METHANOL CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Patent Application No. 62/478,150, filed March 29, 2017, the entire contents of which are hereby incorporated by reference in their entirety.

BACKGROUND [0002] Conversion of synthesis gas (CO and H ₂ ) to methanol (CH3OH) has been studied for some time and is known to be energy intensive (primarily in the production of the syngas). However, the conversion of CO2 and H ₂ to CH3OH has only been attempted recently, as a result of an increased desire to use CO2 captured from plant effluents and H ₂ produced from renewable resources to produce a valuable CH3OH product. [0003] Ternary Cu-ZnO/Al ₂ 03 catalysts that are currently employed for methanol synthesis from mixed syngas (CO/CO2/H2) exhibit limited activity in CO2 hydrogenation. The likely reasons for this are (1) the inhibiting effect of water, which is produced as a by-product during the reaction, (2) low selectivity, owing to the catalyst's activity in the detrimental reverse water- gas shift (RWGS) reaction, and (3) insufficient stability of the catalyst, due to water-induced sintering of the active phase.

[0004] Recently, several new approaches to the conversion of CO2 and H ₂ directly to methanol have been proposed. The first, advanced by researchers Kothandaraman et al. (J. Am. Chem. Soc, 2016, 138:(3) 778-81), involves the use of a homogeneous catalyst based on ruthenium that does not decompose at high temperatures. The second uses a heterogeneous catalyst proposed by Martin et al. (Angewandte Chemie Int 'l., 2016, Vol. 55, 6261-6265). In particular, the second process uses In(N03)3 impregnated on Zr0 ₂ , AI2O3, ZnO, T1O2, Sn0 ₂ , MgO, or carbon, which has then been calcined at no higher than 573 °K (300 °C) to form an In ₂ 03/supported catalyst.

[0005] Although various catalysts for conversion of CO2 to CH3OH have been described, there remains a need for additional catalysts having improved stability and/or catalytic activity. SUMMARY

[0006] A discovery has been made that addresses the above problems. The discovery is premised on increasing the oxygen vacancies in the crystal lattice of a zirconia-based catalyst by incorporating aliovalent metal (M ¹ ) cations into the crystal lattice structure of zirconia. Without wishing to be bound by theory, it is believed that increasing the oxygen vacancies will increase the catalytic activity of the catalyst. In particular instances, aspects of the present invention employ a unique class of aliovalent metal cation doped fluorite catalysts (e.g., an india stabilized zirconia) to selectively convert CO2 and H2 to methanol in high yield. Such catalysts can be less susceptible to poisoning by the water by-product produced during the reaction. The catalysts can also have higher activity than those currently produced using conventional impregnation methods. Process described herein can catalytically convert CO2 and H2 to methanol according the following reaction.

