WO2020142218A1

WO2020142218A1 - Mixed oxide catalyst for oxidative coupling of methane

Info

Publication number: WO2020142218A1
Application number: PCT/US2019/067200
Authority: WO
Inventors: Wugeng Liang; Luanyi LI; Vidya Sagar Reddy SARSANI; David West
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2019-01-04
Filing date: 2019-12-18
Publication date: 2020-07-09
Anticipated expiration: 2021-07-04

Abstract

A supported oxidative coupling of methane (OCM) catalyst composition characterized by the general formula (MO_x)-Mn-Na₂WO₄/SiO₂; wherein M is a metal with redox properties; and wherein x balances the oxidation states. The supported OCM catalyst composition has a weight ratio of MO_x to Mn-Na₂WO₄/SiO₂ of from about 0.01:1 to about 0.2:1.

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 redox metals 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 (O₂) react exothermically over a catalyst to form C₂H , water (H₂O) and heat.

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

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, CH is first oxidatively converted into ethane (C₂H₆), and then into C₂H₄. CH₄ is activated heterogeneously on a catalyst surface, forming methyl radicals (e.g., CH ·), 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, such as poor stability over extended use. Thus, there is an ongoing need for the development of catalyst compositions for OCM processes.

SUMMARY

[0009] Disclosed herein is a supported oxidative coupling of methane (OCM) catalyst composition characterized by the general formula (M0_x)-Mn-Na₂WO₄/SiO₂, wherein M is a metal with redox properties; and wherein x balances the oxidation states.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a detailed description of the preferred aspects of the disclosed methods, reference will now be made to the accompanying drawing in which:

[0011] Figure 1 displays a graph of oxygen (O₂) conversion as a function of time on stream in an oxidative coupling of the methane (OCM) reaction;

[0012] Figure 2 displays a graph of selectivity to ethylene as a function of time on stream in an OCM reaction;

[0013] Figure 3 displays a graph of selectivity to ethane as a function of time on stream in an OCM reaction;

[0014] Figure 4 displays a graph of C₂₊ selectivity as a function of time on stream in an OCM reaction;

[0015] Figure 5 displays another graph of O₂ conversion as a function of time on stream in an OCM reaction;

[0016] Figure 6 displays another graph of selectivity to ethylene as a function of time on stream in an OCM reaction; and

[0017] Figure 7 displays another graph of selectivity to ethane as a function of time on stream in an OCM reaction. DETAILED DESCRIPTION

[0018] 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 (M0_x)-Mn-Na₂WO₄/SiO₂; wherein M is a metal with redox properties; and wherein x balances the oxidation states. The supported OCM catalyst composition as disclosed herein can be characterized by a weight ratio of MO_x to Mn-Na₂WO₄/SiO₂ of from about 0.01 :1 to about 10.0:1. The supported OCM catalyst composition as disclosed herein can be prepared by any suitable methodology.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] As used herein, the term“effective,” means adequate to accomplish a desired, expected, or intended result. [0025] 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.

[0026] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art.

[0027] 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.

[0028] As used herein, the terms“C_x hydrocarbons” and“C_xs” are interchangeable and refer to any hydrocarbon having x number of carbon atoms (C). For example, the terms“C₄ hydrocarbons” and“C₄s” both refer to any hydrocarbons having exactly 4 carbon atoms, such as n-butane, iso-butane, cyclobutane, 1 - butene, 2-butene, isobutylene, butadiene, and the like, or combinations thereof.

[0029] As used herein, the term“C_x+ hydrocarbons” refers to any hydrocarbon having equal to or greater than x carbon atoms (C). For example, the term“C₂₊ hydrocarbons” refers to any hydrocarbons having 2 or more carbon atoms, such as ethane, ethylene, C s, C₄s, C₅s, etc.

[0030] In an aspect, a supported OCM catalyst composition as disclosed herein can be characterized by the general formula (M0_x)-Mn-Na₂WO₄/SiO₂; wherein M is a metal with redox properties (e.g., a redox metal M); 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, M 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 M cations in (MO_x). Without wishing to be limited by theory, the different metals (M, 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 (M, Na, Mn, and W) present in the supported OCM catalyst compositions as disclosed herein can generate formation of surface oxygen vacancies (e.g., uncompensated oxygen vacancies), which can lead to further improvement of catalyst performance, for example in terms of conversion, selectivity, stability, etc., as will be discussed in more detail later herein.

[0031] Without wishing to be limited by theory, an OCM reaction can propagate by following a mechanism according to reactions (l)-(5):

wherein“s” denotes a species adsorbed onto the catalyst surface. As will be appreciated by one of skill in the art, and with the help of this disclosure, two or more of reactions ( 1 )-(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 [O]_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. Ethane can be further converted to ethylene though parallel reactions of thermal dehydrogenation and catalytic oxidative dehydrogenation. For example, ethane can further interact with active adsorbed oxygen sites [O]_s to form an ethyl radical, where the ethyl radical can lead to the formation of ethylene with the participation of an additional active adsorbed oxygen site [O]_s. Ethylene thermal dehydrogenation, as well as the formation of the ethyl radical and the subsequent formation of ethylene have a lower activation energy than the formation of methyl radicals (according to reaction (1)), and thus do 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 [O]_s) to form an oxygenate species [CH O]_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. In addition to reaction (1), the activity of the catalyst can also be influenced by the removal of the hydroxyl group [OH]_s from the catalyst surface according to reaction (5), which re-oxidizes the reduced sites back, and thereby completes the full cycle of the OCM reaction. The adsorbed hydroxyl group [OH]_s can undergo a dehydroxylation reaction step (e.g., removal or elimination of the surface adsorbed hydroxyl group from the catalyst), which creates surface oxygen vacancies (e.g., uncompensated oxygen vacancies). The surface oxygen vacancies can react with molecular oxygen and/or the oxygenate product CH₃O₂ to produce the active adsorbed oxygen sites [O]_s, which in turn activates methane and creates more methyl radicals according to reaction (1), thereby improving methane conversion. Decreasing the amount of oxygenate species can further decrease the formation of deep oxidation products, thereby improving selectivity to desired products (e.g., ethylene). The mechanism of OCM reaction is described in more detail in Lomonosov, V.I. and Sinev, M.Y., Kinetics and Catalysis, 2016, vol. 57, pp. 647-676; which is incorporated by reference herein in its entirety.

