WO2019236514A1

WO2019236514A1 - Mixed oxide catalyst for oxidative coupling of methane

Info

Publication number: WO2019236514A1
Application number: PCT/US2019/035289
Authority: WO
Inventors: Wugeng Liang; Luanyi LI; Vidya Sagar Reddy SARSANI; Hector PEREZ; David West
Original assignee: Sabic Global Technologies, B.V.
Priority date: 2018-06-05
Filing date: 2019-06-04
Publication date: 2019-12-12

Abstract

A supported oxidative coupling of methane (OCM) catalyst composition characterized by the general formula (Z_bE_cD_dO_x)-Mn-Na₂WO₄/SiO₂; wherein Z is a first rare earth element; wherein E is a second rare earth element; wherein D is a third rare earth element; wherein the first rare earth element, the second rare earth element, and the third rare earth element are not the same; wherein b is 1.0; wherein c is from about 0.01 to about 10.0; wherein d is from about 0.01 to about 10.0; and wherein x balances the oxidation states.

Description

MIXED OXIDE CATALYST FOR OXIDATIVE COUPLING OF METHANE

TECHNICAL FIELD

[0001] The present disclosure relates to catalyst compositions for oxidative coupling of methane (OCM), more specifically catalyst compositions based on oxides of rare earth elements and Mn-Na₂W0₄ for OCM, and methods of making and using same.

BACKGROUND

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

[0003] Oxidative coupling of the methane (OCM) has been the target of intense scientific and commercial interest for more than thirty years due to the tremendous potential of such technology to reduce costs, energy, and environmental emissions in the production of ethylene (C2H4). As an overall reaction, in the OCM, methane (CH₄) and oxygen (0₂) react exothermically over a catalyst to form C₂H₄, water (H₂0) and heat.

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

2CH₄ + 0₂ ® C₂H₄ + 2H₂0 DH = - 67 kcal/mol (I)

2CH₄ + l/20₂ ® C₂H₆ + H₂0 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 C₂ hydrocarbon product (e.g., ethylene):

CH₄ + l.50₂ ® CO + 2H₂0 DH = - 124 kcal/mol (III)

CH₄ + 20₂ ® C0₂ + 2H₂0 DH = - 192 kcal/mol (IV)

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

[0006] Additionally, while the overall OCM is exothermic, catalysts are used to overcome the endothermic nature of the C-H bond breakage. The endothermic nature of the bond breakage is due to the chemical stability of methane, which is a chemically stable molecule due to the presence of its four strong tetrahedral C-H bonds (435 kJ/mol). When catalysts are used in the OCM, the exothermic reaction can lead to a large increase in catalyst bed temperature and uncontrolled heat excursions that can lead to catalyst deactivation and a further decrease in ethylene selectivity. Furthermore, the produced ethylene is highly reactive and can form unwanted and thermodynamically favored deep oxidation products.

[0007] Generally, in the OCM, CH₄ is first oxidatively converted into ethane (C₂H₆), and then into C₂H₄. CH₄ is activated heterogeneously on a catalyst surface, forming methyl radicals (e.g., CH₃·), which then couple in a gas phase to form C₂H₆. C₂H₆ subsequently undergoes dehydrogenation to form C₂H₄. An overall yield of desired C₂ 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 C₂ hydrocarbons.

[0008] There are many catalyst systems developed for OCM processes, but such catalyst systems have many shortcomings. For example, conventional catalysts systems for OCM display catalyst performance problems, stemming from a need for high reaction temperatures to achieve desired conversions and selectivities. Thus, there is an ongoing need for the development of catalyst compositions 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 graph of selectivities as a function of methane (CH₄) to oxygen (0₂) ratio in the feed in an oxidative coupling of the methane (OCM) reaction;

[0011] Figure 2 displays a graph of CH₄ conversion and yields as a function of CH₄ to 0₂ ratio in the feed in an OCM reaction;

[0012] Figure 3 displays a graph of selectivities as a function of time on stream in an OCM reaction; and

[0013] Figure 4 displays a graph of CH₄ conversion and yields as a function of time on stream in an OCM reaction. DETAILED DESCRIPTION

[0014] Disclosed herein are supported oxidative coupling of methane (OCM) catalyst compositions and methods of making and using same. In an aspect, a supported OCM catalyst composition can be characterized by the general formula (Z_bE_cD_dCf -MndS^WC SiCh; wherein Z is a first rare earth element; wherein E is a second rare earth element; wherein D is a third rare earth element; wherein the first rare earth element, the second rare earth element, and the third rare earth element are not the same; wherein b is 1.0; wherein c is from about 0.01 to about 10.0; wherein d is from about 0.01 to about 10.0; and wherein x balances the oxidation states.

[0015] A method of making a supported OCM catalyst composition as disclosed herein can generally comprise the steps of (a) contacting silica (S1O2) with one or more OCM catalyst precursor aqueous solutions to form a supported OCM catalyst precursor mixture; wherein each of the one or more OCM catalyst precursor aqueous solutions comprises one or more compounds comprising a manganese (Mn) 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 third rare earth element cation, Na2W0₄, or combinations thereof; wherein the first rare earth element cation, the second rare earth element cation, and the third rare earth element cation are not the same; wherein the supported OCM catalyst precursor mixture is characterized by a molar ratio of the second rare earth element to the first rare earth element of c: 1 , wherein c is from about 0.01 to about 10.0; and wherein the supported OCM catalyst precursor mixture is characterized by a molar ratio of the third rare earth element to the first rare earth element of d: 1 , wherein d is from about 0.01 to about 10.0; (b) drying at least a portion of the supported OCM catalyst precursor mixture to form a dried supported OCM catalyst precursor mixture; and (c) calcining at least a portion of the dried supported OCM catalyst precursor mixture to form the supported OCM catalyst composition.

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

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

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

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

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

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

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

[0023] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art. [0024] Compounds are described herein using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash

that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -CHO is attached through the carbon of the carbonyl group.

[0025] In an aspect, a supported OCM catalyst composition as disclosed can be characterized by the general formula (Z_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂; wherein Z is a first rare earth element; wherein E is a second rare earth element; wherein D is a third rare earth element; wherein the first rare earth element, the second rare earth element, and the third rare earth element are not the same; wherein b is 1.0; 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 skill in the art, and with the help of this disclosure, each of the Z, E and D can have multiple oxidation states within the supported OCM catalyst composition, and as such x can have any suitable value that allows for the oxygen anions to balance all the cations in (Z_bE_cD_dO_x). Without wishing to be limited by theory, the different metals (Z, E, D, Na, Mn, and W) present in the supported OCM catalyst compositions as disclosed herein can 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 (Z, E, D, Na, Mn, and W) present in the supported OCM catalyst compositions as disclosed herein can generate formation of uncompensated oxygen vacancies, which can lead to further improvement of catalyst performance, for example in terms of conversion, selectivity, stability, etc.