[0007] Certain embodiments are directed to an aliovalent metal cation stabilized (doped) metal oxide (M ¹ M ² 0), where M ¹ is aliovalent metal cation and M ² is a Column 4 metal and/or Cerium (Ce)) catalyst capable of catalyzing a carbon dioxide to methanol reaction. The catalyst can include aliovalent metal cations incorporated into the lattice framework of a metal oxide. Thus, the catalyst of the present invention is unsupported in preferred instances. In certain aspects, the catalyst can have a lattice framework that is a cubic fluorite structure. The aliovalent metal cation can be indium (In), scandium (Sc), gallium (Ga), lanthanum (La), praseodymium (Pr), neodymium (Nd), europium (Eu), or mixtures thereof. In certain aspects, the M'M ² 0 catalyst can have a formula of M ^x _x Μ ² ι _-χ θ2-δ, where 0.05 < x < 0.9 and δ is a number that varies such that the composition is charge neutral (e.g., 1.8 to less than 2.0) and M ¹ is In, Sc, Ga, La, Pr, Nd, Eu, or mixtures thereof and M ² is zirconium (Zr), titanium (Ti), Ce or mixtures thereof. In a preferred embodiment, the catalyst is an india stabilized zirconia oxide (InZrO) catalyst capable of catalyzing a carbon dioxide to methanol reaction, and can have a formula of Ιη _χ Ζπ-χθ2-δ, where 0.05 < x < 0.9 and δ is a number that varies such that the composition is charge neutral (e.g, 1.0 to less than 2.0). In certain aspects, x can be about 0.05 and the catalyst can have a formula of Ino.o5Zro.9s02-5. In a further aspect, x can be about 0.1 and the catalyst can have a formula of Ino.iZro.902-5. In still a further aspect, x can be about 0.2 and the catalyst can have a formula of Ino.2Zro.802-5, which can have an X-ray diffraction pattern as shown in FIG. 3, which is indicative of a single fluorite crystal structure. [0008] Other embodiments are directed to methods for producing an aliovalent metal cation zirconia fluorite catalyst, e.g., an india doped zirconia fluorite catalyst. Solid state, sol-gel, or co-precipitation methods can be used in conjunction with calcining or high temperature sintering to produce the catalysts described herein. In some embodiments, the method can include heat-treating a M ¹ OM ² 0 precursor material or a M ¹ ^! ² precursor material at temperatures sufficient to form the aliovalent metal cation zirconia catalyst (M ¹ M ² 0) having a fluorite crystal structure. M ¹ can be an aliovalent metal. Non-limiting examples of such aliovalent metals include indium (In), scandium (Sc), gallium (Ga), lanthanum (La), praseodymium (Pr), neodymium (Nd), europium (Eu), or mixtures thereof. In preferred instances, the aliovalent metal is indium. In embodiments to form the M ¹ OM ² 0 precursor material, the precursor material can be formed by combining an IV^O (e.g., ImCb) particulate material and IV^O (e.g., ZrCh) particular material at a mole fraction of 0.05 :0.95 to 0.9:0.1 to form a precursor mixture. The M ¹ M ² 0 precursor material (e.g. a shape formed particulate material) can be sintered at 1,000 to 1,500 °C to form the aliovalent metal cation doped metal oxide catalyst (M ¹ M ² 0) having a fluorite crystal structure. Sintering conditions can also include (i) heating at about 5 °C per minute from 20 to 1,500 °C, (ii) holding for 12 hours at 1,500 °C, and then (iii) cooling from 1,500 °C to 20 °C at about 5 °C per minute. In some embodiment, a metal oxide (M ^x O) particulate material and a M ² 0 particulate material can be combined in a mole fraction of 0.05 :0.95 to 0.9 to 0.1 to form a precursor mixture. In some embodiments, the M ¹ ^! ² precursor material can be obtained by gelling or co-precipitation a M ¹ precursor and a M ² precursor solution (e.g., M ¹ and Zr nitrate salts) to form a M ¹ ^! ² precursor mixture or co-precipitating a M ¹ precursor and a M ¹ precursor. The M ¹ ^! ² precursor material can be heated and then calcined to form the M ¹ M ² 0 catalyst of the present invention having the fluorite crystal structure. In certain aspects, M ¹ to M ² 0 can be present in a 0.05, 0.1, 0.15, 0.2, 0.5, 0.8, 0.9, or 0.25 to 0.95, 0.25 to 0.90, 0.25 to 0.085, or 0.25 to 0.75 mole fraction.

[0009] Other embodiments are directed to methods for hydrogenating CO2 to form methanol. In one aspect, the method can include contacting CO2 and H2 reactants with an aliovalent metal cation fluorite catalyst of the present invention under conditions sufficient to from methanol (CH3OH). In certain aspects the CO2 and H2 reactants are provided at a C02:H2 molar ratio of about 1 :3. The conditions can comprise a performing the reaction at a temperature of 200° C to 300 °C and/or a pressure of 0.1 to 6 MPa. In a further aspect the conditions can include a gas hourly space velocity (GHSV) of from 500 to 200000 h ^"1 , preferable between 2000 and 50000 h ^"1 , more preferably between 2000 and 20000 h ^"1 . In certain aspects the methods use an aliovalently doped fluorite catalyst having a formula of M ^x _x Μ ² ι-χθ2-δ, where 0.05 < x < 0.9 and δ is a number that varies such that the catalyst is charge neutral, and M ¹ and M ² are defined above. In some instances, the catalyst is InZrO fluorite catalyst. [0010] The following includes definitions of various terms and phrases used throughout this specification.

[0011] The term "milling" refers to the operation of breaking a solid material into a desired grain or particle size.

