyst composition can display catalytic activity in an OCM reaction by itself (e.g., without the Mn/Na ₂ WO ₄ portion). The (E _a D _b O _x ) portion of the OCM catalyst composition can stand (e.g., act, operate, etc.) by itself (e.g., without the Mn/Na ₂ WO ₄ portion) to catalyze an OCM reaction.

[ _0044] In some aspects, (E _a D _b O _x ) (e.g., the (E _a D _b O _x ) portion of the OCM catalyst composition) is a high performance catalyst for an OCM reaction in the absence of Mn/Na ₂ WO ₄ (e.g., the Mn/Na ₂ WO ₄ portion of the OCM catalyst composition). For purposes of the disclosure herein, a“high performance catalyst” for an OCM reaction refers to a catalyst that displays a higher conversion, a higher selectivity, a higher stability, and the like, or combinations thereof, in an OCM reaction, when compared to a conventional OCM catalyst. Nonlimiting examples of conventional OCM catalysts include CeO ₂ , La ₂ O ₃ - CeO ₂ , Ca/CeO ₂ , Mn/Na ₂ WO ₄ , Li ₂ O, Na ₂ O, Cs ₂ O, WO ₃ , Mn ₃ O ₄ , CaO, MgO, SrO, BaO, CaO-MgO, CaO- BaO, Li/MgO, MnO, W ₂ O ₃ , SnO ₂ , Yb ₂ O ₃ , Sm ₂ O ₃ , MnO-W ₂ O ₃ , MnO-W ₂ O ₃ -Na ₂ O, MnO-W ₂ O ₃ -Li ₂ O, SrO/La ₂ O ₃ , Ce ₂ O ₃ , La/MgO, La ₂ O ₃ -CeO ₂ -Na ₂ O, La ₂ O ₃ -CeO ₂ -CaO, La ₂ O ₃ -CeO ₂ -MnO-WO ₃ -SrO, Na-Mn- La ₂ O ₃ /Al ₂ O ₃ , Na-Mn-O/SiO ₂ , Na ₂ WO ₄ -Mn/SiO ₂ , Na ₂ WO ₄ -Mn-O/SiO ₂ , Na/Mn/O, Na ₂ WO ₄ , Mn ₂ O ₃ /Na ₂ WO ₄ , Mn ₃ O ₄ /Na ₂ WO _4, MnWO ₄ /Na ₂ WO ₄ , MnWO ₄ /Na ₂ WO _4, Mn/WO ₄ , Na ₂ WO ₄ /Mn, Sr/Mn- Na ₂ WO ₄ , and the like.

[0045] As will be appreciated by one of skill in the art, and with the help of this disclosure, deactivation of OCM catalysts (e.g., loss of activity in an OCM reaction) can be due to the over-reduction of the OCM catalyst; leaching of active components (e.g., metals, such as Na) from the OCM catalyst; or other reasons. Without wishing to be limited by theory, deactivation of an OCM catalyst can be decreased or minimized by increasing the basicity (e.g., basic properties) of the OCM catalyst, for example by incorporating basic elements (e.g., first rare earth element (E); second rare earth element (D); or both) in the OCM catalyst composition, as disclosed herein. Further, without wishing to be limited by theory, rare earth element oxides can increase the basicity of an OCM catalyst, as well as display catalytic activity in an OCM reaction by participating in a methane activation process for the production of methyl radicals. Further, without wishing to be limited by theory, the OCM catalyst composition as disclosed herein can display two parallel routes of methane activation for the production of methyl radicals involving (i) the participation of the (E _a D _b O _x ) portion of the OCM catalyst composition for methane activation via catalytically active rare earth element oxide centers, such as E-O-D-O catalytically active sites; (ii) the participation of the Mn/Na ₂ WO ₄ portion of the OCM catalyst composition for methane activation via catalytically active metal oxide centers, such as Na-Mn/W-O catalytically active sites; or both (i) and (ii). When the production of methyl radicals involves both (i) the participation of the (E _a D _b O _x ) portion of the OCM catalyst composition, and (ii) the participation of the Mn/Na ₂ WO ₄ portion of the OCM catalyst composition, the (E _a D _b O _x ) portion and the Mn/Na ₂ WO ₄ portion can display an additive effect, a synergistic effect, or both with respect to conversion, selectivity, stability, and the like, or combinations thereof, in an OCM reaction.

[0046] In an aspect, deactivation of a catalyst in an OCM reaction can be avoided or minimized by employing an OCM catalyst composition as disclosed herein. Without wishing to be limited by theory, deactivation of the (E _a D _b O _x ) portion of the OCM catalyst composition can be avoided or minimized owing to the first rare earth element (E); the second rare earth element (D); or both displaying stable performance under the OCM reaction conditions disclosed herein. In some aspects, only a portion (as opposed to all) of the first rare earth element (E) is deactivated under the OCM reaction conditions disclosed herein. In other aspects, the first rare earth element (E) is substantially not deactivated under the OCM reaction conditions disclosed herein. In yet other aspects, only a portion (as opposed to all) of the second rare earth element (D) is deactivated under the OCM reaction conditions disclosed herein. In still yet other aspects, the second rare earth element (D) is substantially not deactivated under the OCM reaction conditions disclosed herein. In still yet other aspects, both the first rare earth element (E) and the second rare earth element (D) are substantially not deactivated under the OCM reaction conditions disclosed herein. Without wishing to be limited by theory, the catalytic route of methane activation for the production of methyl radicals involving the participation of the (E _a D _b O _x ) portion of the OCM catalyst composition can further decrease the formation of NaOH, thereby leading to a decrease in Na leaching from the OCM catalyst composition disclosed herein, which in turn confers to the OCM catalyst composition disclosed herein an increased stability and life time.

[0047] In an aspect, the OCM catalyst composition as disclosed herein (e.g., the (E _a D _b O _x ) portion of the OCM catalyst composition) can comprise one or more oxides of E; one or more oxides of D; or both. The OCM catalyst composition can comprise one or more oxides of a rare earth element, wherein the rare earth element comprises E, and optionally D. In an aspect, the (E _a D _b O _x ) portion of the OCM catalyst composition can comprise, consist of, or consist essentially of the one or more oxides of a rare earth element, wherein the rare earth element comprises E, and optionally D.

[0048] In an aspect, the one or more oxides of a rare earth element (e.g., the (E _a D _b O _x ) portion of the OCM catalyst composition) can be present in the OCM catalyst composition in an amount of from about 0.01 wt.% to about 90 wt.%, alternatively from about 10.0 wt.% to about 80 wt.%, or alternatively from about 25.0 wt.% to about 70 wt.%, based on the total weight of the OCM catalyst composition. In such aspect, the OCM catalyst composition can further comprise a support, as disclosed herein. As will be appreciated by one of skill in the art, and with the help of this disclosure, a portion of the one or more oxides of a rare earth element, in the presence of water, such as atmospheric moisture, can convert to hydroxides, and it is possible that the OCM catalyst composition will comprise some hydroxides, due to exposing the OCM catalyst composition comprising the one or more oxides of a rare earth element to water (e.g., atmospheric moisture). Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, a portion of the one or more oxides of a rare earth element, in the presence of carbon dioxide, such as atmospheric carbon dioxide, can convert to carbonates, and it is possible that the OCM catalyst composition will comprise some carbonates, due to exposing the OCM catalyst composition comprising the one or more oxides of a rare earth element to carbon dioxide (e.g., atmospheric carbon dioxide).

[0049] The one or more oxides of a rare earth element can comprise a single rare earth element oxide, mixtures of single rare earth element oxides, a mixed rare earth element oxide, mixtures of mixed rare earth element oxides, mixtures of single rare earth element oxides and mixed rare earth element oxides, or combinations thereof.

[0050] The single rare earth element oxide comprises one rare earth element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y. A single rare earth element oxide can be characterized by the general formula R _r O _y ; wherein R is a rare earth element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y; and wherein r and y are integers from 1 to 7, alternatively from 1 to 5, or alternatively from 1 to 3. A single rare earth element oxide contains one and only one rare earth element cation. Nonlimiting examples of single rare earth element oxides suitable for use in the OCM catalyst compositions of the present disclosure include La ₂ O ₃ , Sc ₂ O ₃ , Y ₂ O ₃ , CeO ₂ , Ce ₂ O ₃ , Pr ₂ O ₃ , PrO ₂ , Nd ₂ O ₃ , Pm ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Lu ₂ O ₃ , Yb ₂ O ₃ , Tm ₂ O ₃ , and the like, or combinations thereof.

[0051] In an aspect, mixtures of single rare earth element oxides can comprise two or more different single rare earth element oxides, wherein the two or more different single rare earth element oxides have been mixed together to form the mixture of single rare earth element oxides. Mixtures of single rare earth element oxides can comprise two or more different single rare earth element oxides, wherein each single rare earth element oxide can be selected from the group consisting of La ₂ O ₃ , Sc ₂ O ₃ , Y ₂ O ₃ , CeO ₂ , Ce ₂ O ₃ , Pr ₂ O ₃ , PrO ₂ , Nd ₂ O ₃ , Pm ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Lu ₂ O ₃ , Yb ₂ O ₃ , and Tm ₂ O ₃ . Nonlimiting examples of mixtures of single rare earth element oxides suitable for use in the OCM catalyst compositions of the present disclosure include Yb ₂ O ₃ -La ₂ O ₃ , Er ₂ O ₃ -La ₂ O ₃ , CeO ₂ -La ₂ O ₃ , CeO ₂ -Ce ₂ O ₃ - La ₂ O ₃ , CeO ₂ -Er ₂ O ₃ , CeO ₂ -Ce ₂ O ₃ -Er ₂ O ₃ , Tm ₂ O ₃ -La ₂ O ₃ , Sm ₂ O ₃ -La ₂ O ₃ , PrO ₂ -Pr ₂ O ₃ -La ₂ O ₃ , and the like, or combinations thereof.