[0026] Without wishing to be limited by theory, an OCM reaction can propagate by following a mechanism according to reactions (l)-(8):

[0]_s + CH₄ ® [OH]_s + CH₃ (1)

2CH₃ ® C₂H₆ (2)

CH₃ + 0_{2 <}® CH₃0₂ (3)

CH₃ + [0]_s ® [CH₃0]_S (4)

2[OH]_s + l/20₂ ® 2[0]_s + H₂0 (5)

C₂H₆ + I/2O₂— C₂H₄ + H₂O (6)

C₂H₄ + l/20₂ ® C₂H₂ + H₂0 (7) C₂H₄ + 5/2O2 ® CO + C0₂ + 2H₂0 (8) 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 (C2H₆) 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 CH3O2. According to reaction (4), methyl radicals can also re-adsorb onto 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 CO2, and as such the reaction steps according to reactions (3) and (4) are the main reactions controlling the selectivity of various OCM catalysts.

[0027] Further, and without wishing to be limited by theory, as described in reactions (l)-(5), an OCM reaction starts with methyl radical formation, coupling of which leads to the formation of ethane; wherein ethane can be further converted to ethylene through parallel reactions of thermal dehydrogenation and catalytic oxidative dehydrogenation, according to reaction (6). Furthermore, according to reaction (7), ethylene dehydrogenation can produce acetylene. In addition to the oxygenates formed according to reactions (3) and (4), a portion of the C2₊ products formed (e.g., C2H4) can also undergo deep oxidation to form CO and CO2. For example, according to reaction (8), ethylene can undergo deep oxidation to CO and CO2. 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.

[0028] Furthermore, and without wishing to be limited by theory, in order to increase the C2₊ selectivity, catalyst activity for reactions (3) and (4), and for C2₊ deep oxidation in reaction (8) need to be reduced. In order to increase olefin selectivity, catalyst activity for oxidative dehydrogenation according to reaction (6) should be increased; and at the same time the catalyst activity for deep oxidation of ethylene according to reactions (7) and (8) should be decreased.

[0029] 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.

[0030] In an aspect, the supported OCM catalyst composition as disclosed can comprise a rare earth element component (i.e., (Z_bE_cD_dO_x)) and a Na-Mn-W component (i.e., Mn-Na₂W0₄) wherein the rare earth element component and the Na-Mn-W component are supported on silica (Si0₂). 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 rare earth element component and the Na-Mn-W component have different physical and chemical properties, owing to different chemical compositions, and as such can provide for optimum catalytic properties in different OCM reaction steps.

[0031] The supported OCM catalyst composition as disclosed herein can be regarded as a composite comprising the rare earth element component and the Na-Mn-W component, wherein the rare earth element component and the Na-Mn-W component can be interspersed. In some aspects, the supported OCM catalyst composition can comprise a continuous rare earth element component having a discontinuous Na-Mn-W component dispersed therein. In other aspects, the supported OCM catalyst composition can comprise a continuous Na-Mn-W component having a discontinuous rare earth element component dispersed therein. In yet other aspects, the supported OCM catalyst composition can comprise both a continuous rare earth element component and a continuous Na-Mn-W component, wherein the rare earth element component and the Na-Mn-W component contact each other. In still yet other aspects, the supported OCM catalyst composition can comprise regions of rare earth element component and regions of Na-Mn-W component, wherein at least a portion the regions of the rare earth element component contact at least a portion of the regions of the Na-Mn-W component. As will be appreciated by one of skill in the art, and with the help of this disclosure, the amounts of each rare earth element component and Na-Mn-W component present in the supported OCM catalyst composition contribute to the distribution of the rare earth element component and the Na-Mn-W component within the supported OCM catalyst composition. [0032] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by a weight ratio of Z_bE_cD_dO_x to Mn-Na₂W0₄/Si0₂ of from about 0.01 :1 to about 10.0: 1, alternatively from about 0.1 :1 to about 8:1, or alternatively from about 0.5: 1 to about 5: 1.

[0033] In an aspect, the Na-Mn-W component can comprise Mn-Na₂W0₄, Na/Mn/O, Na₂W0₄, Mn₂0₃-Na₂W0₄, Mn₃0₄-Na₂W0₄, MnW0₄-Na₂W0₄, MnW0₄-Na₂W0₄, Mn-W0₄, and the like, or combinations thereof. In an aspect, the Na-Mn-W component can comprise Mn- Na₂W0₄. In an aspect, the Na-Mn-W component can comprise a redox agent, such as manganese (Mn) and/or tungsten (W). 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).

[0034] In an aspect, the supported OCM catalyst composition as disclosed herein can comprise manganese (Mn) in an amount of from about 0.1 wt.% to about 10 wt.%, alternatively from about 0.5 wt.% to about 7.5 wt.%, or alternatively from about 1 wt.% to about 5 wt.%, based on the total weight of the supported OCM catalyst composition.

[0035] In an aspect, the supported OCM catalyst composition as disclosed herein can comprise Na₂W0₄ in an amount of from about 0.1 wt.% to about 15 wt.%, alternatively from about 1 wt.% to about 12.5 wt.%, or alternatively from about 2.5 wt.% to about 10 wt.%, based on the total weight of the supported OCM catalyst composition.

[0036] In an aspect, the rare earth element component can comprise a first rare earth element (Z), a second rare earth element (E), and a third rare earth element (D), wherein Z, E, and D are not the same.

[0037] In an aspect, the first rare earth element (Z), the second rare earth element (E), and the third rare earth element (D) can each independently be selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and combinations thereof; wherein Z, E, and D are not the same.

[0038] 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.

[0039] In an aspect, the second rare earth element (E) is neodymium (Nd). 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 neodymium (Nd). 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 neodymium (Nd), and lanthanum (La), for example; or neodymium (Nd), ytterbium (Yb), and promethium (Pm), as another example; etc.

[0040] In an aspect, the third rare earth element (D) is ytterbium (Yb). 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 thulium (Tm), for example; or thulium (Tm), ytterbium (Yb), and lutetium (Lu), as another example; etc.

[0041] In an aspect, at least one of the first rare earth element (Z), the second rare earth element (E), and the third rare earth element (D) can be selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), and combinations thereof; wherein Z, E, and D are not the same.