[0032] 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 Mn-Na₂WO₄/SiO₂ portion of the supported OCM catalyst composition as disclosed herein can display an enhanced activity towards CH₄ activation to form methyl radicals, for example according to reaction (1); however, if the Mn-Na₂WO₄/SiO₂ portion of the catalyst were to be used in the absence of the MO_x, the Mn-Na₂WO₄/SiO₂ could lead to an increased rate of reaction (1), which could further lead to an increased amount of hydroxyl group [OH]_s on the surface of the catalyst, thus reducing catalyst activity, and potentially resulting in catalyst deactivation. Further, without wishing to be limited by theory, the MO_x portion of the supported OCM catalyst composition as disclosed herein can additionally enhance the re-oxidation step of the OCM reaction according to reaction (5), owing to the redox properties of M and/or MO_x; and consequently the supported OCM catalyst composition as disclosed herein ((MO_x)- Mn-Na₂WO₄/SiO₂) can perform the function of re-activating the reduced catalyst sites, thereby enhancing the activity and stability of the catalyst.

[0033] Furthermore, as will be appreciated by one of skill in the art, and with the help of this disclosure, and without wishing to be limited by theory, an OCM catalyst comprising a single metal might not provide all the necessary properties for an optimum OCM reaction (e.g., best OCM reaction outcome) at the best level, and as such conducting an optimum OCM reaction may require an OCM catalyst with tailored composition in terms of metals present, wherein the different metals can have optimum properties for various OCM reaction steps, and wherein the different metals can provide synergistically for achieving the best performance for the OCM catalyst in an OCM reaction.

[0034] In an aspect, the supported OCM catalyst composition as disclosed can comprise a redox metal oxide component (i.e., (MO_x)) and a Na-Mn-W component (i.e., Mn-Na₂WO₄) wherein the redox metal oxide component and the Na-Mn-W component are supported on silica (SiO₂). 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 redox metal oxide 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.

[0035] The supported OCM catalyst composition as disclosed herein can be regarded as a composite comprising the redox metal oxide component and the Na-Mn-W component, wherein the redox metal oxide component and the Na-Mn-W component can be interspersed. In some aspects, the supported OCM catalyst composition can comprise a continuous redox metal oxide 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 redox metal oxide component dispersed therein. In yet other aspects, the supported OCM catalyst composition can comprise both a continuous redox metal oxide component and a continuous Na-Mn-W component, wherein the redox metal oxide component and the Na-Mn-W component contact each other. In still yet other aspects, the supported OCM catalyst composition can comprise regions of redox metal oxide component and regions of Na-Mn-W component, wherein at least a portion the regions of the redox metal oxide 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 redox metal oxide component and Na-Mn-W component present in the supported OCM catalyst composition contribute to the distribution of the redox metal oxide component and the Na-Mn-W component within the supported OCM catalyst composition.

[0036] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by a weight ratio of MO_x to Mn-Na₂WO₄/SiO₂ of from about 0.01: 1 to about 0.2: 1, or alternatively from about 0.03: 1 to about 0.15: 1.

[0037] In an aspect, the Na-Mn-W component can comprise Mn-Na₂WO₄, Na/Mn/O, Na₂WO₄, Mn₂O₃-Na₂WO₄, Mn₃O₄-Na₂WO₄, MnWO₄-Na₂WO₄, MnWO₄-Na₂WO₄, Mn-WO₄, and the like, or combinations thereof. In an aspect, the Na-Mn-W component can comprise Mn-Na₂WO₄. In an aspect, the Na-Mn-W component can comprise an element with redox properties, such as manganese (Mn) and/or tungsten (W). For purposes of the disclosure herein, a chemical species that has redox properties, can also be referred to as a“redox agent.” A redox agent generally refers to a chemical species that possesses the ability to undergo both an oxidation reaction and a reduction reaction, and such ability usually resides in the chemical species having more than one stable oxidation state other than the oxidation state of zero (0). As will be appreciated by one of skill in the art, and with the help of this disclosure, the redox metal M is a redox agent. Further, and as will be appreciated by one of skill in the art, and with the help of this disclosure, Mn and/or W can also be redox agents. Furthermore, and as will be appreciated by one of skill in the art, and with the help of this disclosure, although each of the redox metal oxide component and the Na-Mn-W component contain metals that are redox agents; all metals of the redox metal oxide component are redox agents; while some metals of the Na-Mn-W component are redox agents (e.g., Mn and/or W) and other metals of the Na-Mn-W component are not redox agents (e.g., Na).

[0038] 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.

[0039] In an aspect, the supported OCM catalyst composition as disclosed herein can comprise Na₂WO₄ 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.

[0040] In an aspect, the redox metal M (e.g., metal M with redox properties, redox agent M) can be selected from the group consisting of tin (Sn), antimony (Sb), bismuth (Bi), iron (Fe), chromium (Cr), molybdenum (Mo), tungsten (W), vanadium (V), tantalum (Ta), niobium (Nb), gallium (Ga), rhenium (Re), lead (Pb), cobalt (Co), nickel (Ni), copper (Cu), and combinations thereof.

[0041] In some aspects, the redox metal M comprises Sn. In other aspects, the redox metal M comprises Sb. As will be appreciated by one of skill in the art, and with the help of this disclosure, in some aspects, the redox metal M can comprise a single redox metal, such as Sn or Sb.

[0042] In yet other aspects, the redox metal M comprises Mo. In still yet other aspects, the redox metal M comprises V. As will be appreciated by one of skill in the art, and with the help of this disclosure, in some aspects, the redox metal M can comprise two or more redox metals. For example, the redox metal M can comprise Mo, Bi and Fe. As another example, the redox metal M can comprise V, Bi and Fe.

[0043] In an aspect, the redox metal M excludes a rare earth element.

[0044] In an aspect, the supported OCM catalyst composition as disclosed herein excludes a rare earth element. In an aspect, the supported OCM catalyst composition as disclosed herein is substantially free of rare earth elements.

[0045] In an aspect, the redox metal M 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 redox metals M that can be considered basic for purposes of the disclosure herein include tantalum (Ta), rhenium (Re), lead (Pb), 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 CFL_t 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).