[0052] The mixed rare earth element oxide comprises two or more different rare earth elements, wherein each rare earth element can be independently selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y. A mixed rare earth element oxide can be characterized by the general formula R ¹

r ₁ R ²

r ₂ O _y ; wherein R ¹ and R ² are rare earth elements; wherein each of the R ¹ and R ² can be independently selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and Y; and wherein r1, r2 and y are integers from 1 to 15, alternatively from 1 to 10, or alternatively from 1 to 7. In some aspects, R ¹ and R ² can be rare earth element cations of different chemical elements, for example R ¹ can be a lanthanum cation and R ² can be an ytterbium cation. In other aspects, R ¹ and R ² can be different cations of the same chemical element, wherein R ¹ and R ² can have different oxidation states. Nonlimiting examples of mixed rare earth element oxides suitable for use in the OCM catalyst compositions of the present disclosure include LaYbO ₃ ; Sm ₂ Ce ₂ O ₇ ; Er ₂ Ce ₂ O ₇ ; and the like; or combinations thereof.

[0053] In an aspect, mixtures of mixed rare earth element oxides can comprise two or more different mixed rare earth element oxides, wherein the two or more different mixed rare earth element oxides have been mixed together to form the mixture of mixed rare earth element oxides. Mixtures of mixed rare earth element oxides can comprise two or more different mixed rare earth element oxides, such as LaYbO ₃ ; Sm ₂ Ce ₂ O ₇ ; Er ₂ Ce ₂ O ₇ ; or combinations thereof.

[0054] In an aspect, mixtures of single rare earth element oxides and mixed rare earth element oxides can comprise at least one single rare earth element oxide and at least one mixed rare earth element oxide, wherein the at least one single rare earth element oxide and the at least one mixed rare earth element oxide have been mixed together to form the mixture of single rare earth element oxides and mixed rare earth element oxides.

[0055] In an aspect, the OCM catalyst composition as disclosed herein (e.g., the Mn/Na ₂ WO ₄ portion of the OCM catalyst composition) can comprise one or more oxides of Mn; one or more oxides of Na; one or more oxides of W; or combinations thereof. The OCM catalyst composition can comprise one or more oxides of a metal (e.g., one or more metal oxides), wherein the metal comprises Mn, Na, W, or combinations thereof. In an aspect, the Mn/Na ₂ WO ₄ portion of the OCM catalyst composition can comprise, consist of, or consist essentially of the one or more metal oxides, wherein the metal comprises Mn, Na, W, or combinations thereof.

[0056] In an aspect, the one or more metal oxides (e.g., the Mn/Na ₂ WO ₄ portion of the OCM catalyst composition), wherein the metal comprises Mn, Na, W, or combinations thereof, can be present in the OCM catalyst composition in an amount of from about 0.1 wt.% to about 90.0 wt.%, alternatively from about 1.0 wt.% to about 80.0 wt.%, or alternatively from about 10.0 wt.% to about 70.0 wt.%, based on the total weight of the OCM catalyst composition. In such aspect, the OCM catalyst composition can further comprise a support, as disclosed herein. In an aspect, Mn is present in the OCM catalyst composition in an amount of from about 0.5 wt.% to about 20 wt.%, alternatively from about 1 wt.% to about 10 wt.%, or alternatively from about 2 wt.% to about 5 wt.%, based on a total weight of the OCM catalyst composition. [0057] As will be appreciated by one of skill in the art, and with the help of this disclosure, a portion of the one or more metal oxides, wherein the metal comprises Mn, Na, W, or combinations thereof, in the presence of water, such as atmospheric moisture, can convert to hydroxides, and it is possible that the OCM catalyst composition will comprise some hydroxides, due to exposing the OCM catalyst composition comprising the one or more metal oxides to water (e.g., atmospheric moisture). Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, a portion of the one or more metal oxides, in the presence of carbon dioxide, such as atmospheric carbon dioxide, can convert to carbonates, and it is possible that the OCM catalyst composition will comprise some carbonates, due to exposing the OCM catalyst composition comprising the one or more metal oxides to carbon dioxide (e.g., atmospheric carbon dioxide).

[0058] The one or more metal oxides, wherein the metal comprises Mn, Na, W, or combinations thereof, can comprise a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, mixtures of single metal oxides and mixed metal oxides, or combinations thereof.

[0059] The single metal oxide comprises one metal selected from the group consisting of Na, W, and Mn. A single metal oxide can be characterized by the general formula M _m O _y ; wherein M is the metal selected from the group consisting of Na, W, and Mn; and wherein m and y are integers from 1 to 7, alternatively from 1 to 5, or alternatively from 1 to 3. A single metal oxide contains one and only one metal cation. Nonlimiting examples of single metal oxides suitable for use in the OCM catalyst compositions of the present disclosure include WO ₃ , MnO ₂ , W ₂ O ₃ , and the like, or combinations thereof.

[0060] In an aspect, mixtures of single metal oxides can comprise two or more different single metal oxides, wherein the two or more different single metal oxides have been mixed together to form the mixture of single metal oxides. Mixtures of single metal oxides can comprise two or more different single metal oxides, wherein each single metal oxide can be selected from the group consisting of WO ₃ , MnO ₂ , and W ₂ O ₃ . Nonlimiting examples of mixtures of single metal oxides suitable for use in the OCM catalyst compositions of the present disclosure include MnO ₂ -W ₂ O ₃ , WO ₃ -W ₂ O ₃ , MnO ₂ -WO ₃ , MnO ₂ -WO ₃ -W ₂ O ₃ , and the like, or combinations thereof.

[0061] The mixed metal oxide comprises two or more different metals, wherein each metal can be independently selected from the group consisting of Na, W, and Mn. A mixed metal oxide can be characterized by the general formula M ¹

m ₁ M ²

m ₂ O _y ; wherein M ¹ and M ² are metals; wherein each of the M ¹ and M ² can be independently selected from the group consisting of Na, W, and Mn; and wherein m1, m2 and y are integers from 1 to 15, alternatively from 1 to 10, or alternatively from 1 to 7. In some aspects, M ¹ and M ² can be metal cations of different chemical elements, for example M ¹ can be a sodium cation and M ² can be a manganese cation. In other aspects, M ¹ and M ² can be different cations of the same chemical element, wherein M ¹ and M ² can have different oxidation states. For example, the mixed metal oxide can comprise Mn ₃ O ₄ , wherein M ¹ can be a Mn (II) cation and M ² can be a Mn (III) cation. Nonlimiting examples of mixed metal oxides suitable for use in the OCM catalyst compositions of the present disclosure include Na/Mn/O; Mn ₃ O ₄ ; Na ₂ WO ₄ ; Mn/Na ₂ WO ₄ ; Na ₂ WO ₄ /Mn; MnWO ₄ ; Mn/WO ₄ ; and the like; or combinations thereof.

[0062] In an aspect, mixtures of mixed metal oxides can comprise two or more different mixed metal oxides, wherein the two or more different mixed metal oxides have been mixed together to form the mixture of mixed metal oxides. Mixtures of mixed metal oxides can comprise two or more different mixed metal oxides, such as Na/Mn/O; Mn ₃ O ₄ ; Na ₂ WO ₄ ; Mn/Na ₂ WO ₄ ; Na ₂ WO ₄ /Mn; MnWO ₄ ; Mn/WO ₄ ; and the like; or combinations thereof.

[0063] In an aspect, mixtures of single metal oxides and mixed metal oxides can comprise at least one single metal oxide and at least one mixed metal oxide, wherein the at least one single metal oxide and the at least one mixed metal oxide have been mixed together to form the mixture of single metal oxides and mixed metal oxides.

[0064] In some aspects, the Mn/Na ₂ WO ₄ portion of the OCM catalyst composition can comprise Mn/Na ₂ WO ₄ , Na/Mn/O, Na ₂ WO ₄ , Mn ₂ O ₃ /Na ₂ WO ₄ , Mn ₃ O ₄ /Na ₂ WO ₄ , MnWO ₄ /Na ₂ WO ₄ , Mn/WO ₄ , Na ₂ WO ₄ /Mn, and the like, or combinations thereof. In an aspect, the Mn/Na ₂ WO ₄ portion of the OCM catalyst composition can comprise, consist of, or consist essentially of Mn/Na ₂ WO ₄ .

[0065] In an aspect, the OCM catalyst composition can comprise one or more oxides of a rare earth element (e.g., one or more oxides of the (E _a D _b O _x ) portion of the OCM catalyst composition) and one or more metal oxides (e.g., one or more oxides of the Mn/Na ₂ WO ₄ portion of the OCM catalyst composition); such as MnO-Yb ₂ O ₃ -La ₂ O ₃ , Mn ₂ O ₃ -Er ₂ O ₃ -La ₂ O ₃ , Na ₂ WO ₄ -CeO ₂ -La ₂ O ₃ , MnWO ₄ -Na ₂ WO ₄ -CeO ₂ -Ce ₂ O ₃ - La ₂ O ₃ , Na ₂ O-CeO ₂ -Er ₂ O ₃ , Na/Mn/O-CeO ₂ -Ce ₂ O ₃ -Er ₂ O ₃ , Mn ₂ O ₃ /Na ₂ WO ₄ -Tm ₂ O ₃ -La ₂ O ₃ , Mn/WO ₄ -Sm ₂ O ₃ - La ₂ O ₃ , Mn/Na ₂ WO ₄ -PrO ₂ -Pr ₂ O ₃ -La ₂ O ₃ , and the like; or combination thereof.