[0042] In an aspect, at least one of the first rare earth element (Z), the second rare earth element (E), and the third rare earth element (D) can be selected from the group consisting of gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and combinations thereof; wherein Z, E, and D are not the same.

[0043] In an aspect, at least one of the first rare earth element (Z), the second rare earth element (E), and the third rare earth element (D) can be a redox agent. 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. [0044] In an aspect, at least one of the first rare earth element (Z), the second rare earth element (E), and 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 lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), 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 CH₄ to form hydroxyl groups [OH] on the OCM catalyst surface, as well as methyl radicals (CH₃·). 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).

[0045] In an aspect, the supported OCM catalyst composition as disclosed herein can comprise one or more oxides of Z; one or more oxides of E; one or more oxides of D; or combinations thereof. The supported OCM catalyst composition can comprise one or more oxides of a rare earth element (e.g., rare earth element oxides), wherein the metal comprises Z, E, and D. In some aspects, the rare earth element component of the supported OCM catalyst composition can comprise, consist of, or consist essentially of the one or more oxides (e.g., rare earth element oxides).

[0046] In an aspect, the one or more rare earth element oxides can be present in the rare earth element component of the supported OCM catalyst composition 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 rare earth element component of the supported OCM catalyst composition. 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 rare earth element oxides, in the presence of water, such as atmospheric moisture, can convert to hydroxides, and it is possible that the rare earth element component of the supported OCM catalyst composition will comprise some hydroxides, due to oxide exposure 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 rare earth element oxides, in the presence of carbon dioxide, such as atmospheric carbon dioxide, can convert to carbonates, and it is possible that the rare earth element component will comprise some carbonates, due to oxide exposure to carbon dioxide (e.g., atmospheric carbon dioxide).

[0047] The one or more rare earth element oxides can comprise a single rare earth element oxide, mixtures of single rare earth element oxides, a mixed rare earth element oxide, mixtures of mixed rare earth element oxides, mixtures of single rare earth element oxides and mixed rare earth element oxides, or combinations thereof.

[0048] The single rare earth element oxide comprises one rare earth element selected from the group consisting of Z, E, and D. A single rare earth element oxide can be characterized by the general formula M_mO_y; wherein M is the rare earth element selected from the group consisting of 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 rare earth element oxide contains one and only one rare earth element cation. Nonlimiting examples of single rare earth element oxides suitable for use in the supported OCM catalyst compositions of the present disclosure include La₂03, Ce0₂, Ce₂0₃, Pr₂0₃, Pr0₂, Nd₂0₃, Pm₂0₃, Sm₂0₃, Eu₂0₃, Gd₂0₃, Tb₂0₃, Dy₂0₃, Ho₂0₃, Er₂0₃, Lu₂0₃, Yb₂0₃, Tm₂0₃, and the like, or combinations thereof.

[0049] In an aspect, mixtures of single rare earth element oxides can comprise two or more different single rare earth element oxides, wherein the two or more different single rare earth element oxides have been mixed together to form the mixture of single rare earth element oxides. Mixtures of single rare earth element oxides can comprise two or more different single rare earth element oxides, wherein each single rare earth element oxide can be selected from the group consisting of La₂0₃, Ce0₂, Ce₂0₃, Pr₂0₃, Pr0₂, Nd₂0₃, Pm₂0₃, Sm₂0₃, Eu₂0₃, Gd₂0₃, Tb₂0₃, Dy₂0₃, HO₂0₃, Er₂0₃, Lu₂0₃, Yb₂0₃, and Tm₂0₃. Nonlimiting examples of mixtures of single rare earth element oxides suitable for use in the supported OCM catalyst compositions of the present disclosure include Yb₂0₃-La₂0₃, Er₂0₃-La₂0₃, Ce0₂-La₂0₃, Tm₂0₃-La₂0₃, Ce0₂-Er₂0₃-La₂0₃, Ce0₂-Ce₂0₃-Er₂0₃-La₂0₃, Sm₂0₃-La₂0₃, Ce0₂-Ce₂0₃-La₂0₃, Pr0₂-Pr₂0₃-La₂0₃, and the like, or combinations thereof.

[0050] The mixed rare earth element oxide comprises two or more different rare earth elements, wherein each rare earth element can be independently selected from the group consisting of Z, E, and D. A mixed rare earth element oxide can be characterized by the general formula M _mlM _m20_y; wherein M and M are rare earth elements; wherein each of the M and M can be independently selected from the group consisting of 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, M¹ and M can be rare earth element cations of different chemical elements, for example M can be a lanthanum cation and M 2 can be a cerium cation. In other aspects, M 1 and M2 can be different cations of the same chemical element, wherein M and M can have different oxidation states.

Nonlimiting examples of mixed rare earth element oxides suitable for use in the supported OCM catalyst compositions of the present disclosure include LaYbC^; Sm₂Ce₂0₇; Er₂Ce₂0₇;

SrCe_(i-y)Yb_y0₃, wherein y can be from about 0.01 to about 0.99; and the like; or combinations thereof.

[0051] In an aspect, mixtures of mixed rare earth element oxides can comprise two or more different mixed rare earth element oxides, wherein the two or more different mixed rare earth element oxides have been mixed together to form the mixture of mixed rare earth element oxides. Mixtures of mixed rare earth element oxides can comprise two or more different mixed rare earth element oxides, such as LaYbC^; Sm₂Ce₂0₇; Er₂Ce₂0₇; SrCe_(i-y)Yb_y0₃, wherein y can be from about 0.01 to about 0.99; and the like; or combinations thereof.

[0052] In an aspect, mixtures of single rare earth element oxides and mixed rare earth element oxides can comprise at least one single rare earth element oxide and at least one mixed rare earth element oxide, wherein the at least one single rare earth element oxide and the at least one mixed rare earth element oxide have been mixed together to form the mixture of single rare earth element oxides and mixed rare earth element oxides.

[0053] In an aspect, the supported OCM catalyst composition as disclosed comprises a silica (Si0₂) support, wherein at least a portion of the supported OCM catalyst composition (e.g., the rare earth element component and the Na-Mn-W component) contacts, coats, is embedded in, is supported by, and/or is distributed throughout at least a portion of the support. As will be appreciated by one of skill in the art, and with the help of this disclosure, the support (i.e., Si0₂) is catalytically inactive or non-selective (e.g., the support cannot catalyze an OCM reaction or cannot give high selectivity). Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, the silica 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 metal oxides, microemulsion techniques, solvothermal techniques, sonochemical techniques, combustion synthesis, etc.