[0046] In an aspect, the supported OCM catalyst composition as disclosed herein can comprise one or more oxides of M (e.g., MO_x). In some aspects, the redox metal oxide component of the supported OCM catalyst composition can comprise, consist of, or consist essentially of the one or more oxides of M (e.g., redox metal M oxides (MO_x)). [0047] In an aspect, the one or more oxides of M (e.g., MO_x) can be present in the redox metal oxide 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 redox metal oxide 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 oxides of M, in the presence of water, such as atmospheric moisture, can convert to hydroxides, and it is possible that the redox metal oxide 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 oxides of M, in the presence of carbon dioxide, such as atmospheric carbon dioxide, can convert to carbonates, and it is possible that the redox metal oxide component of the supported OCM catalyst composition will comprise some carbonates, due to oxide exposure to carbon dioxide (e.g., atmospheric carbon dioxide).

[0048] In an aspect, the one or more oxides of M (e.g., MO_x) can comprise a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, mixtures of single metal oxides and mixed metal oxides, or combinations thereof.

[0049] The single metal oxide comprises one redox metal M (e.g., a single redox metal M). A single metal oxide can be characterized by the general formula M_mO_y; wherein M is the redox metal M; and wherein m and y are integers from 1 to 7, alternatively from 1 to 5, or alternatively from 1 to 3. 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 general formula M_mO_y and the general formula MO_x are equivalent in the case of the single metal oxide, wherein x = y/m. A single metal oxide contains one and only one redox metal M cation. Nonlimiting examples of single metal oxides suitable for use in the supported OCM catalyst compositions of the present disclosure include Sb₂O , SnO₂, Sb₂O₅, SnO, FeO, Fe₂O₃, Fe O₄, Mo₂O₃, Mo₂O₅, MoO₃, W₂O₃, W₂O₅, WO₃, Cr₂O₃, Cr₂O₅, NiO, Ni₂O₃, CoO, Co₂O₃, Co O₄, and the like, or combinations thereof.

[0050] In an aspect, mixtures of single metal oxides can comprise two or more different single metal oxides, wherein the two or more different single metal oxides have been mixed together to form the mixture of single metal oxides. Mixtures of single metal can comprise two or more different single metal oxides, wherein each single metal oxide can be selected from the group consisting of Sb₂O₃, SnO₂, Sb₂O₅, SnO, FeO, Fe₂O₃, Fe O₄, Mo₂O₃, Mo₂O₅, MoO₃, W₂O₃, W₂O₅, WO₃, Cr₂O₃, Cr₂O₅, NiO, Ni₂O₃, CoO, Co₂O₃, and Co O₄. A Nonlimiting example of a mixture of single metal oxides suitable for use in the supported OCM catalyst compositions of the present disclosure is Sb₂O₃-SnO₂. [0051] The mixed metal oxide comprises two or more different redox metals M. A mixed metal oxide can be characterized by the general formula M¹ _mlM² _m2O_y; wherein M¹ and M² are redox metals M; 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 M² can be redox metal M cations of different chemical elements, for example M¹ can be an iron (Fe) cation and M² can be a molybdenum (Mo) cation. In other aspects, M¹ and M² can be different cations of the same chemical element, wherein M¹ and M² can have different oxidation states. Nonlimiting examples of mixed metal oxides suitable for use in the supported OCM catalyst compositions of the present disclosure include FeMoO₄; CoMoO₄; NiMoO₄; FeWO₄; CoWO₄; NiWO₄; PbMoO₄; PbWO₄; CUMOO₄; CUWO₄; and the like; or combinations thereof.

[0052] In an aspect, mixtures of mixed metal oxides can comprise two or more different mixed metal oxides, wherein the two or more different mixed metal oxides have been mixed together to form the mixture of mixed metal oxides. Mixtures of mixed metal oxides can comprise two or more different mixed metal oxides, wherein each mixed metal oxide can be selected from the group consisting of FeMoO₄; CoMoO₄; NiMoO₄; FeWO₄; CoWO₄; NiWO₄; PbMoO₄; PbWO₄; CuMoO₄; and CuWO₄.

[0053] In an aspect, mixtures of single metal oxides and mixed metal oxides can comprise at least one single metal oxide and at least one mixed metal oxide, wherein the at least one single metal oxide and the at least one mixed metal oxide have been mixed together to form the mixture of single metal oxides and mixed metal oxides.

[0054] The redox metal oxide component (e.g., MO_x) of the supported OCM catalyst can have any suitable desired shape and/or size specifications, for example as required by a specific application. In some aspects, the MO_x can comprise nanostructures, wherein a nanostructure is defined as a three-dimensional object characterized by at least one external dimension of less than about 1,000 nm. 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, three-dimensional objects are characterized by three external dimensions. For example, any three- dimensional object can be placed in a three-dimensional Cartesian coordinate system (i.e., a Cartesian coordinate system for a three-dimensional space) having axes x, y, and z, wherein the three-dimensional object is characterized by a first external dimension along x, a second external dimension along y, and a third external dimension along z. In some aspects, the redox metal oxide component (e.g., MO_x) of the supported OCM catalyst can comprise nanoparticles, nanofibers, nanoplates, or combinations thereof; wherein nanoparticles, nanofibers, and nanoplates are three-dimensional objects defined in accordance with ISO/TS 80004-2:2015.

[0055] In an aspect, the supported OCM catalyst composition as disclosed herein comprises a silica (SiO₂) support, wherein at least a portion of the supported OCM catalyst composition (e.g., the redox metal oxide 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., SiO₂) 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.

[0056] 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 CH conversion to CH₃·.

[0057] In an aspect, the supported OCM catalyst composition as disclosed herein can comprise SiO₂ 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 redox metal oxide 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 of the catalytically active material.

[0058] 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.

[0059] 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.).

[0060] 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 (SiO₂), 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 redox metal M cation, Na₂WO₄, or combinations thereof. The supported OCM catalyst precursor mixture can be characterized by a weight ratio of redox metal M to Mn of from about 0.01: 1 to about 10.0:1.

[0061] 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 redox metal M cation can comprise a redox metal M nitrate, a redox metal M oxide, a redox metal M hydroxide, a redox metal M chloride, a redox metal M acetate, a redox metal M carbonate, and the like, or combinations thereof.

