OXIDATIVE COUPLING OF METHANE

TECHNICAL FIELD

[0001] The present disclosure relates to catalysts for oxidative coupling of methane (OCM), more specifically porous catalysts based on oxides of alkaline earth metals and rare earth elements for OCM, and methods of making and using same.

BACKGROUND

[0002] Hydrocarbons, 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 (0 ₂ ) react exothermically over a catalyst to form C ₂ H ₄ , water (H ₂ 0), and heat.

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

2CH ₄ + 0 ₂ ® C ₂ H ₄ + 2H ₂ 0 DH = - 67 kcal/mol (I)

2CH ₄ + l/20 ₂ ® C ₂ H ₆ + H ₂ 0 DH = - 42 kcal/mol (II)

[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):

CH ₄ + l.50 ₂ ® CO + 2H ₂ 0 DH = - 124 kcal/mol (III)

CH ₄ + 20 ₂ ® C0 ₂ + 2H ₂ 0 DH = - 192 kcal/mol (IV)

The excess heat from the reactions in Equations (III) and (IV) further exacerbate 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 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 catalyst systems for OCM display catalyst performance problems, stemming from a need for high reaction temperatures to achieve desired conversions and selectivities, while displaying unstable performance across wide temperature ranges. Thus, there is an ongoing need for the development of catalysts for OCM processes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a detailed description of the preferred aspects of the disclosed methods, reference will now be made to the accompanying drawing in which:

[0010] Figure 1 displays a scanning electron microscope (SEM) micrograph of a reference oxidative coupling of the methane (OCM) catalyst in Example 1 ;

[0011] Figure 2 displays an SEM micrograph of a porous OCM catalyst in Example 1 ;

[0012] Figure 3 displays a graph of oxygen conversion as a function of temperature for an

OCM reaction for different catalysts in Example 1 ;

[0013] Figure 4 displays a graph of C ₂₊ selectivities as a function of temperature for an OCM reaction for different catalysts in Example 1 ; [0014] Figure 5 displays a graph of methane conversion as a function of temperature for an OCM reaction for different catalysts in Example 1 ;

[0015] Figure 6 displays a graph of oxygen conversion as a function of temperature for an OCM reaction for different catalysts in Example 2;

[0016] Figure 7 displays a graph of C ₂₊ selectivities as a function of temperature for an OCM reaction for different catalysts in Example 2;

[0017] Figure 8 displays a graph of oxygen conversion as a function of temperature for an OCM reaction for different catalysts in Example 3; and

[0018] Figure 9 displays a graph of C ₂₊ selectivities as a function of temperature for an OCM reaction for different catalysts in Example 3.

DETAILED DESCRIPTION

[0019] Disclosed herein are porous oxidative coupling of methane (OCM) catalysts and methods of making and using same.

[0020] A method of making a porous OCM catalyst can generally comprise the steps of (a) contacting an OCM catalyst with water to form an OCM catalyst paste, wherein the OCM catalyst paste is characterized by an OCM catalyst to water weight ratio in a range of about 0.25:1 to about 10: 1; (b) drying the OCM catalyst paste at a temperature in a range of about 75°C to about 200°C to form a dried OCM catalyst; and (c) sizing the dried OCM catalyst to form the porous OCM catalyst. In an aspect, the porous OCM catalyst is characterized by the general formula A _a Z _b E _c D _d O _x ; wherein A is an alkaline earth metal; wherein Z is a first rare earth element; wherein E is a second rare earth element; wherein D is a redox agent or a third rare earth element; wherein the first rare earth element, the second rare earth element, and the third rare earth element, when present, are not the same; wherein a is 1.0; wherein b is from about 0.1 to about 10.0; wherein c is from about 0 to about 10.0; wherein d is from about 0 to about 10.0; and wherein x balances the oxidation states.

[0021] In an aspect, the porous OCM catalysts disclosed herein can be employed in autothermal OCM processes.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] As used herein, the term“effective,” means adequate to accomplish a desired, expected, or intended result.

[0028] 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. [0029] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art.

[0030] 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.

[0031] In an aspect, a porous oxidative coupling of methane (OCM) catalyst as disclosed herein can comprise any suitable OCM catalyst that has been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste, as described in more detail later herein. The porous OCM catalyst can have any suitable desired specific surface area specifications, for example as required by a specific application. For example, the porous OCM catalyst can be characterized by a specific surface area of equal to or greater than about 5 m /g, alternatively equal to or greater than about 10 m /g, alternatively equal to or greater than about 12.5 m /g, or alternatively equal to or greater than about 15 m /g, as determined by measuring nitrogen adsorption according to the Brunauer, Emmett and Teller (BET) method; although any other suitable porous OCM catalysts specific surface areas can be employed. Generally, the specific surface area of a solid material refers to the total surface area of the material divided by the mass of the material. Specific surface area can be determined by measuring the amount of physically adsorbed gas (e.g., nitrogen) according to the BET method. As will be appreciated by one of skill in the art, and with the help of this disclosure, as the porosity of a material increases, the specific surface area of the material increases as well. Generally, the porosity of a material refers to the percentage volume occupied by pores or void space within a total volume of the material. For purposes of the disclosure herein, the porous OCM catalyst can also be referred to as “treated OCM catalyst,” and the terms“porous OCM catalyst” and“treated OCM catalyst” can be used interchangeably. Further, and as will be appreciated by one of skill in the art, and with the help of this disclosure, while untreated OCM catalysts can also display a certain degree of porosity, such porosity is generally lower than a porosity of treated OCM catalysts formed from the untreated OCM catalysts; and for purposes of the disclosure herein, only the treated OCM catalyst(s) will be referred to as“porous OCM catalyst(s).” Furthermore, for purposes of the disclosure herein, the term“treated OCM catalyst” refers to an OCM catalyst that has been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste, i.e., an OCM catalyst that has been treated with water; and the term“untreated OCM catalyst” refers to an OCM catalyst that has not been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste, i.e., an OCM catalyst that has not been treated with water. In an aspect, a treated OCM catalyst can be formed by treating an untreated OCM catalyst with water, e.g., a treated OCM catalyst can be formed by subjecting an untreated OCM catalyst to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste. In such aspect, the treated OCM catalyst (e.g., porous OCM catalyst) is characterized by a porosity that is higher than a porosity of the untreated OCM catalyst.

[0032] In an aspect, the porous OCM catalyst as disclosed herein can be characterized by an open pore structure. Generally, an open pore structure refers to the pores of a porous material being fluidly connected to each other and to the exterior of the material, i.e., a gas or liquid can travel from one pore to another (e.g., a gas or liquid can diffuse between pores in a material having an open pore structure) and from the exterior of the material into the pores and vice versa. By contrast, a closed pore structure refers to the pores of a porous material being partially or completely surrounded by solid material, wherein the pores are not fully fluidly connected to each other, i.e., a gas or liquid cannot travel or travel with high resistance from one pore to another (e.g., a gas or liquid cannot diffuse between pores in a material having a closed pore structure). As will be appreciated by one of skill in the art, and with the help of this disclosure, some pores located proximal to an exterior surface of a material having a closed pore structure can be fluidly connected to the exterior of the material.