[0054] In an aspect, the support can be a porous support. As will be appreciated by one of skill in the art, and with the help of this disclosure, a porous material (e.g., support) can provide for an enhanced surface area of contact between the supported OCM catalyst composition and a reactant mixture, which in turn would result in a higher CH₄ conversion to CH3·.

[0055] In an aspect, the supported OCM catalyst composition as disclosed herein can comprise Si0₂ in an amount of from about 5 wt.% to about 95 wt.%, alternatively from about 25 wt.% to about 75 wt.%, or alternatively from about 35 wt.% to about 65 wt.%, based on the total weight of the supported OCM catalyst composition. As will be appreciated by one of skill in the art, and with the help of this disclosure, the amount of catalytically active material composition (e.g., the rare earth element component and the Na-Mn-W component) on the support, and consequently the amount of support in the catalyst composition, depends on the catalytic activity on the catalytically active material.

[0056] In an aspect, the supported OCM catalyst composition as disclosed herein can be in the form of powders, particles, pellets, monoliths, foams, honeycombs, and the like, or combinations thereof. Nonlimiting examples of supported OCM catalyst composition particle shapes include cylindrical, discoidal, spherical, tabular, ellipsoidal, equant, irregular, cubic, acicular, and the like, or combinations thereof.

[0057] The supported OCM catalyst can have any suitable desired particle specifications, for example as required by a specific application. For example, the supported 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.). [0058] The supported OCM catalyst composition as disclosed herein can be made by using any suitable methodology. In an aspect, a method of making a supported OCM catalyst composition can comprise a step of contacting silica (Si0₂), e.g., silica gel, with one or more OCM catalyst precursor aqueous solutions to form a supported OCM catalyst precursor mixture; wherein each of the one or more OCM catalyst precursor aqueous solutions comprises one or more compounds comprising a manganese (Mn) 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 third rare earth element (D) cation, Na₂W0₄, or combinations thereof; wherein the first rare earth element (Z) cation, the second rare earth element (E) cation, and the third rare earth element (D) cation are not the same. The supported OCM catalyst precursor mixture can be characterized by a molar ratio of the second rare earth element (E) to the first rare earth element (Z) of c: 1 , 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. The supported OCM catalyst precursor mixture can be characterized by a molar ratio of the third rare earth element (D) to the first rare earth element (Z) of d: 1 , 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.

[0059] The one or more compounds comprising a manganese (Mn) cation can comprise a Mn nitrate, a Mn oxide, a Mn hydroxide, a Mn chloride, a Mn acetate, a Mn 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 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.

[0060] In some aspects, the one or more OCM catalyst precursor aqueous solutions can be formed by contacting water or any suitable aqueous medium with one or more compounds comprising a Mn 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 third rare earth element (D) cation, Na₂W0₄, or combinations thereof. The aqueous medium can be water, or an aqueous solution. As will be appreciated by one of skill in the art, and with the help of this disclosure, at least a portion of one or more compounds comprising a Mn 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 third rare earth element (D) cation, Na₂W0₄, or combinations thereof can be soluble in water (e.g., can be solubilized in water). Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, the one or more compounds comprising a Mn 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 third rare earth element (D) cation, Na₂W0₄, or combinations thereof can be dissolved in an aqueous medium in any suitable order.

[0061] In some aspects, the one or more compounds comprising a Mn 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 third rare earth element (D) cation, Na₂W0₄, or combinations thereof can be first mixed together and then dissolved in an aqueous medium. For example, at least a portion of the one or more compounds comprising a Mn 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 third rare earth element (D) cation, Na₂W0₄, or combinations thereof can be contacted with each other in the absence of water (e.g., substantial absence of water; without adding water, etc.); for example by grinding, dry blending, or otherwise intimately mixing to obtain a homogeneous mixture; wherein such homogeneous mixture can be further contacted with water or any suitable aqueous medium to form the one or more OCM catalyst precursor aqueous solutions. 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 a Mn 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 third rare earth element (D) cation, Na₂W0₄, or combinations thereof 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, for example by forming a paste; wherein such paste can be further contacted with water or any suitable aqueous medium to form the one or more OCM catalyst precursor aqueous solutions.

[0062] Without wishing to be limited by theory, some of the one or more compounds comprising a Mn 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 third rare earth element (D) cation, Na₂W0₄, or combinations thereof can be insoluble in water, or only partially soluble in water (e.g., lanthanum oxide, ytterbium oxide, neodymium oxide, etc.); and in such instances, these compounds will not be fully dissolved in water, but could be suspended in the one or more OCM catalyst precursor aqueous solutions.

[0063] In an aspect, a method of making a supported OCM catalyst composition as disclosed herein can comprise a step of drying at least a portion of the supported OCM catalyst precursor mixture to form a dried supported OCM catalyst precursor mixture. In an aspect, at least a portion of the supported OCM catalyst precursor mixture 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 dried supported OCM catalyst precursor mixture. The supported OCM catalyst precursor mixture can be dried for a time period of equal to or greater than about 4 hours, alternatively equal to or greater than about 8 hours, or alternatively equal to or greater than about 12 hours.

[0064] In some aspects, a supported OCM catalyst precursor mixture can be dried to form an intermediate dried supported OCM catalyst precursor mixture. In such aspects, the intermediate dried supported OCM catalyst precursor mixture can be further contacted with an OCM catalyst precursor aqueous solution, and dried, to form the dried supported OCM catalyst precursor mixture.

[0065] For example, a silica support can be contacted with a Mn nitrate aqueous solution to form a manganese impregnated silica (e.g., first supported OCM catalyst precursor mixture), wherein the manganese impregnated silica can be further dried to form dried manganese impregnated silica (e.g., first intermediate dried supported OCM catalyst precursor mixture). The dried manganese impregnated silica can be contacted with an aqueous solution comprising a first rare earth element (Z) cation, a second rare earth element (E) cation, and a third rare earth element (D) cation to form a manganese and rare earth elements impregnated silica (e.g., second supported OCM catalyst precursor mixture). The manganese and rare earth elements impregnated silica can be dried to form dried manganese and rare earth elements impregnated silica (e.g., second intermediate dried supported OCM catalyst precursor mixture). The dried manganese and rare earth elements impregnated silica can be contacted with a Na₂W0₄ aqueous solution to form a Mn, Na, W and rare earth elements impregnated silica (e.g., third supported OCM catalyst precursor mixture). The Mn, Na, W and rare earth elements impregnated silica can be dried to form dried Mn, Na, W and rare earth elements impregnated silica (e.g., dried supported OCM catalyst precursor mixture).