[0062] 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 manganese (Mn) cation, one or more compounds comprising a redox metal M cation, Na₂WO₄, 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 the one or more compounds comprising a manganese (Mn) cation, one or more compounds comprising a redox metal M cation, Na₂WO₄, 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 manganese (Mn) cation, one or more compounds comprising a redox metal M cation, Na₂WO₄, or combinations thereof can be dissolved in an aqueous medium in any suitable order.

[0063] In some aspects, the one or more compounds comprising a manganese (Mn) cation, one or more compounds comprising a redox metal M cation, Na₂WO₄, 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 manganese (Mn) cation, one or more compounds comprising a redox metal M cation, Na₂WO₄, 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 manganese (Mn) cation, one or more compounds comprising a redox metal M cation, Na₂WO₄, 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.

[0064] Without wishing to be limited by theory, some of the one or more compounds comprising a manganese (Mn) cation, one or more compounds comprising a redox metal M cation, Na₂WO₄, or combinations thereof can be insoluble in water, or only partially soluble in water; and in such instances, these compounds will not be fully dissolved in water, but could be suspended or slurried in the one or more OCM catalyst precursor aqueous solutions (e.g., suspensions or slurries).

[0065] 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. 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 100°C, or alternatively of equal to or greater than about 125°C, to yield the dried supported OCM catalyst. 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.

[0066] 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 then further dried, to form the dried supported OCM catalyst.

[0067] 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 redox metal M cation to form a manganese and redox metal M impregnated silica (e.g., second supported OCM catalyst precursor mixture). The manganese and redox metal M impregnated silica can be dried to form dried manganese and redox metal M impregnated silica (e.g., second intermediate dried supported OCM catalyst precursor mixture). The dried manganese and redox metal M impregnated silica can be contacted with a Na₂WO₄ aqueous solution to form a Mn, Na, W and redox metal M impregnated silica (e.g., third supported OCM catalyst precursor mixture). The Mn, Na, W and redox metal M impregnated silica can be dried to form dried Mn, Na, W and redox metal M impregnated silica (e.g., dried supported OCM catalyst).

[0068] In some aspects, the dried supported OCM catalyst can be employed in an OCM process without any further processing (e.g., without calcining). In such aspects, the dried supported OCM catalyst can be referred to as the“supported OCM catalyst composition.”

[0069] In other aspects, the dried supported OCM catalyst can be subjected to additional processing (e.g., calcining to form the supported OCM catalyst composition) prior to being employed in an OCM process.

[0070] 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 to form the supported OCM catalyst composition, wherein the supported OCM catalyst composition is characterized by the general formula (M0_x)-Mn-Na₂WO₄/SiO₂; wherein M is a metal with redox properties; and wherein x balances the oxidation states. The dried supported OCM catalyst 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 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.

[0071] In some aspects, at least a portion of the dried supported OCM catalyst 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 redox metal oxide component (e.g., MO_x) of the supported OCM catalyst compositions can originate in the oxidizing atmosphere used for calcining the dried supported OCM catalyst. Further, without wishing to be limited by theory, the oxygen in the redox metal oxide component (e.g., MO_x) of the supported OCM catalyst compositions can originate in the one or more compounds comprising a redox metal M 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.

[0072] In an aspect, a method of making a supported OCM catalyst composition as disclosed herein can comprise contacting MO_x with Mn-Na₂WO₄/SiO₂ to form an OCM catalyst mixture, wherein the OCM catalyst mixture is characterized by a weight ratio of MO_x to Mn-Na₂WO₄/SiO₂ of from about 0.01 :1 to about 10.0:1. Mn-Na₂WO₄/SiO₂ can be prepared by using any suitable methodology. For example, silica (SiO₂), e.g., silica gel, can be contacted with one or more Na-Mn-W component precursor aqueous solutions to form a supported Na-Mn-W component precursor mixture; wherein each of the one or more Na-Mn-W component precursor aqueous solutions comprises one or more compounds comprising a manganese (Mn) cation and/or Na₂WO₄.

[0073] In some aspects, the one or more Na-Mn-W component precursor aqueous solutions can be formed by contacting water or any suitable aqueous medium with one or more compounds comprising a manganese (Mn) cation, and/or Na₂WO₄. 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 the one or more compounds comprising a manganese (Mn) cation, and/or Na₂WO₄ 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 manganese (Mn) cation and Na₂WO₄ can be dissolved in an aqueous medium in any suitable order. [0074] In some aspects, the one or more compounds comprising a manganese (Mn) cation and/or Na₂WO₄ 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 manganese (Mn) cation and/or Na₂WO₄ 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, crushing, milling, chopping, mixing, blending (e.g., 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 Na-Mn-W component 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 manganese (Mn) cation and/or Na₂WO₄ 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 Na-Mn-W component precursor aqueous solutions.

[0075] In an aspect, at least a portion of the one or more Na-Mn-W component precursor aqueous solutions can be dried to form a dried Na-Mn-W component precursor. In an aspect, at least a portion of the one or more Na-Mn-W component precursor aqueous solutions can be dried at a temperature of equal to or greater than about 75°C, alternatively of equal to or greater than about 100°C, or alternatively of equal to or greater than about 125°C, to yield the dried Na-Mn-W component precursor. The one or more Na-Mn-W component precursor aqueous solutions 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.

[0076] In an aspect, at least a portion of the dried Na-Mn-W component precursor can be calcined to form Mn-Na₂WO₄/SiO₂. The dried Na-Mn-W component precursor can be calcined, for example in an oxidizing atmosphere, 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 Mn-Na₂WO₄/SiO₂. The dried Na-Mn-W component precursor can be calcined for a time period of equal to or greater than about 2 hours, alternatively equal to or greater than about 4 hours, or alternatively equal to or greater than about 6 hours.

[0077] In an aspect, the redox metal oxide component (e.g., MO_x) and Mn-Na₂WO₄/SiO₂ can be contacted with each other in the absence of water (e.g., substantial absence of water; without adding water, etc.) to form the supported OCM catalyst mixture; for example by grinding, crushing, milling, chopping, mixing, blending (e.g., dry blending), or otherwise intimately mixing to obtain a homogeneous mixture. As will be appreciated by one of skill in the art, and with the help of this disclosure, while the redox metal oxide component (e.g., MO_x) and Mn-Na₂WO₄/SiO₂ 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.