[0066] The OCM catalyst compositions suitable for use in the present disclosure can be supported OCM catalyst compositions and/or unsupported OCM catalyst compositions. In some aspects, the supported OCM catalyst compositions can comprise a support, wherein the support can be catalytically active (e.g., the support can catalyze an OCM reaction, such as MgO). In other aspects, the supported OCM catalyst compositions can comprise a support, wherein the support can be catalytically less active (e.g., the support cannot catalyze an OCM reaction, such as SiO ₂ ), for example a support that is less active than a catalytically active support, such as MgO. In yet other aspects, the supported OCM catalyst compositions can comprise a catalytically active support and a catalytically less active support (e.g., a support that is less active than a catalytically active support). Nonlimiting examples of a support suitable for use in the present disclosure include MgO, Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ , and the like, or combinations thereof. As will be appreciated by one of skill in the art, and with the help of this disclosure, the support can be purchased or can be prepared by using any suitable methodology, such as for example precipitation/co-precipitation, sol- gel techniques, templates/surface derivatized metal oxides synthesis, solid-state synthesis of mixed metal oxides, microemulsion techniques, solvothermal techniques, sonochemical techniques, combustion synthesis, etc.

[0067] In an aspect, the OCM catalyst composition can further comprise a support, wherein at least a portion of the OCM catalyst composition contacts, coats, is embedded in, is supported by, and/or is distributed throughout at least a portion of the support. In such aspect, the support can be in the form of a powder, a particle, a pellet, a monolith, a foam, a honeycomb, and the like, or combinations thereof. Nonlimiting examples of support particle shapes include cylindrical, discoidal, spherical, tabular, ellipsoidal, equant, irregular, cubic, acicular, and the like, or combinations thereof.

[0068] In an aspect, the OCM catalyst composition can further comprise a porous support. As will be appreciated by one of skill in the art, and with the help of this disclosure, a porous material (e.g., support) can provide for an enhanced surface area of contact between the OCM catalyst composition and the reactant mixture, which in turn would result in a higher CH ₄ conversion to

[0069] The OCM catalyst composition can be made by using any suitable methodology. In an aspect, a method of making an OCM catalyst composition can comprise a step of forming an OCM catalyst precursor mixture, wherein the OCM catalyst precursor mixture comprises one or more compounds comprising a first rare earth element cation, optionally one or more compounds comprising a second rare earth element cation, one or more compounds comprising a Mn cation, and Na ₂ WO ₄ ; and wherein the first rare earth element cation and the second rare earth element cation are different. The OCM catalyst precursor mixture can be characterized by a molar ratio of second rare earth element to first rare earth element of b:1, wherein b is from about 0 to about 10.0, alternatively from about 0.1 to about 8, or alternatively from about 0.5 to about 5; and wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone.

[0070] The one or more compounds comprising a first rare earth element cation comprises a first rare earth element nitrate, a first rare earth element oxide, a first rare earth element hydroxide, a first rare earth element chloride, a first rare earth element acetate, a first rare earth element carbonate, and the like, or combinations thereof. The one or more compounds comprising a second rare earth element cation comprises a second rare earth element nitrate, a second rare earth element oxide, a second rare earth element hydroxide, a second rare earth element chloride, a second rare earth element acetate, a second rare earth element carbonate, and the like, or combinations thereof. The one or more compounds comprising a Mn cation comprises a Mn nitrate, a Mn oxide, a Mn hydroxide, a Mn chloride, a Mn acetate, a Mn carbonate, and the like, or combinations thereof. [0071] In an aspect, the step of forming the OCM catalyst precursor mixture can comprise forming one or more aqueous solutions, such as a Mn precursor aqueous solution, a rare earth element precursor aqueous solution, a Na ₂ WO ₄ aqueous solution, etc. For purposes of the disclosure herein, the term“aqueous solution” encompasses both a homogeneous solution, such as a solution wherein a solute is completely dissolved in water; as well as a heterogeneous solution, such as slurries (e.g., aqueous slurry solution), suspensions (e.g., aqueous slurry solution), dispersions (e.g., aqueous dispersion solution), etc., such as a solution wherein a solute is suspended in water and/or partially dissolved in water.

[0072] Aqueous solutions used in a step of forming the OCM catalyst precursor mixture can be formed by solubilizing (e.g., dissolving, dispersing, slurrying, suspending, etc.) one or more compounds (e.g., a one or more compounds comprising a Mn cation for forming a Mn precursor aqueous solution; one or more compounds comprising a first rare earth element cation and optionally one or more compounds comprising a second rare earth element cation for forming a rare earth element precursor aqueous solution; Na ₂ WO ₄ for forming a Na ₂ WO ₄ aqueous solution) in an aqueous medium to form the aqueous solution. The aqueous medium can be water, or any other suitable aqueous medium. The aqueous solutions used in a step of forming the OCM catalyst precursor mixture can be formed by dissolving the one or more compounds in water or any suitable aqueous medium. As will be appreciated by one of skill in the art, and with the help of this disclosure, when more than one compound is used for making an aqueous solution (e.g., one or more compounds comprising a first rare earth element cation and optionally one or more compounds comprising a second rare earth element cation), the compounds can be dissolved in an aqueous medium in any suitable order. In aspects where more than one compound is used for making an aqueous solution, such compounds can be first mixed together and then dissolved in an aqueous medium.

[0073] In an aspect, the step of forming the OCM catalyst precursor mixture can comprise forming a rare earth element precursor aqueous solution comprising one or more compounds comprising a first rare earth element cation and optionally one or more compounds comprising a second rare earth element cation; wherein the first rare earth element cation and the second rare earth element cation are different; wherein the rare earth element precursor aqueous solution is characterized by a molar ratio of second rare earth element to first rare earth element of b:1, wherein b is from about 0 to about 10.0; and wherein when b is 0, the first rare earth element is not La alone or Ce alone.

[0074] In an aspect, the step of forming the OCM catalyst precursor mixture can comprise forming a Mn precursor (e.g., a Mn precursor aqueous solution, a supported Mn precursor, a dried supported Mn precursor) comprising one or more compounds comprising a Mn cation. In some aspects, the Mn precursor aqueous solution can be further contacted with a support to form a supported Mn precursor. The supported Mn precursor can be dried to form a dried supported Mn precursor. In an aspect, the supported Mn precursor can be dried at a temperature of equal to or greater than about 75 ^o C, alternatively equal to or greater than about 100 ^o C, or alternatively equal to or greater than about 125 ^o C, to yield the dried supported Mn precursor. The supported Mn precursor can be dried for a time period of equal to or greater than about 4 hours, alternatively equal to or greater than about 8 hours, or alternatively equal to or greater than about 12 hours.

[0075] In an aspect, the step of forming the OCM catalyst precursor mixture can comprise forming a Na ₂ WO ₄ aqueous solution.

[0076] In some aspects, the Mn precursor (e.g., Mn precursor aqueous solution, supported Mn precursor, dried supported Mn precursor) can be contacted with the Na ₂ WO ₄ aqueous solution to form a Mn/Na ₂ WO ₄ precursor (e.g., Mn/Na ₂ WO ₄ precursor aqueous solution, supported Mn/Na ₂ WO ₄ precursor, dried supported Mn/Na ₂ WO ₄ precursor, calcined supported Mn/Na ₂ WO ₄ precursor).

[0077] In aspects where the Mn/Na ₂ WO ₄ precursor comprises a Mn/Na ₂ WO ₄ precursor aqueous solution, the Mn/Na ₂ WO ₄ precursor aqueous solution can be contacted with a support to form a supported Mn/Na ₂ WO ₄ precursor. In aspects where the Mn precursor comprises a supported Mn precursor and/or dried supported Mn precursor, the Mn/Na ₂ WO ₄ precursor can comprise a supported Mn/Na ₂ WO ₄ precursor.

[0078] The supported Mn/Na ₂ WO ₄ precursor can be further dried to form a dried supported Mn/Na ₂ WO ₄ precursor. In an aspect, the supported Mn/Na ₂ WO ₄ precursor can be dried at a temperature of equal to or greater than about 75 ^o C, alternatively equal to or greater than about 100 ^o C, or alternatively equal to or greater than about 125 ^o C, to yield the dried supported Mn/Na ₂ WO ₄ precursor. The supported Mn/Na ₂ WO ₄ precursor can be dried for a time period of equal to or greater than about 4 hours, alternatively equal to or greater than about 8 hours, or alternatively equal to or greater than about 12 hours.

[0079] In some aspects, the dried supported Mn/Na ₂ WO ₄ precursor can be further calcined at a temperature of equal to or greater than about 700 ^o C, alternatively equal to or greater than about 750 ^o C, or alternatively equal to or greater than about 800 ^o C, to yield a calcined supported Mn/Na ₂ WO ₄ precursor. The dried supported Mn/Na ₂ WO ₄ precursor can be calcined for a time period of equal to or greater than about 2 hours, alternatively equal to or greater than about 4 hours, or alternatively equal to or greater than about 6 hours.