[0066] In an aspect, a method of making a supported OCM catalyst composition as disclosed herein can comprise a step of calcining at least a portion of the dried supported OCM catalyst precursor mixture to form the supported OCM catalyst composition, wherein the supported OCM catalyst composition is characterized by the general formula formula (Z_bE_cD_dO_x)-Mn- Na₂W0₄/Si0₂; wherein Z is a first rare earth element; wherein E is a second rare earth element; wherein D is a third rare earth element; wherein the first rare earth element, the second rare earth element, and the third rare earth element are not the same; wherein b is 1.0; wherein c is from about 0.01 to about 10.0; wherein d is from about 0.01 to about 10.0; and wherein x balances the oxidation states. The dried supported OCM catalyst precursor mixture can be calcined at a temperature of equal to or greater than about 700°C, alternatively 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 supported OCM catalyst composition. The dried supported OCM catalyst precursor mixture can be calcined for a time period of equal to or greater than about 2 hours, alternatively equal to or greater than about 4 hours, or alternatively equal to or greater than about 6 hours.

[0067] In some aspects, at least a portion of the dried supported 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 supported OCM catalyst composition. Without wishing to be limited by theory, the oxygen in the rare earth element component (Z_bE_cD_dO_x) of the supported OCM catalyst compositions can originate in the oxidizing atmosphere used for calcining the dried supported OCM catalyst precursor mixture. Further, without wishing to be limited by theory, the oxygen in the rare earth element component (Z_bE_cD_dO_x) of the supported OCM catalyst compositions can originate in the one or more compounds comprising a first rare earth element cation, one or more compounds comprising a second rare earth element cation, and one or more compounds comprising 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.

[0068] In an aspect, a method of making a supported OCM catalyst composition as disclosed herein can comprise a step of sizing the supported OCM catalyst composition to form the supported OCM catalyst composition into desired particle specifications (e.g., required particle specifications). The supported OCM catalyst composition can be sized by using any suitable methodology. In an aspect, the supported OCM catalyst composition can be subjected to grinding, crushing, milling, chopping, and the like, or combinations thereof to form the supported OCM catalyst composition into desired particle specifications (e.g., required particle specifications). As previously described herein, the supported OCM catalyst composition can have any suitable desired particle specifications, for example as required by a specific application.

[0069] In an aspect, a method for producing olefins as disclosed herein can comprise (a) introducing a reactant mixture (e.g., OCM reactant mixture) to an OCM reactor comprising the supported OCM catalyst composition as disclosed herein, wherein the reactant mixture comprises methane (CH₄) and oxygen (0₂); and (b) allowing at least a portion of the reactant mixture to contact at least a portion of the supported OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins.

[0070] 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., CH₄), liquefied petroleum gas comprising C -C hydrocarbons, C₆₊ heavy hydrocarbons (e.g., C to C 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 and 0₂.

[0071] The 0 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.

[0072] 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.

[0073] The OCM reactor can comprise an adiabatic reactor, an autothermal reactor, an isothermal reactor, a tubular reactor, a cooled tubular reactor, a continuous flow reactor, a fixed bed reactor, a fluidized bed reactor, a moving bed reactor, and the like, or combinations thereof. In an aspect, the OCM reactor can comprise a catalyst bed comprising the supported OCM catalyst composition.

[0074] The OCM reaction mixture can be introduced to the OCM reactor at a temperature of from about l50°C to about l,000°C, alternatively from about 225°C to about 900°C, or alternatively from about 250°C to about 800°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 CH₄, as the C-H bonds of CH₄ are very stable, and the formation of methyl radicals from CH₄ is endothermic. In an aspect, the OCM reaction mixture can be introduced to the OCM reactor at a temperature effective to promote an OCM reaction.

[0075] The OCM reactor can be characterized by a temperature of from about 400°C to about l,200°C, alternatively from about 500°C to about l,l00°C, or alternatively from about 600°C to about l,000°C.

[0076] The OCM reactor can be characterized by a pressure of from about ambient pressure (e.g., atmospheric pressure) to about 500 psig, alternatively from about ambient pressure to about 200 psig, or alternatively from about ambient pressure to about 150 psig. In an aspect, the method for producing olefins as disclosed herein can be carried out at ambient pressure.

[0077] The OCM 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. GHSY is usually measured at standard temperature and pressure. [0078] In an aspect, the method for producing olefins as disclosed herein can comprise recovering at least a portion of the product mixture from the OCM reactor, wherein the product mixture can comprise olefins, water, CO, C0₂, 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 C₂₊ hydrocarbons (including olefins), unreacted methane, and optionally a diluent. The C₂₊ hydrocarbons can comprise C₂ hydrocarbons and C₃ hydrocarbons. In an aspect, the C₂₊ hydrocarbons can further comprise C₄ hydrocarbons (C₄s), such as for example butane, iso-butane, n-butane, butylene, etc. The C₂ hydrocarbons can comprise ethylene (C₂H₄) and ethane (C₂H₆). The C₂ hydrocarbons can further comprise acetylene (C₂H₂). The C₃ hydrocarbons can comprise propylene (C₃H₆) and propane (C₃H₈).

[0079] 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.

[0080] 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).

[0081] 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.

[0082] In an aspect, the 0₂ 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 0₂ 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 (9):

w h r in 02 number of moles of 0₂ that entered the OCM reactor as part of the reactant mixture; and = number of moles of 0₂ that was recovered from the OCM reactor as part of the product mixture.

[0083] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by a C₂₊ selectivity that is increased when compared to a C₂₊ selectivity of an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn- Na₂W0₄.

[0084] 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., C₂ selectivity, C₂₊ selectivity, etc.) can be calculated by dividing a number of moles of carbon (C) from CH₄ that were converted into the desired product (e.g., Cam, Cam, etc.) by the total number of moles of C from CH₄ that were converted (e.g., Ca , Cam, C m, Cc3_H6 C₍ 3i is- Cc_4s, C₍ 02_' C_{( (},. etc.). Cam = number of moles of C from CH₄ that were converted into C₂H₄; C_C2H₆ ⁼ number of moles of C from CH₄ that were converted into C₂H₆; Ca = number of moles of C from CH₄ that were converted into C₂H₂; C_C3H₆ ⁼ number of moles of C from CH₄ that were converted into 0₃H₆; Cc3_H8 ⁼ number of moles of C from CH₄ that were converted into C₃H₈; Cc_4s = number of moles of C from CH₄ that were converted into C₄ hydrocarbons (C₄s); Cco2 = number of moles of C from CH₄ that were converted into C0₂; Cco = number of moles of C from CH₄ that were converted into CO; etc.