[0078] In an aspect, at least a portion of the supported OCM catalyst mixture can be dried at a temperature of equal to or greater than about 75°C to form the supported OCM catalyst composition; wherein the supported OCM catalyst composition can be employed in an OCM process without any further processing. In some aspects, the supported OCM catalyst composition can be further calcined, for example, in an oxidizing atmosphere, at a temperature of equal to or greater than about 700°C, prior to being employed in an OCM process.

[0079] 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.

[0080] 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 (O₂); 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.

[0081] The OCM reactant mixture can be a gaseous mixture. The OCM reactant mixture can comprise a hydrocarbon or mixtures of hydrocarbons, and oxygen. In some aspects, the hydrocarbon or mixtures of hydrocarbons can comprise natural gas (e.g., CH ), liquefied petroleum gas comprising C₂-C₅ hydrocarbons, C₆₊ heavy hydrocarbons (e.g., C₆ to C₂₄ 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 CH₄ and O₂.

[0082] The O₂ 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.

[0083] 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.

[0084] 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.

[0085] In an aspect, the OCM reactor can be characterized by any suitable OCM reactor operational parameters, such as temperature (e.g., feed preheat temperature, reactor effluent temperature, etc.), pressure, flow rate (e.g., space velocity), and the like, or combinations thereof.

[0086] The OCM reaction mixture can be introduced to the OCM reactor at a temperature (e.g., feed preheat temperature) of from about 150°C to about 1,000°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 CH , as the C-H bonds of CH₄ are very stable, and the formation of methyl radicals from CH 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.

[0087] The OCM reactor can be characterized by a reactor effluent temperature of from about 400°C to about 1,200°C, alternatively from about 500°C to about 1,100°C, or alternatively from about 600°C to about 1,000°C.

[0088] 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.

[0089] The OCM reactor can be characterized by a gas hourly space velocity (GHSV) of from about 500 h^-1 to about 10,000,000 h^-1, alternatively from about 500 h^-1 to about 1,000,000 h^-1, alternatively from about 500 h^-1 to about 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 GHSV relates a reactant (e.g., reactant mixture) gas flow rate to a reactor volume. GHSV is usually measured at standard temperature and pressure.

[0090] 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, CO₂, 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 C 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 (C H₆) and propane (C₃H₈).

[0091] The water produced from the OCM reaction and the water used as a diluent (if water diluent is used) can be separated from the product mixture prior to separating any of the other product mixture components. For example, by cooling down the product mixture to a temperature where the water condenses (e.g., below 100°C at ambient pressure), the water can be removed from the product mixture, by using a flash chamber for example.

[0092] 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).

[0093] 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.

[0094] In an aspect, the O₂ 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 O₂ conversion is fairly high in OCM processes, most often approaching 90%-100%. Without wishing to be limited by theory, oxygen is usually a limiting reagent in OCM processes. The oxygen conversion can be calculated by using equation (6):

[0095] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by an O₂ 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 an O₂ conversion of an otherwise similar supported OCM catalyst composition (i) without MO_x, or (ii) without Mn-Na₂WO₄.

[0096] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by a catalyst activity variation within about + 10%, alternatively within about + 9%, alternatively within about + 8%, alternatively within about + 7%, alternatively within about + 6%, alternatively within about + 5%, alternatively within about + 4%, alternatively within about + 3%, alternatively within about + 2%, or alternatively within about + 1 % of a target catalyst activity over a time period of equal to or greater than about 50 hours (h), alternatively equal to or greater than about 100 h, alternatively equal to or greater than about 250 h, alternatively equal to or greater than about 500 h, alternatively equal to or greater than about 1,000 h, or alternatively equal to or greater than about 5,000 h, wherein the catalyst activity is defined as the O₂ conversion under a set of given OCM reactor operational parameters, and wherein the target catalyst activity is defined as a target O₂ conversion equal to or greater than about 90% under the same set of given OCM reactor operational parameters. In some aspects, the target O₂ conversion 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%.

[0097] 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 MO_x, or (ii) without Mn-Na₂WO₄. In some aspects, the supported OCM catalyst composition as disclosed herein can be characterized by a C₂₊ selectivity that is equal to or greater than the C₂₊ selectivity of the Na-Mn-W component (e.g., C₂₊ selectivity of Mn-Na₂WO₄/SiO₂).

[0098] 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., C_C2H4, C_C2H6, etc.) by the total number of moles of C from CH₄ that were converted (e.g., C_C2H4, C_C2H6, C_C2H2, C_C3H6, C_C3H8, C_C4s, C_CO2, C_CO, etc.). C_C2H4 = number of moles of C from CH₄ that were converted into C₂H₄; C_C2H6 = number of moles of C from CH₄ that were converted into C₂H₆; C_C2H2 = 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 C₃H₆; C_C3H8 = number of moles of C from CH₄ that were converted into C₃H₈; C_C4s = number of moles of C from CH₄ that were converted into C₄ hydrocarbons (C₄s); C_CO2 = number of moles of C from CH₄ that were converted into CO₂; C_CO = number of moles of C from CH₄ that were converted into CO; etc.

[0099] 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, CO₂ and CO. For example, the C₂₊ selectivity can be calculated by using equation (7):

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

[00100] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by a C₂₌ selectivity (selectivity to ethylene) that is increased when compared to a C₂₌ selectivity of an otherwise similar supported OCM catalyst composition (i) without MO_x or (ii) without Mn-Na₂WO₄.

[00101] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by a selectivity to ethane that is decreased 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 selectivity to ethane of an otherwise similar supported OCM catalyst composition without MO_x.

[00102] With the increase of C₂₌ selectivity and decrease of ethane selectivity, the supported OCM catalyst composition as disclosed herein can be characterized by an increase of C₂₌/C₂ ratio, equal or greater than about 10%, alternatively equal or greater than about 20%, or alternatively equal or greater than about 30%, when compared to a C₂₌/C₂ ratio of an otherwise similar supported OCM catalyst composition (i) without MO_x or (ii) without Mn-Na₂WO₄. [00103] 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 (CO₂). Without wishing to be limited by theory, when the selectivity to desired products (e.g., C₂₊ selectivity, C₂₌ selectivity) of an OCM process increases, less methane is converted to undesirable products, such as deep oxidation products (e.g., CO, CO₂), 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.