[0080] In some aspects, the rare earth element precursor aqueous solution can be contacted with the Mn/Na ₂ WO ₄ precursor (e.g., Mn/Na ₂ WO ₄ precursor aqueous solution, supported Mn/Na ₂ WO ₄ precursor, dried supported Mn/Na ₂ WO ₄ precursor, calcined supported Mn/Na ₂ WO ₄ precursor) to form the OCM catalyst precursor mixture (e.g., OCM catalyst precursor mixture aqueous solution, supported OCM catalyst precursor mixture, dried supported OCM catalyst precursor mixture).

[ _0081] In aspects where the Mn/Na ₂ WO ₄ precursor comprises a supported Mn/Na ₂ WO ₄ precursor, a dried supported Mn/Na ₂ WO ₄ precursor, a calcined supported Mn/Na ₂ WO ₄ precursor, or combinations thereof; the OCM catalyst precursor mixture can comprise a supported OCM catalyst precursor mixture. [0082] In other aspects, the rare earth element precursor aqueous solution can be contacted with the Mn precursor (e.g., Mn precursor aqueous solution, supported Mn precursor, dried supported Mn precursor) to form a Mn-rare earth element precursor (e.g., Mn-rare earth element precursor aqueous solution, supported Mn-rare earth element precursor, dried supported Mn-rare earth element precursor).

[0083] In aspects where the Mn-rare earth element precursor comprises a Mn-rare earth element precursor aqueous solution, the Mn-rare earth element precursor aqueous solution can be contacted with a support to form a supported Mn-rare earth element precursor. In aspects where the Mn precursor comprises a supported Mn precursor and/or a dried supported Mn precursor; the Mn-rare earth element precursor can comprise a supported Mn-rare earth element precursor.

[0084] The supported Mn-rare earth element precursor can be further dried to form a dried supported Mn-rare earth element precursor. In an aspect, the supported Mn-rare earth element precursor can be dried at a temperature of equal to or greater than about 75 ^o C, alternatively equal to or greater than about 100 ^o C, or alternatively equal to or greater than about 125 ^o C, to yield the dried supported Mn-rare earth element precursor. The supported Mn-rare earth element precursor can be dried for a time period of equal to or greater than about 4 hours, alternatively equal to or greater than about 8 hours, or alternatively equal to or greater than about 12 hours.

[0085] In an aspect, the Mn-rare earth element precursor (e.g., Mn-rare earth element precursor aqueous solution, supported Mn-rare earth element precursor, dried supported Mn-rare earth element precursor) can be contacted with Na ₂ WO ₄ aqueous solution to form the OCM catalyst precursor mixture (e.g., OCM catalyst precursor mixture aqueous solution, supported OCM catalyst precursor mixture, dried supported OCM catalyst precursor mixture).

[0086] In aspects where the Mn-rare earth element precursor comprises a supported Mn-rare earth element precursor and/or a dried supported Mn-rare earth element precursor, the OCM catalyst precursor mixture can comprise a supported OCM catalyst precursor mixture.

[0087] In aspects where the OCM catalyst precursor mixture comprises an OCM catalyst precursor mixture aqueous solution, the OCM catalyst precursor mixture aqueous solution can be contacted with a support to form a supported OCM catalyst precursor mixture.

[0088] In an aspect, the OCM catalyst precursor mixture can be further dried to form a dried OCM catalyst precursor mixture. In an aspect, the OCM catalyst precursor mixture can be dried at a temperature of equal to or greater than about 75 ^o C, alternatively equal to or greater than about 100 ^o C, or alternatively equal to or greater than about 125 ^o C, to yield the dried OCM catalyst precursor mixture. The OCM catalyst precursor mixture can be dried for a time period of equal to or greater than about 4 hours, alternatively equal to or greater than about 8 hours, or alternatively equal to or greater than about 12 hours. [0089] In an aspect, the supported OCM catalyst precursor mixture can be further dried to form a dried supported OCM catalyst precursor mixture. In an aspect, the supported OCM catalyst precursor mixture can be dried at a temperature of equal to or greater than about 75 ^o C, alternatively equal to or greater than about 100 ^o C, or alternatively equal to or greater than about 125 ^o C, to yield the dried supported OCM catalyst precursor mixture. The supported OCM catalyst precursor mixture can be dried for a time period of equal to or greater than about 4 hours, alternatively equal to or greater than about 8 hours, or alternatively equal to or greater than about 12 hours.

[0090] In an aspect, a method of making an OCM catalyst composition can comprise a step of calcining the OCM catalyst precursor mixture (e.g., dried OCM catalyst precursor mixture, supported OCM catalyst precursor mixture, dried supported OCM catalyst precursor mixture) to form the OCM catalyst composition, wherein the OCM catalyst composition is characterized by the general formula (E _a D _b O _x )- Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not La alone or Ce alone; and wherein x balances the oxidation states. The OCM catalyst precursor mixture can be calcined at a temperature of equal to or greater than about 700 ^o C, alternatively equal to or greater than about 750 ^o C, or alternatively equal to or greater than about 800 ^o C, to yield the OCM catalyst composition. The OCM catalyst precursor mixture can be calcined for a time period of equal to or greater than about 2 hours, alternatively equal to or greater than about 4 hours, or alternatively equal to or greater than about 6 hours.

[0091] In some aspects, at least a portion of the OCM catalyst precursor mixture can be calcined in an oxidizing atmosphere (e.g., in an atmosphere comprising oxygen, for example in air) to form the OCM catalyst composition. Without wishing to be limited by theory, the oxygen in the (E _a D _b O _x ) portion of the OCM catalyst compositions characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ can originate in the oxidizing atmosphere used for calcining the OCM catalyst precursor mixture. Further, without wishing to be limited by theory, the oxygen in the (E _a D _b O _x ) portion of the OCM catalyst compositions characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ can originate in the one or more compounds comprising a first rare earth element cation, one or more compounds comprising a second rare earth element cation, or both; provided that at least one of these compounds comprises oxygen in its formula, as is the case with nitrates, oxides, hydroxides, acetates, carbonates, etc.

[0092] In some aspects, the method of making an OCM catalyst composition can comprise forming the OCM catalyst composition in the presence of the support, as previously described herein, such that the resulting OCM catalyst composition (after the calcining step) comprises the support. [0093] In other aspects, the method of making an OCM catalyst composition can further comprise contacting the OCM catalyst composition with a support to yield a supported catalyst (e.g., an OCM supported catalyst, an OCM supported catalyst composition, etc.).

[0094] In an aspect, a method for producing olefins can comprise allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising olefins.

[0095] The product mixture comprises coupling products, partial oxidation products (e.g., deep oxidation products, partial conversion products, such as CO, H ₂ , CO ₂ ), and unreacted methane. The coupling products can comprise olefins (e.g., alkenes, characterized by a general formula C _n H _2n ) and paraffins (e.g., alkanes, characterized by a general formula C _n H _2n+2 ).

[0096] The product mixture can comprise C ₂₊ hydrocarbons, wherein the C ₂₊ hydrocarbons can comprise C ₂ hydrocarbons and C ₃ hydrocarbons. In an aspect, the C ₂₊ hydrocarbons can further comprise C ₄ hydrocarbons (C ₄ s), such as for example butane, iso-butane, n-butane, butylene, etc. The C ₂ hydrocarbons can comprise ethylene (C ₂ H ₄ ) and ethane (C ₂ H ₆ ). The C ₂ hydrocarbons can further comprise acetylene (C ₂ H ₂ ). The C ₃ hydrocarbons can comprise propylene (C ₃ H ₆ ) and propane (C ₃ H ₈ ).

[0097] In some aspects, an O ₂ conversion for the OCM as disclosed herein can be equal to or greater than about 90%, alternatively equal to or greater than about 95%, alternatively equal to or greater than about 99%, alternatively equal to or greater than about 99.9%, or alternatively about 100%. Generally, a conversion of a reagent or reactant refers to the percentage (usually mol%) of reagent that reacted to both undesired and desired products, based on the total amount (e.g., moles) of reagent present before any reaction took place. For purposes of the disclosure herein, the conversion of a reagent is a % conversion based on moles converted. As will be appreciated by one of skill in the art, and with the help of this disclosure, the reactant mixture in OCM reactions is generally characterized by a methane to oxygen molar ratio of greater than 1:1, and as such the O ₂ conversion is fairly high in OCM processes, most often approaching 90%-100%. Without wishing to be limited by theory, oxygen is usually a limiting reagent in OCM processes. The oxygen conversion can be calculated by using equation (1):

i w ^herein O ^{number of moles of O2 that entered the reactor as part of the reactant mixture; and}

n ^{umber of moles of O2 that was recovered from the reactor as part of the product mixture. As} will be appreciated by one of skill in the art, and with the help of this disclosure, as an OCM catalyst ages (e.g., deactivates), for example while actively catalyzing an OCM reaction, the O ₂ conversion can decrease, owing to a decreased ability of the catalyst to catalyze the OCM reaction. OCM catalyst deactivation can be due to leaching out catalyst components over time, such as Na, as disclosed herein.

[0098] In an aspect, the OCM catalyst composition can be characterized by an O ₂ conversion that decreases by less than about 10%, alternatively less than about 7.5%, or alternatively less than about 5%, over a period of time of equal to or greater than about 50 hours, alternatively equal to or greater than about 100 hours, alternatively equal to or greater than about 200 hours, alternatively equal to or greater than about 300 hours, alternatively equal to or greater than about 400 hours, alternatively equal to or greater than about 500 hours, alternatively equal to or greater than about 750 hours, or alternatively equal to or greater than about 1,000 hours.