[0085] A C₂₊ selectivity (e.g., selectivity to C₂₊ hydrocarbons) refers to how much C₂H₄, C₃H₆, C₂H₂, C₂H₆, C₃H₈, and C₄s were formed divided by the total products formed, including C₂H₄, C₃H₆, C₂H₂, C₂H₆, C₃H₈, C₄S, C0₂ and CO. For example, the C₂₊ selectivity can be calculated by using equation (10):

C₂₊ selectivity -

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.

[0086] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by a C_2- selectivity (selectivity to ethylene) that is increased when compared to a C_2- selectivity of an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄.

[0087] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by a C_2º selectivity (selectivity to acetylene) that is decreased by equal to or greater than about 25%, alternatively equal to or greater than about 40%, or alternatively equal to or greater than about 50% when compared to a C_2º selectivity of an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄.

[0088] In an aspect, the method for producing olefins as disclosed herein can further comprise minimizing deep oxidation of methane to CO_x products, such as carbon monoxide (CO) and/or carbon dioxide (C0₂). Without wishing to be limited by theory, when the selectivity to desired products (e.g., C₂₊ selectivity, C_2- selectivity) of an OCM process increases, less methane is converted to undesirable products, such as deep oxidation products (e.g., CO, C0₂), which in turn means that more oxygen (which is often the limiting reagent in OCM processes) is available for the conversion of methane to desirable products (e.g., C₂ products, C₂H₄, C₂₊ products, etc.), thus enabling an increased yield of desired C₂₊ products. [0089] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by a Cco2 selectivity that is decreased by equal to or greater than about 5%, alternatively equal to or greater than about 10%, or alternatively equal to or greater than about 15% when compared to a Cco2 selectivity of an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄.

[0090] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by a CH₄ conversion that is increased by equal to or greater than about 10%, alternatively equal to or greater than about 15%, or alternatively equal to or greater than about 20% when compared to a CH₄ conversion of an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄. The CH₄ conversion can be calculated by using equation (1 1):

wherein number of moles of C from CH₄ that entered the reactor as part of the reactant

mixture; and number of moles of C from CH₄ that was recovered from the reactor as

part of the product mixture.

[0091] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by the general formula (La_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂; wherein E is selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), and combinations thereof; wherein D is selected from the group consisting of gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and combinations thereof; wherein b is 1.0; wherein c 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 d 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; 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 La, E and D can have multiple oxidation states within the supported OCM catalyst composition, and as such x can have any suitable value that allows for the oxygen anions to balance all the cations in the rare earth element component of the supported OCM catalyst composition.

[0092] In an aspect of the supported OCM catalyst composition characterized by the general formula (La_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂, E is Nd, and D is Yb. In such aspect, the supported OCM catalyst composition can be characterized by the general formula (La_bNd_cYb_dO_x)-Mn- Na₂W0₄/Si0₂; wherein b is 1.0; wherein c is from about 0.1 to about 10.0; wherein d is from about 0.1 to about 10.0; and wherein x balances the oxidation states.

[0093] In an aspect, the supported OCM catalyst compositions characterized by the general formula (Z_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂; wherein Z is a first rare earth element; wherein E is a second rare earth element; wherein D is a third rare earth element; wherein the first rare earth element, the second rare earth element, and the third rare earth element are not the same; wherein b is 1.0; wherein c is from about 0.01 to about 10.0; wherein d is from about 0.01 to about 10.0; and wherein x balances the oxidation states; and methods of making and using same, as disclosed herein can advantageously display improvements in one or more composition characteristics when compared to conventional OCM catalysts, e.g., an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄.

[0094] The supported OCM catalyst compositions characterized by the general formula (Z_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂, as disclosed herein, can advantageously display improved conversion, selectivity, and yield when compared to the conversion, selectivity, and yield, respectively, of an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄. Specifically, the supported OCM catalyst compositions characterized by the general formula (Z_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂, as disclosed herein, can display improved selectivity to desired products, such as olefins, and decreased selectivity to undesired products, such as alkynes. The yield can be calculated for a particular product by using equation (12):

Yield = Selectivity x CH₄ conversion x 100% (12)

[0095] The supported OCM catalyst compositions characterized by the general formula (Z_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂, as disclosed herein, can advantageously display decreased C_2º selectivity, when compared to the C_2º selectivity of an otherwise similar supported OCM catalyst composition without Z_bE_cD_dO_x,. [0096] The supported OCM catalyst compositions characterized by the general formula (Z_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂, as disclosed herein, can advantageously display stable performance in an OCM process over time.

[0097] In an aspect, the composition of supported OCM catalyst compositions characterized by the general formula (Z_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂, as disclosed herein, can be advantageously adjusted as necessary, based on the needs of the OCM reaction, to meet target criteria, such as a target selectivity and/or a target conversion, owing to a broad range of Z, E and D content; and as such the supported OCM catalyst compositions as disclosed herein can display better performance when compared to otherwise similar supported OCM catalyst compositions (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄. Additional advantages of the supported OCM catalyst compositions characterized by the general formula (Z_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂, as disclosed herein; and methods of making and using same, can be apparent to one of skill in the art viewing this disclosure.

EXAMPLES

[0098] 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

[0099] Oxidative coupling of methane (OCM) catalyst compositions were prepared as follows.

[00100] A reference catalyst (Mn-Na₂W0₄/Si0₂) was prepared by using the following procedure. Silica gel (18.6 g, Davisil® Grade 646) was used after drying overnight. Mn(N0₃)_2'4H₂0 (1.73 g) was dissolved in deionized water (18.5 mL), and then added dropwise onto the silica gel. The resulting manganese impregnated silica material was dried overnight. Na₂W0₄-4H₂0 (1.22 g) was dissolved in deionized water (18.5 mL), and the solution obtained was added onto the dried manganese silica material above. The resulting material obtained was dried overnight at l25°C, and then calcined at 800°C for 6 hours under airflow to obtain the Mn-Na₂W0₄/Si0₂ catalyst.