[00104] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by the general formula (Sn0_x)-Mn-Na₂WO₄/SiO₂; 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, Sn 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 redox metal oxide component (e.g., SnO_x) of the supported OCM catalyst composition. In such aspect, SnO_x can comprise SnO₂.

[00105] In an aspect, the supported OCM catalyst composition as disclosed herein can be characterized by the general formula (Sb0_x)-Mn-Na₂WO₄/SiO₂; 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, Sb 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 redox metal oxide component (e.g., SbO_x) of the supported OCM catalyst composition. In such aspect, SbO_x can comprise Sb₂O₃.

[00106] In an aspect, the supported OCM catalyst compositions characterized by the general formula (M0_x)-Mn-Na₂WO₄/SiO₂; wherein M is redox metal; 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 MO_x, or (ii) without Mn-Na₂WO₄.

[00107] The supported OCM catalyst compositions characterized by the general formula (MO_x)-Mn- Na₂WO₄/SiO₂, as disclosed herein, can advantageously display improved conversion, selectivity, activity and stability when compared to the conversion, selectivity, activity and stability, respectively, of an otherwise similar supported OCM catalyst composition (i) without MO_x, or (ii) without Mn-Na₂WO₄. Specifically, the supported OCM catalyst compositions characterized by the general formula (MO_x)-Mn- Na₂WO₄/SiO₂, as disclosed herein, can display improved selectivity to desired products, such as olefins, and decreased selectivity to less desired products, such as alkanes. Furthermore, the supported OCM catalyst compositions characterized by the general formula (M0_x)-Mn-Na₂WO₄/SiO₂, as disclosed herein, can display an improved (i.e., increased) C₂₌/C₂ ratio. [00108] The supported OCM catalyst compositions characterized by the general formula (MO_x)-Mn- Na₂WO₄/SiO₂, as disclosed herein, can advantageously display decreased selectivity to ethane, when compared to the selectivity to ethane of an otherwise similar supported OCM catalyst composition without MO_x. Without wishing to be limited by theory, the supported OCM catalyst compositions characterized by the general formula (M0_x)-Mn-Na₂WO₄/SiO₂, as disclosed herein, can advantageously display an increased ability to convert ethane to ethylene.

[00109] The supported OCM catalyst compositions characterized by the general formula (MO_x)-Mn- Na₂WO₄/SiO₂, as disclosed herein, can advantageously display stable performance in an OCM process over time. The supported OCM catalyst compositions characterized by the general formula (MO_x)-Mn- Na₂WO₄/SiO₂, as disclosed herein, can advantageously display stable catalyst activity (e.g., oxygen conversion), as well as stable selectivity over time (e.g., with time on stream). Additional advantages of the supported OCM catalyst compositions characterized by the general formula (M0_x)-Mn-Na₂WO₄/SiO₂, as disclosed herein; and methods of making and using same, can be apparent to one of skill in the art viewing this disclosure.

EXAMPLES

[00110] 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

[00111] Oxidative coupling of methane (OCM) catalyst compositions were prepared as follows.

[00112] A reference catalyst (Mn-Na₂WO₄/SiO₂) was prepared by using the following procedure. Silica gel (18.6 g, Davisil® Grade 646) was used after drying overnight. Mn(NO₃)₂-4H₂O (1.73 g) was dissolved in deionized water (18.6 mL), and then added dropwise onto the silica gel. The resulting manganese impregnated silica material was dried overnight. Na₂WO₄-4H₂O (1.13 g) was dissolved in deionized water (18.6 mL), and the solution obtained was added onto the dried manganese silica material above. The resulting material obtained was dried overnight at 125°C, and then calcined at 800°C for 6 hours under airflow to obtain the Mn-Na₂WO₄/SiO₂ reference catalyst.

[00113] Different (M0_x)-Mn-Na₂WO₄/SiO₂ catalysts were prepared as follows and compared with the reference catalyst.

[00114] Catalyst #1 (Sb₂O₃)-Mn-Na₂WO₄/SiO₂ was prepared by using the following method. 0.11 g of Sb₂O₃ (with particle size of 80-200 nm) was mixed with deionized water (6.0 mL) to form a slurry. The slurry was then added onto 3.3 g of calcined reference catalyst (Mn-Na₂WO₄/SiO₂ reference catalyst) prepared as described above. The resulting mixture was dried overnight at 125°C, and then calcined at 800°C for 6 hours under airflow to obtain the (3 wt.% Sb₂O₃)-Mn-Na₂WO₄/SiO₂ (Catalyst #1 - 3 wt.% C; C = calcined). With the same method, but a higher Sb₂O₃ loading (10 wt.%), another catalyst was obtained: (10 wt.% Sb₂O₃)-Mn-Na₂WO₄/SiO₂ (Catalyst #1 - 10 wt.% C).

[00115] With the same method of making used above for Catalyst #1, but without the calcining step, two more catalysts were obtained: (3 wt.% Sb₂O₃)-Mn-Na₂WO₄/SiO₂ (Catalyst #1 - 3 wt.% D; D = dried) and (10 wt.% Sb₂O₃)-Mn-Na₂WO₄/SiO₂ (Catalyst #1 - 10 wt.% D).

[00116] Catalyst #2 (SnO₂)-Mn-Na₂WO₄/SiO₂ was prepared by using the following method. 0.10 g of SnO₂ (with particle size of 18 nm) was mixed with deionized water (6.0 mL) to form a slurry. The slurry was then added onto 3.3 g of calcined reference catalyst (Mn-Na₂WO₄/SiO₂ reference catalyst) prepared as described above. The resulting mixture was dried overnight at 125°C, and then calcined at 800°C for 6 hours under airflow to obtain the (3 wt.% SnO₂)-Mn-Na₂WO₄/SiO₂ (Catalyst #1 - 3 wt.% C). With the same method, but a higher SnO₂ loading (10 wt.%), another catalyst was obtained: (10 wt.% SnO₂)-Mn- Na₂WO₄/SiO₂ (Catalyst #2 - 10 wt.% C).