[0099] In an aspect, the OCM catalyst composition can be characterized by a deactivation rate of less than about 0.5 %/hr, alternatively less than about 0.25 %/hr, or alternatively less than about 0.1 %/hr over a period of time of equal to or greater than about 50 hours, alternatively equal to or greater than about 100 hours, alternatively equal to or greater than about 200 hours, alternatively equal to or greater than about 300 hours, alternatively equal to or greater than about 400 hours, alternatively equal to or greater than about 500 hours, alternatively equal to or greater than about 750 hours, or alternatively equal to or greater than about 1,000 hours. For purposes of the disclosure herein, the deactivation rate of an OCM catalyst composition refers to the reduction of reaction rate constant, more specifically, the reduction of oxygen conversion rate constant.

[00100] In an aspect, the OCM catalyst composition can be characterized by a deactivation rate that is decreased by equal to or greater than about 50%, alternatively equal to or greater than about 60%, alternatively equal to or greater than about 75%, when compared to a deactivation rate of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ .

[00101] In an aspect, the OCM catalyst composition can be characterized by a life time of equal to or greater than about 1,000 h, alternatively equal to or greater than about 1,500 h, or alternatively equal to or greater than about 2,000 h. For purposes of the disclosure herein, the catalyst life of a catalyst refers to the amount of time that the catalyst provides its catalytic performance (e.g., O ₂ conversion, CH ₄ conversion, selectivity) without losing it.

[00102] In an aspect, the OCM catalyst composition can be characterized by a life time that is increased by equal to or greater than about 50%, alternatively equal to or greater than about 60%, alternatively equal to or greater than about 75%, when compared to a life time of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ . [00103] In an aspect, a method for producing olefins can comprise recovering at least a portion of the product mixture from the reactor. In an aspect, a method for producing olefins can comprise recovering at least a portion of the C ₂ hydrocarbons from the product mixture. The product mixture can comprise C ₂₊ hydrocarbons (including olefins), unreacted methane, and optionally a diluent. The water produced from the OCM reaction and the water used as a diluent (if water diluent is used) can be separated from the product mixture prior to separating any of the other product mixture components. For example, by cooling down the product mixture to a temperature where the water condenses (e.g., below 100 ^o C at ambient pressure), the water can be removed from the product mixture, by using a flash chamber for example.

[ _00104] In an aspect, at least a portion of the C ₂₊ hydrocarbons can be separated (e.g., recovered) from the product mixture to yield recovered C ₂₊ hydrocarbons. The C ₂₊ hydrocarbons can be separated from the product mixture by using any suitable separation technique. In an aspect, at least a portion of the C ₂₊ hydrocarbons can be separated from the product mixture by distillation (e.g., cryogenic distillation).

[00105] In an aspect, at least a portion of the recovered C ₂₊ hydrocarbons can be used for ethylene production. In some aspects, at least a portion of ethylene can be separated from the product mixture (e.g., from the C ₂₊ hydrocarbons, from the recovered C ₂₊ hydrocarbons) to yield recovered ethylene and recovered hydrocarbons, by using any suitable separation technique (e.g., distillation). In other aspects, at least a portion of the recovered hydrocarbons (e.g., recovered C ₂₊ hydrocarbons after olefin separation, such as separation of C ₂ H ₄ and C ₃ H ₆ ) can be converted to ethylene, for example by a conventional steam cracking process.

[00106] A method for producing olefins can comprise recovering at least a portion of the olefins from the product mixture. In an aspect, at least a portion of the olefins can be separated from the product mixture by distillation (e.g., cryogenic distillation). As will be appreciated by one of skill in the art, and with the help of this disclosure, the olefins are generally individually separated from their paraffin counterparts by distillation (e.g., cryogenic distillation). For example, ethylene can be separated from ethane by distillation (e.g., cryogenic distillation). As another example, propylene can be separated from propane by distillation (e.g., cryogenic distillation).

[00107] In an aspect, at least a portion of the unreacted methane can be separated from the product mixture to yield recovered methane. Methane can be separated from the product mixture by using any suitable separation technique, such as for example distillation (e.g., cryogenic distillation). At least a portion of the recovered methane can be recycled to the reactant mixture.

[00108] In an aspect, the OCM catalyst composition can be characterized by the general formula (La _a Ce _b O _x )-Mn/Na ₂ WO ₄ ; wherein a is 1.0; wherein b is from about 0.01 to about 10.0, alternatively from about 0.1 to about 8, or alternatively from about 0.5 to about 5; and wherein x balances the oxidation states. As will be appreciated by one of the skill in the art, and with the help of this disclosure, at least one of the La and Ce can have multiple oxidation states within the OCM catalyst composition (e.g., within a (La _a Ce _b O _x ) portion of the OCM catalyst composition), and as such x can have any suitable value that allows for the oxygen anions to balance all the cations within the (La _a Ce _b O _x ) portion of the OCM catalyst composition.

[00109] In another aspect, the OCM catalyst composition can be characterized by the general formula (Sm _a O _x )-Mn/Na ₂ WO ₄ ; wherein a is 1.0; and wherein x balances the oxidation states (e.g., x balances the oxidation state of Sm cations).

[ _00110] In an aspect of the OCM catalyst composition characterized by the general formula (Sm _a O _x )- Mn/Na ₂ WO ₄ , the (Sm _a O _x ) portion of the OCM catalyst composition can comprise Sm ₂ O ₃ . In some aspects, the (Sm _a O _x ) portion of the OCM catalyst composition can comprise, consist of, or consist essentially of Sm ₂ O ₃ .

[00111] In an aspect, a method of making an OCM catalyst composition can comprise the steps of (a) forming a Mn precursor aqueous solution comprising a Mn nitrate; (b) contacting the Mn precursor aqueous solution with a support to form a supported Mn precursor; (c) optionally drying the supported Mn precursor at a temperature of equal to or greater than about 100 ^o C to form a dried supported Mn precursor; (d) forming a rare earth element precursor aqueous solution comprising a first rare earth element nitrate and a second rare earth element nitrate; wherein the first rare earth element nitrate and the second rare earth element nitrate are different; wherein the rare earth element precursor aqueous solution is characterized by a molar ratio of second rare earth element to first rare earth element of b:1, wherein b is from about 0 to about 10.0; and wherein when b is 0, the first rare earth element is not La alone or Ce alone; (e) contacting the rare earth element precursor aqueous solution with the supported Mn precursor and/or the dried supported Mn precursor to form a supported Mn-rare earth element precursor; (f) optionally drying the supported Mn-rare earth element precursor at a temperature of equal to or greater than about 100 ^o C to form a dried supported Mn-rare earth element precursor; (g) forming a Na ₂ WO ₄ aqueous solution; (h) contacting the Na ₂ WO ₄ aqueous solution with the supported Mn-rare earth element precursor and/or the dried supported Mn-rare earth element precursor to form a supported OCM catalyst precursor mixture; (i) drying the supported OCM catalyst precursor mixture at a temperature of equal to or greater than about 100 ^o C to form a dried supported OCM catalyst precursor mixture; and (j) calcining the dried supported OCM catalyst precursor mixture at a temperature of equal to or greater than about 800 ^o C to form the OCM catalyst composition. In such aspect, the OCM catalyst composition can be characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not La alone or Ce alone; and wherein x balances the oxidation states. [00112] In an aspect, a method of making an OCM catalyst composition can comprise the steps of (a) forming a Mn precursor aqueous solution comprising a Mn nitrate; (b) contacting the Mn precursor aqueous solution with a support to form a supported Mn precursor; (c) optionally drying the supported Mn precursor at a temperature of equal to or greater than about 100 ^o C to form a dried supported Mn precursor; (d) forming a Na ₂ WO ₄ aqueous solution; (e) contacting the Na ₂ WO ₄ aqueous solution with the supported Mn precursor and/or the dried supported Mn precursor to form a supported Mn/Na ₂ WO ₄ precursor; (f) optionally drying the supported Mn/Na ₂ WO ₄ precursor at a temperature of equal to or greater than about 100 ^o C to form a dried supported Mn/Na ₂ WO ₄ precursor; (g) optionally calcining the supported Mn/Na ₂ WO ₄ precursor and/or the dried supported Mn/Na ₂ WO ₄ precursor at a temperature of equal to or greater than about 800 ^o C to form a calcined supported Mn/Na ₂ WO ₄ precursor; (h) forming a rare earth element precursor aqueous solution comprising a first rare earth element nitrate, and a second rare earth element nitrate; wherein the first rare earth element nitrate and the second rare earth element nitrate are different; wherein the rare earth element precursor aqueous solution is characterized by a molar ratio of second rare earth element to first rare earth element of b:1, wherein b is from about 0 to about 10.0; and wherein when b is 0, the first rare earth element is not La alone or Ce alone; (i) contacting the rare earth element precursor aqueous solution with the supported Mn/Na ₂ WO ₄ precursor, dried supported Mn/Na ₂ WO ₄ precursor, calcined supported Mn/Na ₂ WO ₄ precursor, or combinations thereof to form a supported OCM catalyst precursor mixture; (j) drying the supported OCM catalyst precursor mixture at a temperature of equal to or greater than about 100 ^o C to form a dried supported OCM catalyst precursor mixture; and (k) calcining the dried supported OCM catalyst precursor mixture at a temperature of equal to or greater than about 800 ^o C to form the OCM catalyst composition. In such aspect, the OCM catalyst composition can be characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not La alone or Ce alone; and wherein x balances the oxidation states.

[00113] In an aspect, a method for producing ethylene can comprise the steps of (a) introducing a reactant mixture to a reactor comprising an OCM catalyst composition; wherein the reactant mixture comprises CH ₄ and O ₂ ; wherein the OCM catalyst composition is characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not La alone or Ce alone; and wherein x balances the oxidation states; (b) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising olefins, wherein the olefins comprise ethylene; (c) recovering at least a portion of the product mixture from the reactor; and (d) recovering at least a portion of the ethylene from the product mixture.