[0033] The porous OCM catalyst can have any suitable desired average pore diameter specifications, for example as required by a specific application. For example, the porous OCM catalyst as disclosed herein can be characterized by an average pore diameter from about 375 angstroms to about 1,000 angstroms, alternatively from about 400 angstroms to about 1,000 angstroms, alternatively from about 450 angstroms to about 950 angstroms, alternatively from about 500 angstroms to about 900 angstroms, alternatively equal to or greater than about 375 angstroms, alternatively equal to or greater than about 400 angstroms, alternatively equal to or greater than about 500 angstroms, or alternatively equal to or greater than about 600 angstroms, as determined according to the BET method; although any other suitable porous OCM catalysts average pore diameters can be employed. For purposes of the disclosure herein, the average pore diameter refers to an arithmetic mean of pore diameters, wherein the diameter refers to the largest dimension of any two dimensional cross section through a pore. The average pore diameter can be determined according to the BET method.

[0034] The porous OCM catalyst can have any suitable desired total pore volume specifications, for example as required by a specific application. For example, the porous OCM catalyst as disclosed herein can be characterized by a total pore volume of equal to or greater than about 0.05 cc/g, alternatively equal to or greater than about 0.1 cc/g, alternatively equal to or greater than about 0.15 cc/g, or alternatively equal to or greater than about 0.2 cc/g, as determined according to the BET method; although any other suitable porous OCM catalysts total pore volumes can be employed. Generally, the total pore volume of a porous material refers to the total void volume of the material divided by the mass of the material.

[0035] Without wishing to be limited by theory, an increased catalyst specific surface area and pore volume can reduce diffusion resistance (e.g., diffusion resistance of reactant mixture components, reactive species, product mixture components, etc.). Further, and without wishing to be limited by theory, a porous catalyst structure can provide for an increased number of catalytically active sites being accessible to reactants, thereby resulting in higher catalyst activity.

[0036] Without wishing to be limited by theory, the OCM reaction can propagate by following a mechanism according to reactions (l)-(5):

[0] _s + CH ₄ ® [OH] _s + CH ₃ (1)

2CH ₃ ® C ₂ H ₆ (2)

CH ₃ + 0 _{2 <} ® CH ₃ 0 ₂ (3)

CH ₃ + [0] _s ® [CH ₃ 0] _S (4)

2[OH] _s + l/20 ₂ ® 2[0] _s + H ₂ 0 (5) wherein“s” denotes a species adsorbed onto the catalyst surface. As will be appreciated by one of skill in the art, and with the help of this disclosure, two or more of reactions (l)-(5) can occur concurrently (as opposed to sequentially). According to reaction (1), the activation of methane occurs with the participation of active adsorbed oxygen sites [0] _s , leading to the formation of methyl radicals and adsorbed hydroxyl group [OH] _s . According to reaction (2), the coupling of methyl radicals to form the coupling product ethane (C ₂ H ₆ ) occurs in gas phase; wherein reaction (2) has a low activation energy, and therefore, does not limit the overall reaction rate. According to reaction (3), methyl radicals can react with gas phase oxygen to form an oxygenate product CH ₃ O ₂ . According to reaction (4), methyl radicals can also re-adsorb on to the catalyst surface and react with surface oxygen (e.g., active adsorbed oxygen sites [0] _s ) to form an oxygenate species [CH30] _s . The oxygenates formed according to reactions (3) and (4) can further form CO and C0 ₂ , and as such the reaction steps according to reactions (3) and (4) are the main reactions controlling the selectivity of various OCM catalysts. The mechanism of OCM reaction is described in more detail in Lomonosov, Y.I. and Sinev, M.Y., Kinetics and Catalysis, 2016, vol. 57, pp. 647-676; which is incorporated by reference herein in its entirety.

[0037] Further, and without wishing to be limited by theory, if the methyl radical can leave the catalyst surface once it is formed (e.g., owing to an increased specific surface area due to increased porosity), then the methyl radical will have less opportunity to form oxygenate species onto the catalyst surface (according to reaction (4)), which oxygenate species can be further oxidized to CO and C0 ₂ . Furthermore, and without wishing to be limited by theory, a reduction in oxygenate species formation (e.g., owing to an increased specific surface area due to increased porosity) can increase the selectivity of the OCM reaction.

[0038] In an aspect, the porous OCM catalyst as disclosed herein can be in the form of powders, particles, pellets, monoliths, foams, honeycombs, and the like, or combinations thereof. Nonlimiting examples of porous OCM catalyst particle shapes include cylindrical, discoidal, spherical, tabular, ellipsoidal, equant, irregular, cubic, acicular, and the like, or combinations thereof.

[0039] The porous OCM catalyst can have any suitable desired particle specifications, for example as required by a specific application. For example, the porous OCM catalyst can be characterized by a size suitable for use in a particular reactor (e.g., OCM reactor). As will be appreciated by one of skill in the art, and with the help of this disclosure, the catalyst size can be determined for a particular application to achieve the best performance for the OCM reaction (e.g., desired conversion, desired selectivity, etc.).

[0040] In some aspects, the porous OCM catalyst as disclosed herein can optionally comprise nanoplates, nanosheets, nanoparticles, nanorods, and the like, or combinations thereof, wherein the nanorods are characterized by an aspect ratio of from about 2:1 to about 9: 1, alternatively from about 2.5: 1 to about 7: 1, or alternatively from about 3: 1 to about 5: 1. For purposes of the disclosure herein, nanostructures, such as nanoplates, nanosheets, nanoparticles, nanorods, and the like, or combinations thereof; are defined as three-dimensional structures that have at least one dimension less than about 1,000 nm, alternatively less than about 500 nm, or alternatively less than about 100 nm. Nanoplates and nanosheets have at least one dimension less than about 1,000 nm, alternatively less than about 500 nm, or alternatively less than about 100 nm. Nanoparticles and nanorods have each of the three dimensions less than about 1 ,000 nm, alternatively less than about 500 nm, or alternatively less than about 100 nm.

[0041] In an aspect, a porous OCM catalyst as disclosed herein excludes nanofibers (e.g., nanowires), wherein nanofibers are characterized by an aspect ratio of equal to or greater than about 10:1, alternatively equal to or greater than about 25: 1, or alternatively equal to or greater than about 100:1.

[0042] In an aspect, a porous OCM catalyst suitable for use in the present disclosure can comprise a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof.

[0043] In an aspect, a porous OCM catalyst as disclosed herein can be characterized by the general formula A _a Z _b E _c D _d O _x ; wherein A is an alkaline earth metal; wherein Z is a first rare earth element; wherein E is a second rare earth element; wherein D is a redox agent or a third rare earth element; wherein the first rare earth element, the second rare earth element, and the third rare earth element, when present, are not the same; wherein a is 1.0; wherein b is from about 0.1 to about 10.0, alternatively from about 0.5 to about 8, or alternatively from about 1 to about 5; wherein c 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 d 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 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 A, Z, E and D can have multiple oxidation states within the porous OCM catalyst, and as such x can have any suitable value that allows for the oxygen anions to balance all the cations. Without wishing to be limited by theory, the different metals (A, Z, E, and D) present in the porous OCM catalyst as disclosed herein display synergetic effects in terms of conversion and selectivity. Further, and without wishing to be limited by theory, different ion radii and valences of the multiple metals (A, Z, E, and D) present in the porous OCM catalyst 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. [0044] The porous OCM catalyst as disclosed herein can comprise an alkaline earth metal (A). The alkaline earth metal (A) can be selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and combinations thereof. In an aspect, the alkaline earth metal (A) is strontium (Sr).