[00101] Different (Z_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂ catalysts are prepared and compared with the following reference catalyst. [00102] OCM catalyst #1 (Lao₉Ndo ₇Ybo₃Ox)o i-(Mn-Na₂W0₄/Si0₂)o₉ was prepared by using the following method. Silica gel (18.6 g, Davisil® Grade 646) was used after drying overnight. Mh(N0₃)₂·4H₂q (1.74 g) was dissolved in deionized water (18.5 mL), and then added dropwise onto the silica gel. The resulting manganese impregnated silica material was dried overnight. 2.16 g of La(N0₃)₃.6H₂0, 1.71 g of Nd(N0₃)₃.6H₂0 and 0.75 g of Yb(N0₃)₃.6H₂0 were dissolved in deionized water (18.5 ml), and then added dropwise onto the dried material obtained above. The resulting Mn-La-Nd-Yb impregnated material was dried overnight at l25°C. Na₂W0₄-4H₂0 (1.22 g) was dissolved in deionized water (18.5 mL), and the solution obtained was added onto the above dried silica material above. The resulting material obtained was dried overnight at l25°C, and then calcined at 800°C for 6 hours under airflow to obtain the (Lao₉Ndo₇Ybo₃Ox)o i-(Mn-Na₂W0₄/Si0₂)o₉ OCM catalyst #1.

[00103] OCM catalyst #2 (Lao₉Ndo ₇Ybo₃Ox)o i-(Mn-Na₂W0₄/Si0₂)o₉ was prepared by using the following method. Silica gel (18.6 g, Davisil® Grade 646) was used after drying overnight. Mn(N0₃)_2'4H₂0 (1.74 g) was dissolved in deionized water (18.5 mL), and then added dropwise onto the silica gel. The resulting manganese impregnated silica material was dried overnight. 2.16 g of La(N0₃)₃.6H₂0, 1.71 g of Nd(N0₃)₃.6H₂0 and 0.75 g of Yb(N0₃)₃.6H₂0 were dissolved in deionized water (18.5 ml), and then added dropwise onto the dried material obtained above. The resulting Mn-La-Nd-Yb impregnated material was dried overnight at l25°C. Na₂W0₄-4H₂0 (1.22 g) was dissolved in deionized water (18.5 mL), and the solution obtained was added onto the above dried silica material above. The resulting material obtained was dried overnight at l25°C, and then calcined at 900°C for 6 hours under airflow to obtain the (Lao9Ndo7Ybo₃Ox)o i-(Mn-Na2W0₄/Si02)o9 OCM catalyst #2.

[00104] OCM catalyst #3 (Lao₉Ndo ₇Ybo₃Ox)o i₅-(Mn-Na₂W0₄/Si0₂)o ₈₅ was prepared by using the following method. Silica gel (18.6 g, Davisil® Grade 646) was used after drying overnight. Mn(N0₃)_2'4H₂0 (1.74 g) was dissolved in deionized water (18.5 mL), and then added dropwise onto the silica gel. The resulting manganese impregnated silica material was dried overnight. 3.24 g of La(N0₃)₃.6H₂0, 2.56 g of Nd(N0₃)₃.6H₂0 and 1.13 g of Yb(N0₃)₃.6H₂0 were dissolved in deionized water (18.5 ml), and then added dropwise onto the dried material obtained above. The resulting Mn-La-Nd-Yb impregnated material was dried overnight at l25°C. Na₂W0₄-4H₂0 (1.22 g) was dissolved in deionized water (18.5 mL), and the solution obtained was added onto the above dried silica material above. The resulting material obtained was dried overnight at l25°C, and then calcined at 800°C for 6 hours under airflow to obtain the (Lao 9Ndo 7Ybo₃Ox)o i5-(Mn-Na2W0₄/Si02)o85 OCM catalyst #3.

EXAMPLE 2

[00105] The performance of the supported OCM catalyst compositions prepared as described in Example 1 was investigated. Specifically, the performance of OCM catalysts #1, #2, and #3 was compared to the performance of the reference catalyst. OCM reactions were conducted by using catalysts prepared as described in Example 1 as follows.

[00106] Performance test. The catalysts obtained as described in Example 1 were performance tested in a 4.0 mm ID quartz tube reactor. The reactor was loaded with 100 mg of catalyst. A mixture of methane and oxygen at a fixed CH₄:0₂ 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.

[00107] The performance obtained with (LaNdYb0x)-Mn-Na₂W0₄/Si0₂ is shown in Table 1, compared to the reference catalyst.

Table 1. Performance comparison at 850 °C reactor temperature

[00108] It can be seen that with the promotions with multi component rare earth oxides, the C₂₊ selectivity is increased. The increase in C₂₊ mainly comes from the reduction of C0₂ formation in the products, indicating the reduction of deep oxidation activity with the promoters.

[00109] In all the olefins formed, the most important ones are ethylene and propylene. With the reduction of deep oxidation activity, catalyst ethylene and propylene selectivities increases; which is demonstrated in Table 1 as well.

[00110] As will be appreciated by one of skill in the art, and with the help of this disclosure, acetylene can have a detrimental effect in ethylene production processes, as it has to be converted back to ethylene by hydrogenation with additional hydrogenation catalyst and reactor, adding more capital cost. Therefore, low acetylene selectivity is important for an OCM catalyst. From the data shown in Table 1, the formation of acetylene is also reduced with the promoted catalyst, low acetylene selectivity is another advantage of the novel catalyst discovered in this disclosure. The C₂₊ selectivity minus C_2º is also shown in Table 1, and this selectivity is defined as useful C₂₊ selectivity. It can be seen that much better useful selectivity is obtained with the promoted catalyst.

[00111] It can be seen that the new catalyst system demonstrated increased activity for reaction (6), while at the same time, reduced the activity for reactions (3) and (4), and reactions (7) and (8), so that C₂₊ selectivity and olefin selectivity is increased, and acetylene selectivity and CO_x selectivity are reduced.

[00112] Without wishing to be limited by theory, under the testing condition with CH₄ to 0₂ ratio of 7.4, oxygen is the limiting agent. With more C0₂ formed in the product, because C0₂ formation uses more 0₂ than other products, there will be less oxygen available for CH₄ conversion. Therefore, there is less CH₄ conversion with the reference catalyst, compared to the promoted catalysts. The ethylene and propylene yield and useful C₂₊ yield obtained are also shown in Table 1, and it can be seen that much better yields are obtained with the promoted catalyst than the reference one.

[00113] In an aspect, the catalyst performance can be adjusted with the change of CH₄ to 0₂ ratio in the feed. The ethylene and propylene selectivity and useful C₂₊ selectivity obtained under different CH₄ to 0₂ ratio are shown in Figure 1. With the increase the ratio, the C₂₊ selectivity increases; and the ethylene and propylene selectivities increase as well. [00114] Although the selectivity is beher under high ratio, CH₄ conversion is lower under higher ratios, as shown in Figure 2. With the lower CH₄ conversion, the yield obtained under higher ratios are lower. With OCM catalyst #1, the ethylene and propylene yield obtained at ratio of 5 was 13.6% and the useful C₂₊ yield was 19.3%.

[00115] The stability of performance of the new catalysts are demonstrated in Figures 3 and 4. Figure 3 shows the ethylene and propylene selectivity and useful C₂₊ selectivity under the same condition for more than 30 hours time on stream, it can be seen that stable selectivities are obtained. Figure 4 shows the CH₄ conversion, ethylene and propylene yield and C₂₊ yield during the more than 30 hours time on stream testing, it is clear that stable performance was obtained.

[00116] 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.

[00117] 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.

[00118] 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.

[00119] 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.

Claims

CLAIMS What is claimed is:

1. A supported oxidative coupling of methane (OCM) catalyst composition characterized by the general formula (Z_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂; wherein Z is a first rare earth element; wherein E is a second rare earth element; wherein D is a third rare earth element; wherein the first rare earth element, the second rare earth element, and the third rare earth element are not the same; wherein b is 1.0; wherein c is from about 0.01 to about 10.0; wherein d is from about 0.01 to about 10.0; and wherein x balances the oxidation states.

2. The supported OCM catalyst composition of claim 1, wherein a weight ratio of Z_bE_cD_dO_x to Mn-Na2W0₄/Si02 is from about 0.01 :1 to about 10.0:1.

3. The supported OCM catalyst composition of claim 1, wherein the supported OCM catalyst composition comprises manganese (Mn) in an amount of from about 0.1 wt.% to about 10 wt.%, based on the total weight of the supported OCM catalyst composition.

4. The supported OCM catalyst composition of claim 1, wherein the supported OCM catalyst composition comprises Na₂W0₄ in an amount of from about 0.1 wt.% to about 15 wt.%, based on the total weight of the supported OCM catalyst composition.

5. The supported OCM catalyst composition of claim 1, wherein the first rare earth element, the second rare earth element and the third rare earth element can each independently be selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and combinations thereof.

6. The supported OCM catalyst composition of claim 1, wherein at least one of the first rare earth element, the second rare earth element and the third rare earth element is selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), and combinations thereof.

7. The supported OCM catalyst composition of claim 1, wherein at least one of the first rare earth element, the second rare earth element and the third rare earth element is selected from the group consisting of gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and combinations thereof.

8. The supported OCM catalyst composition of claim 1 comprising one or more oxides of Z; one or more oxides of E; one or more oxides of D; or combinations thereof.

9. The supported OCM catalyst composition of claim 1 having the general formula (La_bE_cD_d0_x)-Mn-Na₂W0₄/Si0₂; wherein E is selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), and combinations thereof; and wherein D is selected from the group consisting of gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and combinations thereof.

10. The supported OCM catalyst composition of claim 9 having the general formula (La_bNd_cYb_d0_x)-Mn-Na₂W0₄/Si0₂; wherein b is 1.0; wherein c is from about 0.01 to about 10.0; wherein d is from about 0.01 to about 10.0; and wherein x balances the oxidation states.

11. A method of making a supported oxidative coupling of methane (OCM) catalyst

composition comprising:

(a) contacting silica (S1O₂) with one or more OCM catalyst precursor aqueous solutions to form a supported OCM catalyst precursor mixture; wherein each of the one or more OCM catalyst precursor aqueous solutions comprises one or more compounds comprising a manganese (Mn) 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 third rare earth element cation, Na₂W0₄, or combinations thereof; wherein the first rare earth element cation, the second rare earth element cation, and the third rare earth element cation are not the same; wherein the supported OCM catalyst precursor mixture is characterized by a molar ratio of the second rare earth element to the first rare earth element of c: 1 , wherein c is from about 0.01 to about 10.0; and wherein the supported OCM catalyst precursor mixture is characterized by a molar ratio of the third rare earth element to the first rare earth element of d: 1 , wherein d is from about 0.01 to about 10.0;

(b) drying at least a portion of the supported OCM catalyst precursor mixture to form a dried supported OCM catalyst precursor mixture; and

(c) calcining at least a portion of the dried supported OCM catalyst precursor mixture to form the supported OCM catalyst composition of any of claims 1-10.

12. The method of claim 11, wherein the step (a) of contacting silica (Si0₂) with one or more OCM catalyst precursor aqueous solutions to form a supported OCM catalyst precursor mixture further comprises solubilizing the one or more compounds comprising a manganese (Mn) 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 third rare earth element cation, Na₂W0₄, or combinations thereof in an aqueous medium to form the one or more OCM catalyst precursor aqueous solutions.

13. The method of claim 11, wherein the supported OCM catalyst precursor mixture is dried at a temperature of equal to or greater than about 75 °C.

14. The method of claim 11, wherein the dried supported OCM catalyst precursor mixture is calcined at a temperature of equal to or greater than about 700°C.

15. The method of claim 11 further comprising sizing the supported OCM catalyst composition.

16. A method for producing olefins comprising:

(a) introducing a reactant mixture to an oxidative coupling of methane (OCM) reactor comprising the supported OCM catalyst composition of any of claims 1-10, wherein the reactant mixture comprises methane (CH₄) and oxygen (0₂);

(b) allowing at least a portion of the reactant mixture to contact at least a portion of the supported OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins;

(c) recovering at least a portion of the product mixture from the OCM reactor; and

(d) recovering at least a portion of the olefins from the product mixture.

17. The method of claim 16, wherein the supported OCM catalyst composition is characterized by a C₂₊ selectivity that is increased when compared to a C₂₊ selectivity of an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄.

18. The method of claim 16, wherein the supported OCM catalyst composition is characterized by a C_2— selectivity (selectivity to ethylene) that is increased when compared to a C_2- selectivity of an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄.

19. The method of claim 16, wherein the supported OCM catalyst composition is characterized by a C_2º selectivity (selectivity to acetylene) that is decreased by equal to or greater than about 25% when compared to a C_2º selectivity of an otherwise similar supported OCM catalyst composition without Z_bE_cD_dO_x.

20. The method of claim 16, wherein the supported OCM catalyst composition is characterized by (1) a Cco2 selectivity that is decreased by equal to or greater than about 5% when compared to a Cco2 selectivity of an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄; and (2) a CH₄ conversion that is increased by equal to or greater than about 10% when compared to a CH₄ conversion of an otherwise similar supported OCM catalyst composition (i) without Z_bE_cD_dO_x, or (ii) without Mn-Na₂W0₄.