[00114] In an aspect, the OCM catalyst compositions characterized by the general formula (E _a D _b O _x )- Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not La alone or Ce alone; and wherein x balances the oxidation states; and methods of making and using same, as disclosed herein can advantageously display improvements in one or more composition characteristics when compared to an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ .

[00115] In an aspect, the composition of OCM catalyst compositions characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not La alone or Ce alone; and wherein x balances the oxidation states; as disclosed herein can be advantageously adjusted as necessary, based on the needs of the OCM reaction, to meet target criteria, such as a target selectivity and/or a target conversion, owing to a broad range of Mn, Na, W, E and D content; and as such the OCM catalyst compositions as disclosed herein can display better performance when compared to otherwise similar OCM catalyst compositions comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ .

[00116] In an aspect, the composition of OCM catalyst compositions characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not La alone or Ce alone; and wherein x balances the oxidation states; as disclosed herein can be advantageously characterized by a reaction temperature that is lower when compared to a reaction temperature of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ . In some aspects, OCM catalyst compositions characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ , as disclosed herein, can reach the same oxygen conversion at a lower temperature when compared to a temperature necessary for reaching the same oxygen conversion of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ . Without wishing to be limited by theory, the presence of both the (E _a D _b O _x ) portion and the Mn/Na ₂ WO ₄ portion in the OCM catalyst compositions characterized by the general formula (E _a D _b O _x )- Mn/Na ₂ WO ₄ , as disclosed herein, can broaden the useful temperature range for such OCM catalyst compositions, by providing increased catalyst activity at lower temperatures, and by facilitating reaching the same conversion (e.g., oxygen conversion, methane conversion, etc.) at lower temperatures.

[00117] In some aspects, OCM catalyst compositions characterized by the general formula (E _a D _b O _x )- Mn/Na ₂ WO ₄ , as disclosed herein, can advantageously maintain high selectivity at lower temperatures; e.g., higher selectivity at lower temperatures when compared to a selectivity at the same lower temperatures of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ . In some aspects, OCM catalyst compositions characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ , as disclosed herein, can be advantageously characterized by a lower ignition temperature when compared to an ignition temperature of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ . As will be appreciated by one of skill in the art, and with the help of this disclosure, a decrease in the ignition temperature for the OCM reaction and/or a decrease in the temperature needed to achieve a 100% oxygen conversion can lead to a decrease in the overall OCM reaction temperature and to a decreased catalyst bed temperature, which can further lead to a lower temperature of hot spots within a catalyst bed, which can enhance catalyst stability. Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, the ability to use very low temperatures in OCM processes can advantageously result in saving costs, due to savings in energy costs, savings in costs associated with manufacturing materials used in OCM reactors and associated equipment, etc.

[00118] The OCM catalyst compositions characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not La alone or Ce alone; and wherein x balances the oxidation states; can advantageously display an enhanced stability of performance (e.g., in terms of conversion and selectivity) over time when compared to the stability of performance of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ . For example, the OCM catalyst compositions characterized by the general formula (E _a D _b O _x )- Mn/Na ₂ WO ₄ as disclosed herein can maintain improved conversion and selectivity over a time frame that is greater than a time frame where an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ , can maintain its conversion and selectivity values. The OCM catalyst compositions characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ as disclosed herein can have a life time that is greater than a life time of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ . As will be appreciated by one of skill in the art, and with the help of this disclosure, over time, the performance of catalysts can degrade (e.g., decay), owing to catalyst deactivation (e.g., Na leaching); and the longer a catalyst can maintain a desired performance (e.g., in terms of conversion and selectivity), the better the catalyst is. Additional advantages of the OCM catalyst compositions characterized by the general formula (E _a D _b O _x )- Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not La alone or Ce alone; and wherein x balances the oxidation states; and methods of making and using same, as disclosed herein can be apparent to one of skill in the art viewing this disclosure.

EXAMPLES

[00119] The subject matter having been generally described, the following examples are given as particular embodiments of the disclosure and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification of the claims to follow in any manner.

EXAMPLE 1

[00120] Oxidative coupling of methane (OCM) catalyst compositions were prepared as follows.

[00121] A reference catalyst composition (reference catalyst) following the general formula Mn/Na ₂ WO ₄ /SiO ₂ was prepared as follows. Silica gel (18.6 g, Davisil ^® Grade 646) was used after drying overnight. Mn(NO ₃ ) ₂ ·4H ₂ O (1.73 g) was dissolved in deionized water (18.6 mL), and then added dropwise onto the silica gel. The resulting manganese impregnated silica material was dried overnight. Na ₂ WO ₄ ·4H ₂ O (1.13 g) was dissolved in deionized water (18.6 mL), and the solution obtained was added onto the dried manganese silica material above. The resulting material obtained was dried overnight at 125°C, and then calcined at 800°C for 6 hours under airflow to obtain the Mn/Na ₂ WO ₄ /SiO ₂ reference catalyst.

[00122] A catalyst composition containing both La and Ce (catalyst #1) and following the general formula (La ₁₀ Ce ₁ O _x )-Mn/Na ₂ WO ₄ /SiO ₂ was prepared as follows. Silica gel (17.6 g, Davisil ^® Grade 646) was used after drying overnight. Mn(NO ₃ ) ₂ ·4H ₂ O (1.74 g) was dissolved in deionized water (17.6 mL), and then added dropwise onto the silica gel. The resulting manganese impregnated silica material was dried overnight. 5.61 g of La(NO ₃ ) ₃ ·6H ₂ O and 0.62 g of Ce(NO ₃ ) ₃ ·6H ₂ O were dissolved in deionized water (17.6 ml), and then added dropwise onto the dried manganese impregnated silica material obtained above. The resulting Mn-La-Ce silica impregnated material was dried overnight at 125°C. Na ₂ WO ₄ ·4H ₂ O (1.12 g) was dissolved in deionized water (17.6 mL), and the solution obtained was added onto the dried Mn-La-Ce silica impregnated material obtained above. The resulting material obtained was dried overnight at 125°C, and then calcined at 800°C for 6 hours under airflow to obtain the (La ₁₀ Ce ₁ O _x )-Mn/Na ₂ WO ₄ /SiO ₂ catalyst (catalyst #1). [00123] A catalyst composition containing Sm (catalyst #2) and following the general formula (Sm ₂ 0 ₃ )-Mn/Na ₂ W0 ₄ /Si0 ₂ was prepared as follows. 0.1 1 g of Sm ₂ 0 ₃ (with a particle size of about 15-45 nm) was mixed with deionized water (6.0 ml) to obtain an aqueous slurry solution. The obtained aqueous slurry solution was added onto 3.3 g of the reference catalyst prepared as described above. The resulting material obtained was dried overnight at 125°C, and then calcined at 800°C for 6 hours under airflow to obtain the (Sm ₂ 0 ₃ )-Mn/Na ₂ W0 ₄ /Si0 ₂ catalyst (catalyst #2).

EXAMPLE 2

[00124] The performance of the OCM catalyst compositions prepared as described in Example 1 was investigated.

[00125] OCM reactions were conducted by using catalysts prepared as described in Example 1 as follows. A mixture of methane and oxygen along with an internal standard, an inert gas (neon) were fed to a quartz reactor with an internal diameter (I.D.) of 5.0 mm heated by traditional clamshell furnace. A catalyst (e.g., catalyst bed) loading was 0.5 ml, and a total flow rate of reactants was 66.7 or 100.0 standard cubic centimeters per minute (seem). The reactor was first heated to a desired temperature under an inert gas flow and then a desired gas mixture was fed to the reactor. All OCM reactions were conducted at a methane to oxygen (CH ₄ :0 ₂ ) molar ratio of 7.4, and a reactor temperature of 825°C. The gas hourly space velocity (GHSV) was 8,000 h ^"1 , or 12,000 h ^"1 . The products obtained from the OCM reaction were analyzed by using an online Agilent 7890 gas chromatograph (GC) with a thermal conductivity detector (TCD) and a flame ionization detector (FID).

[00126] The oxygen conversion was calculated according to equation (1).

[00127] The methane conversion was calculated by usin equation (2):

wherein number of moles of C from CH4 that entered the reactor as part of the reactant number of moles of C from CH ₄ that was recovered from the reactor as part of

the product mixture.

[00128] Generally, a selectivity to a desired product or products refers to how much desired product was formed divided by the total products formed, both desired and undesired. For purposes of the disclosure herein, the selectivity to a desired product is a % selectivity based on moles converted into the desired product. Further, for purposes of the disclosure herein, a C _x selectivity (e.g., C ₂ selectivity, C ₂₊ selectivity, etc.) can be calculated by dividing a number of moles of carbon (C) from CH ₄ that were converted into the desired product (e.g., C _C2H4 , C _C2H6 , etc.) by the total number of moles of C from CH ₄ that were converted to any products, both desired and undesired (e.g., C _C2H4 , C _C2H6 , C _C2H2 , C _C3H6 , C _C3H8 , C _C4s , C _CO2 , C _CO , etc.). C _C2H4 = number of moles of C from CH ₄ that were converted into C ₂ H ₄ ; C _C2H6 = number of moles of C from CH ₄ that were converted into C ₂ H ₆ ; C _C2H2 = number of moles of C from CH ₄ that were converted into C ₂ H ₂ ; C _C3H6 = number of moles of C from CH ₄ that were converted into C ₃ H ₆ ; C _C3H8 = number of moles of C from CH ₄ that were converted into C ₃ H ₈ ; C _C4s = number of moles of C from CH ₄ that were converted into C ₄ hydrocarbons (C ₄ s); C _CO2 = number of moles of C from CH ₄ that were converted into CO ₂ ; C _CO = number of moles of C from CH ₄ that were converted into CO; etc.