[0045] The porous OCM catalyst as disclosed herein can comprise a first rare earth element (Z). The first rare earth element (Z) can be selected from the group consisting of lanthanum (La), scandium (Sc), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), yttrium (Y), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and combinations thereof. In an aspect, the first rare earth element (Z) is lanthanum (La). As will be appreciated by one of skill in the art, and with the help of this disclosure, in some aspects, the first rare earth element (Z) can comprise a single rare earth element, such as lanthanum (La). Further, and as will be appreciated by one of skill in the art, and with the help of this disclosure, in some aspects, the first rare earth element (Z) can comprise two or more rare earth elements, such as lanthanum (La), and neodymium (Nd), for example; or lanthanum (La), neodymium (Nd), and promethium (Pm), as another example; etc.

[0046] The porous OCM catalyst as disclosed herein can comprise a second rare earth element (E) and/or a third rare earth element (D), wherein E and D are different. The second rare earth element (E) and the third rare earth element (D) can each independently be selected from the group consisting of scandium (Sc), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), yttrium (Y), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and combinations thereof.

[0047] As will be appreciated by one of skill in the art, and with the help of this disclosure, in some aspects, the second rare earth element (E) can comprise a single rare earth element, such as ytterbium (Yb). Further, and as will be appreciated by one of skill in the art, and with the help of this disclosure, in some aspects, the second rare earth element (E) can comprise two or more rare earth elements, such as ytterbium (Yb), and neodymium (Nd), for example; or ytterbium (Yb), and thulium (Tm), as another example; or ytterbium (Yb), neodymium (Nd), and thulium (Tm), as yet another example; etc. [0048] As will be appreciated by one of skill in the art, and with the help of this disclosure, in some aspects, the third rare earth element (D) can comprise a single rare earth element, such as ytterbium (Yb). Further, and as will be appreciated by one of skill in the art, and with the help of this disclosure, in some aspects, the third rare earth element (D) can comprise two or more rare earth elements, such as ytterbium (Yb), and neodymium (Nd), for example; or ytterbium (Yb), neodymium (Nd), and lutetium (Lu), as another example; etc.

[0049] The porous OCM catalyst as disclosed herein can comprise a redox agent (D). As will be appreciated by one of skill in the art, and with the help of this disclosure, D can be either a redox agent or a third rare earth element. The redox agent (D) can be selected from the group consisting of manganese (Mn), tungsten (W), bismuth (Bi), antimony (Sb), tin (Sn), cerium (Ce), praseodymium (Pr), and combinations thereof. A redox agent generally refers to a chemical species that possesses the ability to undergo both an oxidation reaction and a reduction reaction, and such ability usually resides in the chemical species having more than one stable oxidation state other than the oxidation state of zero (0). As will be appreciated by one of skill in the art, and with the help of this disclosure, some rare earth elements, such as Ce and Pr, can also be considered redox agents. Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, when D is Ce and/or Pr, D can be considered either a redox agent or a third rare earth element.

[0050] In some aspects, the redox agent (D) is manganese (Mn). In other aspects, the redox agent (D) is tungsten (W).

[0051] As will be appreciated by one of skill in the art, and with the help of this disclosure, in some aspects, the redox agent (D) can comprise a single element, such as manganese (Mn). Further, and as will be appreciated by one of skill in the art, and with the help of this disclosure, in some aspects, the redox agent (D) can comprise two or more redox elements, such as manganese (Mn), and tungsten (W), for example; or manganese (Mn), tungsten (W), and praseodymium (Pr), as another example; etc.

[0052] In an aspect, the second rare earth element (E) and/or the third rare earth element (D) can be basic (e.g., can exhibit some degree of basicity; can have affinity for hydrogen; can exhibit some degree of affinity for hydrogen). Nonlimiting examples of rare earth elements that can be considered basic for purposes of the disclosure herein include scandium (Sc), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), ytrium (Y), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and 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). Furthermore, 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). Furthermore, 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.

[0053] In an aspect, the porous OCM catalyst as disclosed herein can comprise one or more oxides of A; one or more oxides of Z; one or more oxides of E; one or more oxides of D; or combinations thereof. The porous OCM catalyst can comprise one or more oxides of a metal, wherein the metal comprises A, Z, and optionally E and/or D. In some aspects, the porous OCM catalyst can comprise, consist of, or consist essentially of the one or more oxides.

[0054] In an aspect, the one or more oxides can be present in the porous OCM catalyst in an amount of from about 0.01 wt.% to about 100.0 wt.%, alternatively from about 0.1 wt.% to about 99.0 wt.%, alternatively from about 1.0 wt.% to about 95.0 wt.%, alternatively from about 10.0 wt.% to about 90.0 wt.%, or alternatively from about 30.0 wt.% to about 70.0 wt.%, based on the total weight of the porous OCM catalyst. 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, in the presence of water, such as atmospheric moisture, can convert to hydroxides, and it is possible that the porous OCM catalyst will comprise some hydroxides, due to exposing the porous OCM catalyst comprising the one or more 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 oxides, in the presence of carbon dioxide, such as atmospheric carbon dioxide, can convert to carbonates, and it is possible that the porous OCM catalyst will comprise some carbonates, due to exposing the porous OCM catalyst comprising the one or more oxides to carbon dioxide (e.g., atmospheric carbon dioxide).

[0055] The one or more oxides 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.

[0056] The single metal oxide comprises one metal selected from the group consisting of A, Z, E, and D. 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 A, Z, E, and D; 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 porous OCM catalyst of the present disclosure include CaO, MgO, SrO, BaO, La ₂ 03, Sc ₂ 0 ₃ , Y ₂ 0 ₃ , Ce0 ₂ , Ce ₂ 0 ₃ , Pr ₂ 0 ₃ , Pr0 ₂ , Nd ₂ 0 ₃ , Pm ₂ 0 ₃ , Sm ₂ 0 ₃ , Eu ₂ 0 ₃ , Gd ₂ 0 ₃ , Tb ₂ 0 ₃ , Dy ₂ 0 ₃ , Ho ₂ 0 ₃ , Er ₂ 0 ₃ , LU ₂ 0 ₃ , Yb ₂ 0 ₃ , Tm ₂ 0 ₃ , W0 ₃ , Mn0 ₂ , W ₂ 0 ₃ , Sn0 ₂ , and the like, or combinations thereof.

[0057] 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 CaO, MgO, SrO, BaO, La ₂ 0 ₃ , Sc ₂ 0 ₃ , Y ₂ 0 ₃ , Ce0 ₂ , Ce ₂ 0 ₃ , Pr ₂ 0 ₃ , Pr0 ₂ , Nd ₂ 0 ₃ , Pm ₂ 0 ₃ , Sm ₂ 0 ₃ , Eu ₂ 0 ₃ , Gd ₂ 0 ₃ , Tb ₂ 0 ₃ , Dy ₂ 0 ₃ , Ho ₂ 0 ₃ , Er ₂ 0 ₃ , Lu ₂ 0 ₃ , Yb ₂ 0 ₃ , Tm ₂ 0 ₃ , W0 ₃ , Mn0 ₂ , W ₂ 0 ₃ , and Sn0 ₂ . Nonlimiting examples of mixtures of single metal oxides suitable for use in the OCM catalysts of the present disclosure include Sr0-La ₂ 0 ₃ , Sr0-Mg0-La ₂ 0 ₃ , Sr0-Yb ₂ 0 ₃ -La ₂ 0 ₃ , Sr0-Er ₂ 0 ₃ -La ₂ 0 ₃ Sr0-Ce0 ₂ -La ₂ 0 ₃ , Sr0-Mn0 ₂ -La ₂ 0 ₃ , Sr0-W0 ₃ -W ₂ 0 ₃ -La ₂ 0 ₃ , SrO-W0 ₃ -

Tm ₂ 0 ₃ -La ₂ 0 ₃ , Sr0-W0 ₃ -Tm ₂ 0 ₃ -La ₂ 0 ₃ , Sr0-Ba0-Ce0 ₂ -Er ₂ 0 ₃ -La ₂ 0 ₃ , Sr0-Ce0 ₂ -Ce ₂ 0 ₃ -Er ₂ 0 ₃ - La ₂ 0 ₃ , Sr0-Ba0-W0 ₃ -W ₂ 0 ₃ -La ₂ 0 ₃ , Sr0-Ba0-Sm ₂ 0 ₃ -W0 ₃ -W ₂ 0 ₃ -La ₂ 0 ₃ , SrO-MgO-Ce0 ₂ - Ce203-W03-W203-La ₂ 03, SrO-CaO-PrC^-P^Cb-MnO-M^Cb-I^Cb, and the like, or combinations thereof.

[0058] The mixed metal oxide comprises two or more different metals, wherein each metal can be independently selected from the group consisting of A, Z, E, and D. A mixed metal oxide can be characterized by the general formula M _ml M _m2 0 _y ; wherein M and M are metals; wherein each of the M and M can be independently selected from the group consisting of A, Z, E, and D; and wherein ml, m2 and y are integers from 1 to 15, alternatively from 1 to 10, or alternatively from 1 to 7. In some aspects, M and M can be metal cations of different chemical elements, for example M 1 can be a lanthanum cation and M2 can be a strontium cation. In other aspects, M 1 and

M can be different cations of the same chemical element, wherein M and M can have different oxidation states. For example, the mixed metal oxide can comprise Mn30 ₄ , wherein M ¹ can be a

Mn (II) cation and M can be a Mn (III) cation. Nonlimiting examples of mixed metal oxides suitable for use in the porous OCM catalyst of the present disclosure include La/SrO; LaYbC^;

SrYb ₂ 0 ₄ ; Sr ₂ Ce0 ₄ ; M¾0 ₄ ; La/MgO; Sm ₂ Ce ₂ 0 ₇ ; Er ₂ Ce ₂ 0 ₇ ; CaTni ₂ 0 ₄ ; MgYb ₂ 0 ₄ ; SrCe _(i-y) Yb _y 03, wherein y can be from about 0.01 to about 0.99; and the like; or combinations thereof.

[0059] 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 La/SrO; LaYbC^; SrYh ₂ 0 ₄ ; Sr ₂ Ce0 ₄ ; M¾0 ₄ ;

La/MgO; Sni ₂ Ce ₂ 0 ₇ ; Er ₂ Ce ₂ 0 ₇ ; CaTni ₂ 0 ₄ ; MgYb ₂ 0 ₄ ; SrCe _(i-y) Yb _y 03, wherein y can be from about 0.01 to about 0.99; and the like; or combinations thereof.

[0060] 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.

[0061] The porous OCM catalysts suitable for use in the present disclosure can be supported porous OCM catalysts and/or unsupported porous OCM catalysts. In some aspects, the supported porous OCM catalysts 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 porous OCM catalysts can comprise a support, wherein the support can be catalytically inactive (e.g., the support cannot catalyze an OCM reaction, such as S1O2). In yet other aspects, the supported porous OCM catalysts can comprise a catalytically active support and a catalytically inactive support. Nonlimiting examples of a support suitable for use in the present disclosure include MgO, Al ₂ 0 ₃ , Si0 ₂ , Zr0 ₂ , Ti0 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.

[0062] In an aspect, the porous OCM catalyst can further comprise a support, wherein at least a portion of the porous OCM catalyst 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 powders, particles, pellets, monoliths, foams, honeycombs, 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.

[0063] A supported porous OCM catalyst can have any suitable desired particle specifications, for example as required by a specific application.

[0064] In an aspect, the porous OCM catalyst 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 a further enhanced surface area of contact between the porous OCM catalyst and a reactant mixture, which in turn would result in a higher CH ₄ conversion to CH3·. 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, the support (e.g., porous support) should have a suitable pore volume (e.g., a fairly large pore volume) that allows for a sufficient amount of catalyst to be loaded onto the support, thereby reducing the mass transfer resistance for the reaction.

[0065] The porous OCM catalyst as disclosed herein can be made by using any suitable methodology. In an aspect, a method of making a porous OCM catalyst as disclosed herein can comprise a step of contacting an OCM catalyst with water to form an OCM catalyst paste. Any suitable OCM catalyst can be used for making the OCM catalyst paste, such as any suitable oxide based OCM catalyst. For purposes of the disclosure herein, the OCM catalyst used for preparing the porous OCM catalyst can also be referred to as“untreated OCM catalyst,” and the terms “OCM catalyst” and“untreated OCM catalyst” can be used interchangeably. [0066] The OCM catalyst can be made by using any suitable methodology. In an aspect, a method of making an OCM catalyst can comprise a step of forming an OCM catalyst precursor mixture; wherein the OCM catalyst precursor mixture can comprise one or more compounds comprising an alkaline earth metal cation; one or more compounds comprising a rare earth element cation; one or more compounds comprising a redox agent cation; or combinations thereof.

[0067] In some aspects, the OCM catalyst precursor mixture can comprise one or more compounds comprising an alkaline earth metal (A) cation, one or more compounds comprising a first rare earth element (Z) cation, one or more compounds comprising a second rare earth element (E) cation, and one or more compounds comprising a redox agent or a third rare earth element (D) cation; wherein the first rare earth element cation, the second rare earth element cation, and the third rare earth element cation, when present, are not the same (i.e., are different). In such aspects, the OCM catalyst precursor mixture can be characterized by a molar ratio of first rare earth element to alkaline earth metal of b: 1 , wherein b is from about 0.1 to about 10.0, alternatively from about 0.5 to about 8, or alternatively from about 1 to about 5. The OCM catalyst precursor mixture can be characterized by a molar ratio of second rare earth element to alkaline earth metal of c: 1 , wherein c 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. The OCM catalyst precursor mixture can be characterized by a molar ratio of redox agent or third rare earth element to alkaline earth metal of d: 1 , wherein d 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.

[0068] The one or more compounds comprising an alkaline earth metal cation can comprise an alkaline earth metal nitrate, an alkaline earth metal oxide, an alkaline earth metal hydroxide, an alkaline earth metal chloride, an alkaline earth metal acetate, an alkaline earth metal carbonate, and the like, or combinations thereof. The one or more compounds comprising a first rare earth element cation can comprise 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 can comprise 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 redox agent cation can comprise a redox agent nitrate, a redox agent oxide, a redox agent hydroxide, a redox agent chloride, a redox agent acetate, a redox agent carbonate, and the like, or combinations thereof. The one or more compounds comprising a third rare earth element cation can comprise a third rare earth element nitrate, a third rare earth element oxide, a third rare earth element hydroxide, a third rare earth element chloride, a third rare earth element acetate, a third rare earth element carbonate, and the like, or combinations thereof.

[0069] In some aspects, the OCM catalyst precursor mixture can be formed in the presence of water, for example by contacting water or any suitable aqueous medium with one or more compounds comprising an alkaline earth metal (A) cation, one or more compounds comprising a first rare earth element (Z) cation, and optionally one or more compounds comprising a second rare earth element (E) cation and/or one or more compounds comprising a redox agent or a third rare earth element (D) cation. In such aspects, the OCM catalyst precursor mixture comprises water.

[0070] In other aspects, the OCM catalyst precursor mixture can be formed in the absence of water (e.g., substantial absence of water; without adding water, etc.), for example by contacting the one or more compounds comprising an alkaline earth metal (A) cation, one or more compounds comprising a first rare earth element (Z) cation, and optionally one or more compounds comprising a second rare earth element (E) cation and/or one or more compounds comprising a redox agent or a third rare earth element (D) cation with each other. In such aspects, the one or more compounds comprising an alkaline earth metal (A) cation, one or more compounds comprising a first rare earth element (Z) cation, and optionally one or more compounds comprising a second rare earth element (E) cation and/or one or more compounds comprising a redox agent or a third rare earth element (D) cation can be mixed together, for example by grinding, dry blending, or otherwise intimately mixing to obtain a homogeneous mixture (e.g., OCM catalyst precursor mixture). As will be appreciated by one of skill in the art, and with the help of this disclosure, while the one or more compounds comprising an alkaline earth metal (A) cation, one or more compounds comprising a first rare earth element (Z) cation, and optionally one or more compounds comprising a second rare earth element (E) cation and/or one or more compounds comprising a redox agent or a third rare earth element (D) cation can be mixed without adding water, in some instances, a small amount of water can be added to promote or enable an uniform mixing of the compounds (e.g., an amount of water effective to promote the formation of a homogeneous mixture). Further, and as will be appreciated by one of skill in the art, and with the help of this disclosure, whether water is used or not for forming the OCM catalyst precursor mixture, the OCM catalyst precursor mixture can be further subjected to a step of drying and/or calcining as disclosed herein.

[0071] Without wishing to be limited by theory, some of the one or more compounds comprising an alkaline earth metal (A) cation, one or more compounds comprising a first rare earth element (Z) cation, one or more compounds comprising a second rare earth element (E) cation, one or more compounds comprising a redox agent or a third rare earth element (D) cation, or combinations thereof can be insoluble in water, or only partially soluble in water (e.g., lanthanum oxide, ytterbium oxide, strontium carbonate, neodymium oxide, etc.); and in such instances, these compounds cannot be solubilized in water, but rather mixed as dry materials, or with little water as to (e.g., an amount of water effective to) form a homogeneous mixture.

[0072] Further, without wishing to be limited by theory, and as will be appreciated by one of skill in the art, and with the help of this disclosure, even when the OCM catalyst precursor mixture is formed without water addition, the OCM catalyst precursor mixture can contain a small amount of water, for example water from atmospheric moisture.

[0073] In an aspect, the step of forming the OCM catalyst precursor mixture can comprise solubilizing one or more compounds comprising a metal cation, wherein the metal cation is selected from the group consisting of an alkaline earth metal cation, a rare earth element cation, a redox agent cation, and combinations thereof to form an OCM catalyst precursor aqueous solution. Solubilizing one or more compounds comprising a metal cation can comprise solubilizing the one or more compounds comprising an alkaline earth metal cation, one or more compounds comprising a first rare earth element cation, one or more compounds comprising a second rare earth element cation, and one or more compounds comprising a redox agent cation or a third rare earth element cation in an aqueous medium to form an OCM catalyst precursor aqueous solution. The aqueous medium can be water, or an aqueous solution. The OCM catalyst precursor aqueous solution can be formed by dissolving the one or more compounds comprising an alkaline earth metal cation, 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 redox agent cation or a third rare earth element cation, or combinations thereof, 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, the one or more compounds comprising an alkaline earth metal cation, one or more compounds comprising a first rare earth element cation, one or more compounds comprising a second rare earth element cation, and one or more compounds comprising a redox agent cation or a third rare earth element cation can be dissolved in an aqueous medium in any suitable order. In some aspects, the one or more compounds comprising an alkaline earth metal cation, one or more compounds comprising a first rare earth element cation, one or more compounds comprising a second rare earth element cation, and one or more compounds comprising a redox agent cation or a third rare earth element cation can be first mixed together and then dissolved in an aqueous medium.

[0074] The OCM catalyst precursor aqueous solution can be dried to form the OCM catalyst precursor mixture. In an aspect, at least a portion of the OCM catalyst precursor aqueous solution can be dried at a temperature of equal to or greater than about 75°C, alternatively of equal to or greater than about l00°C, or alternatively of equal to or greater than about l25°C, to yield the OCM catalyst precursor mixture. The OCM catalyst precursor aqueous solution can be dried for a time period of equal to or greater than about 4 hours (h), alternatively equal to or greater than about 8 h, or alternatively equal to or greater than about 12 h.

[0075] In an aspect, a method of making an OCM catalyst can comprise a step of calcining at least a portion of the OCM catalyst precursor mixture to form a calcined OCM catalyst, wherein the calcined OCM catalyst is characterized by the general formula A _a Z _b E _c D _d O _x ; wherein A is an alkaline earth metal; wherein Z is a first rare earth element; wherein E is a second rare earth element; wherein D is a redox agent or a third rare earth element; wherein the first rare earth element, the second rare earth element, and the third rare earth element, when present, are not the same; wherein a is 1.0; wherein b is from about 0.1 to about 10.0; wherein c is from about 0 to about 10.0; wherein d is from about 0 to about 10.0; 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 750°C, alternatively equal to or greater than about 800°C, or alternatively equal to or greater than about 900°C, to yield the calcined OCM catalyst. The OCM catalyst precursor mixture can be calcined for a time period of equal to or greater than about 2 h, alternatively equal to or greater than about 4 h, or alternatively equal to or greater than about 6 h.

[0076] 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 calcined OCM catalyst. Without wishing to be limited by theory, the oxygen in the OCM catalysts (e.g., calcined OCM catalysts, porous OCM catalysts) characterized by the general formula A _a Z _b E _c D _d O _x 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 OCM catalysts (e.g., calcined OCM catalysts, porous OCM catalysts) characterized by the general formula A _a Z _b E _c D _d O _x can originate in the one or more compounds comprising an alkaline earth metal cation, one or more compounds comprising a first rare earth element cation, one or more compounds comprising a second rare earth element cation, and one or more compounds comprising a redox agent cation or a third rare earth element cation, provided that at least one of these compounds comprises oxygen in its formula, as is the case with nitrates, oxides, hydroxides, acetates, carbonates, etc.

[0077] In some aspects, the method of making an OCM catalyst can further comprise contacting the OCM catalyst with a support to yield a supported catalyst (e.g., an OCM supported catalyst).

[0078] In other aspects, the method of making an OCM catalyst can comprise forming the OCM catalyst in the presence of the support, such that the resulting OCM catalyst (after the calcining step) comprises the support. For example, at least a portion of the OCM catalyst precursor aqueous solution can be contacted with a support to yield a supported OCM catalyst precursor. In an aspect, at least a portion of the supported OCM catalyst precursor can be further dried (e.g., at a temperature of equal to or greater than about 75°C) and calcined (e.g., at a temperature of equal to or greater than about 750°C) to form the calcined OCM catalyst (e.g., supported calcined OCM catalyst).

[0079] In an aspect, a method of making an OCM catalyst can comprise a step of sizing the calcined OCM catalyst (e.g., supported calcined OCM catalyst, unsupported calcined OCM catalyst) to form the OCM catalyst. The calcined OCM catalyst can be sized by using any suitable methodology. In an aspect, the calcined OCM catalyst (e.g., supported calcined OCM catalyst, unsupported calcined OCM catalyst) can be subjected to grinding, crushing, milling, chopping, and the like, or combinations thereof to form the OCM catalyst. The OCM catalyst can have any suitable desired particle specifications, for example as required by a specific application.

[0080] In an aspect, the OCM catalyst can be contacted with water or any other suitable aqueous medium (e.g., aqueous solution) to form an OCM catalyst paste, wherein the OCM catalyst paste is characterized by an OCM catalyst to water weight ratio in a range of about 0.25: 1 to about 10:1, alternatively about 0.40: 1 to about 5: 1, or alternatively about 0.50: 1 to about 1 : 1. In such aspect, contacting an OCM catalyst with water further comprises mixing, stirring, agitating, blending, etc. the OCM catalyst with the water to form a homogeneous paste. The OCM catalyst can be contacted with water in any suitable manner. For example, water can be added to the OCM catalyst, and then the water and OCM catalyst mixture can be mixed, stirred, agitated, blended, etc. to form a homogeneous paste. As another example, the OCM catalyst can be added to the water, and then the water and OCM catalyst mixture can be mixed, stirred, agitated, blended, etc. to form a homogeneous paste. As yet another example, the OCM catalyst can be contacted with water while mixing, stirring, agitating, blending, etc. to form a homogeneous paste.

[0081] In an aspect, the OCM catalyst paste can be characterized by a relatively uniform dispersion or distribution of OCM catalyst (e.g., OCM catalyst particles) in the OCM catalyst paste as a whole. In an aspect, a volumetric concentration of the OCM catalyst (e.g., OCM catalyst particles) in any 1 mm of OCM catalyst paste differs by less than about 10%, alternatively by less than about 7.5%, or alternatively by less than about 5% from an average volumetric concentration of the OCM catalyst (e.g., OCM catalyst particles) in the OCM catalyst paste as a whole.

[0082] In an aspect, the method of making the porous OCM catalyst as disclosed herein can comprise a step of drying the OCM catalyst paste to form a dried OCM catalyst. The OCM catalyst paste can be dried at a temperature in a range of about 75°C to about 200°C, alternatively about 90°C to about l75°C, or alternatively about l00°C to about l50°C, to form the dried OCM catalyst. The OCM catalyst paste can be dried for a time period in a range of about 4 h to about 24 h, alternatively about 8 h to about 20 h, or alternatively about 10 h to about 16 h.

[0083] In an aspect, a method of making the porous OCM catalyst as disclosed herein can comprise a step of sizing the dried OCM catalyst to form the porous OCM catalyst into desired particle specifications (e.g., required particle specifications). The dried OCM catalyst can be sized by using any suitable methodology. In an aspect, the dried OCM catalyst can be subjected to grinding, crushing, milling, chopping, and the like, or combinations thereof to form the porous OCM catalyst. As previously described herein, the porous OCM catalyst can have any suitable desired particle specifications, for example as required by a specific application.

[0084] In some aspects, a method of making the porous OCM catalyst as disclosed herein can comprise forming the porous OCM catalyst in the presence of a support, such that the resulting porous OCM catalyst comprises the support. For example, at least a portion of the OCM catalyst paste can be contacted with a support to yield a supported OCM catalyst paste. In some aspects, the OCM catalyst paste can be formed in the presence of a support, thereby yielding a supported OCM catalyst paste. In an aspect, at least a portion of the supported OCM catalyst paste can be further dried (e.g., at a temperature in a range of about 75°C to about 200°C) and sized as disclosed herein to form the porous OCM catalyst (e.g., supported porous OCM catalyst).

[0085] In an aspect, the porous OCM catalyst (e.g., treated OCM catalyst) as disclosed herein can be characterized by a specific surface area that is increased by equal to or greater than about 20%, alternatively equal to or greater than about 50%, alternatively equal to or greater than about 100%, alternatively equal to or greater than about 300%, or alternatively equal to or greater than about 600%, when compared to a specific surface area of an otherwise similar OCM catalyst that has not been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste (e.g., untreated OCM catalyst); and wherein the specific surface area is determined by measuring nitrogen adsorption according to the BET method. As will be appreciated by one of skill in the art, and with the help of this disclosure, the composition of the OCM catalyst doesn’t change substantially, if at all during the step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste; and as such the composition of the porous OCM catalyst and the composition of the OCM catalyst used to make the porous OCM catalyst (e.g., otherwise similar OCM catalyst, untreated OCM catalyst) are substantially the same, although the porosity of the porous OCM catalyst and the porosity of the OCM catalyst used to make the porous OCM catalyst (e.g., otherwise similar OCM catalyst, untreated OCM catalyst) are different (e.g., different specific surface area, different total pore volume, different average pore diameter, etc.)

[0086] In an aspect, the porous OCM catalyst (e.g., treated OCM catalyst) as disclosed herein can be characterized by a total pore volume that is increased by equal to or greater than about 10%, alternatively equal to or greater than about 25%, alternatively equal to or greater than about 50%, or alternatively equal to or greater than about 100%, when compared to a total pore volume of an otherwise similar OCM catalyst that has not been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste (e.g., untreated OCM catalyst); and wherein the total pore volume is determined by measuring nitrogen adsorption according to the BET method.

[0087] In an aspect, the porous OCM catalyst (e.g., treated OCM catalyst) as disclosed herein can be characterized by an average pore diameter that is increased by equal to or greater than about 10%, alternatively equal to or greater than about 20%, or alternatively equal to or greater than about 50%, when compared to an average pore diameter of an otherwise similar OCM catalyst that has not been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste (e.g., untreated OCM catalyst); and wherein the average pore diameter is determined by measuring nitrogen adsorption according to the BET method.

[0088] In an aspect, a method for producing olefins as disclosed herein can comprise (a) introducing a reactant mixture (e.g., OCM reactant mixture) to a reactor (e.g., an adiabatic reactor) comprising the porous OCM catalyst as disclosed herein, wherein the reactant mixture comprises methane (CH ₄ ) and oxygen (0 ₂ ); and (b) allowing at least a portion of the reactant mixture to contact at least a portion of the porous OCM catalyst and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins, wherein the OCM reaction is characterized by an ignition temperature.

[0089] The OCM reactant mixture can be a gaseous mixture. The OCM 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 OCM reactant mixture can comprise CH ₄ and 0 ₂ .

[0090] The 0 ₂ used in the OCM 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.

[0091] The OCM 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 (e.g., steam), nitrogen, inert gases, and the like, or combinations thereof. In an aspect, the diluent can be present in the OCM reactant mixture in an amount of from about 0.5% to about 80%, alternatively from about 5% to about 50%, or alternatively from about 10% to about 30%, based on the total volume of the OCM reactant mixture.

[0092] In an aspect, the OCM reactant mixture can be introduced to an adiabatic reactor at a temperature in a range of about 200°C to about 800°C, alternatively about 225°C to about 650°C, or alternatively about 250°C to about 500°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.

[0093] In an aspect, the OCM reactant mixture can be introduced to the adiabatic reactor (e.g., a continuous flow adiabatic reactor) comprising the porous OCM catalyst, wherein the reactor can be operated autothermally. Generally, autothermal reactions or processes create products by using only the heat produced by the reaction or process itself (i.e., without additional or external heat input). In the case of OCM reactions, a reactor can be operated autothermally (or substantially autothermally) when the reactant mixture either doesn’t have to be preheated prior to introducing to the reactor, or it has to be minimally pre-heated, owing to the OCM process generating enough heat of reaction to ignite the reactant mixture (e.g., start the OCM reaction, generate methyl radicals).

[0094] In an aspect, the OCM reactant mixture can be introduced to the reactor at a temperature effective to promote an OCM reaction. In an aspect, the OCM reaction can be characterized by an ignition temperature in a range of about 200°C to about 800°C, alternatively about 225°C to about 650°C, alternatively about 200°C to about 500°C, alternatively about 250°C to about 500°C, alternatively about 225°C to about 475°C, or alternatively about 250°C to about 450°C.

[0095] In an aspect, the OCM reaction conducted in the presence of a porous OCM catalyst (e.g., treated OCM catalyst) as disclosed herein can be characterized by an ignition temperature that is decreased by from about 50°C to about 500°C, alternatively from about 75 °C to about 400°C, or alternatively from about l00°C to about 300°C, when compared to an ignition temperature of an otherwise similar OCM reaction conducted in the presence of an OCM catalyst that has not been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste (e.g., untreated OCM catalyst). As will be appreciated by one of skill in the art, and with the help of this disclosure, employing a porous OCM catalyst can afford a lower ignition temperature, and as such the heat input for the feed (e.g., OCM reactant mixture) that is necessary to start the reaction can be lowered, resulting in energy savings.

[0096] In an aspect, the OCM reaction conducted in the presence of a porous OCM catalyst (e.g., treated OCM catalyst) as disclosed herein can be characterized by a reaction temperature needed to achieve a 100% oxygen conversion that is decreased by from about 20°C to about 500°C, alternatively from about 50°C to about 400°C, or alternatively from about 75°C to about 300°C when compared to a reaction temperature needed to achieve a 100% oxygen conversion of an otherwise similar OCM reaction conducted in the presence of an OCM catalyst that has not been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste (e.g., untreated OCM catalyst). Without wishing to be limited by theory, the increased specific surface area of the porous OCM catalyst increases catalyst activity by providing more accessible catalytically active sites per volume of catalyst, which in turn allows the porous OCM catalyst to reach the same oxygen conversion at a lower temperature. Further, without wishing to be limited by theory, the increased specific surface area of the porous OCM catalyst can shift the entire temperature profile of an OCM reaction towards lower temperatures, by increasing catalyst activity and facilitating reaching the same conversion (e.g., oxygen conversion, methane conversion, etc.) and selectivity at lower temperatures.

[0097] In an aspect, the ignition temperature as disclosed herein (e.g., from about 200°C to about 800°C), along with an overall decrease in the reaction temperature (e.g., a temperature needed to achieve 100% oxygen conversion), can minimize hot spots formation within the reactor (e.g., hot spots formation in a catalyst bed). Generally, hot spots are portions (e.g., areas) of catalyst that exceed the reaction temperature, and such hot spots can lead to thermal deactivation of the catalyst and/or enhancement of deep oxidation reactions. Deep oxidation reactions include oxidation of methane to CO _y (e.g., CO, C0 ₂ ).

[0098] In an aspect, the adiabatic 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 100 psig. In an aspect, the method for producing olefins as disclosed herein can be carried out at ambient pressure.

[0099] In an aspect, the adiabatic reactor can be characterized by a gas hourly space velocity (GHSY) 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 100,000 h ¹ , alternatively from about 500 h ¹ to about 50,000 h ¹ , alternatively from about 1,000 h ¹ to about 40,000 h ¹ , or alternatively from about 1,500 h ¹ to about 25,000 h ¹ . Generally, the GHSY relates a reactant (e.g., reactant mixture) gas flow rate to a reactor volume. GHSV is usually measured at standard temperature and pressure. [00100] In an aspect, the method for producing olefins as disclosed herein can comprise recovering at least a portion of the product mixture from the reactor, wherein the product mixture can comprise olefins, water, CO, C0 ₂ , and unreacted methane. In an aspect, a method for producing olefins as disclosed herein can comprise recovering at least a portion of the olefins from the product mixture. The product mixture can comprise C ₂₊ hydrocarbons (including olefins), unreacted methane, and optionally a diluent. 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 ).

[00101] 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 l00°C at ambient pressure), the water can be removed from the product mixture, by using a flash chamber for example.

[00102] A method for producing olefins as disclosed herein 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).

[00103] 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.

[00104] In an aspect, the 0 ₂ conversion of the OCM reaction 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 0 ₂ conversion is fairly high in OCM processes, most often approaching 90%-l00%. 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 (6): w h r in Ol number of moles of 0 ₂ that entered the adiabatic reactor as part of the reactant mixture; and oT = number of moles of 0 ₂ that was recovered from the adiabatic reactor as part of the product mixture.

[00105] In an aspect, the porous OCM catalyst (e.g., treated OCM catalyst) as disclosed herein can be characterized by an 0 ₂ conversion at the same reaction temperature that is increased by equal to or greater than about 25%, alternatively by equal to or greater than about 40%, or alternatively by equal to or greater than about 50%, when compared to an 0 ₂ conversion at the same reaction temperature of an otherwise similar OCM catalyst that has not been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste (e.g., untreated OCM catalyst).

[00106] In an aspect, the porous OCM catalyst (e.g., treated OCM catalyst) as disclosed herein can be characterized by a methane conversion at the same reaction temperature that is increased by equal to or greater than about 20%, alternatively by equal to or greater than about 30%, or alternatively by equal to or greater than about 40%, when compared to a methane conversion at the same reaction temperature of an otherwise similar OCM catalyst that has not been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste (e.g., untreated OCM catalyst). The methane conversion can be calculated by using equation (7):

^ _{t i} n

wherein ^C CH ₄ number of moles of C from CH ₄ that entered the adiabatic reactor as part of

OUt

the reactant mixture; and of moles of C from CH ₄ that was recovered from

^C CH number

4 the adiabatic reactor as part of the product mixture.

[00107] In an aspect, the porous OCM catalysts as disclosed herein can be characterized by the general formula Sr _a La _b Yb _c D _d O _x ; wherein D is selected from the group consisting of neodymium (Nd), thulium (Tm), lutetium (Lu), and combinations thereof; wherein a is 1.0; wherein b is from about 0.1 to about 10.0, alternatively from about 0.5 to about 8, or alternatively from about 1 to about 5; wherein c 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; wherein d 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 some of the Sr, La, Yb and D can have multiple oxidation states within the porous OCM catalyst, and as such x can have any suitable value that allows for the oxygen anions to balance all the cations.

[00108] In an aspect, the porous OCM catalyst (e.g., treated OCM catalyst), and methods of making and using same, as disclosed herein can advantageously display improvements in one or more catalyst characteristics when compared to conventional OCM catalysts, e.g., untreated OCM catalysts. In the case of conventional OCM catalysts (e.g., untreated OCM catalysts), if the reaction (e.g., OCM reaction) is mass transfer controlled by diffusion resistance or hindrances due to low porosity, the apparent activity of the conventional OCM catalyst will be significantly lower than its intrinsic activity. The porous OCM catalyst as disclosed herein advantageously displays an increased the number of catalytically active sites, when compared to conventional OCM catalysts (e.g., untreated OCM catalysts).

[00109] The porous OCM catalyst as disclosed herein advantageously provides for a physical catalyst structure that displays low diffusion resistance or hinderance, for example when compared to an otherwise similar OCM catalyst that has not been subjected to a step of contacting with water to form an OCM catalyst paste followed by a step of drying the paste. Without wishing to be limited by theory, the increased porosity of the porous OCM catalyst as disclosed herein allows methyl radicals to leave the catalyst surface more easily, thereby providing the methyl radicals with fewer chances to be re-adsorbed and be oxidized. Furthermore, and without wishing to be limited by theory, the increase in surface area of the porous OCM catalyst as disclosed herein provides more opportunity for interaction of the reactants with active sites, which further benefits catalyst activity.

[00110] The porous OCM catalyst as disclosed herein can advantageously be cost effective and/or commercially feasible. Additional advantages of the porous OCM catalyst as disclosed herein; and methods of making and using same, can be apparent to one of skill in the art viewing this disclosure.

EXAMPLES

[00111] 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

[00112] Reference catalyst #1 (Sri oYbo ₁ Lao ₉ Ndo ₇ O _x ) was prepared with the following preparation method. To obtain 20 g of Sri oYbo ₁ Lao ₉ Ndo ₇ O _x catalyst, 10.58 g of Sr(N0 ₃ ) ₂ , l9.48g of La(N0 ₃ ) ₃ x 6H ₂ 0, 15.35 g of Nd(N0 ₃ ) ₃ x 6H ₂ 0 and 2.26 g of Yb(N0 ₃ ) ₃ x 5H ₂ 0 were mixed and dissolved into 100 mL of DI water. The mixture obtained was dried at l20°C overnight. The dried material was then calcined at 900°C for 6 hours to produce the reference catalyst #1.

[00113] The same calcined catalyst was also“treated” by mixing the catalyst with sufficient DI water to form a thick paste (2.25 g dry reference catalyst #1 + 4 mL water), and subsequently dried at l20°C overnight. This was done to test the effects of excessive moisture on catalyst performance. The resultant catalyst was named catalyst #1. Catalyst #1 is also characterized by general formula Sr ₁ oYbo ₁ Lao ₉ Ndo ₇ O _x . [00114] Other catalysts, with different compositions, were also treated with DI water to test whether the effects observed can be achieved in other formulations, and the results are displayed in Examples 2 and 3.

[00115] Performance test. The catalysts obtained above were performance tested in a 2.3 mm ID quartz tube reactor. The reactor was loaded with 20 mg of catalyst, which was sized to 35 to 60 mesh. A mixture of methane and oxygen at a fixed CH ₄ :0 ₂ ratio of 7.4 was fed to the reactor at a total flow rate of 40.0 seem. Products obtained were analyzed by using online GC with TCD and FID detectors.

[00116] Scanning Electron Microscope (SEM) images. The SEM images of the catalysts are obtained by using JEOL 7800F.

[00117] Surface area and pore volume were obtained by measuring nitrogen adsorption according to the Brunauer, Emmett and Teller (BET) method.

[00118] Sr_ _j _nYbrn Lan Ndo70 - based catalysts. The SEM image of the reference catalyst #1 is shown in Figure 1. It can be seen that this catalyst consists of plate-like layered crystals. The thickness of these plate-like layers are - 100 nm or less.

[00119] The SEM image of catalyst #1 is shown in Figure 2. In the image, it can be seen that the former plate-like layered crystals observed for reference catalyst #1 are changed after “treatment” with DI water. Such change created by the addition of water opens up the pores, increasing porosity.

[00120] BET surface area, pore volume and average pore diameter results are presented in Table 1, and it can be seen that surface area, pore volume and average pore diameter are increased significantly with water treatment. As discussed earlier, the increase in surface area provides more opportunity for reactants interaction with active sites, which will benefit catalyst activity. The increase in pore volume and pore diameter will reduce the mass transfer resistance and benefit the catalyst activity as well.

Table 1. BET Surface Area, Pore Volume and average pore diameter for Reference

Catalyst #1 and Catalyst #1

[00121] Performance comparisons between the two catalysts (reference catalyst #1 and catalyst #1) are shown in Figures 3-5. A noticeable improvement in catalyst activity is observed with the addition of water (i.e., to form catalyst #1) to the original catalyst (reference catalyst #1). For 0 ₂ conversion, catalyst #1 reaches 90% or higher oxygen conversion at 550°C, while the original (reference catalyst #1) sample requires 650°C to reach 90% or higher oxygen conversion, indicating a much higher activity increase with the water treated sample. Such significant temperature reduction to achieve high 0 ₂ conversion will strongly benefit the low inlet temperature operation.

[00122] The best C ₂₊ selectivity obtained with catalyst #1 was 79.0%, while the original sample (reference catalyst #1) reached 79.5%. Thus, a marked improvement in activity was obtained via water treatment without seeing a clear loss in C ₂₊ selectivity.

[00123] 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., Cam, Cam, etc.) by the total number of moles of C from CH ₄ that were converted (e.g., Cam, Cam, C m, Cc3 _H 6 _? C _C 3 _H 8 _? C _C4s , C _{( ()2} . C ₍ o, etc.). Cam = number of moles of C from CH ₄ that were converted into C ₂ H ₄ ; C _C2 H ₆ ⁼ number of moles of C from CH ₄ that were converted into C ₂ H ₆ ; Ca = number of moles of C from CH ₄ that were converted into C ₂ H ₂ ; Cc3 _H 6 ⁼ number of moles of C from CH ₄ that were converted into C ₃ H ₆ ; Cc3 _H 8 ⁼ number of moles of C from CH ₄ that were converted into C ₃ H ₈ ; Cc _4s = number of moles of C from CH ₄ that were converted into C ₄ hydrocarbons (C ₄ s); Cco2 = number of moles of C from CH ₄ that were converted into C0 ₂ ; Cco ⁼ number of moles of C from CH ₄ that were converted into CO; etc.

[00124] 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, C0 ₂ and CO. For example, the C ₂₊ selectivity can be calculated by using equation (8):

[00125] 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 Cc _x is 0, and the term is simply removed from selectivity calculations.

[00126] A much higher methane conversion was achieved at low temperatures for the water- treated sample (catalyst #1) than for the original sample (reference catalyst #1) (16.07% vs 4.51% at 550°C), which is consistent with increased 0 ₂ conversion.

EXAMPLE 2

[00127] Reference catalyst #2 (Sri oYbo ₁ Lao ₉ Tmo ₇ O _x ) and catalyst #2 were prepared and tested as disclosed in Example 1. To prepare catalyst #2, 0.6 g dry reference catalyst #2 + 1.3 mL water were used to form a thick paste that was subsequently dried at l20°C overnight.

[00128] The performance comparisons of untreated reference catalyst #2 and water treated catalyst #2 are shown in Figures 6 and 7. Again, an improvement in catalyst activity was observed via the addition and mixture of water into the calcined catalyst, while the selectivity observed was similar to the one without water treatment.

EXAMPLE 3

[00129] Reference catalyst #3 (Sri oYbo ₁ Lao ₉ Luo ₃ O _x ) and catalyst #3 were prepared and tested as disclosed in Example 1. To prepare catalyst #3, 1.0 g dry reference catalyst #3 + 1.4 mL water were used to form a thick paste that was subsequently dried at l20°C overnight.

[00130] The performance comparisons of untreated reference catalyst #3 and water treated catalyst #3 are shown in Figures 8 and 9. Again, a similar trend was observed with an improvement in catalyst activity with the water treatment; wherein the selectivities obtained were close.

[00131] Table 2 summarizes catalytic activity improvement with water treatment. The 0 ₂ conversion obtained at 550°C was used for comparison. “Activity increase” was calculated based on 0 ₂ conversion reaction rate constant change before and after the water treatment. As shown in Table 2, the addition of water yields a 4.4-fold increase in activity for catalyst #1 ; 4.5- fold increase for catalyst #2; and 1.8-fold increase for catalyst #3. As previously discussed herein, such activity improvement is important for the catalyst to be used with autothermal operation with low feed temperature.

Table 2. Activity Comparison Before and After Water Treatment

[00132] With the porous OCM catalyst as disclosed herein, the following advantage was demonstrated experimentally comparing to the reference catalyst: significantly improved catalyst activity; which enables the reaction to be carried out autothermally at low feed temperature.

[00133] 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.

[00134] 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. [00135] 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.

[00136] 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.