[0012] The term "aliovalent" refers to an atom having a different valence than the native atom it replaces. By way of example, in a metal oxide, a metal atom that is replacing an original metal atom of the metal oxide is of a different oxidation state than the original metal atom. Aliovalent substitutions change the overall charge within the crystal structure of the metal oxide, but the metal oxide remains neutral in charge through loss of oxygen or incorporation of a cationic counter ion (e.g., Na ⁺ , H ⁺ , or H4 ⁺ ). [0013] The phrase "fluorite structure" refers to one of the crystal structures of the AX2 type (A is one or more metal atoms and X is oxygen) where the A atoms are arranged in face centered cubic lattice in which four A atoms are contained in a unit lattice.

[0014] The term "calcination" refers to a thermal treatment process applied to a metal precursor, in the presence of an oxygen source (e.g. air), to oxidize the metal precursor to its corresponding metal oxide.

[0015] The term "sintering" refers to heat treatment of a metal oxide at temperatures 0.3 times the metal boiling point (e.g., above 1000 °C for InZrO) without melting the metal oxide to point of liquefaction.

[0016] The term "bulk metal oxide catalyst" as that term is used in the specification and/or claims, means that the catalyst includes one metal, and does not require a carrier or a support.

[0017] The terms "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%. [0018] The terms "wt.%," "vol.%," or "mol.%" refers to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt.% of component. [0019] The term "substantially" and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

[0020] The terms "inhibiting" or "reducing" or "preventing" or "avoiding" or any variation of these terms, when used in the claims and/or the specification includes any measurable decrease or complete inhibition to achieve a desired result. [0021] The term "effective," as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0022] The use of the words "a" or "an" when used in conjunction with any of the terms "comprising," "including," "containing," or "having" in the claims, or the specification, may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one."

[0023] The words "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 "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0024] The catalysts of the present invention can "comprise," "consist essentially of," or "consist of particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phase "consisting essentially of," in one non- limiting aspect, a basic and novel characteristic of the catalysts of the present invention is the incorporation of an aliovalent metal cation into the lattice framework of the catalysts, which provides for stable catalysts that can efficiently catalyze a direct hydrogenation of carbon dioxide to methanol reaction.

[0025] In the context of the present invention at least the following twenty embodiments are provided. Embodiment 1 relates to an aliovalent metal (M ¹ ) cation stabilized fluorite catalyst, the catalyst containing an aliovalent metal (M ¹ ) cation incorporated into the lattice framework of the metal oxide (M ² 0), wherein M ¹ comprises indium (In), scandium (Sc), gallium (Ga), lanthanum (La), praseodymium (Pr), neodymium (Nd), europium (Eu), or mixtures thereof, and M ² comprises a Column 4 metal, cerium (Ce) or mixtures thereof. Embodiment 2 relates to the M ¹ M ² 0 catalyst of embodiment 1, wherein the lattice framework is a cubic fluorite structure. Embodiment 3 relates to the M ¹ M ² 0 catalyst of any one of embodiments 1 to 2, wherein the Column 4 metal is zirconium (Zr), or titanium (Ti), preferably Zr. Embodiment 4 relates to the M ¹ M ² 0 catalyst of embodiment 3, having a formula of M ^x _x Μ ² ι-χθ2-δ, where 0.05 < x < 0.9 and δ is a number that varies such that the catalyst is charge neutral. Embodiment 5 relates to the MZrO catalyst of embodiment 4, wherein M ¹ is In and M ² is Zr and x is about 0.5, and the catalyst has a formula of Ino.sZro.sC -s. Embodiment 6 relates to the MZrO catalyst of embodiment 4, wherein M ¹ is In and M ² is Zr and x is about 0.9, and the catalyst has a formula of Ino.9Zro.i02-5. Embodiment 7 relates to the MZrO catalyst of embodiment 4, wherein M ¹ is In and M ² is Zr and x is about 0.05, and the catalyst has a formula of Ino.2Zro. ₈ 02-5. Embodiment 8 relates to the MZrO catalyst of embodiment 7, having the X- ray diffraction pattern of:

0

2Θ

[0026] Embodiment 9 relates to a method for producing an aliovalent (Ml) cation stabilized metal (M2) oxide (M1M20) fluorite catalyst. This method includes the steps of heat-treating a M10M20 precursor material or a M1M2 precursor material at temperatures sufficient to form the (M1M20) catalyst having a fluorite crystal structure. Embodiment 10 relates to the method of embodiment 9, further including the step of forming the M1M20 precursor material by combining a MIO particulate material and a M202 particulate material at a mole fraction of 0.05:0.95 to form a precursor mixture, and wherein heat-treating includes sintering the mixture at 1,000 to 1,500 °C to form the M1M20 having a fluorite crystal structure, preferably 1200 to 1500 °C. Embodiment 11 relates to the method of embodiment 9, further including the step of forming the M1M2 precursor mixture by gelling or co-precipitating a Ml precursor and a M2 precursor solution to form a M1M2 precursor material, and wherein heat-treating includes calcining the M1M2 precursor material at 800 to 1000 °C to form the M1M20 having a fluorite crystal structure. Embodiment 12 relates to the method of any one of embodiments 9 to 11, wherein Ml is selected from the group consisting of indium (In), scandium (Sc), gallium (Ga), lanthanum (La), praseodymium (Pr), neodymium (Nd), europium (Eu), or mixtures thereof. Embodiment 13 relates to the method of any one of embodiments 9 to 12, wherein M2 is zirconium (Zr), titanium (Ti), cerium (Ce), or mixtures thereof. Embodiment 14 relates to the method of embodiment 13, wherein M1M20 is InZrO. Embodiment 15 relates to the method of any one of embodiments 9 to 14, wherein M1M20 fluorite catalyst is a bulk catalyst.

[0027] Embodiment 16 relates to a method for hydrogenating C02 to form methanol. This method includes the steps of contacting C02 and H2 with the aliovalent metal cation doped fluorite catalyst of any one of embodiments 1 to 9 under conditions sufficient to from methanol (CH30H). Embodiment 17 relates to the method of embodiment 16, wherein the C02 and H2 are provided at a C02:H2 molar ratio of about 1 :3. Embodiment 18 relates to the method of any one of embodiments 16 to 17, wherein the conditions include a temperature of 200° C to 300 °C, a pressure of 0.1 to 6 MPa, or both. Embodiment 19 relates to the method of any one of embodiments 16 to 18, wherein the conditions include a gas hourly space velocity (GHSV) of from 500 to 200,000 h-1, preferably between 2000 and 50,000 h-1, more preferably between 2,000 and 20,000 h-1. Embodiment 20 relates to the method of any one of embodiments 16 to 19, wherein the aliovalently doped fluorite catalyst has a formula of Μ1χΜ21-χ02-δ, where: 0.05 < x < 0.9 and δ is a number that varies such that the catalyst is charge neutral; Ml is indium (In), scandium (Sc), gallium (Ga), lanthanum (La), praseodymium (Pr), neodymium (Nd), europium (Eu), or mixtures thereof; and M2 is a Column 4 metal, cerium (Ce) or mixtures thereof.

[0028] Other obj ects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

DESCRIPTION OF THE DRAWINGS

[0029] The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of the specification embodiments presented herein.

[0030] FIG. 1 is an illustration of india stabilized zirconia (or ISZ) structure.

[0031] FIG. 2 is a schematic of a method to produce methanol using the catalysts of the present invention. [0032] FIG. 3 is an X-ray diffraction (XRD) pattern for Ino.2Zro.802-5 of the present invention.

[0033] FIG. 4 is a prior art XRD pattern for ImCb on ZrCh support.

DESCRIPTION

[0034] A discovery has been made that addresses the problems of catalytic conversion of carbon dioxide to methanol, notably, deactivation of the catalyst by water and/or high temperatures. The solution is premised on using an unsupported aliovalent metal cation metal oxide catalyst. Specifically, a catalyst having a fluorite crystal structure with metal +4 ion (e.g., Zr, Ti, Ce ion) replaced with an aliovalent cation (e.g., In, Sc, Ga, La, Pr, Nd, Eu, +3 cations or mixtures thereof) is disclosed. [0035] These and other non-limiting aspects of the present invention are discussed in the following subsections.

A. Catalyst Structure [0036] Embodiments of the inventions utilize an aliovalently doped fluorite catalyst, (e.g., india stabilized zirconia (ISZ or InZrO)). By substituting +3 valence ion (M ¹⁺³ ) for one of the +4 valent M ²⁺⁴ (e.g., Zr, Ti, or Ce) ions in M ² 0 ₂ crystal lattice, an oxygen vacancy can be created. By way of example, In ⁺³ can be substituted for a Zr ⁺⁴ atom in the crystal structure of zirconia, thus forming one or more oxygen vacancies. FIG. 1 is an illustration of In replacing Zr in a fluorite crystal structure. The oxygen vacancy can participate actively in chemical reactions, such as methanol synthesis, oxidative coupling of methane, oxygen separation and others. Another advantage of the catalyst of the present invention is that the catalyst can have a single crystal structure as determined by known crystallography methods such as XRD. By way of example, the XRD pattern exemplified in FIG. 3 of the Examples demonstrates that InZrO is a single crystal structure. Due to the single crystal structure the catalyst can have more oxygen vacancies, which provides increase catalyst activity as compared to catalyst having a metal impregnated in a zirconia support.

[0037] The catalyst of the present invention can have the general formula of: where:

M ¹ is In, Sc, Ga, La, Pr, Nd, Eu, or mixtures thereof; M ² is Zr, Ti, Ce, or mixtures thereof; and

0.05 < x < 0.9 and δ is a number that varies such that the composition is charge neutral. [0038] In certain embodiments, the oxidation state of the M ¹ is +3 (e.g., In ⁺³ , Sc ⁺³ , Ga ⁺³ , La ⁺³ , Pr ⁺³ , Nd ⁺³ , Eu ⁺³ , or mixtures thereof). In certain embodiments, the x is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or any value there between. By way of example, M ¹ can be In ⁺³ , M ² can be Zr, and x can be 0.05, 0.1, 0.2, 0.5, or 0.8 and the formula for the InZrO catalyst can be Ino.o5Zro.950 ₂ -5, Ino.iZro.90 ₂ -5, Ino.2Zro.80 ₂ -5, Ino.sZro.sC -s, Ino.8Zro.20 ₂ -5, respectively.

B. Methods of Making the Catalysts of the Present Invention

[0039] The catalysts of the present invention can be prepared by a number of routes, including sol-gel, co-precipitation, or solid state synthesis that results in a single crystal structure being formed. In certain aspects, the catalyst can include 5, 10, 15, 20, 30, 50, 80 or 90 mol. % of the lower valent metal cation.

1. Solid State Method

[0040] In a solid state method, the aliovalent metal oxide (e.g., ImCb) and M ² 0 (e.g., ZrCh) can be combined in the proper ratios. In certain aspects, the catalyst includes 5 to 90, 10 to 85, or 20 to 70, mol.% or about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85 or 90 mol% or any range or value there between of the lower valent metal cation, based on the total moles of moles of metal in the catalyst (e.g. moles of In plus moles of Zr). The particulate materials can be milled intensively for 24 hours in a solvent (e.g., an alcohol such as isopropanol), dried, milled again to form a homogeneously mixed particulate material (e.g., a powder). In some embodiments, pore formers are added to the solution prior to sintering. The homogenously mixed particulate material can be sintered at 1,000 to 1,500 °C (e.g., 1000, 1100, 1200, 1300, 1400, or 1500 °C, or any value there between) for sufficient time to create the desired single crystal structure having the aliovalent metal cation incorporated into the M ² 0 (e-g-, ZrCte) fluorite crystal structure. In some embodiments, the sintering temperature can be about 1,500 °C. Without wishing to be bound by theory, it is believed that sintering at an elevated temperature results in the aliovalent metal cation diffusing into the M ² crystal structure producing oxygen vacancies. In certain aspects, the sintering process can include (i) heating at about 5 °C per minute to the desired temperature (e.g., 1,000 to 1,500 °C, or about 1,500 °C), (ii) holding for 10, 12, 14 or 24 hours at the desired temperature (e.g., 1,000 to 1,500 °C, or about 1,500 °C), and then (iii) cooling from the desired temperature (e.g., 1,000 to 1,500 °C, or about 1,500 °C to 20 °C at about 5 °C per minute. In other embodiments, cooling can be achieved by natural convection. In certain aspects the sintering is performed in the presence of an inert gas (e.g., Ar, He, N ₂ ). [0041] In some embodiments, prior to sintering the aliovalent metal, M ¹ , oxide / M ² oxide precursor material can be shape formed. Shape forming can include pelletizing, tableting, or extruding a particulate material into a desired form (e.g. pellet, tablet or the like) under pressure (e.g., using a hydraulic press at 1 to 80 MPa in the absence of additives (e.g., binders, surfactants, etc). In certain aspects the precursor mixture is pelletized. The pellets can be any size or thickness that is suitable for a reactor. In some embodiments, the pellets are about 10 to 30 mm in diameter and about 0.5 to 50 mm thick. 2. Sol-Gel Method

[0042] In some embodiments, the M ¹ ^! ² precursor material is made using a gel containing the aliovalent metal (M ¹ ) and M ² compounds. By way of example, a metal precursor solution, e.g., a zirconium alkoxide solution can be combined with a desired aliovalent dopant in the form of a solution or as a soluble particulate material containing a desired metal dopant precursor in hydrolysable form. Forming a gel from the mixture and drying the gel. The dried gel can be heat-treated at 750 °C to 850 °C in the presence of air to form the aliovalent doped zirconia catalyst having a fluorite crystal structure. By way of example, zirconium oxynitrate and indium nitrate can be dissolved in a nitric acid solution. Citric acid can be added to create a metal citrate in a molar ratio of metal to citric acid from 1 : 1 to 1 :5, preferably 1 :3. Ethylene glycol can be added in a molar ratio of ethylene glycol to citric acid from 1 :2 to 2: 1 preferably 1 :2. The pH can be adjusted to 6 to 8 using a base (e.g., ammonium hydroxide). The solution can be then stirred at a temperature 65 °C to 75 °C to initiate polyesterification of the metal citrate with glycol for a desired amount of time (e.g., 2 h). The solution can be concentrated (e-g-, water can be removed by heating at 80 °C to 90 °C) until formation of the gel. The resulting gel can be dried 220 °C for a desired period of time (e.g. 10 to 16 h) to form a particulate material. The resulting powder can be calcined at 650 to 1200 °C, preferably 800 °C at a 10 °C per min ramp rate, and held at the final calcination temperature for a desired amount of time (e.g., 4 hours) and then cooled. In some embodiments, templating agents (e.g., polyvinyl alcohol) during the gel formation. The templating agents are removed upon heating the powder at higher temperatures (e.g., 220 to 1200 °C).

3. Co-precipitation Method

[0043] Other methods can include co-precipitation methods where metal salts are precipitated and heat-treated to form a catalyst as described herein. Certain methods include adding an alkali solution to an aqueous solution of M ² salt and M ¹ dopant salts to obtain a co- precipitation of M ² and aliovalent dopant (M ¹ ) salts with respect to the added alkali. The resulting solution can be filtered, washed, dried, shaped, and heat-treated to form the catalyst. The quantity and concentration of the alkali should be enough to thoroughly precipitate the ions. Non-limiting examples of the alkali solution include aqueous ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, or mixtures thereof. The co-precipitated precursor mixture can be heat- treated at an elevated temperature 800 to 1200 °C to form the aliovalent M ¹ doped M ² 0 catalyst having a fluorite crystal structure. By way of example, zirconium nitrate and indium chloride can be dissolved into water at 50 °C to 70 °C. Nitric acid can be added to ensure full dissolution. An ammonium carbonate solution can be added to the metal solution until precipitation of the metal carbonate. The resulting precipitate can solid is rinse several times with water, and then dried overnight at 110 to 130 °C, preferably about 120 °C. The resulting powder can be heated at 800 to 1200 °C for a desired amount of time, and then cooled to form the In doped Zr fluorite crystal structure. For example, to 1000 °C at a 10 °C ramp rate and hold at 800 °C temperature for 4 h.

[0044] The catalyst shape made by the methods of the present invention is not limited. For example, the catalyst shape can be a sphere, a cylinder, a ring, a semi-annular shape or any other shapes, or even formed as particles having a size of 10 μιη (or larger) suitable for use in a fluidized bed.

[0045] In some embodiments, pore formers are added to the solution prior to gel formation, calcination, or sintering. Non-limiting examples, of pore formers include carbon, graphite, corn starch, rice hulls, or the like mixed with the precursor prior to sintering. When taken to elevated temperatures in an oxidizing atmosphere, the pore former is removed, leaving a microporous structure, which can provide enhanced contact of the gas phase reactants with the catalyst.

C. Production of Methanol Using the Catalysts of the Present Invention

[0046] The catalysts of the present invention can be used to produce methanol from CO2 and H2. Conditions sufficient for the hydrogenation of CO2 reaction include temperature, time, space velocity, and pressure. The temperature range for the hydrogenation reaction can range from about 200 °C to 300 °C, from about 210 °C to 290 °C, preferably from about 225 °C to about 250 °C or about 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C, 290 °C, 300 °C, or any value or range there between. The gas hourly space velocity (GHSV) for the hydrogenation reaction can range from about 500 h ^"1 to about 200,000 h ^"1 , from about 2,000 h ^"1 to about 50,000 h ^"1 , and preferably from about 2,000 h ^"1 to about 20,000 h ^"1 . The average pressure for the hydrogenation reaction can range from about 0.1 MPa to about 6 MPa, or 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6 MPa and all ranges or values there between. The upper limit on pressure can be determined by the reactor used. The conditions for the hydrogenation of CO2 to produce methanol as well as the manner in which the CO2 and H2 are added to the reactor can be varied based on the type of the reactor. In preferred instances, the CO2 and the H2 are both in the gas phase.

[0047] Referring to FIG. 2, a system 10 is illustrated, which can be used to perform the process of the present invention of converting a reaction mixture of H2 and carbon dioxide (CO2) to methanol using an aliovalent metal cation doped M ² 0 catalyst of the present system. System 10 can include reactor 12, H2 source 14, and CO2 gas source 16. In some embodiments, the CO2 gas source includes carbon monoxide (CO). H2 source 14 and CO2 gas source 16 can be configured to be in fluid communication with reactor 12 via one or more inlets or gas manifolds (not shown) on the reactor. H2 source 14 and CO2 gas source 16 can be configured such that they regulate the amount of reactants entering reactor 12. As shown, H2 source 14 and CO2 gas source 16 are two sources feeding into reactor 12. However, it should be understood that the number of inlets and/or separate feed sources can be adjusted to reactor sizes and/or configurations {e.g. both sources can be feed together as a mixture). Reactor 12 can include reaction zone 18 having the aliovalent metal doped M ² 0 catalyst 20 described herein {e.g., InZrO catalyst). Reactor 12 can include various automated and/or manual controllers, valves, heat exchangers, gauges, etc. necessary for the operation of the reactor and maintain the reactants in a gaseous phase. The reactor can have the necessary insulation and/or heat exchangers to heat or cool the reactor as necessary. The heating/cooling source can be configured to heat or cool the reaction zone 18 to a temperature sufficient {e.g., 200 to 300 °C) to convert CO2 in the reactant mixture to methanol. Non-limiting examples of a heating/cooling source can be a temperature controlled furnace or an external, electrical heating block, heating coils, or a heat exchanger. The amounts of the reactant feed sources and the catalyst used can be modified as desired to achieve a given amount of product produced by the system 10. Non-limiting examples of continuous flow reactors that can be used in the context of the present invention include fixed-bed reactors, fluidized reactors, bubbling bed reactors, slurry reactors, rotating kiln reactors, moving bed reactors or any combinations thereof when two or more reactors are used. In reaction zone 18, H2 and CO2 can form a reaction mixture that contacts catalyst 20 under conditions suitable to produce product stream 22 that includes methanol. In the reaction zone 18, the CO2 conversion can be at least 10%, at least 40%, or at least 80%, or 10% to 100%, 50% to 95%, or 10%, 20%, 40%, 50%, 60%, 70%, 80%, 90%, 99%), 100%), or any range or value there between. The methanol selectivity can be at least 40%, at least 50%, at least 80% or at least 100%, or 40% to 100%, 50% to 90%, or 40%, 50%, 60%, 70%, 80%, 90%, 100%. [0048] In some aspects, the catalyst can be included in the product stream. Product stream 20 can exit reactor 12 and be collected, stored, or transported to other processing units. In some instances, product stream is subjected to a purification step to purify the methanol and/or remove unreacted CO2 and/or H2. In a non-limiting example, the product stream can be provided to a separation unit or a series of separation units that are capable of separating the gaseous components from the product stream. Any unreacted H2 or CO2, can be recycled and included in the reactant feed to further maximize the overall conversion of CO2 to methanol, which increases the efficiency and commercial value of the CO2 conversion process of the present invention. In some embodiments, the methanol is suitable for sale and/or use in other processes without purification.

D. Materials

[0049] Carbon dioxide, hydrogen, carbon monoxide or mixtures thereof can be obtained from various sources. In one non-limiting instance, the carbon dioxide can be obtained from a waste or recycle gas stream (e.g. from a plant on the same site, like for example from ammonia synthesis) or after recovering the carbon dioxide from a gas stream. A benefit of recycling such carbon dioxide as a starting material in the process of the invention is that it can reduce the amount of carbon dioxide emitted to the atmosphere (e.g., from a chemical production site). The hydrogen may be from various sources, including streams coming from other chemical processes, like water splitting (e.g., photocatalysis, electrolysis, or the like), syngas production, ethane cracking, methanol synthesis, or conversion of methane to aromatics. In a particular aspect, the reactant gases used in the current embodiments can be derived from syngas that includes CO2 or from addition of CO2 to the syngas. The H2/CO2 or H2/(CO+C02) reactant gas streams ratio for the hydrogenation reaction can range from 1 to 3, from 1.5 to 2.9, and preferably from 1.9 to 2.9. In one instance the reactant gas stream includes 30 to 80 % H2, 1 to 30 % CO2, and 0 to 60 % CO, or 40 to 70 % H ₂ , 5 to 25 % CO2, and 0 to 20 % CO. In another instance the reactant gas stream includes 1 % to 20 % CO2, preferably 5 % to 15 % CO2, and more preferably 8 % to 12% CO2. In some instances CO is not used. In some instances, the remainder of the reactant gas stream can include another gas or gases provided the gas or gases are inert, such as argon (Ar) or nitrogen (N2), and do not negatively affect the reaction. All possible percentages of CO2 + H2 + inert gas or CO2 + CO + H2 + inert gas in the current embodiments can have the described H2/CO2 or H2/(CO+C02) ratios herein. Preferably the reactant mixture is highly pure and substantially devoid of water or steam. In some embodiments, the carbon dioxide can be dried prior to use (e.g., pass through a drying media) or contains a minimal amount of or no water.

EXAMPLES

[0050] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

(Solid-State Synthesis of InZrO of the Present Invention)

[0051] ln ₂ 0 ₃ (99.99 % purity) and Zr0 ₂ (99.0% purity) were obtained from Sigma- Aldrich® (U.S.A.). Stoichiometric amounts of ImCb and Zr0 ₂ were dried overnight in a vacuum oven at a temperature of 200 °C. Amounts of each component, as indicated in Table 1 below, were combined and milled using an automated mortar and pestle for 60 minutes. A portion of the milled particulate material was pressed using a manual hydraulic press at 5 tons without additives into pellets having a diameter 20 mm and a thickness of approximately 1 mm. The remainder was saved as the original particulate material. The pressing and releasing rates were very low so as to produce good pellets. Samples of the particulate material and the pellets were then sintered in a muffle furnace in air using the following sequence: heat at 5 °C/min from 20 to 1,500 °C, hold for 12 hours at 1,500 °C, and then cool from 1,500 °C to 20 °C at approximately 5 °C/min. Of note, cooling can also be achieved by natural convection at lower temperature values.

[0052] X-ray diffraction analysis was performed using Rietveld analysis if data sets collected using a PANalytical Empyrean diffractometer in Bragg-Brentano geometry fitted with a copper tube operating at 45 kV and 40 mA and a linear position sensitive detector (opening 2.9). The diffractometer was configured with a 1/4° diverging slit, 1/2° anti scattering slit, 0.04 rad Soller slits, and aNi beta filter. The data sets were acquired in continuous scanning mode (0.021°/s) over the 2Θ range 5-100°, using a step interval of 0.013° and time per step 49.725 s. X-ray analysis was performed on the IZO-20 powder (10 mole % ln ₂ 0 ₃ ) sintered to 1,500 °C; and the XRD pattern is shown in FIG. 3. From the XRD, it was determined that the catalyst of the present invention has a single crystal structure. By comparing the XRD, with the XRD pattern of the prior art (e.g., Martin et al., FIG. 4 PRIOR ART), it was determined that the two catalysts are different. The prior art catalyst produced using the impregnation showed individual components as distinctly separate phases and that there was no diffusion of ImCb into the Zr0 ₂ lattice structure. Thus, the catalyst described herein and those described in the prior art are structurally different.

Table 1

Example 2

(Production of Methanol from InZrO Catalyst of the Present Invention)

[0053] The IZO-50 catalyst of Example 1 was used to produce methanol. A reaction mixture of 70.2 H ₂ vol.% H ₂ , 7.2 vol.% CO2, 12.6 vol.% CO with the balance being Ar was contacted with the catalyst at 230 °C (503 K) produced 60 The methanol production using the catalyst of the present invention is similar to that of the prior art {See, FIG. 1 of Martin et al) using indium supported on ZrO at 500 K (227 °C) was 40