[ _00129] A C ₂₊ selectivity (e.g., selectivity to C ₂₊ hydrocarbons) refers to how much C ₂ H ₄ , C ₃ H ₆ , C ₂ H ₂ , C ₂ H ₆ , C ₃ H ₈ , and C ₄ s were formed divided by the total products formed, including C ₂ H ₄ , C ₃ H ₆ , C ₂ H ₂ , C ₂ H ₆ , C ₃ H ₈ , C ₄ s, CO ₂ and CO.

[00130] The C ₂₊ selectivity was calculated by using equation (3):

[00131] As will be appreciated by one of skill in the art, and with the help of this disclosure, if a specific product and/or hydrocarbon product is not produced in a certain OCM reaction/process, then the corresponding C _Cx is 0, and the term is simply removed from selectivity calculations.

[00132] The performance differences between the catalysts prepared as described in Example 1 are demonstrated in Tables 1 and 2, wherein both tables display data collected at a GHSV of 8,000 h ^-1 .

Table 1

[00133] The data in Table 1 demonstrate that the addition of rate earth elements (La and Ce) to the Mn/Na ₂ WO ₄ /SiO ₂ in catalyst #1 allows for maintaining the same high selectivity and conversions as for the reference catalyst. The data in Table 2 demonstrate that the addition of a rare earth element (Sm) to the Mn/Na ₂ WO ₄ /SiO ₂ in catalyst #2 allows for maintaining the same high selectivity and conversions as for the reference catalyst.

[00134] However, in order to test the stability over time for the studied catalysts, a higher flowrate of 12,000 h ^-1 (as opposed to 8,000 h ^-1 in Tables 1 and 2) was employed to accelerate catalyst deactivation, and the data is displayed in Figure 1 for catalyst #1 by comparison to the reference catalyst, and in Figure 2 for catalyst #2 by comparison to the reference catalyst.

[00135] The deactivation rate of the reference catalyst for the data shown in Figure 1 was 0.63%/hr; and the deactivation rate of catalyst #1 for the data shown in Figure 1 was 0.32%/hr. The data indicate that when the OCM catalyst contains (e.g., is promoted with) rare earth element oxides, such as (La ₁₀ Ce ₁ O _x ), in addition to the Mn/Na ₂ WO ₄ /SiO ₂ , the deactivation rate is reduced and the stability over time for the resulting catalyst (catalyst #1) is improved significantly. The reference catalyst in Figure 1 has a deactivation rate that is about twice as large as the deactivation rate of the catalyst #1 that contains rare earth element oxides, such as (La ₁₀ Ce ₁ O _x ), in addition to the Mn/Na ₂ WO ₄ /SiO ₂ . Without wishing to be limited by theory, the presence of the rare earth element oxides (e.g., (La ₁₀ Ce ₁ O _x )) in the catalyst composition of catalyst #1 can increase the overall basicity of the catalyst composition, consequently increasing catalyst activity (e.g., ability of the catalyst to promote methyl radical formation); lowering the deactivation rate of the catalyst; and increasing catalyst stability over time.

[00136] The deactivation rate of the reference catalyst for the data shown in Figure 2 was 0.76%/hr; and the deactivation rate of catalyst #2 for the data shown in Figure 2 was 0.41%/hr.

[00137] The data indicate that when the OCM catalyst contains (e.g., is promoted with) rare earth element oxides, such as (Sm ₂ O ₃ ), in addition to the Mn/Na ₂ WO ₄ /SiO ₂ , the deactivation rate is reduced and the stability over time for the resulting catalyst (catalyst #2) is improved significantly. The reference catalyst in Figure 2 has a deactivation rate that is almost twice as large as the deactivation rate of the catalyst #2 that contains rare earth element oxides, such as (Sm ₂ O ₃ ), in addition to the Mn/Na ₂ WO ₄ /SiO ₂ . Without wishing to be limited by theory, the presence of the rare earth element oxides (e.g., (Sm ₂ O ₃ )) in the catalyst composition of catalyst #2 can increase the overall basicity of the catalyst composition, consequently increasing catalyst activity (e.g., ability of the catalyst to promote methyl radical formation); lowering the deactivation rate of the catalyst; and increasing catalyst stability over time.

[00138] The data in Examples 1 and 2 indicate that the rare earth metals (E, and D) present in the OCM catalysts compositions as disclosed herein allow for retaining high selectivity and conversion properties of the Mn/Na ₂ WO ₄ catalyst, while conferring improved stability to the OCM catalysts prepared as disclosed herein.

[00139] For the purpose of any U.S. national stage filing from this application, all publications and patents mentioned in this disclosure are incorporated herein by reference in their entireties, for the purpose of describing and disclosing the constructs and methodologies described in those publications, which might be used in connection with the methods of this disclosure. Any publications and patents discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior invention.

[00140] In any application before the United States Patent and Trademark Office, the Abstract of this application is provided for the purpose of satisfying the requirements of 37 C.F.R. § 1.72 and the purpose stated in 37 C.F.R. § 1.72(b)“to enable the United States Patent and Trademark Office and the public generally to determine quickly from a cursory inspection the nature and gist of the technical disclosure.” Therefore, the Abstract of this application is not intended to be used to construe the scope of the claims or to limit the scope of the subject matter that is disclosed herein. Moreover, any headings that can be employed herein are also not intended to be used to construe the scope of the claims or to limit the scope of the subject matter that is disclosed herein. Any use of the past tense to describe an example otherwise indicated as constructive or prophetic is not intended to reflect that the constructive or prophetic example has actually been carried out.

[00141] The present disclosure is further illustrated by the following examples, which are not to be construed in any way as imposing limitations upon the scope thereof. On the contrary, it is to be clearly understood that resort can be had to various other aspects, embodiments, modifications, and equivalents thereof which, after reading the description herein, can be suggest to one of ordinary skill in the art without departing from the spirit of the present invention or the scope of the appended claims.

ADDITIONAL DISCLOSURE

[00142] A first aspect, which is an oxidative coupling of methane (OCM) catalyst composition characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states.

[00143] A second aspect, which is the OCM catalyst composition of the first aspect, wherein the first rare earth element and the second rare earth element can each independently be selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), yttrium (Y), and combinations thereof.

[00144] A third aspect, which is the OCM catalyst composition of any one of the first and the second aspects, wherein the first rare earth element is basic; the second rare earth element is basic; or both.

[00145] A fourth aspect, which is the OCM catalyst composition of any one of the first through the third aspects comprising one or more oxides of E; one or more oxides of D; or both.

[00146] A fifth aspect, which is the OCM catalyst composition of any one of the first through the fourth aspects comprising a single rare earth element oxide, mixtures of single rare earth element oxides, a mixed rare earth element oxide, mixtures of mixed rare earth element oxides, mixtures of single rare earth element oxides and mixed rare earth element oxides, or combinations thereof.

[00147] A sixth aspect, which is the OCM catalyst composition of any one of the first through the fifth aspects, wherein (E _a D _b O _x ) is a catalyst for an OCM reaction in the absence of Mn/Na ₂ WO ₄ .

[00148] A seventh aspect, which is the OCM catalyst composition of any one of the first through the sixth aspects having the general formula (La _a Ce _b O _x )-Mn/Na ₂ WO ₄ ; wherein a is 1.0; wherein b is from about 0.01 to about 10.0; and wherein x balances the oxidation states.

[00149] An eighth aspect, which is the OCM catalyst composition of any one of the first through the sixth aspects having the general formula (Sm _a O _x )-Mn/Na ₂ WO ₄ ; wherein a is 1.0; and wherein x balances the oxidation states.

[00150] A ninth aspect, which is the OCM catalyst composition of the eighth aspect comprising Sm ₂ O ₃ .

[00151] A tenth aspect, which is the OCM catalyst composition of any one of the first through the ninth aspects further comprising a support, wherein at least a portion of the OCM catalyst composition contacts, coats, is embedded in, is supported by, and/or is distributed throughout at least a portion of the support.

[00152] An eleventh aspect, which is the OCM catalyst composition of the tenth aspect, wherein the support comprises MgO, Al ₂ O ₃ , SiO ₂ , ZrO ₂ , TiO ₂ , or combinations thereof.

[00153] A twelfth aspect, which is the OCM catalyst composition of any one of the first through the eleventh aspects, wherein the support is in the form of a powder, a particle, a pellet, a monolith, a foam, a honeycomb, or combinations thereof.

[00154] A thirteenth aspect, which is the OCM catalyst composition of any one of the first through the twelfth aspects, wherein Mn is present in the OCM catalyst composition in an amount of from about 0.5 wt.% to about 20 wt.%, based on a total weight of the OCM catalyst composition. [00155] A fourteenth aspect, which is the OCM catalyst composition of any one of the first through the thirteenth aspects, wherein the OCM catalyst composition is characterized by an O ₂ conversion that decreases by less than about 10% over a period of time of equal to or greater than about 50 hours.

[00156] A fifteenth aspect, which is the OCM catalyst composition of any one of the first through the fourteenth aspects, wherein the OCM catalyst composition is characterized by a deactivation rate of less than about 0.5 %/hr over a period of time of equal to or greater than about 50 hours.