[00117] With the same method of making used above for Catalyst #2, but without the calcining step, two more catalysts were obtained: (3 wt.% SnO₂)-Mn-Na₂WO₄/SiO₂ (Catalyst #2 - 3 wt.% D) and (10 wt.% SnO₂)-Mn-Na₂WO₄/SiO₂ (Catalyst #2 - 10 wt.% D).

EXAMPLE 2

[00118] The performance of the supported OCM catalyst compositions prepared as described in Example 1 was investigated. Specifically, the performance of Catalysts #1, and #2 was compared to the performance of the reference catalyst. OCM reactions were conducted by using catalysts prepared as described in Example 1 as follows.

[00119] Performance test. The catalysts obtained as described in Example 1 were performance tested in a 5.0 mm ID quartz tube reactor. The reactor was loaded with 0.5 cc of catalyst. A mixture of methane and oxygen at a fixed CH :O₂ ratio of 7.4 was fed to the reactor at a total flow rate of 66.7 seem and 100 seem, and the GHSV for these two flow rates were 8,000 h^-1 and 12,000 h^-1, respectively. Products obtained were analyzed by using online GC with TCD and FID detectors.

[00120] The performance obtained with (Sb₂O₃)-Mn-

Na₂WO₄/SiO₂ (Catalyst #1) is shown in Tables 1 and 2, compared to the reference catalyst.

Table 1. Performance comparison at 8,000 h^-1 flowrate and 775 °C reactor temperature

Table 2. Performance comparison at 12,000 h^-1 flowrate and full O₂ Conversion

[00121] It can be seen that with the promotion with Sb₂O₃, catalyst activity is increased (Table 1). 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, for OCM reactions, catalyst selectivity is related to oxygen conversion. For OCM reactions, it is generally more meaningful to compare selectivities obtained under full or close to full oxygen conversion. The selectivities obtained with Sb₂O₃ promoted catalysts by comparison to the reference catalyst under full oxygen conversion are displayed in Table 2. From the data in Table 2 it can be seen that the same or slightly better selectivities are obtained with Sb₂O₃ promotion.

[00122] The impact of Sb₂O₃ promoter on catalyst stability is shown in Figure 1. For the data in Figure 1, catalysts were tested at 12,000 h^-1 and 825 °C. For the reference catalyst (Mn-Na₂WO₄/SiO₂), its oxygen conversion decreased from 97.7% to 83.6% only after 50 hours time on stream. With Sb₂O₃ promotion, the oxygen conversion declined from 100% to 98.2% within the same time period on stream, and the stability improved significantly with Sb₂O₃ promotion. Based on the data in Figure 1, the Catalyst #1 - 3 wt.% C is about 2.5 times more stable than the reference catalyst (Mn-Na₂WO₄/SiO₂). The stability ratio is calculated based on the data shown in Figure 1. For Example, for the reference catalyst, the reaction rate constant at the beginning and the end of the run, k₃ and k₂ is determined using the equation: k=-Ln(l-X_O2/100), where X_O2 is the oxygen conversion, and the deactivation rate of this catalyst is determined by using the equation: deactivation rate= [(k₁-k₂)/k₁]/(t₂-t₁), where t₂-t₁ is the time duration between these two results. The same deactivation rate is then determined for the other catalysts, and the ratio of 2.5 is the ratio of the deactivation rates of these two catalysts.

[00123] Similar to the oxygen conversion, the CH₄ conversion for the reference catalyst (Mn- Na₂WO₄/SiO₂) declines fast with time on stream; while the CH conversion for the Sb₂O₃ promoted catalysts was much more stable by comparison to the reference catalyst. Generally, the CH conversion can be calculated by using equation (8):

[00124] In addition to the fast decline of the activity of the reference catalyst (Mn-Na₂WO₄/SiO₂), its selectivity also changed with time on stream. Ethylene and ethane selectivities variation with time on stream are displayed in Figures 2 and 3. For the data in Figures 2 and 3, catalysts were tested at 12,000 h- ¹ and 825 °C. From Figures 2 and 3 it can be seen that for the reference catalyst (Mn-Na₂WO₄/SiO₂) its ethylene selectivity decreases, while its ethane selectivity increases with time on stream. As will be appreciated by one of skill in the art, and with the help of this disclosure, ethylene is a more valuable product than ethane. Consequently, the selectivity variation for the reference catalyst (Mn-Na₂WO₄/SiO₂) will result in a less valuable product with time on stream. The selectivity variation for the Sb₂O₃ promoted catalyst is also displayed in Figures 2 and 3, for comparison. With Sb₂O₃ promotion, the catalyst #1 demonstrated higher ethylene selectivity by comparison to the reference catalyst, and by contrast to the reference catalyst, the Sb₂O₃ promoted catalyst demonstrated an increase in ethylene selectivity with time on stream. At the same time, the ethane selectivity for the Sb₂O₃ promoted catalyst displayed no change with time on stream.

[00125] The total C₂₊ selectivity comparison for the reference catalyst (Mn-Na₂WO₄/SiO₂) and the Sb₂O₃ promoted catalyst is displayed in Figure 4. For the data in Figure 4, catalysts were tested at 12,000 h^-1 and 825 °C. There is no significant difference between the C₂₊ selectivity for the reference catalyst (Mn-Na₂WO₄/SiO₂) and the C₂₊ selectivity for the Sb₂O₃ promoted catalyst, although the C₂₊ selectivity for the Sb₂O₃ promoted catalyst appears to be higher.

[00126] In summary, Sb₂O₃ promotion improves catalyst activity stability, so that more stable oxygen and methane conversions are obtained with time on stream. Further, Sb₂O₃ promotion also improves ethylene selectivity stability by comparison to the reference catalyst. It is clearly advantageous to employ Sb₂O₃ promotion.

[00127] The performance obtained with (SnO₂)-Mn-

Na₂WO₄/SiO₂ (Catalyst #2) is shown in Tables 3 and 4, compared to the reference catalyst. Table 3. Performance comparison at 10,000 h^-1 flowrate and 800 °C reactor temperature

Table 4. Performance comparison at 12,000 h^-1 flowrate and full O₂ Conversion

[00128] It can be seen that with the promotion with SnO₂, catalyst activity is increased (Table 3). The selectivities obtained with SnO₂ promoted catalysts by comparison to the reference catalyst under full oxygen conversion are displayed in Table 4. From the data in Table 4 it can be seen that the same or slightly better selectivities are obtained with SnO₂ promotion for Catalyst #2 - 10 wt.% C, Catalyst #2 - 3 wt.% D, and Catalyst #2 - 10 wt.% D.

[00129] The effect of SnO₂ promotion on catalyst stability is shown in Figures 5, 6, and 7. For the data in Figures 5, 6, and 7, catalysts were tested at 12,000 h^-1 and 825 °C. For the reference catalyst (Mn- Na₂WO₄/SiO₂), its oxygen conversion decreased from 97.7% to 83.6% only after 50 hours time on stream. With SnO₂ promotion, the oxygen conversion declined from 98.7% to 94.1% within the same time period on stream, and the stability improved significantly with SnO₂ promotion. Based on the data in Figure 5, the Catalyst #2 - 3 wt.% D is about 1.9 times more stable than the reference catalyst (Mn- Na₂WO₄/SiO₂). Similar to Sb₂O₃ promotion, SnO₂ promotion also improves catalyst selectivity stability, especially ethylene selectivity stability. Slightly different from Sb₂O₃ promoted catalysts, SnO₂ promoted catalysts show higher ethylene selectivity than Sb₂O₃ promoted catalysts. SnO₂ promotion also improves catalyst olefin to paraffin ratio.

[00130] 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.

[00131] 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.

[00132] 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.

[00133] 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 (M0_x)-Mn-Na₂WO₄/SiO₂; wherein M is a metal with redox properties; and wherein x balances the oxidation states.

2. The supported OCM catalyst composition of claim 1, wherein a weight ratio of MO_x to Mn- Na₂WO₄/SiO₂ 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 Na₂WO₄ 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 metal M is selected from the group consisting of tin (Sn), antimony (Sb), bismuth (Bi), iron (Fe), chromium (Cr), molybdenum (Mo), vanadium (V), tantalum (Ta), niobium (Nb), gallium (Ga), rhenium (Re), lead (Pb), cobalt (Co), nickel (Ni), copper (Cu), and combinations thereof.

6. The supported OCM catalyst composition of claim 1, wherein MO_x comprise a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, mixtures of single metal oxides and mixed metal oxides, or combinations thereof.

7. The supported OCM catalyst composition of claim 1, wherein MO_x comprise nanostructures, wherein a nanostructure is defined as a three-dimensional object characterized by at least one external dimension of less than about 1,000 nm.

8. The supported OCM catalyst composition of claim 1 having the general formula (SnO_x)-Mn- Na₂WO₄/SiO₂.

9. The supported OCM catalyst composition of claim 1 having the general formula (SbO_x)-Mn- Na₂WO₄/SiO₂.

10. A method of making a supported oxidative coupling of methane (OCM) catalyst composition comprising:

(a) contacting silica (SiO₂) 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 metal M cation, Na₂WO₄, or combinations thereof; wherein the metal M has redox properties; and wherein the supported OCM catalyst precursor mixture is characterized by a weight ratio of metal M to Mn of from about 0.01 : 1 to about 0.2: 1;

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

(c) calcining at least a portion of the dried supported OCM catalyst to form the supported OCM catalyst composition of claim 1.

11. The method of claim 10, wherein the step (a) of contacting silica (SiO₂) 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 metal M cation, Na₂WO₄, or combinations thereof in an aqueous medium to form the one or more OCM catalyst precursor aqueous solutions.

12. The method of claim 10, wherein the supported OCM catalyst precursor mixture is dried at a temperature of equal to or greater than about 75°C.

13. The method of claim 10, wherein the dried supported OCM catalyst precursor mixture is calcined at a temperature of equal to or greater than about 700°C.

14. A method of making a supported oxidative coupling of methane (OCM) catalyst composition comprising:

(a) contacting MO_x with Mn-Na₂WO₄/SiO₂ to form an OCM catalyst mixture, wherein the OCM catalyst mixture is characterized by a weight ratio of MO_x to Mn-Na₂WO₄/SiO₂ of from about 0.01 : 1 to about 0.2:1; and

(b) drying at least a portion of the supported OCM catalyst mixture at a temperature of equal to or greater than about 75°C to form the supported OCM catalyst composition of claim 1.

15. The method of claim 14 further comprising calcining the supported OCM catalyst composition at a temperature of equal to or greater than about 700°C.

16. The method of claim 14, wherein the step (a) further comprises mixing, blending, grinding, crushing, milling, chopping, or combinations thereof the OCM catalyst mixture.

17. 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 claim 1 , wherein the reactant mixture comprises methane (CH ) and oxygen (O₂);

(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.

18. The method of claim 17, wherein the supported OCM catalyst composition is characterized by a selectivity to ethylene (C₂₌ selectivity) that is increased when compared to a C₂₌ selectivity of an otherwise similar supported OCM catalyst composition (i) without MO_x or (ii) without Mn-Na₂WO₄.

19. The method of claim 17, wherein the supported OCM catalyst composition is characterized by (A) a selectivity to ethane that is decreased by equal to or greater than about 10% when compared to a selectivity to ethane of an otherwise similar supported OCM catalyst composition without MO_x.; (B) a C₂₌/C₂ ratio that is increased by equal or greater than about 10% when compared to a C₂₌/C₂ ratio of an otherwise similar supported OCM catalyst composition (i) without MO_x or (ii) without Mn-Na₂WO₄; or both (A) and (B).

20. The method of claim 17, wherein the supported OCM catalyst composition is characterized by an O₂ conversion that is increased by equal to or greater than about 10% when compared to an O₂ conversion of an otherwise similar supported OCM catalyst composition (i) without MO_x, or (ii) without Mn-Na₂WO₄; and wherein the supported OCM catalyst composition is characterized by a catalyst activity variation within about + 10% of a target catalyst activity over a time period of equal to or greater than about 50 hours (h), wherein the catalyst activity is defined as the O₂ conversion under a set of given OCM reactor operational parameters, and wherein the target catalyst activity is defined as a target O₂ conversion of equal to or greater than about 90% under the same set of given OCM reactor operational parameters.