[00157] A sixteenth aspect, which is the OCM catalyst composition of any one of the first through the fifteenth aspects, wherein the OCM catalyst composition is characterized by a deactivation rate that is decreased by equal to or greater than about 50% when compared to a deactivation rate of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ .

[00158] A seventeenth aspect, which is the OCM catalyst composition of any one of the first through the sixteenth aspects, wherein the OCM catalyst composition is characterized by a life time of equal to or greater than about 1,000 h.

[00159] An eighteenth aspect, which is the OCM catalyst composition of any one of the first through the seventeenth aspects, wherein the OCM catalyst composition is characterized by a life time that is increased by equal to or greater than about 50% when compared to a life time of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ .

[00160] A nineteenth aspect, which is a method of making an oxidative coupling of methane (OCM) catalyst composition comprising (a) forming an OCM catalyst precursor mixture; wherein the OCM catalyst precursor mixture comprises one or more compounds comprising a first rare earth element cation, one or more compounds comprising a second rare earth element cation, one or more compounds comprising a Mn cation, and Na ₂ WO ₄ ; wherein the first rare earth element cation and the second rare earth element cation are different; wherein the OCM catalyst precursor mixture is characterized by a molar ratio of second rare earth element to first rare earth element of b:1; and wherein b is from about 0 to about 10.0, and wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and (b) calcining the OCM catalyst precursor mixture to form the OCM catalyst composition.

[00161] A twentieth aspect, which is the method of the nineteenth aspect, wherein the OCM catalyst composition is characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states. [00162] A twenty-first aspect, which is the method of any one of the nineteenth and the twentieth aspects, wherein the OCM catalyst composition comprises Mn in an amount of less than about 20 wt.%, based on a total weight of the OCM catalyst composition.

[00163] A twenty-second aspect, which is the method of any one of the nineteenth through the twenty-first aspects further comprising (i) drying at least a portion of the OCM catalyst precursor mixture to form a dried OCM catalyst precursor mixture; and (ii) calcining the dried OCM catalyst precursor mixture to form the OCM catalyst composition.

[00164] A twenty-third aspect, which is the method of the twenty-second aspect, wherein the OCM catalyst precursor mixture is dried at a temperature of equal to or greater than about 75 ^o C.

[00165] A twenty-fourth aspect, which is the method of any one of the nineteenth through the twenty- third aspects, wherein at least a portion of the OCM catalyst precursor mixture is contacted with a support to yield a supported OCM catalyst precursor mixture.

[00166] A twenty-fifth aspect, which is the method of the twenty-fourth aspect, wherein at least a portion of the supported OCM catalyst precursor mixture is further dried and calcined to form the OCM catalyst composition.

[00167] A twenty-sixth aspect, which is the method of any one of the nineteenth through the twenty- fifth aspects, wherein the OCM catalyst precursor mixture is calcined at a temperature of equal to or greater than about 700 ^o C.

[00168] A twenty-seventh aspect, which is the method of any one of the nineteenth through the twenty-sixth aspects, wherein the one or more compounds comprising a first rare earth element cation comprises a first rare earth element nitrate, a first rare earth element oxide, a first rare earth element hydroxide, a first rare earth element chloride, a first rare earth element acetate, a first rare earth element carbonate, or combinations thereof; wherein the one or more compounds comprising a second rare earth element cation comprises a second rare earth element nitrate, a second rare earth element oxide, a second rare earth element hydroxide, a second rare earth element chloride, a second rare earth element acetate, a second rare earth element carbonate, or combinations thereof; and wherein the one or more compounds comprising a Mn cation comprises a Mn nitrate, a Mn oxide, a Mn hydroxide, a Mn chloride, a Mn acetate, a Mn carbonate, or combinations thereof.

[00169] A twenty-eighth aspect, which is an OCM catalyst produced by the method of any one of the nineteenth through the twenty-seventh aspects.

[00170] A twenty-ninth aspect, which is a method of making an oxidative coupling of methane (OCM) catalyst composition comprising (a) forming a Mn precursor comprising a Mn nitrate; (b) forming a rare earth element precursor aqueous solution comprising a first rare earth element nitrate and a second rare earth element nitrate; wherein the first rare earth element nitrate and the second rare earth element nitrate are different; wherein the rare earth element precursor aqueous solution is characterized by a molar ratio of second rare earth element to first rare earth element of b:1, wherein b is from about 0 to about 10.0; and wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; (c) contacting the rare earth element precursor aqueous solution with the Mn precursor to form a Mn-rare earth element precursor; (d) forming a Na ₂ WO ₄ aqueous solution; (e) contacting the Na ₂ WO ₄ aqueous solution with the Mn-rare earth element precursor to form an OCM catalyst precursor mixture; (f) contacting the OCM catalyst precursor mixture with a support to yield a supported OCM catalyst precursor mixture; (g) drying the supported OCM catalyst precursor mixture at a temperature of equal to or greater than about 75 ^o C to form a dried supported OCM catalyst precursor mixture; and (h) calcining the dried supported OCM catalyst precursor mixture at a temperature of equal to or greater than about 750 ^o C to form the OCM catalyst composition.

[00171] A thirtieth aspect, which is the method of the twenty-ninth aspect, wherein wherein the OCM catalyst composition is characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states.

[00172] A thirty-first aspect, which is a method of making an oxidative coupling of methane (OCM) catalyst composition comprising (a) forming a Mn precursor comprising a Mn nitrate; (b) forming a Na ₂ WO ₄ aqueous solution; (c) contacting the Na ₂ WO ₄ aqueous solution with the Mn precursor to form a Mn/Na ₂ WO ₄ precursor; (d) forming a rare earth element precursor aqueous solution comprising a first rare earth element nitrate, and a second rare earth element nitrate; wherein the first rare earth element nitrate and the second rare earth element nitrate are different; wherein the rare earth element precursor aqueous solution is characterized by a molar ratio of second rare earth element to first rare earth element of b:1, wherein b is from about 0 to about 10.0; and wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; (e) contacting the rare earth element precursor aqueous solution with the Mn/Na ₂ WO ₄ precursor to form an OCM catalyst precursor mixture; (f) contacting the OCM catalyst precursor mixture with a support to yield a supported OCM catalyst precursor mixture; (g) drying the supported OCM catalyst precursor mixture at a temperature of equal to or greater than about 75 ^o C to form a dried supported OCM catalyst precursor mixture; and (i) calcining the dried supported OCM catalyst precursor mixture at a temperature of equal to or greater than about 750 ^o C to form the OCM catalyst composition.

[00173] A thirty-second aspect, which is the method of the thirty-first aspect, wherein the OCM catalyst composition is characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states.

[00174] A thirty-third aspect, which is an oxidative coupling of methane (OCM) catalyst composition produced by (a) forming an OCM catalyst precursor mixture; wherein the OCM catalyst precursor mixture comprises a first rare earth element nitrate, a second rare earth element nitrate, a Mn nitrate, and Na ₂ WO ₄ ; wherein the first rare earth element nitrate and the second rare earth element nitrate are different; wherein the OCM catalyst precursor mixture is characterized by a molar ratio of second rare earth element to first rare earth element of b:1, wherein b is from about 0 to about 10.0; and wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; (b) drying at least a portion of the OCM catalyst precursor mixture at a temperature of equal to or greater than about 75 ^o C to form a dried OCM catalyst precursor mixture; and (c) calcining the dried OCM catalyst precursor mixture at a temperature of equal to or greater than about 750 ^o C to form the OCM catalyst composition.

[00175] A thirty-fourth aspect, which is the OCM catalyst composition of the thirty-third aspect, wherein the OCM catalyst composition is characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states.

[00176] A thirty-fifth aspect, which is a method for producing olefins comprising (a) introducing a reactant mixture to a reactor comprising an oxidative coupling of methane (OCM) catalyst composition; wherein the reactant mixture comprises methane (CH ₄ ) and oxygen (O ₂ ); wherein the OCM catalyst composition is characterized by the general formula (E _a D _b O _x )-Mn/Na ₂ WO ₄ ; wherein E is a first rare earth element; wherein D is a second rare earth element; wherein the first rare earth element and the second rare earth element are different; wherein a is 1.0; wherein b is from about 0 to about 10.0; wherein when b is 0, the first rare earth element is not lanthanum (La) alone or cerium (Ce) alone; and wherein x balances the oxidation states; (b) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising olefins; (c) recovering at least a portion of the product mixture from the reactor; and (d) recovering at least a portion of the olefins from the product mixture.

[00177] A thirty-sixth aspect, which is the method of the thirty-fifth aspect, wherein the first rare earth element and the second rare earth element can each independently be selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), yttrium (Y), and combinations thereof.

[00178] A thirty-seventh aspect, which is the method of any one of the thirty-fifth and the thirty-sixth aspects, wherein the first rare earth element and the second rare earth element can each independently be selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Gd), and combinations thereof.

[00179] A thirty-eighth aspect, which is the method of any one of the thirty-fifth through the thirty- seventh aspects, wherein the OCM catalyst composition is characterized by a life time that is increased by equal to or greater than 50% when compared to a life time of an otherwise similar OCM catalyst composition comprising (i) Mn/Na ₂ WO ₄ without (E _a D _b O _x ); or (ii) (E _a D _b O _x ) without Mn/Na ₂ WO ₄ .

[00180] While embodiments of the disclosure have been shown and described, modifications thereof can be made without departing from the spirit and teachings of the invention. The embodiments and examples described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention.

[00181] Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the detailed description of the present invention. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference.