A composite oxide containing tungstate nanoclusters, a preparation method thereof, and uses thereof

Abstract

The present invention belongs to the field of catalysts, and particularly relates to a composite oxide containing tungstate nanoclusters, a preparation method thereof, and uses thereof. The composite oxide containing tungstate nanoclusters contains an alkali metal element A, a tungsten element W, a promoter element M, and an oxygen element O, and the alkali metal element A, the tungsten element W, and the promoter element M all form a complex with the oxygen element O. As a cocatalyst, the composite oxide can significantly improve the C2 selectivity and C2 yield in the OCM bed reactor with co-feed of methane and oxygen, and has great application value.

Description

Technical Field:

[0001] The present invention belongs to the field of catalysts, and particularly relates to a composite oxide containing tungstate nanoclusters, a preparation method thereof, and uses thereof. Background Art:

[0002] Nanoclusters are ultra-fine particles formed by the aggregation of several to thousands or even more atoms, and their diameters are usually less than 10 nm (Journal of Molecular Catalysis A: Chemical 1999, 145, 1-44). In this scale range, substances undergo a transformation from microscopic atoms and molecules to macroscopic condensed materials, so nanoclusters often exhibit many unique properties that are different from both macroscopic and microscopic ones. In the past few decades, nanoclusters have been widely studied by people, and their application fields include quantum dots, sensors, biomedicine, catalysis, etc. (Nanoscale, 2021, 13, 6283-6340; Chemical Society Reviews 2020, 49, 6443-6514).

[0003] Currently, the synthesis of the vast majority of nanoclusters is aimed at metal nanoclusters and oxide nanoclusters, while the research on inorganic salt nanoclusters is very limited. Taking the composite oxide of tungsten-containing oxide nanoclusters as an example, in the prior art (such as Nature Chemistry 2009, 1, 722-728; ACS Catal. 2017, 7, 2181–2198), the methods for synthesizing tungsten oxide nanoclusters can be summarized as follows: by impregnation method or co-precipitation method, a thermally decomposable tungsten-containing compound (ammonium metatungstate, tungstic acid, etc.) is loaded on a support (usually an oxide or hydroxide), and then the tungsten-containing compound (tungstic acid or tungstate) is decomposed by high-temperature calcination to form tungsten oxide (WO x ). Since there is a strong interaction between the support (such as zirconia, alumina) and WO x (a W-O-M bond can be formed, where M is a non-oxygen element in the support, such as Zr, Al, Si, Ti), WO x can exist stably in the form of nanoclusters. The composite oxides of tungsten-containing oxide nanoclusters (such as WO3 / ZrO2, WO3 / Al2O3, WO3 / SiO2) are often used as solid acid catalysts, mainly because the W x on the surface of WO 6+ exists in a distorted octahedral configuration (WO6), and can form Bronsted acid sites - H δ+ (WO3) n δ-(J.Catal.2004,227,479–491). Since alkali metal tungstates (such as Na2WO4) cannot be decomposed by high-temperature calcination to form WO x , and the presence of alkali metal ions will destroy the acidity of the compound. In order to avoid the loaded tungsten-containing compound on the carrier containing alkali metal ions, the methods used in the prior art usually do not use alkali solutions and alkali metal tungstate raw materials. In the extremely few synthesis methods that use Na2WO4 as the tungsten source (Topics in Catalysis 1998,6,87–99; Advances in Chemical Engineering and Science,2014,4,250-257), people will also add HCl solution to load tungstate ions on the carrier in the form of tungstic acid without alkali metal, which helps to decompose to form WO x . It is worth mentioning that in alkali metal tungstates such as Na2WO4, W exists in the form of WO4 tetracoordination (J.Phys.Chem.C 2008,112,6869-6879), which is quite different from the WO6 configuration in WO x . Therefore, the interaction between alkali metal tungstates and oxide carriers must also be different from the interaction between WO x and oxide carriers. In this context, how to controllably synthesize alkali metal tungstate nanoclusters, especially high-concentration alkali metal tungstate nanoclusters, will be full of challenges. In addition, the uses of alkali metal tungstate nanoclusters are rarely involved.

[0004] Tungsten-manganese catalysts are a class of classical OCM catalysts, whose composition includes alkali metals, tungsten, manganese and carriers. This type of catalyst was first developed by the research group of Li Shuben from Lanzhou Institute of Chemical Physics in 1992 (Journal of Molecular Catalysis 1992,6,427-433). It is usually prepared by impregnating sodium tungstate and manganese salts on silica gel and then calcining at high temperature. This type of catalyst has high OCM catalytic performance and good thermal stability, and has received extensive attention (ACS Catalysis 2019,9,5912-5928). The typical composition of the tungsten-manganese catalyst is 1.9wt% Mn - 5wt% Na2WO4 / SiO2, where the Mn element accounts for 1.9% of the catalyst mass and Na2WO4 accounts for 5% of the catalyst mass. Under the experimental conditions of 800 °C, methane space velocity of 36000 mL / g / h, and CH4:O2:N2 = 3:1:2.6, the conversion rate of methane is 36.8%, and the yield of C2 hydrocarbons reaches 23.9%. In addition, the OCM performance of tungsten-manganese catalysts can also be optimized by means of element doping, composition regulation, reaction condition regulation, etc. (Applied Catalysis A:General 2012,425,53-61).

[0005] The tungsten-manganese catalyst is a classic OCM catalyst, and its composition includes alkali metals, tungsten, manganese, and a carrier. This type of catalyst was first developed by the research group of Li Shuben at the Lanzhou Institute of Chemical Physics in 1992 (Journal of Molecular Catalysis 1992, 6, 427 - 433). It is usually prepared by using sodium tungstate and manganese salts as precursors, loading them onto silica gel by methods such as impregnation, and then calcining at high temperature. This type of catalyst has high OCM catalytic performance and good thermal stability, and has received extensive attention (ACS Catalysis 2019, 9, 5912 - 5928). The typical composition of the tungsten-manganese catalyst is 1.9 wt% Mn - 5 wt% Na2WO4 / SiO2, where the Mn element accounts for 1.9% of the catalyst mass, and Na2WO4 accounts for 5% of the catalyst mass. Calculated based on all non-oxygen elements (Na, Mn, W, Si) in the catalyst, the atomic percentage of W is 1%, and the atomic percentage of Na is 2%. Under the experimental conditions of 800 °C, a methane space velocity of 36000 mL / g / h, and CH4:O2:N2 = 3:1:2.6, the conversion rate of methane is 36.8%, and the yield of C2 hydrocarbons reaches 23.9%. Subsequently, people have optimized the performance of the tungsten-manganese catalyst through various means such as element doping, composition regulation, and reaction condition regulation (Applied Catalysis A: General 2012, 425, 53 - 61; Applied Catalysis A: General 225 (2002) 271–284). In the preparation of the tungsten-manganese catalyst, the main role of Na is to induce the carrier SiO2 to change from the amorphous phase to the cristobalite phase, thereby improving the dispersion of tungsten. The main source of Na is usually the Na carried in the tungsten source Na2WO4 (Applied Catalysis A: General 2012, 425, 53 - 61; Applied Catalysis A: General 225 (2002) 271–284). In a few catalyst preparation methods that do not use Na2WO4 as the Na source, alkaline Na salts are not used as the Na source either. This is mainly because using alkaline Na salts as the Na source will cause the manganese element to exist in the form of Mn 4+ rather than the active Mn2O3 form, which will significantly reduce the OCM catalytic activity of the tungsten-manganese catalyst (Ind. Eng. Chem. Res. 2006, 45, 7077 - 7083).

[0006] Oxidative coupling of methane (OCM) to ethane and ethylene is one of the key technologies for the direct utilization of methane and is the technical basis for realizing a new chemical route in the petrochemical industry by replacing petroleum with natural gas as raw material (Energy Conversion and Management, 2019, 198, 111789; Chinese Journal of Catalysis 2021, 42, 1117 - 1125). Traditional studies generally believe that the OCM reaction follows a "heterogeneous - homogeneous" catalytic reaction mechanism. After methane is activated on the catalyst surface to generate methyl radicals, homogeneous coupling occurs in the gas phase to produce products such as ethane and ethylene (J. Am. Chem. Soc. 1987, 109, 7900 - 7901; J. Mol. Catal. A: Chem. 2017, 426, 326 - 342). The challenge of this reaction mechanism is that the catalyst only plays a role in generating methyl radicals, and the homogeneous coupling of methyl radicals in the gas phase cannot be regulated by catalyst optimization (ACS Catal. 2016, 6, 4340–4346). Driven by thermodynamics, methyl radicals and C2 species tend to react with oxygen in the gas phase to form fully oxidized products such as CO2. Therefore, it is difficult to achieve a breakthrough in the selectivity and yield of C2 in the traditional OCM catalytic system ( Figure 1 ). Arutyunov et al. (J. Mol. Catal. A: Chem. 2017, 426, 326) used kinetic simulations of gas - phase reactions to obtain the upper limit of the C2 species yield. They pointed out that only when the catalyst can play a role in the step of methyl radical coupling, the yield of C2 species is likely to exceed 25% ( Figure 3)。In the past few decades, more than 1,000 catalysts involving 68 elements have been developed, but there has been no breakthrough in their reaction mechanisms (ChemCatChem, 2011, 3, 1935-1947). The optimization methods for OCM catalysts in the prior art (Appl. Catal. A 2012, 425-426, 53-61) can be summarized as follows: by means of element substitution / doping, promoter addition, catalyst morphology control, support regulation, etc. to adjust the activation of oxygen / methane on the catalyst surface, thereby optimizing the generation of methyl radicals and improving the OCM reaction performance. These means all start from the composition and structure of the methane activation catalyst, and the final regulation is all about the step of generating methyl radicals from methane activation, and the controllable conversion of methyl radicals has not been achieved. Theoretically speaking, if a catalyst capable of controllably coupling methyl radicals can be developed and coupled with the catalyst that generates methyl radicals from methane activation, it is expected to break through the limitations of the traditional OCM reaction mechanism and achieve a breakthrough in its performance. An excellent catalyst for the controllable conversion of methyl radicals must meet the following conditions: 1) It has a strong ability to adsorb methyl radicals and can enrich methyl radicals in the gas phase on the catalyst surface; 2) The methyl radicals enriched on the catalyst surface can be highly selectively converted into C2 products; 3) It has weak oxidation ability (or is difficult to activate oxygen) and will not convert methyl radicals and C2 products into CO and CO2 on the catalyst surface. From the above conditions, it can be seen that an excellent methyl radical coupling catalyst itself must not have significant OCM activity because it has weak oxidation ability and is difficult to activate methane to generate methyl radicals; at the same time, because it has a strong adsorption effect on methyl radicals, methyl radicals are difficult to desorb into the gas phase and do not meet the requirements of the traditional OCM reaction mechanism for OCM catalysts. In the prior art, it is generally believed that methyl radicals are too active under OCM reaction conditions (high temperature and the presence of oxygen), and it is almost an impossible miracle to achieve the controllable coupling of methyl radicals on the catalyst surface (ACS Catal. 2016, 6, 4340–4346). Therefore, there is currently no technology to design and optimize catalysts from the perspective of the controllable surface coupling of methyl radicals, and no one has improved the C2 selectivity and yield of the reaction by physically mixing a promoter with no significant OCM performance into a traditional OCM catalyst. Summary of the Invention:

[0007] To break through the limitations of the traditional methane oxidative coupling (OCM) reaction mechanism and achieve breakthroughs in its performance (C2 selectivity and C2 yield), the present invention has conducted in-depth research and developed a composite oxide containing tungstate nanoclusters, which is used as a co-catalyst for controllably coupling methyl radicals. This co-catalyst itself cannot be used alone as a catalyst to catalyze the OCM reaction and does not significantly have OCM activity. However, when it is combined with a traditional OCM catalyst as a co-catalyst, it can increase both the C2 selectivity and C2 yield of the traditional OCM catalyst by more than 1.2 times ( Figure 4 ). Therefore, the effect of the present invention is that by using the composite oxide containing tungstate nanoclusters developed in the present invention as a co-catalyst, when the cluster enrichment index reaches the necessary density, the selectivity of a traditional OCM catalyst (such as 1.9 wt% Mn - 5 wt% Na2WO4 / SiO2) in the oxidative coupling of methane (OCM) to produce ethane and ethylene can reach more than 70%, and the yield can reach more than 30%.

[0008] Using the composite oxide containing tungstate nanoclusters developed in the present invention and the classical OCM catalyst 1.9 wt% Mn - 5 wt% Na2WO4 / SiO2 as a catalyst composition in an OCM bed reactor with co-feed of methane and oxygen, it is possible to achieve C2 selectivity ≥ 70% and C2 single-pass yield ≥ 35%; more preferably, in the OCM bed reactor with co-feed of methane and oxygen, the catalyst composition can achieve C2 selectivity ≥ 70% and C2 single-pass yield ≥ 40%; more preferably, in the OCM bed reactor with co-feed of methane and oxygen, the catalyst composition can achieve C2 selectivity ≥ 70% and C2 single-pass yield ≥ 45%.

[0009] The explanation of the complex herein: In the composite oxide, the valences of the alkali metal A, tungsten element W, and promoter element M are all positive, and they all achieve charge balance by combining with oxygen elements with negative valence. The compounds formed by the alkali metal A, tungsten element W, and promoter element M with oxygen elements can all be written in the form of oxides. For example, Na2WO4 can be written as Na2O·WO3; ZrW2O8 can be written as ZrO2·2WO3. Detection means: The valences of the alkali metal element A, tungsten element W, promoter element M, and oxygen element can be determined by X-ray photoelectron spectroscopy (XPS), and the crystal structure of the composite oxide can be determined by X-ray powder diffraction (XRD).

[0010] Herein, the atomic percentages (including A, W, and M), the atomic percentages do not include oxygen. The atomic percentage of an element in the composite oxide is defined as follows:

[0011]

[0012] The atomic percentage refers to the percentage of all elements in the dried catalyst measured by X-ray fluorescence spectroscopy according to the atomic ratio, with an allowable test error of ±10%, preferably ±5%.

[0013] Among them, the general formula of the tungstate nanocluster is A x WO y , where 0 < x ≤ 2, and y represents the number of oxygen atoms required to satisfy the charge balance of the general formula. For example: when A is Na and x = 2, Na is +1 valence, W is +6 valence, O is -2 valence, all positive charges are 2*1 + 1*6 = 8, all negative charges are 2*y. According to charge balance, positive charge = negative charge, so 2*y = 8, and y = 4 is obtained; when A is Mg and x = 1, Mg is +2 valence, W is +6 valence, O is -2 valence, all positive charges are 1*2 + 1*6 = 8, all negative charges are 2*y. According to charge balance, positive charge = negative charge, so 2*y = 8, and y = 4 is obtained.

[0014] More preferably, the particle size of the tungstate nanocluster ≤ 10.0 nm, preferably ≤ 5.0 nm, further preferably ≤ 2.0 nm, and even more preferably ≤ 1.0 nm. The particle size of the tungstate nanocluster refers to the average diameter of the nanocluster; the detection method is: observing the composite oxide under a high-resolution transmission electron microscope, randomly selecting 100 tungstate nanoclusters, counting their diameters, and taking the average value. The magnification during the high-resolution transmission electron microscope observation is 2 million - 30 million times, preferably 5 million - 10 million times.

[0015] The single-pass C2 selectivity refers to the C2 selectivity obtained when the feed gas passes through the catalyst bed once, and the C2 selectivity refers to the selectivity of the products ethane and ethylene, and its calculation method is:

[0016] C2 selectivity = (2*n C2H6 + 2*n C2H4 ) / (2*n C2H6 + 2*n C2H4 + n CO + n CO2 + 3*n C3H8 + 3*n C3H6 );

[0017] The C2 yield is obtained by multiplying the C2 selectivity by the CH4 conversion rate. The CH4 conversion rate refers to the methane conversion efficiency, and its calculation method is:

[0018]

[0019] Unless otherwise specified, the methane conversion rate, C2 selectivity, and C2 yield mentioned in the following content are all the results of the single-pass OCM reaction in a bed reactor with co-fed methane and oxygen.

[0020] The present invention provides a composite oxide containing tungstate nanoclusters. The composite oxide contains an alkali metal element A, a tungsten element W, a promoter element M, and an oxygen element O, and the alkali metal element A, the tungsten element W, and the promoter element M all form complexes with the oxygen element O.

[0021] The alkali metal element A is selected from any one or more of Li, Na, K, Mg, Ca, Sr, and Ba.

[0022] The promoter element M is selected from any one or more of Si, Zr, Ti, Al, La, Ce, and Co.

[0023] The atomic percentage of the alkali metal element A is 5% - 67%; the atomic percentage of the tungsten element W is 1% - 60%; the atomic percentage of the promoter element M is 20% - 94%; the content of oxygen element in the composite oxide is the sum of the number of oxygen atoms required to satisfy the charge balance of the alkali metal element A, the tungsten element W, and M.

[0024] The atomic percentage of a certain element is calculated according to the following formula.

[0025]

[0026] Among them, the tungstate nanocluster is composed of the alkali metal element A, the tungsten element W, and the oxygen element O. The general formula of the tungstate nanocluster is A x WO y , where 0 < x ≤ 2, and y represents the number of oxygen atoms required to satisfy the charge balance of the general formula; and the tungstate nanocluster satisfies the cluster enrichment index. The cluster enrichment index refers to that in any region of 10×10nm 2 containing the tungstate nanocluster, the number of tungstate nanoclusters ≥ 3; preferably, the number of tungstate nanoclusters ≥ 5, more preferably ≥ 10, and further preferably ≥ 20.

[0027] Preferably, the method for detecting the cluster enrichment index: Observe the composite oxide under a high-resolution transmission electron microscope. In the region of the tungstate nanocluster containing three elements of the alkali metal element A, the tungsten element W, and the oxygen element O, randomly select 5 regions of 10×10nm 2For the region, count the number of tungstate nanoclusters contained in this region and take the average value; preferably, the magnification during high-resolution transmission electron microscopy observation is 2 million - 30 million times, preferably 5 million - 10 million times; preferably, the particle size of the tungstate nanoclusters ≤ 10.0 nm, preferably ≤ 5.0 nm, more preferably ≤ 2.0 nm, even more preferably ≤ 1.0 nm;

[0028] Preferably, the specific surface area of the composite oxide is 0.1 - 10 g / m 2 , more preferably 0.5 - 5 g / m 2 , further preferably 1 - 2 g / m 2 ;

[0029] Preferably, the three elements of alkali metal element A, tungsten element W, and oxygen element O in the tungstate nanoclusters are uniformly distributed. The uniform distribution means that any region in the tungstate clusters contains alkali metal element A, tungsten element W, and oxygen element O; preferably, the detection method for the uniform distribution is: observe the composite oxide under a high-resolution transmission electron microscope, and perform compositional analysis on the tungstate nanoclusters using the X-ray energy spectrometer (EDS) area scan mode. Randomly select 10 clusters, and any region in the clusters contains alkali metal element A, tungsten element W, and oxygen element O; more preferably, the magnification during high-resolution transmission electron microscopy observation is 2 million - 30 million times, preferably 5 million - 10 million times;

[0030] Preferably, the atomic percentage of alkali metal element A in the composite oxide is 10% - 65%, more preferably 15% - 50%; further preferably 10% - 60% by atom, more preferably 20% - 50%, further preferably 30% - 40%; the atomic percentage of tungsten element W is 2% - 55%, more preferably 5% - 50%, further preferably 10% - 40%, more preferably 20% - 30%; the atomic percentage of the promoter element M is 22% - 92% or more, more preferably 25% - 90%, preferably 30% - 80%, further preferably 40% - 70%, further preferably 50% - 60%;

[0031] Preferably, the tungsten element in the tungstate nanoclusters exists in the form of tetracoordinated tungstate. The tetracoordination means that one tungsten atom is bonded to exactly four oxygen atoms; more preferably, the detection method for the tetracoordination structure is: perform X-ray fine structure spectrum testing on the composite oxide, collect the L1-edge and L3-edge X-ray absorption near-edge structure spectra (XANES) and extended X-ray absorption fine structure (EXAFS) of the tungsten element in the composite, and obtain the coordination number of the tungsten atom through qualitative analysis and data fitting;

[0032] Preferably, after the composite oxide is calcined in air at 800 °C for 6 h, the particle size change value Δ1 of the tungstate nanoclusters is ≤ 20%, more preferably Δ1 ≤ 10%; the calculation formula is as follows:

[0033]

[0034] The change value Δ2 of the cluster enrichment index of the tungstate nanoclusters after calcination is ≤ 20%; more preferably Δ2 ≤ 10%; the calculation formula is as follows:

[0035]

[0036] Furthermore, the alkali metal element A is at least Na, the promoter element M is at least Zr or Al, the composite oxides containing tungstate nanoclusters are respectively expressed as NaWZr or NaWAl, the tungstate nanoclusters are composed of the alkali metal element Na, the tungsten element W and the oxygen element O, and the general formula of the tungstate nanoclusters is Na x WO y , 0 < x ≤ 2, and y represents the number of oxygen atoms required to satisfy the charge balance of the general formula;

[0037] The atomic percentage of Na in the composite oxide is 5% - 67%; the atomic percentage of the tungsten element W is 1% - 60%; the atomic percentage of the promoter element M is 20% - 94%;

[0038] Preferably, the atomic percentage of Na in the composite oxide is 10% - 65%, more preferably 15% - 50%; further preferably 10% - 60%, more preferably 20% - 50%, further preferably 30% - 40%; the atomic percentage of the tungsten element W is 2% - 55%, more preferably 5% - 50%, further preferably 10% - 40%, more preferably 20% - 30%; the atomic percentage of the promoter element Zr or Al is 22% - 92% or more, more preferably 25% - 90%, preferably 30% - 80%, further preferably 40% - 70%, further preferably 50% - 60%;

[0039] In the composite oxide, 0 < Na:W molar ratio ≤ 5, preferably, 0.1 ≤ Na:W molar ratio ≤ 4, more preferably 0.8 ≤ Na:W molar ratio ≤ 3.5; further preferably 1.0 ≤ Na:W molar ratio ≤ 3.0; further preferably 1.5 ≤ Na:W molar ratio ≤ 2.0; further preferably 1.4 ≤ Na:W molar ratio ≤ 1.6;

[0040] The molar ratio of W:Zr in the composite oxide is ≥ 0.1; preferably, 0.2 ≤ molar ratio of W:Zr ≤ 100; more preferably, 0.23 ≤ molar ratio of W:Zr ≤ 10; more preferably, 0.3 ≤ molar ratio of W:Zr ≤ 1; more preferably, 0.4 ≤ molar ratio of W:Zr ≤ 0.5.

[0041] The present invention also provides a method for preparing a composite oxide containing tungstate nanoclusters, comprising the following steps:

[0042] 1) Prepare solution system 1 and solution system 2 respectively. Both solution system 1 and solution system 2 are transparent solutions. Here, the transparent solution means that there are no obvious suspensions in the solution, and the solution will not layer. When light passes through the solution, the Tyndall effect will not occur.

[0043] 2) While stirring solution system 2, add solution system 1 completely into solution system 2 within 2 - 200 minutes until a turbid solution appears. Stir the turbid solution for more than 1 hour, preferably more than 2 hours, more preferably more than 3 hours; preferably, the dropping time is 2 - 200 minutes, preferably 10 - 100 minutes, more preferably 20 - 60 minutes; preferably, the stirring is rapid stirring, and the rotation speed of the rapid stirring is 500 - 1000 revolutions per minute, more preferably 750 - 900 revolutions per minute; preferably, the stirring time is 10 minutes - 2 hours, and the more preferred stirring time is 30 minutes - 1 hour.

[0044] 3) Without any treatment, directly remove the solvent from the product obtained in step 2), and then dry the obtained solid to obtain a dried solid product. Specifically, the "without any treatment" means any washing, centrifugation, and filtration steps.

[0045] Preferably, the method for removing the solvent is to dry the solvent. Preferably, the drying method is to place the product obtained in step 2) in an atmosphere at a temperature of 30 - 50°C until the solution evaporates; preferably, the temperature is 40°C.

[0046] Preferably, the temperature for drying the solid is 60 - 100°C, more preferably 80 - 90°C; preferably, the drying time is more than 12 hours, and the more preferred time is more than 24 hours.

[0047] 4) Calcinate the solid product obtained in step 3) to obtain a composite oxide containing tungstate nanoclusters. Preferably, the calcination temperature is 700 - 900°C, more preferably 750 - 850°C, and even more preferably 800°C; the calcination time is 3 - 8 hours, preferably 4 - 6 hours; the heating rate of the calcination is 2 - 10°C per minute, more preferably 3 - 5°C per minute.

[0048] The preparation method of the solution system 1 is: dissolving an alkali metal element precursor of a compound raw material containing the element in an appropriate amount of water, and stirring it sufficiently to form a transparent solution, thereby obtaining the solution system 1, wherein the pH of the transparent solution is greater than 7, and more preferably pH ≥ 10;

[0049] The preparation method of the solution system 2 is selected from any one of the following: a) mixing a tungsten element precursor, an auxiliary element precursor and an appropriate amount of water and stirring rapidly to form a transparent solution, i.e., obtaining a solution system 2-1; b) mixing a tungsten element precursor, an auxiliary element precursor and an appropriate amount of alcohol and stirring rapidly to form a transparent solution, i.e., obtaining a solution system 2-2;

[0050] The ratio of the alkali metal element precursor, the tungsten element precursor, and the auxiliary element precursor added to the solution system 1 and the solution system 2 conforms to the following formula:

[0051] In solution system 1 and solution system 2, the atomic percentage of an element is calculated according to the following formula:

[0052]

[0053] The atomic percentage of the alkali metal element A is 5%-67%; the atomic percentage of the tungsten element W is 1%-60%; the atomic percentage of the auxiliary element M is 20%-94%;

[0054] Preferably, the atomic percentage of the alkali metal element A in the composite oxide is 10%-65%, more preferably 15%-50%; more preferably 10%-60%, more preferably 20%-50%, more preferably 30%-40%; the atomic percentage of the tungsten element W is 2%-55%, more preferably 5%-50%, more preferably 10%-40%, more preferably 20%-30%; the atomic percentage of the auxiliary element M is 22%-92%, more preferably 25%-90%, preferably 30%-80%, more preferably 40%-70%, more preferably 50%-60%.

[0055] Preferably, the concentration of the alkali metal element precursor in the solution system 1 is 1-40wt%, preferably 10-30wt%, more preferably 15-25wt%; preferably, the concentration of the tungsten element precursor in the solution systems 2-1 and 2-2 is 1-30wt%, preferably 5-25wt%, more preferably 10-20wt%; preferably, the concentration of the auxiliary element precursor in the solution systems 2-1 and 2-2 is 1-50wt%, preferably 10-40wt%, more preferably 20-35wt%;

[0056] Preferably, the alkali metal element precursor in the preparation method of the solution system 1 is selected from any one or more of lithium hydroxide, sodium hydroxide, lithium carbonate, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, magnesium acetate, calcium hydroxide, calcium acetate, strontium hydroxide, and barium hydroxide;

[0057] Preferably, the promoter element precursor in the preparation method of the solution system 2-1 is selected from any one or more of sodium silicate, zirconyl nitrate, zirconium nitrate, zirconium oxychloride, bis(acetato-O)oxozirconium, zirconium citrate, titanium nitrate, aluminum nitrate, lanthanum nitrate, lanthanum acetate, lanthanum chloride, cerium nitrate, cerium acetate, cerium chloride, cobalt nitrate, and cobalt acetate; the tungsten element precursor is selected from any one or more of sodium tungstate, cesium tungstate, tungsten ethanolate, ammonium tungsten oxide, ammonium tungsten oxide hydrate, strontium tungstate, magnesium tungstate, barium tungstate, ammonium pentahydrate tungstate, ammonium metatungstate hydrate, calcium tungstate, barium tungstate, and strontium tungstate;

[0058] Preferably, the tungsten element precursor in the preparation method of the solution system 2-2 is selected from any one or two of sodium tungstate and tungsten chloride; the promoter element precursor is selected from any one or more of tetraethyl orthosilicate, zirconium nitrate, zirconium n-butoxide, zirconyl nitrate, zirconium oxychloride, bis(acetato-O)oxozirconium, zirconium citrate, tetrabutyl titanate, aluminum sec-butoxide, aluminum isopropoxide, lanthanum nitrate, aluminum nitrate, cerium nitrate, and cobalt nitrate; the alcohol solution is selected from any one or more of methanol, ethanol, propanol, and butanol.

[0059] Further, the alkali metal element precursor is a sodium element precursor, the promoter element precursor is selected from a zirconium element precursor or an aluminum element precursor, and the composite oxide containing tungstate nanoclusters prepared is NaWZr or NaWAl. The tungstate nanoclusters are composed of alkali metal element Na, tungsten element W, and oxygen element O, and the general formula of the tungstate nanoclusters is Na x WO y , 0 < x ≤ 2, and y represents the number of oxygen atoms required to balance the charge of the general formula;

[0060] Preferably, the alkali metal precursor in the preparation method of the solution system 1 is selected from any one or more of sodium hydroxide, sodium carbonate, and sodium bicarbonate;

[0061] Preferably, the promoter element precursor in the preparation method of the solution system 2-1 is selected from any one or more of zirconyl nitrate, zirconium nitrate, zirconium oxychloride, bis(acetato-O)oxozirconium, zirconium citrate, and aluminum nitrate; the tungsten element precursor is selected from any one or more of sodium tungstate, cesium tungstate, tungsten ethanolate, ammonium tungsten oxide, ammonium tungsten oxide hydrate, strontium tungstate, magnesium tungstate, barium tungstate, ammonium pentahydrate tungstate, ammonium metatungstate hydrate, calcium tungstate, barium tungstate, and strontium tungstate;

[0062] Preferably, the tungsten element precursor in the solution system 2-2 is selected from any one or two of sodium tungstate and tungsten chloride; the promoter element precursor is selected from any one or more of zirconium nitrate, zirconium butoxide, zirconyl nitrate, zirconium oxychloride, bis(acetato-O)oxozirconium, zirconium citrate, aluminum sec-butoxide, aluminum isopropoxide, and aluminum nitrate; the alcohol solution is selected from any one or more of methanol, ethanol, propanol, and butanol;

[0063] Preferably, in the preparation method of the solution system 2-2, the promoter element precursor is zirconium butoxide, and the tungsten element precursor is tungsten chloride; more preferably, the molar ratio of the tungsten element to the zirconium element is ≥1:9, preferably ≥2:9, more preferably ≥3:9; more preferably, the solution system 1 is an aqueous NaOH solution, and the mass percentage of NaOH is 1% - 60%, preferably 10% - 50%, more preferably 15% - 40%;

[0064] Preferably, in the preparation method of the solution system 2-2, the promoter element precursor is aluminum isopropoxide, the tungsten element precursor is tungsten chloride, and the molar ratio of the tungsten element to the aluminum element is ≥1:9, preferably ≥2:9, more preferably ≥3:9; more preferably, the solution system 1 is an aqueous NaOH solution, and the mass percentage of NaOH is 1% - 60%, preferably 10% - 50%, more preferably 15% - 40%;

[0065] Preferably, in the preparation method of the solution system 2-2, the promoter element precursor is zirconium butoxide, the tungsten element precursor is sodium tungstate, and the molar ratio of the tungsten element to the zirconium element is ≥1:9, preferably ≥2:9, more preferably ≥3:9; more preferably, the solution system 1 is an aqueous KOH solution with a mass percentage of KOH of 1% - 60%, preferably 10% - 50%, more preferably 15% - 40%;

[0066] Preferably, in the preparation method of the solution system 2-2, the promoter element precursor is aluminum isopropoxide, the tungsten element precursor is sodium tungstate, and the molar ratio of the tungsten element to the aluminum element is ≥1:9, preferably ≥2:9, more preferably ≥3:9; more preferably, the solution system 1 is an aqueous KOH solution with a mass percentage of KOH of 1% - 60%, preferably 10% - 50%, more preferably 15% - 40%.

[0067] The present invention also provides a cocatalyst, and the cocatalyst contains the composite oxide containing tungstate nanoclusters;

[0068] Preferably, the cocatalyst cannot be used alone as a catalyst for the oxidative coupling of methane (OCM) reaction; preferably, the cocatalyst does not have significant OCM activity; preferably, the detection method for the lack of significant OCM activity is as follows: in a bed reactor with co-feed of methane and oxygen, when the catalyst is used as a methane oxidation catalyst at a gas hourly space velocity of greater than or equal to 20,000 mL / g / h, a catalyst bed temperature of 800 °C or lower, and a reaction pressure of 1 atmosphere, its single-pass C2 yield is not higher than 5%; preferably, the yield is quantitatively measured by gas chromatography.

[0069] The present invention also provides a catalyst composition, which comprises the composite oxide as claimed in the claims and at least one catalyst with OCM activity. catalyst ;

[0070] Preferably, the having OCM activity means that it can be used alone as a catalyst for the OCM reaction; preferably, the meaning of having OCM activity is: in a bed reactor with co-feed of methane and oxygen, when the catalyst is used as an oxidative coupling of methane catalyst at a gas hourly space velocity of greater than or equal to 20,000 mL / g / h, a catalyst bed temperature of 800 °C or lower, and a reaction pressure of 1 atmosphere, it has a C2 single-pass yield of greater than 5%.

[0071] Preferably, the OCM catalyst has significant OCM activity, and its meaning is: in a bed reactor with co-feed of methane and oxygen, when the catalyst is used as an oxidative coupling of methane catalyst at a gas hourly space velocity of greater than or equal to 20,000 mL / g / h, a catalyst bed temperature of 800 °C or lower, and a reaction pressure of 1 atmosphere, it has a C2 single-pass yield of greater than 15%.

[0072] Preferably, the OCM catalyst has a mass ratio with the composite oxide of 0.1 - 50.0; more preferably, the mass ratio is 0.5 - 20.0:1.0; more preferably, the mass ratio is 1.0 - 10.0:1.0; more preferably, the mass is 2.0 - 4.0:1.0.

[0073] Preferably, the yield is quantitatively measured by gas chromatography.

[0074] Preferably, the OCM catalyst is selected from any one or more of tungsten manganese catalysts, rare earth metal oxides, perovskite compounds, alkali metal and alkaline earth metal oxides, and derivatives of the above catalysts; more preferably, it is a tungsten manganese catalyst, lanthanum oxide, samarium oxide, Li / MgO, Ca / CeO2; preferably, the tungsten manganese catalyst is Mn-Na2WO4 / SiO2.

[0075] Preferably, the OCM catalyst is at a distance of ≤ 3 mm from the composite oxide;

[0076] Preferably, the catalyst composition is formed by compounding the composite oxide and OCM catalyst by physical mixing;

[0077] Preferably, the OCM catalyst is a composite containing a second alkali metal element, tungsten element, manganese element, oxygen element and a fifth component element; more preferably, the fifth component element is selected from any one or more of Al, Si, Ti, Zr, C, N; further more preferably, the fifth component element is selected from any one or more of Al, Si, Ti; more preferably, the fifth component element is selected from Si; more preferably, the second alkali metal is selected from any one or more of Li, Na, K; more preferably, the second alkali metal is selected from Na;

[0078] Preferably, the mass percentage of the second alkali metal element in the OCM catalyst is 0.1 - 2.0 wt.%; more preferably, the mass percentage of the second alkali metal element in the OCM catalyst is 0.5 - 1.5 wt.%;

[0079] Preferably, the mass percentage of the tungsten element in the OCM catalyst is 0.1 - 5.0 wt.%, preferably, the mass percentage of the tungsten element in the OCM catalyst is 2.0 - 4.0 wt.%;

[0080] Preferably, the mass percentage of the manganese element in the OCM catalyst is 0.1 - 10.0 wt.%, preferably, the mass percentage of the manganese element in the OCM catalyst is 1.0 - 4.0 wt.%;

[0081] Preferably, the catalyst further comprises an additive; more preferably, the additive is selected from any one or more of a heat dissipation aid, a mass transfer aid, a shaping aid, an abrasion resistance enhancer, a dispersant, a stabilizer, etc.

[0082] Preferably, under the same reaction conditions, the selectivity and yield of the OCM reaction catalyzed by the catalyst composition are both increased by more than 1.2 times compared with using only OCM catalyst ;

[0083] Preferably, in the OCM bed reactor with co-feed of methane and oxygen, the catalyst composition can achieve a C2 selectivity ≥ [selectivity value] and a C2 single-pass yield ≥ [single-pass yield value]; more preferably, in the OCM bed reactor with co-feed of methane and oxygen, the catalyst composition can achieve a C2 selectivity ≥ [selectivity value] and a C2 single-pass yield ≥ 40%; even more preferably, in the OCM bed reactor with co-feed of methane and oxygen, the catalyst composition can achieve a C2 selectivity ≥ [selectivity value] and a C2 single-pass yield ≥ 45%.

[0084] Further, the OCM catalyst is Mn / Na2WO4 / SiO2, and the composite oxide is the composite oxide of Na, W, and Zr, NaWZr; preferably, the mass ratio of the OCM catalyst to the composite oxide is 4:1 - 0.5:1; more preferably 2:1 - 1:1; preferably, in the OCM bed reactor with co-feed of methane and oxygen, the catalyst composition can achieve a C2 selectivity ≥ 70% and a C2 single-pass yield ≥ 35%; more preferably, in the OCM bed reactor with co-feed of methane and oxygen, the catalyst composition can achieve a C2 selectivity ≥ [selectivity value] and a C2 single-pass yield ≥ 40%; even more preferably, in the OCM bed reactor with co-feed of methane and oxygen, the catalyst composition can achieve a C2 selectivity ≥ [selectivity value] and a C2 single-pass yield ≥ 45%;

[0085] Preferably, in the OCM bed reactor with co-feed of methane and oxygen, the C2 selectivity of the catalyst composition Mn / Na2WO4 / SiO2 - NaWZr can be increased to 1.3 times that of Mn / Na2WO4 / SiO2, and its C2 single-pass yield is 1.2 times that of Mn / Na2WO4 / SiO2.

[0086] Further, the OCM catalyst is La2O3, the composite oxide is the composite oxide of Na, W, and Zr, NaWZr, and the mass ratio of the OCM catalyst to the composite oxide is 4:1 - 1:1; more preferably 2:1 - 1:1;

[0087] Preferably, in the OCM bed reactor with co-feed of methane and oxygen, the C2 selectivity of La2O3 - NaWZr can be increased to 1.3 times that of La2O3, and its C2 single-pass yield is 1.2 times that of La2O3.

[0088] Further, the OCM catalyst is Sm2O3, the composite oxide is the composite oxide of Na, W, and Zr, NaWZr, and the OCM catalystThe mass ratio to the composite oxide is 4:1 - 1:1; more preferably 2:1 - 1:1;

[0089] Preferably, in the OCM bed reactor with co-feed of methane and oxygen, the C2 selectivity of the catalyst composition Sm2O3-NaWZr can be increased to 2.0 times that of Sm2O3, and its C2 single-pass yield is 1.8 times that of Sm2O3.

[0090] Furthermore, the OCM catalyst is Li / MgO, the composite oxide is the composite oxide NaWZr of Na, W, and Zr, and the OCM catalyst The mass ratio to the composite oxide is 4:1 - 1:1; more preferably 2:1 - 1:1;

[0091] Preferably, in the OCM bed reactor with co-feed of methane and oxygen, the C2 selectivity of the catalyst composition Li / MgO-NaWZr can be increased to 2.0 times that of Li / MgO, and its C2 single-pass yield is 1.45 times that of Li / MgO.

[0092] Furthermore, the OCM catalyst is Ca / CeO2, the composite oxide is the composite oxide NaWZr of Na, W, and Zr, and the OCM catalyst The mass ratio to the composite oxide is 4:1 - 1:1; more preferably 2:1 - 1:1;

[0093] Preferably, in the OCM bed reactor with co-feed of methane and oxygen, the C2 selectivity of the catalyst composition Ca / CeO2-NaWZr can be increased to 1.3 times that of Ca / CeO2, and its C2 single-pass yield is 1.5 times that of Ca / CeO2;

[0094] Furthermore, the catalyst composition is Mn-Na2WO4 / SiO2-NaWAl, wherein the OCM catalyst is Mn-Na2WO4 / SiO2, the composite oxide is the composite oxide NaWAl of Na, W, and Al, and the OCM catalyst The mass ratio to the composite oxide is 4:1 - 1:1; more preferably 2:1 - 1:1;

[0095] Preferably, the catalyst composition Mn-Na2WO4 / SiO2-NaWAl can achieve a C2 selectivity ≥ 70% and a C2 single-pass yield ≥ 35% in an OCM bed reactor with co-feed of methane and oxygen; more preferably, the catalyst composition can achieve a C2 selectivity ≥ selectivity response and a C2 single-pass yield ≥ 40% in an OCM bed reactor with co-feed of methane and oxygen; even more preferably, the catalyst composition can achieve a C2 selectivity ≥ selectivity response and a C2 single-pass yield ≥ 45% in an OCM bed reactor with co-feed of methane and oxygen;

[0096] Preferably, in an OCM bed reactor with co-feed of methane and oxygen, the C2 selectivity of Mn-Na2WO4-NaWAl in the catalyst composition can be increased to 1.3 times that of Mn-Na2WO4, and its C2 single-pass yield is 1.2 times that of Mn / Na2WO4 / SiO2.

[0097] Furthermore, the OCM catalyst is La2O3, the composite oxide is the composite oxide NaWAl of Na, W, and Al, and the mass ratio of the OCM catalyst to the composite oxide is 4:1 - 1:1; more preferably 2:1 - 1:1;

[0098] Preferably, in an OCM bed reactor with co-feed of methane and oxygen, the C2 selectivity of La2O3-NaWAl in the catalyst composition can be increased to 1.3 times that of La2O3, and its C2 single-pass yield is 1.2 times that of La2O3.

[0099] Furthermore, the OCM catalyst is Sm2O3, the composite oxide is the composite oxide NaWAl of Na, W, and Al, and the mass ratio of the OCM catalyst to the composite oxide is 4:1 - 1:1; more preferably 2:1 - 1:1;

[0100] Preferably, in an OCM bed reactor with co-feed of methane and oxygen, the C2 selectivity of Sm2O3-NaWAl in the catalyst composition can be increased to 1.2 times that of Sm2O3, and its C2 single-pass yield is 1.5 times that of Sm2O3.

[0101] Furthermore, the OCM catalyst is Li / MgO, the composite oxide is the composite oxide NaWAl of Na, W, and Al, and the mass ratio of the OCM catalyst to the composite oxide is 4:1 - 1:1; more preferably 2:1 - 1:1;

[0102] Preferably, in the OCM bed reactor where the catalyst composition Li / MgO-NaWAl co-feeds methane and oxygen, the C2 selectivity of Li / MgO-NaWAl can be increased to 1.7 times that of Li / MgO, and its C2 single-pass yield is 1.8 times that of Li / MgO.

[0103] Further, the OCM catalyst is Ca / CeO2, the composite oxide is the composite oxide NaWAl of Na, W, and Al, and the mass ratio of the OCM catalyst to the composite oxide is 4:1 - 1:1; more preferably 2:1 - 1:1;

[0104] Preferably, in the OCM bed reactor where the catalyst composition Ca / CeO2-NaWAl co-feeds methane and oxygen, the C2 selectivity of Ca / CeO2-NaWAl can be increased to 1.3 times that of Ca / CeO2, and its C2 single-pass yield is 1.6 times that of Ca / CeO2.

[0105] The present invention also provides a use of the catalyst composition in a chemical reaction; preferably, the chemical reaction is a radical conversion reaction; more preferably, the chemical reaction is a catalytic oxidative coupling of methane reaction. The catalytic oxidative coupling of methane reaction refers to the process in which methane, under the action of a catalyst, the carbon-hydrogen bond is broken, the hydrogen released reacts with oxygen to form water, and at the same time, carbon-carbon bonds are formed to produce hydrocarbons with two or more carbon atoms.

[0106] Further, the catalytic oxidative coupling of methane reaction uses methane and oxygen as raw material gases and reacts in a bed reactor, and its products include C2 hydrocarbons, carbon oxides, and C3 hydrocarbons;

[0107] Preferably, the raw material gas further contains a diluent gas; more preferably, the diluent gas is selected from at least one of nitrogen, helium, and argon;

[0108] The ratio of methane to oxygen is 1.0 - 20.0, preferably 2.0 - 6.0, more preferably 2.0 - 5.0;

[0109] Preferably, the pressure of the raw material gas is 0.1 - 20.0 MPa, preferably 1.0 - 8.0 MPa, more preferably 2.0 - 6.0 MPa;

[0110] Preferably, the temperature of the reaction is 600 - 900 °C, preferably 700 - 850 °C;

[0111] Preferably, the space velocity of the reaction is 500 - 50000 h -1 , preferably 1000 - 35000 h -1 .

[0112] The effect of the present invention is that when the composite oxide containing tungstate nanoclusters of the present invention has a cluster enrichment index reaching the necessary density, the selectivity in the oxidative coupling of methane (OCM) to ethane and ethylene can reach more than 70%, and the yield can reach more than 30%.

[0113] Among them, it is particularly mentioned that since researchers of traditional tungsten-manganese OCM catalysts have optimized catalyst synthesis from the perspective of improving OCM performance, those skilled in the art have no motivation to use alkaline sodium salts (Na2CO3, Na2SiO3) or alkaline solutions of Na such as NaOH (pH>7) to prepare tungsten-manganese catalysts. In this context, the vast majority of tungsten-manganese catalysts are synthesized by the impregnation method using Na2WO4 and manganese salts as precursors, and almost no researchers use the co-precipitation method with alkaline solutions of Na to prepare tungsten-manganese catalysts. In the research of the present inventor, it was unexpectedly found that in the sodium tungstate-containing catalyst prepared by the co-precipitation method using alkaline solutions of Na such as NaOH, sodium tungstate exists in the form of nanoclusters, and the sodium tungstate clusters satisfy the cluster enrichment index (referring to that in any area of 10×10nm 2 containing the tungstate nanoclusters, the number of the tungstate nanoclusters ≥ 3). This catalyst containing sodium tungstate nanoclusters itself does not have OCM activity (in a bed reactor with co-feed of methane and oxygen, when the catalyst is used as an oxidative coupling of methane catalyst at a gas hourly space velocity of greater than or equal to 20000 mL / g / h, a catalyst bed temperature of 800 °C or below, and a reaction pressure of 1 atmosphere, the single-pass C2 yield is not higher than 5%), but it can be used as a promoter to improve the C2 selectivity and yield of traditional OCM catalysts. This prompted the present inventor to further study composite oxides containing tungstate nanoclusters with different compositions as promoters to further complete the present invention. The research of the present invention is significantly different from the research of traditional tungsten-manganese catalysts, and there is no similar research reported in other literatures at present. Description of the Drawings:

[0114] Figure 1 It is a reaction route diagram of OCM and a corresponding schematic diagram of Gibbs free energy.

[0115] Figure 2 It is a schematic diagram of a bed reactor with co-feed of methane and oxygen.

[0116] Figure 3(a) OCM reaction network diagram (Literature: Beck, B. et al. Catal. Today 2014, 228, 212), (b) Correlation between C2 yield and methyl radical generation rate (Weff / Wtherm) obtained from kinetic simulation (Literature: Arutyunov, V. et al. J. Mol. Catal. A: Chem. 2017, 426, 326).

[0117] Figure 4 Experimental result diagram of the NaMnW-NaWZr system for the results of Example 1.

[0118] Figure 5 Structure characterization diagram of NaWZr. Among them, (a, b) Representative high-angle annular dark field (HAADF) and bright field (BF) STEM images of NaWZr. If there are no other regulations, the molar ratio of tungsten to zirconium is 3:9. (c) Figure 5 EDS point spectrum of the area shown by the red circle in a of. The Cu signal comes from the Cu grid. (d) Na in NaWZr x WO y Size distribution of clusters. (e) Na in NaWZr with different W-Zr ratios x WO y Rough statistics of the cluster density. (f) W L3-edge XANES spectra of NaWZr, Na2WO4 and WO3.

[0119] Figure 6 Energy dispersive spectroscopy (EDS) analysis diagram of Example 1.

[0120] Figure 7 HAADF-STEM diagram of Example 1. Among them, some Na x WO y Clusters are marked with green squares.

[0121] Figure 8 EDSmapping diagram of Example 1.

[0122] Figure 9 Raman spectrum diagram of Example 1 (compared with commercially available ZrO2). Among them, the characteristic Raman band at about 925 cm –1 can be attributed to the W-O-Zr bond.

[0123] Figure 10 Zr K-edge XANES spectrum diagram of Example 1. Compared with ZrO2, the Zr K-edge of NaWZr is significantly blue-shifted, indicating that Zr transfers charge to W through the Zr-O-W bond.

[0124] Figure 11Representative BF and HAADF-STEM images of NaWZr with a W:Zr molar ratio of 1:9. Among them, some atomically dispersed and aggregated W species are marked with red circles; NaxWOy clusters are marked with green squares.

[0125] Figure 12 Representative HAADF-STEM image of NaWZr with a W:Zr molar ratio of 2:9. Among them, some atomically dispersed and aggregated W species are marked with red circles. NaxWOy clusters are marked with green squares.

[0126] Figure 13 Representative BF and HAADF-STEM images of NaWZr with a W:Zr molar ratio of 4:9. Among them, some NaxWOy clusters are marked with green squares.

[0127] Figure 14 Representative BF and HAADF-STEM images of NaWZr with a W:Zr molar ratio of 5:9. Among them, some NaxWOy clusters are marked with green squares.

[0128] Figure 15 Typical bright field (BF) and high angle annular dark field HAADF-STEM images of NaWZr with a W:Zr molar ratio of 0.5:9. Among them, some atomically dispersed species are marked with red circles.

[0129] Figure 16 Typical high angle annular dark field (HAADF) STEM image of the NaWAl catalyst.

[0130] Figure 17 STEM spectrum of Na2WO4 in the form of large particles.

[0131] Figure 18 Schematic diagram of the influence of the distance between the OCM catalyst and the composite oxide on the OCM catalytic performance.

[0132] The influence of the distance between the OCM catalyst and the composite oxide on the OCM catalytic performance was studied in a fixed bed reactor. Specifically, when loading the catalyst in the fixed bed reactor, the distance between the OCM catalyst and the composite oxide was changed, and then catalytic tests were carried out to analyze the influence of the distance between the two on the catalytic performance. From Figure 18 It can be seen that the distance between the OCM catalyst and the composite oxide ≤ 3 mm shows a better effect than the OCM catalyst. Specifically, the smaller the distance, the better the effect. Specific implementation method:

[0133] The following is a description of specific embodiments for a better understanding of the present invention, but it does not limit the present invention.

[0134] Among them, the relevant methods in the following embodiments are described as follows:

[0135] 1. The Mn / Na2WO4 / SiO2 catalyst can be commercially purchased or synthesized by the wet impregnation method with reference to the literature (Journal of Molecular Catalysis 1992, 6, 427 - 433). The specific synthesis steps are as follows: Usually, an aqueous solution of manganese(II) nitrate (50 wt.%) and sodium tungstate dihydrate are dissolved in an appropriate amount of deionized water. Under continuous stirring, a commercially available SiO2 support with a surface area of 200 m 2 / g is added to the above solution, and then dried overnight at 105 °C. The ratio of manganese nitrate to sodium tungstate is such that the mass percentage of manganese (Mn) element in the Mn / Na2WO4 / SiO2 catalyst is 2 wt.%, and the mass percentage of sodium tungstate (Na2WO4) in the Mn / Na2WO4 / SiO2 catalyst is 5 wt%. Thereafter, the dried solid is calcined at 800 °C for 4 hours to obtain the final catalyst.

[0136] 2. In the following embodiments, the composition of the samples was determined using a Shimadzu XRF-1800 X-ray fluorescence spectrometer; the specific surface area of the samples was determined using the N2 adsorption / desorption method, and the instrument used was a Micromeritics ASAP2020 automatic physical and chemical adsorption instrument in the United States. The measured specific surface area refers to the BET specific surface area; high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images and elemental energy distribution surface scanning analysis maps (EDS Mapping) were obtained on a spherical aberration corrected Titan Chemi-STEM transmission electron microscope with an accelerating voltage of 200 kV. The Raman spectra of the catalysts were measured at room temperature using visible light laser excitation (532 nm) on a Horiba-Jobin-Yvon. The X-ray absorption fine structure (XAFS) spectra at the W L3 edge of the samples were measured on the 7-BM beamline of the National Synchrotron Light Source II at Brookhaven National Laboratory in the United States.

[0137] 3. The OCM test was carried out in a quartz fixed-bed reactor tube with an inner diameter of 8 mm at 1 atmospheric pressure. The catalyst bed was placed on a quartz wool plug in the isothermal zone of the furnace. A thermocouple with an outer diameter of 6 mm was inserted into the quartz reactor to monitor the bed temperature and further reduce the free space volume. CH4, O2, and N2 were introduced into the reactor through mass flow controllers in a ratio of 3:1:2.7. The total flow rate was 67 mL / min. The products were analyzed by an on-line gas chromatography equipped with an FID detector and a TCD detector. A molecular sieve 5A column and a Porapak N column were coupled with the TCD to separate CO2, CH4, O2, and N2, while an alumina capillary column was coupled with the FID to separate CO2 and hydrocarbon products (CH4, C2H4, C2H6, C3H6, and C3H8). CH4, C2H4, and C2H6 were used as a reference bridge between the FID and the TCD. The OCM was tested separately. catalyst (such as Mn / Na2WO4 / SiO2, La2O3, etc.), the catalyst dosage was 200 mg. When testing the promoter (such as NaWZr) alone, the catalyst dosage was 100 mg. For the OCM test catalyst When testing the catalyst composition formed with the promoter, if not otherwise specified, for the OCM catalyst the dosage was 200 mg, and the dosage of the promoter was 100 mg.

[0138] The CH4 conversion and product selectivity were calculated based on the total number of carbon atoms in the inlet and outlet gases. N2 was used as an internal standard, and the outlet gas was corrected for gas expansion.

[0139]

[0140] where x is the number of carbon atoms in the product.

[0141] The product selectivity was calculated based on the carbon atoms in the outlet products (i.e., C2H4, C2H6, CO, CO2, C3H6, and C3H8). The C2 products included C2H4 and C2H6.

[0142]

[0143] The carbon balance was calculated according to the following formula:

[0144]

[0145] where x is the number of carbon atoms in the product. Generally, the carbon balance was higher than 95%.

[0146] Example 1:

[0147] Weigh a certain amount of NaOH and dissolve it in water to obtain a clear NaOH aqueous solution 1 with a mass concentration of 23 wt%. Weigh 3.453 g of zirconium butoxide (80 wt.%) and 1.188 g of tungsten hexachloride, add them to 30 mL of ethanol, and stir well to dissolve to obtain a clear solution 2. Under rapid stirring (stirring speed: 800 revolutions per minute), add 2 mL of NaOH aqueous solution 1 to solution 2 within 10 minutes and continue stirring for 3 hours to obtain a turbid liquid. Dry the obtained turbid liquid at 40 °C to remove the solvent, then place it in an oven at 80 °C and dry for 12 hours. Subsequently, calcine the obtained solid in air at 800 °C for 5 hours to obtain the catalyst. The atomic ratio of W atoms to Zr atoms in this promoter is 3:9.

[0148] The high-resolution transmission electron microscopy images of this catalyst are as Figure 5 shown in a of Fig. 5 and b of Fig. 5. It can be clearly seen from the figure that this catalyst is rich in nanoclusters. Perform elemental point scanning analysis on the white clusters and the dark non-cluster regions in the figure ( Figure 5 as shown in c of Fig. 5 and Figure 6 ), and it is found that the white clusters are NaxWOy clusters rich in Na, W, and O elements, while the non-cluster regions are mainly the oxide ZrO2 formed by the promoter element Zr. By counting Figure 5 the sizes of the nanoclusters in a of Fig. 5 and Figure 7 Fig. 5, it is found that the average particle size of the Na x WO y nanoclusters in this catalyst is 0.8 nm (as shown in d of Figure 5 Fig. 5). Further count the number of Na 2 WO x nanoclusters in a 10*10 nm y area, and it is found that the number is 21 (as shown in e of Figure 5 Fig. 5).

[0149] The EDS Mapping of this catalyst is as Figure 8 shown. It can be seen from the figure that Na, W, and Zr elements are evenly distributed in the catalyst.

[0150] The WL3-edge XANES of this catalyst is as Figure 5 shown in f of Fig. 5. The WL3-edge XANES spectrum of this catalyst is very similar to that of commercially available Na2WO4 crystals, but is completely different from the WL3-edge XANES spectrum of WO3, indicating that the W in this catalyst mainly exists in the form of four coordination.

[0151] The Raman of this catalyst is as Figure 9 shown. Compared with pure ZrO2, in the Raman spectrum of this catalyst, it can be found at 925 cm -1A new characteristic peak was observed at [specific location], and this peak can be attributed to the characteristic signal of W-O-Zr. In addition, the ZrK-edge XANES spectrum of this catalyst is as shown in Figure 10 , compared with ZrO2, the Zr K-edge of NaWZr shows an obvious blue shift, indicating that Zr transfers charge to W through the Zr-O-W bond. The existence of the Zr-O-W bond and the strong interaction between Zr and W are the key to realizing the enrichment index of Na x WO y nanoclusters. On the one hand, it can stabilize the Na x WO y nanoclusters and allow them to exist in the form of nanoclusters; on the other hand, it also avoids the sintering and agglomeration of adjacent Na x WO y nanoclusters, so that multiple Na 2 can exist within the area of 10*10nm x WO y nanoclusters.

[0152] Examples 2-29 were synthesized by referring to the method described in Example 1, and there were slight differences in the parameters during the synthesis compared with Example 1. The specific synthesis parameters and structural parameters are shown in Table 1-1, Table 1-2, Table 1-3, and Table 1-4.

[0153] The difference between Example 2 and Example 1 is that the promoter element used in Example 2 is Al. The high-resolution transmission electron microscopy image of this catalyst is as shown in Figure 16 . It can be clearly seen from the figure that this catalyst is rich in nanoclusters. By counting the sizes of the nanoclusters in the figure, it is found that the average particle size of the Na x WO y nanoclusters in this catalyst is 0.9 nm. Further counting the number of Na 2 in the 10*10nm x WO y nanoclusters in the area, it is found that the number is 21.

[0154] By analyzing the structural parameters (Table 1-1) of Examples 1-7, it can be concluded that when the alkali metal elements are Na, K, Li, and the promoter elements are Zr or Al, composite oxides containing tungstate nanoclusters can be obtained. The average particle size of the Na x WO y nanoclusters in these composite oxides is 0.8 - 0.9 nm, and the number of Na 2 in the 10*10nm x WO y nanoclusters is ~21.

[0155] By analyzing Example 1 and Example 8, it can be known that either a chloride or sodium tungstate can be used as the tungsten source to obtain a composite oxide containing tungstate nanoclusters. In these composite oxides, Na x WO y The average particle size of the nanoclusters is 0.8 - 0.9 nm, and the number of Na 2 WO x nanoclusters in the 10 * 10 nm y area is ~21.

[0156] By analyzing Example 1 and Examples 14 - 16, it can be known that using methanol, ethanol, propanol, or butanol as the solvent in System 2 can obtain a composite oxide containing tungstate nanoclusters. In these composite oxides, Na x WO y The average particle size of the nanoclusters is 0.8 - 0.9 nm, and the number of Na 2 WO x nanoclusters in the 10 * 10 nm y area is ~21.

[0157] The STEM images of Examples 9 - 13 respectively correspond to Figures 11 - 15 . The difference between Examples 9 - 13 and Example 1 lies in the different molar ratios of W:Zr in the system. As can be seen from Figures 11 - 15 , when the molar ratios of W:Zr are 1:9, 2:9, 3:9, 4:9, 5:9, and 0.5:9, composite oxides containing tungstate nanoclusters can all be obtained. However, the molar ratio of W:Zr will affect the enrichment index of Na x WO y nanoclusters. Plotting the number of tungstate nanoclusters in the 10 * 10 nm 2 area in Example 1 and Examples 9 - 13 against their W:Zr molar ratios gives a graph as shown in Figure 5 e. The STEM image of Example 13 (W:Zr = 0.5:9) is shown in Figure 15 . As can be seen from the figure, when the molar ratio of W:Zr is 0.5:9, Na x WO y in the composite oxide cannot form nanoclusters, indicating that the synthesis of tungstate nanoclusters requires meeting the requirement of the percentage content of the W element. Too low a W content cannot obtain nanoclusters. As the molar ratio of W:Zr increases, the number of Na x WO y nanoclusters gradually increases and finally reaches saturation.

[0158] Examples 30 - 49 involve catalytic testing of OCM catalyst , co - catalyst, and catalyst composition.

[0159] All reaction conditions, parameters, and product parameters are shown in (Tables 2-1 and 2-2). The reaction steps are summarized as follows: 0.3 g of the catalyst was charged into a quartz reactor with an inner diameter of 4 mm according to a Q / P mass ratio of 2 / 1. A mixed gas of CH 4、 N 2、 O2 was continuously passed through the catalyst bed. The reaction gas space velocity (GHSV) was 13400 h -1 g -1 . The reaction was carried out at atmospheric pressure, and the reaction products were detected online by gas chromatography ( Figure 2 ). The catalytic reaction results are shown in (Tables 2-1 and 2-2).

[0160] Example 30 is the catalytic result after testing the promoter synthesized by the preparation method described in Example 1 and the classical Mn / Na2WO4 / SiO2 catalyst under the above conditions. It can be seen that the catalyst composition exhibits extremely high C2 selectivity and yield.

[0161] By analyzing the catalytic performance of Examples 31-36 (Table 2-1), it can be concluded that the promoters prepared when the alkali metal element is Na, K, Li, and the promoter element is Zr or Al all exhibit catalytic performance similar to that of Example 30 after being mixed with the classical Mn / Na2WO4 / SiO2 catalyst.

[0162] By analyzing the catalytic performance of Examples 30 and 37 (Table 2-1), it can be concluded that although the catalytic performance of the composite oxide containing tungstate nanoclusters obtained when the tungsten source is sodium tungstate after being mixed with the classical Mn / Na2WO4 / SiO2 catalyst is inferior to that when the tungsten source is tungsten chloride, its improvement on the classical Mn / Na2WO4 / SiO2 catalyst is still very significant.

[0163] By analyzing the catalytic performance of Examples 30 and 38-41 (Tables 2-1 and 2-2), it can be concluded that the promoters synthesized when the molar ratio of W:Zr is 1:9.2:9, 3:9, 4:9, and 5:9 all show a very obvious performance improvement after being mixed with the classical Mn / Na2WO4 / SiO2 catalyst, and exhibit a "volcano-type" performance trend.

[0164] By analyzing the catalytic performance of Example 42 (Table 2-2), it can be concluded that the performance of the promoter synthesized when the molar ratio of W:Zr is 0.5:9 is inhibited after being mixed with the classical Mn / Na2WO4 / SiO2 catalyst because its W content is too low to obtain nanoclusters, so it exhibits lower performance.

[0165] By analyzing the catalytic performance of Examples 30 and 43-45 (Table 2-2), it can be concluded that when the promoters prepared using different alcohol solutions are mixed with the classical Mn / Na2WO4 / SiO2 catalyst, the performance improvement is very obvious.

[0166] By analyzing the catalytic performance of Examples 46-49 (Table 2-2), it can be concluded that when different classical OCM catalysts are mixed with the promoter synthesized by the preparation method described in Example 1, different performance improvements are shown.

[0167] Table 1-1

[0168]

[0169]

[0170] Table 1-2

[0171]

[0172] Table 1-3

[0173]

[0174]

[0175] Table 1-4

[0176]

[0177]

[0178] Table 2-1

[0179]

[0180]

[0181] Table 2-2

[0182]

[0183] Comparative Example 1:

[0184] Comparative Example 1 is WO3 / ZrO2. Its preparation method is the same as that of Example 1. The only difference is that no alkali metal Na is added during the synthesis of Comparative Example 1. The transmission electron microscope results show that the nanoclusters in this catalyst are tungsten oxide rather than sodium tungstate.

[0185] Comparative Example 1 and Mn / Na2WO4 / SiO2 were tested in the manner shown in Example 30, and the results are as follows:

[0186] The C2 selectivity of Mn / Na2WO4 / SiO2 is 48.4%, and the C2 yield is 8.1%. While the C2 selectivity of the catalyst composition of Mn / Na2WO4 / SiO2 and Comparative Example 1 is 46.8%, and the C2 yield is 7.6%.

[0187] From the above results, it can be seen that Comparative Example 1 not only fails to improve the selectivity and yield of Mn / Na2WO4 / SiO2 but instead has an inhibitory effect. This indicates that the component that truly acts as a cocatalyst is not the tungsten oxide nanoclusters but the tungstate nanoclusters. In the synthesis of the cocatalyst, alkali metal elements are essential. Comparative Example 2:

[0188] The catalyst was synthesized using the same preparation method as in Example 1, with the only difference being that the auxiliary element M was not added during the synthesis of Comparative Example 2. In this case, after System 1 was added to System 2, it remained a clear solution, and the corresponding solid catalyst could not be prepared. From this result, it can be seen that the auxiliary element is crucial for the synthesis of tungstate nanoclusters.

[0189] Comparative Example 3:

[0190] The catalyst was synthesized using the same preparation method as in Example 1, with the only difference being that tungsten element was not added during the synthesis of Comparative Example 3. In this case, the obtained Comparative Example 3 does not contain Na x WO y nanoclusters.

[0191] Comparative Example 3 and Mn / Na2WO4 / SiO2 were tested in the manner shown in Example 30, and the results are as follows:

[0192] The C2 selectivity of Mn / Na2WO4 / SiO2 is 48.4%, and the C2 yield is 8.1%. While the C2 selectivity of the catalyst composition of Mn / Na2WO4 / SiO2 and Comparative Example 3 is 45.4%, and the C2 yield is 6.8%. From the above results, it can be seen that Comparative Example 3 not only fails to improve the selectivity and yield of Mn / Na2WO4 / SiO2 but instead has an inhibitory effect. This indicates that tungsten element is an essential active component in the cocatalyst.

[0193] Comparative Example 4:

[0194] The catalyst was synthesized using the same preparation method as in Example 1, with the only difference being that the chloride was replaced with molybdenum chloride during the synthesis of Comparative Example 4, that is, the W element in Example 1 was replaced with the Mo element.

[0195] Comparative Example 4 and Mn / Na2WO4 / SiO2 were tested in the manner shown in Example 30, and the results are as follows:

[0196] The C2 selectivity of Mn / Na2WO4 / SiO2 was 48.4%, and the C2 yield was 8.1%. While the C2 selectivity of the catalyst composition of Mn / Na2WO4 / SiO2 and Comparative Example 4 was 48.2%, and the C2 yield was 8.0%. From the above results, it can be seen that Comparative Example 4 did not improve the selectivity and yield of Mn / Na2WO4 / SiO2, indicating that tungsten is an essential active component in the cocatalyst.

[0197] Comparative Example 5:

[0198] The catalyst was synthesized using the same preparation method as in Example 1, with the only difference being that System 1 was added to System 2 completely within 1 minute during the synthesis of Comparative Example 5.

[0199] The high-resolution electron microscope image of Comparative Example 5 is as Figure 17 shown. It can be seen from the figure that sodium tungstate in Comparative Example 5 mainly exists in the form of large sodium tungstate particles (>10nm) rather than nanoclusters, indicating that the dropping rate of System 1 into System 2 has an important impact on the structure of the catalyst. Slowly adding System 1 (adding time ≥ 2 minutes) to System 2 can enable the precursors of tungsten and promoter elements to slowly hydrolyze and crosslink under the action of alkali metals, thus contributing to the formation of tungstate nanoclusters. Too fast addition will cause the precursors of promoter elements to hydrolyze rapidly, preventing the uniform dispersion of tungstate in the formed oxide species of the promoter element.

[0200] Comparative Example 5 and Mn / Na2WO4 / SiO2 were tested in the manner shown in Example 30, and the results are as follows:

[0201] The C2 selectivity of Mn / Na2WO4 / SiO2 was 48.4%, and the C2 yield was 8.1%. While the C2 selectivity of the catalyst composition of Mn / Na2WO4 / SiO2 and Comparative Example 5 was 47.5%, and the C2 yield was 7.6%. From the above results, it can be seen that Comparative Example 5 did not improve the selectivity and yield of Mn / Na2WO4 / SiO2, indicating that tungstate nanoclusters are the active structure of the cocatalyst, and the dropping rate of System 1 will affect the tungstate structure in the cocatalyst and thus its reaction performance.

[0202] Comparative Example 6:

[0203] The catalyst was synthesized using the same preparation method as in Example 1, with the only difference being that the solvent used for System 2 during the synthesis of Comparative Example 6 was acetone.

[0204] Comparative Example 6 and Mn / Na2WO4 / SiO2 were tested in the manner shown in Example 30, and the results are as follows:

[0205] The C2 selectivity of Mn / Na2WO4 / SiO2 is 48.4%, and the C2 yield is 8.1%. For the catalyst composition of Mn / Na2WO4 / SiO2 and Comparative Example 6, the C2 selectivity is 40.3%, and the C2 yield is 6.3%. From the above results, it can be seen that Comparative Example 6 does not improve the selectivity and yield of Mn / Na2WO4 / SiO2, indicating that a suitable solvent must be used in the cocatalyst synthesis.

[0206] Comparative Example 7:

[0207] The catalyst was synthesized using the same preparation method as in Example 1. The only difference was that in the synthesis of Comparative Example 7, in step 3), centrifugal washing was used instead of directly drying to remove the solvent without treatment (i.e., drying the solvent at 40 °C and then drying in an 80 °C oven for 12 hours). XRF measurement showed that the wt% of tungsten element in Comparative Example 7 was less than 0.1%. This indicates that the centrifugal washing step causes the loss of tungsten element in the catalyst.

[0208] Comparative Example 7 and Mn / Na2WO4 / SiO2 were tested in the same manner as in Example 30, and the results are as follows:

[0209] The C2 selectivity of Mn / Na2WO4 / SiO2 is 48.4%, and the C2 yield is 8.1%. For the catalyst composition of Mn / Na2WO4 / SiO2 and Comparative Example 7, the C2 selectivity is 44.2%, and the C2 yield is 6.9%. From the above results, it can be seen that Comparative Example 7 does not improve the selectivity and yield of Mn / Na2WO4 / SiO2.

[0210] The above results indicate that directly drying to remove the solvent without treatment described in step 3) of the synthesis method is a very important technical feature.

[0211] Comparative Example 8:

[0212] The catalyst was synthesized using the same preparation method as in Example 1. The only difference was that in the synthesis of Comparative Example 8, the alkali metal element precursor used in System 1 was sodium nitrate instead of NaOH. In this case, the pH of System 1 was neutral.

[0213] Comparative Example 8 and Mn / Na2WO4 / SiO2 were tested in the same manner as in Example 30, and the results are as follows:

[0214] The C2 selectivity of Mn / Na2WO4 / SiO2 is 48.4%, and the C2 yield is 8.1%. For the catalyst composition of Mn / Na2WO4 / SiO2 and Comparative Example 8, the C2 selectivity is 39.5% and the C2 yield is 5.9%. From the above results, it can be seen that Comparative Example 8 cannot improve the selectivity and yield of Mn / Na2WO4 / SiO2, indicating that the selection of the alkali metal precursor in System 1 and the pH of the system in the synthesis method are very important technical parameters.

Claims

1. A composite oxide containing tungstate nanoclusters, characterized in that: The composite oxide contains a metal element A, a tungsten element W, a promoter element M, and an oxygen element O, and the metal element A, the tungsten element W, and the promoter element M all form a composite with the oxygen element O. The fact that the metal element A, the tungsten element W, and the promoter element M all form compounds with the oxygen element O means that the composite oxide can be written in the following general formula: aAOx·bWO3·cMOy, where x and y are the numbers of oxygen atoms required to satisfy the charge balance of the oxides formed by the metal element A and the promoter element M, respectively; a, b, and c are the atomic percentages of the metal element A, the tungsten element W, and the promoter element M in all non-oxygen elements in the composite oxide, 5% ≤ a ≤ 67%, 1% ≤ b ≤ 60%, 20% ≤ c ≤ 94%. The metal element A is selected from any one or more of Li, Na, K, Mg, Ca, Sr, and Ba. The promoter element M is selected from any one or more of Si, Zr, Ti, Al, La, Ce, and Co. The atomic percentage of the metal element A is 5% - 67%; the atomic percentage of the tungsten element W is 1% - 60%; the atomic percentage of the promoter element M is 20% - 94%; the content of the oxygen element in the composite oxide is the sum of the numbers of oxygen atoms required to satisfy the charge balance of the metal elements A, W, and M. The atomic percentage of an element is calculated according to the following formula. Among them, the tungstate nanocluster is composed of the metal element A, the tungsten element W, and the oxygen element O. The general formula of the tungstate nanocluster is A x WO y , where 0 < x ≤ 2, and y represents the number of oxygen atoms required to satisfy the charge balance of the general formula; and the tungstate nanocluster satisfies the cluster enrichment index, which refers to the number of tungstate nanoclusters ≥ 3 in any 10×10 nm 2 area containing the tungstate nanocluster.

2. The composite oxide according to claim 1, wherein The number of the tungstate nanoclusters ≥ 5.

3. The composite oxide according to claim 1, characterized in that, The number of the tungstate nanoclusters ≥ 10.

4. The composite oxide according to claim 1, wherein The number of the tungstate nanoclusters ≥ 20.

5. The composite oxide according to claim 1, characterized in that, The particle size of the tungstate nanoclusters ≤ 10.0 nm.

6. The composite oxide according to claim 1, wherein The particle size of the tungstate nanoclusters ≤ 5.0 nm.

7. The composite oxide according to claim 1, characterized in that, The particle size of the tungstate nanoclusters is ≤ 2.0 nm.

8. The composite oxide according to claim 1, characterized in that, The particle size of the tungstate nanoclusters is ≤ 1.0 nm.

9. The composite oxide according to claim 1, wherein The specific surface area of the composite oxide is 0.1 - 10 g / m 2 .

10. The composite oxide according to claim 1, wherein The specific surface area of the composite oxide is 0.5 - 5 g / m 2 .

11. The composite oxide according to claim 1, characterized in that, The specific surface area of the composite oxide is 1-2 g / m 2 .

12. The composite oxide according to claim 1, wherein The atomic percentage of the metal element A in the composite oxide is 10% - 65%.

13. The composite oxide according to claim 1, characterized in that, The atomic percentage of the metal element A in the composite oxide is 10% - 60%.

14. The composite oxide according to claim 1, wherein, The atomic percentage of the metal element A in the composite oxide is 15% - 50%.

15. The composite oxide according to claim 1, wherein The atomic percentage of the metal element A in the composite oxide is 20% - 50%.

16. The composite oxide according to claim 1, characterized in that, The atomic percentage of the metal element A in the composite oxide is 30% - 40%.

17. The composite oxide according to claim 1, wherein The atomic percentage of the tungsten element W in the composite oxide is 2% - 55%.

18. The composite oxide according to claim 1, characterized in that, The atomic percentage of the tungsten element W in the composite oxide is 5% - 50%.

19. The composite oxide according to claim 1, wherein The atomic percentage of the tungsten element W in the composite oxide is 10% - 40%.

20. The composite oxide according to claim 1, characterized in that, The atomic percentage of the tungsten element W in the composite oxide is 20% - 30%.

21. The composite oxide according to claim 1, wherein The atomic percentage of the promoter element M in the composite oxide is 22% - 92%.

22. The composite oxide according to claim 1, wherein The atomic percentage of the promoter element M in the composite oxide is 25% - 90%.

23. The composite oxide according to claim 1, wherein, The atomic percentage of the promoter element M in the composite oxide is 30% - 80%.

24. The composite oxide according to claim 1, characterized in that, The atomic percentage of the promoter element M in the composite oxide is 40% - 70%.

25. The composite oxide according to claim 1, characterized in that, The atomic percentage of the promoter element M in the composite oxide is 50% - 60%.

26. The composite oxide according to claim 1, characterized in that, In the tungstate nanoclusters, tungsten exists in the form of tetracoordinated tungstate, where "tetracoordinated" means that one tungsten atom is bonded to exactly four oxygen atoms.

27. The composite oxide according to claim 1, wherein After the composite oxide is calcined in air at 800 °C for 6 h, the particle size change value Δ1 of the tungstate nanoclusters ≤ 20%, and the calculation formula is as follows: The change value Δ2 of the cluster enrichment index of the tungstate nanoclusters after calcination ≤ 20%; the calculation formula is as follows:

28. The composite oxide according to claim 27, wherein After the composite oxide is calcined in air at 800 °C for 6 h, the particle size change value Δ1 of the tungstate nanoclusters ≤ 10%.

29. The composite oxide according to claim 27, wherein The change value Δ2 of the cluster enrichment index of the tungstate nanoclusters after calcination ≤ 10%.

30. The composite oxide according to claim 1, wherein: The metal element A is at least Na, the promoter element M is at least Zr or Al, the composite oxide containing tungstate nanoclusters is expressed as NaWZr or NaWAl respectively, the tungstate nanoclusters are composed of the alkali metal element Na, the tungsten element W and the oxygen element O, and the general formula of the tungstate nanoclusters is Na x WO y , 0 < x ≤ 2, and y represents the number of oxygen atoms required to satisfy the charge balance of the general formula; The atomic percentage of Na in the composite oxide is 5% - 67%; the atomic percentage of tungsten element W is 1% - 60%; the atomic percentage of the promoter element M is 20% - 94%; In the composite oxide, 0 < molar ratio of Na:W ≤ 5, and the molar ratio of W:Zr in the composite oxide ≥ 0.

1.

31. The composite oxide according to claim 30, characterized in that, The atomic percentage of Na in the composite oxide is 10% - 65%.

32. The composite oxide according to claim 30, characterized in that, The atomic percentage of Na in the composite oxide is 10% - 60%.

33. The composite oxide according to claim 30, wherein, The atomic percentage of Na in the composite oxide is 15% - 50%.

34. The composite oxide according to claim 30, wherein The atomic percentage of Na in the composite oxide is 20% - 50%.

35. The composite oxide according to claim 30, characterized in that, The atomic percentage of Na in the composite oxide is 30% - 40%.

36. The composite oxide according to claim 30, wherein, The atomic percentage of tungsten element W is 2% - 55%.

37. The composite oxide according to claim 30, wherein The atomic percentage of tungsten element W is 5% - 50%.

38. The composite oxide according to claim 30, wherein, The atomic percentage of tungsten element W is 10% - 40%.

39. The composite oxide according to claim 30, wherein, The atomic percentage of tungsten element W is 20% - 30%.

40. The composite oxide according to claim 30, wherein The atomic percentage of the promoter element Zr or Al is 22% - 92%.

41. The composite oxide according to claim 30, characterized in that, The atomic percentage of the promoter element Zr or Al is 25% - 90%.

42. The composite oxide according to claim 30, wherein, The atomic percentage of the promoter element Zr or Al is 30% - 80%.

43. The composite oxide according to claim 30, wherein, The atomic percentage of the promoter element Zr or Al is 40% - 70%.

44. The composite oxide according to claim 30, characterized in that, The atomic percentage of the promoter element Zr or Al is 50% - 60%.

45. The composite oxide according to claim 30, wherein, In the composite oxide, 0.1 ≤ molar ratio of Na:W ≤ 4.

46. The composite oxide according to claim 30, characterized in that, In the composite oxide, 0.8 ≤ molar ratio of Na:W ≤ 3.

5.

47. The composite oxide according to claim 30, wherein In the composite oxide, 1.0 ≤ molar ratio of Na:W ≤ 3.

0.

48. The composite oxide according to claim 30, wherein, In the composite oxide, 1.5 ≤ molar ratio of Na:W ≤ 2.

0.

49. The composite oxide according to claim 30, wherein, In the composite oxide, 1.4 ≤ molar ratio of Na:W ≤ 1.

6.

50. The composite oxide according to claim 30, wherein, In the composite oxide, 0.2 ≤ molar ratio of W:Zr ≤ 100.

51. The composite oxide according to claim 30, characterized in that, In the composite oxide, 0.23 ≤ molar ratio of W:Zr ≤ 10.

52. The composite oxide according to claim 30, wherein, In the composite oxide, 0.3 ≤ molar ratio of W:Zr ≤ 1.

53. The composite oxide according to claim 30, wherein In the composite oxide, 0.4 ≤ molar ratio of W:Zr ≤ 0.

5.

54. The preparation method of the composite oxide containing tungstate nanoclusters according to any one of claims 1-53, characterized in that, Comprising the following steps: 1) Prepare solution system 1 and solution system 2 respectively. Both solution system 1 and solution system 2 are transparent solutions, where a "transparent solution" means that there are no obvious suspensions in the solution, and the solution will not stratify. When light passes through the solution, the Tyndall effect will not occur; 2) While stirring the solution system 2, the solution system 1 is completely added to the solution system 2 within 2 - 200 minutes, and the dropping time is 2 - 200 minutes until a turbid solution appears, and the turbid solution is continuously stirred for more than 1 hour; 3) Without any treatment (any washing, centrifugation, or filtration steps), the solvent of the product obtained in step 2) is directly removed, and the resulting solid is dried to obtain a dried solid product; 4) The solid product obtained in step 3) is calcined to obtain a composite oxide containing tungstate nanoclusters; The preparation method of the solution system 1 is as follows: Dissolve the metal element precursor of the compound raw material containing this element in an appropriate amount of water, and fully stir to form a transparent solution, that is, the solution system 1 is obtained, and the pH of the transparent solution is greater than 7; The preparation method of the solution system 2 is selected from any one of the following: a) Mix the tungsten element precursor, the promoter element precursor, and an appropriate amount of water and stir rapidly to form a transparent solution, that is, the solution system 2 - 1 is obtained; b) Mix the tungsten element precursor, the promoter element precursor, and an appropriate amount of alcohol and stir rapidly to form a transparent solution, that is, the solution system 2 - 2 is obtained; Among them, the ratio of the metal element precursor, the tungsten element precursor, and the promoter element precursor added to the solution system 1 and the solution system 2 conforms to the following formula: In the solution system 1 and the solution system 2, calculate the atomic percentage of a certain element according to the following formula, The atomic percentage of the metal element A is 5% - 67%; the atomic percentage of the tungsten element W is 1% - 60%; the atomic percentage of the promoter element M is 20% - 94%.

55. The preparation method according to claim 54, characterized in that, In step 2), the turbid solution is continuously stirred for more than 2 hours.

56. The preparation method according to claim 54, characterized in that, In step 2), the turbid solution is continuously stirred for more than 3 hours.

57. The preparation method according to claim 54, wherein, In step 2), the stirring is rapid stirring, and the rotation speed of the rapid stirring is 500 - 1000 revolutions per minute.

58. The preparation method according to claim 54, wherein In step 2), the rotation speed of the rapid stirring is 750 - 900 revolutions per minute.

59. The preparation method according to claim 54, characterized in that, The stirring time is 10 minutes - 2 hours.

60. The preparation method according to claim 54, characterized in that, The stirring time is 30 minutes - 1 hour.

61. The preparation method according to claim 54, characterized in that, In step 2), the dropping time is 10 - 100 minutes.

62. The preparation method according to claim 54, characterized in that, In step 2), the dropping time is 20 - 60 minutes.

63. The preparation method according to claim 54, wherein, In step 3), the method for removing the solvent is to dry the solvent.

64. The preparation method according to claim 63, characterized in that, The drying method is to place the product obtained in step 2) in an atmosphere at a temperature of 30 - 50 °C and dry it until the solution volatilizes.

65. The method according to claim 64, wherein The temperature is 40 °C.

66. The preparation method according to claim 54, wherein, In step 3), the temperature for drying the solid is 60 - 100 °C.

67. The preparation method according to claim 54, wherein In step 3), the temperature for drying the solid is 80 - 90 °C.

68. The preparation method according to claim 54, characterized in that, In step 3), the drying time is more than 12 hours.

69. The preparation method according to claim 54, characterized in that, In step 3), the drying time is more than 24 hours.

70. The preparation method according to claim 54, characterized in that, In step 4), the calcination temperature is 700 - 900 °C.

71. The preparation method according to claim 54, characterized in that, In step 4), the calcination temperature is 750 - 850 °C.

72. The preparation method according to claim 54, characterized in that, In step 4), the calcination temperature is 800 °C.

73. The preparation method according to claim 54, characterized in that, In step 4), the calcination time is 3 - 8 hours.

74. The preparation method according to claim 54, wherein, In step 4), the calcination time is 4 - 6 hours.

75. The preparation method according to claim 54, characterized in that, In step 4), the heating rate of the calcination is 2 - 10 °C / minute.

76. The preparation method according to claim 54, characterized in that, In step 4), the heating rate of the roasting is 3-5 °C / minute.

77. The preparation method according to claim 54, wherein In the preparation method of the solution system 1, the pH of the transparent solution is ≥10.

78. The preparation method according to claim 54, characterized in that, The atomic percentage of metal element A in the composite oxide is 10%-65%.

79. The preparation method according to claim 54, wherein, The atomic percentage of metal element A in the composite oxide is 10%-60%.

80. The preparation method according to claim 54, wherein, The atomic percentage of metal element A in the composite oxide is 15%-50%.

81. The preparation method according to claim 54, characterized in that, The atomic percentage of metal element A in the composite oxide is 20%-50%.

82. The preparation method according to claim 54, characterized in that, The atomic percentage of metal element A in the composite oxide is 30%-40%.

83. The preparation method according to claim 54, characterized in that, The atomic percentage of tungsten element W is 2%-55%.

84. The preparation method according to claim 54, characterized in that, The atomic percentage of tungsten element W is 5%-50%.

85. The preparation method according to claim 54, characterized in that, The atomic percentage of tungsten element W is 10%-40%.

86. The preparation method according to claim 54, characterized in that, The atomic percentage of tungsten element W is 20%-30%.

87. The preparation method according to claim 54, characterized in that, The atomic percentage of the promoter element M is 22%-92%.

88. The preparation method according to claim 54, characterized in that, The atomic percentage of the promoter element M is 25%-90%.

89. The preparation method according to claim 54, characterized in that, The atomic percentage of the promoter element M is 30%-80%.

90. The preparation method according to claim 54, characterized in that, The atomic percentage of the promoter element M is 40%-70%.

91. The preparation method according to claim 54, characterized in that, The atomic percentage of the promoter element M is 50%-60%.

92. The preparation method according to claim 54, characterized in that, The concentration of the metal element precursor in the solution system 1 is 1-40 wt%.

93. The preparation method according to claim 54, characterized in that, The concentration of the metal element precursor in the solution system 1 is 10-30 wt%.

94. The preparation method according to claim 54, characterized in that, The concentration of the metal element precursor in the solution system 1 is 15-25 wt%.

95. The preparation method according to claim 54, characterized in that, The concentration of the tungsten element precursor in the solution systems 2-1 and 2-2 is 1-30 wt%.

96. The preparation method according to claim 54, characterized in that, The concentration of the tungsten element precursor in the solution systems 2-1 and 2-2 is 5-25 wt%.

97. The preparation method according to claim 54, wherein, The concentration of the tungsten element precursor in the solution systems 2-1 and 2-2 is 10-20 wt%.

98. The preparation method according to claim 54, characterized in that, The concentration of the promoter element precursor in the solution systems 2-1 and 2-2 is 1-50 wt%.

99. The preparation method according to claim 54, characterized in that, The concentration of the promoter element precursor in the solution systems 2-1 and 2-2 is 10-40 wt%.

100. The preparation method according to claim 54, wherein, The concentration of the promoter element precursor in the solution systems 2-1 and 2-2 is 20-35 wt%.

101. The preparation method according to claim 54, characterized in that, The metal element precursor in the preparation method of the solution system 1 is selected from any one or more of lithium hydroxide, sodium hydroxide, lithium carbonate, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, magnesium acetate, calcium hydroxide, calcium acetate, strontium hydroxide, and barium hydroxide.

102. The preparation method according to claim 54, characterized in that, The promoter element precursor in the preparation method of the solution system 2-1 is selected from any one or more of sodium silicate, zirconyl nitrate, zirconium nitrate, zirconium oxychloride, bis(acetato-O)oxozirconium, zirconium citrate, titanium nitrate, aluminum nitrate, lanthanum nitrate, lanthanum acetate, lanthanum chloride, cerium nitrate, cerium acetate, cerium chloride, cobalt nitrate, and cobalt acetate; the tungsten element precursor is selected from any one or more of sodium tungstate, cesium tungstate, tungsten ethanolate, ammonium tungstate oxide, ammonium tungstate oxide hydrate, strontium tungstate, magnesium tungstate, barium tungstate, ammonium tungstate pentahydrate, ammonium metatungstate hydrate, and calcium tungstate.

103. The preparation method according to claim 54, characterized in that, The tungsten element precursor in the preparation method of solution system 2-2 is selected from any one or two of sodium tungstate and tungsten chloride; the promoter element precursor is selected from any one or more of tetraethyl orthosilicate, zirconium nitrate, zirconium n-butoxide, zirconyl nitrate, zirconium oxychloride, zirconium bis(acetato-O)oxo, zirconium citrate, tetrabutyl titanate, sec-butyl alcohol aluminum, isopropyl alcohol aluminum, lanthanum nitrate, aluminum nitrate, cerium nitrate, and cobalt nitrate; the alcohol solution is selected from any one or more of methanol, ethanol, propanol, and butanol.

104. The preparation method according to claim 54, wherein The metal element precursor is a sodium element precursor, the promoter element precursor is selected from a zirconium element precursor or an aluminum element precursor, and the prepared composite oxide containing tungstate nanoclusters is NaWZr or NaWAl. The tungstate nanoclusters are composed of an alkali metal element Na, a tungsten element W, and an oxygen element O, and the general formula of the tungstate nanoclusters is Na x WO y , where 0 < x ≤ 2, and y represents the number of oxygen atoms required to balance the charge of the general formula.

105. The preparation method according to claim 104, wherein The metal precursor in the preparation method of the solution system 1 is selected from any one or more of sodium hydroxide, sodium carbonate, and sodium bicarbonate.

106. The preparation method according to claim 104, characterized in that, The promoter element precursor in the preparation method of the solution system 2-1 is selected from any one or more of zirconyl nitrate, zirconium nitrate, zirconium oxychloride, zirconium bis(acetato-O)oxo, zirconium citrate, and aluminum nitrate; the tungsten element precursor is selected from any one or more of sodium tungstate, cesium tungstate, tungsten ethanolate, ammonium tungstate oxide, ammonium tungstate oxide hydrate, strontium tungstate, magnesium tungstate, barium tungstate, ammonium tungstate pentahydrate, ammonium metatungstate hydrate, and calcium tungstate.

107. The preparation method according to claim 104, characterized in that, The tungsten element precursor in the solution system 2-2 is selected from any one or two of sodium tungstate and tungsten chloride; the promoter element precursor is selected from any one or more of zirconium nitrate, zirconium n-butoxide, zirconyl nitrate, zirconium oxychloride, zirconium bis(acetato-O)oxo, zirconium citrate, sec-butyl alcohol aluminum, isopropyl alcohol aluminum, and aluminum nitrate; the alcohol solution is selected from any one or more of methanol, ethanol, propanol, and butanol.

108. The preparation method according to claim 54, characterized in that, The promoter element precursor in the preparation method of the solution system 2-2 is zirconium n-butoxide, and the tungsten element precursor is tungsten chloride.

109. The preparation method according to claim 108, wherein The molar ratio of the tungsten element to the zirconium element ≥ 1:

9.

110. The preparation method according to claim 108, wherein, The molar ratio of the tungsten element to the zirconium element is ≥ 2:

9.

111. The preparation method according to claim 108, characterized in that, The molar ratio of the tungsten element to the zirconium element is ≥ 3:

9.

112. The preparation method according to claim 108, characterized in that, The solution system 1 is an aqueous NaOH solution, and the mass percentage of NaOH is 1% - 60%.

113. The preparation method according to claim 112, wherein, The mass percentage of NaOH is 10% - 50%.

114. The preparation method according to claim 112, characterized in that, The mass percentage of NaOH is 15% - 40%.

115. The preparation method according to claim 54, characterized in that, The promoter element precursor in the preparation method of the solution system 2-2 is isopropyl alcohol aluminum, the tungsten element precursor is tungsten chloride, and the molar ratio of the tungsten element to the aluminum element ≥ 1:

9.

116. The preparation method according to claim 115, wherein, The molar ratio of the tungsten element to the aluminum element is ≥ 2:

9.

117. The preparation method according to claim 115, wherein, The molar ratio of the tungsten element to the aluminum element ≥ 3:

9.

118. The preparation method according to claim 115, characterized in that, The solution system 1 is an aqueous NaOH solution, and the mass percentage of NaOH is 1% - 60%.

119. The preparation method according to claim 118, characterized in that, The mass percentage of NaOH is 10% - 50%.

120. The preparation method according to claim 118, wherein, The mass percentage of NaOH is 15% - 40%.

121. The preparation method according to claim 54, characterized in that, The promoter element precursor in the preparation method of the solution system 2-2 is zirconium n-butoxide, the tungsten element precursor is sodium tungstate, and the molar ratio of the tungsten element to the zirconium element ≥ 1:

9.

122. The preparation method according to claim 121, characterized in that, The molar ratio of the tungsten element to the zirconium element ≥ 2:

9. The preparation method according to claim 121, characterized in that, The molar ratio of the tungsten element to the zirconium element ≥ 3:

9.

124. The preparation method according to claim 121, characterized in that, The solution system 1 is an aqueous KOH solution, and the mass percentage of KOH is 1% - 60%.

125. The preparation method according to claim 124, characterized in that, The mass percentage of KOH is 10% - 50%.

126. The preparation method according to claim 124, characterized in that, The mass percentage of KOH is 15% - 40%.

127. The preparation method according to claim 54, characterized in that, The promoter element precursor in the preparation method of the solution system 2-2 is aluminum isopropoxide, the tungsten element precursor is sodium tungstate, and the molar ratio of tungsten element to aluminum element ≥ 1:

9.

128. The preparation method according to claim 127, characterized in that, The molar ratio of tungsten element to aluminum element is ≥ 2:

9.

129. The preparation method according to claim 127, characterized in that, The molar ratio of tungsten element to aluminum element is ≥ 3:

9.

130. The preparation method according to claim 127, characterized in that, The solution system 1 is an aqueous KOH solution, and the mass percentage of KOH is 1% - 60%.

131. The preparation method according to claim 130, characterized in that, The mass percentage of KOH is 10% - 50%.

132. The preparation method according to claim 130, characterized in that, The mass percentage of KOH is 15% - 40%.

133. A promoter, characterized in that, The co-catalyst described contains the composite oxide containing tungstate nanoclusters according to any one of claims 1-53. The co-catalyst cannot be used alone as a catalyst for the oxidative coupling of methane (OCM) reaction, and the co-catalyst does not have significant OCM activity.

134. A catalyst composition, characterized in that, The catalyst composition described above comprises the composite oxide according to any one of claims 1-53 and at least one OCM catalyst having OCM activity. catalyst , and the OCM activity means that it can be used alone as a catalyst for the OCM reaction.

135. The catalyst composition according to claim 134, wherein The OCM catalyst has a mass ratio to the composite oxide of 0.1 - 50.

0.

136. The catalyst composition according to claim 134, characterized in that, The mass ratio described is 0.5 - 20.0:1.

0. The catalyst composition according to claim 136, wherein The mass ratio described is 1.0 - 10.0:1.

0. The catalyst composition according to claim 136, characterized in that, The mass ratio described is 2.0 - 4.0:1.

0. The catalyst composition according to claim 134, wherein, The OCM catalyst is selected from any one or more of tungsten manganese catalysts, rare earth metal oxides, perovskite compounds, alkali metal and alkaline earth metal oxides, and derivatives of the above catalysts. The catalyst composition according to claim 134, wherein, The OCM catalyst is selected from a tungsten-manganese catalyst, lanthanum oxide, samarium oxide, Li / MgO, and Ca / CeO2.

141. The catalyst composition according to claim 134, characterized in that, The tungsten-manganese catalyst is Mn-Na2WO4 / SiO2.

142. The catalyst composition according to claim 141, characterized in that, The OCM mentioned above catalyst The distance between it and the composite oxide is ≤ 3 mm. The catalyst composition according to claim 134, characterized in that, The described catalyst composition is formed by compounding the composite oxide and OCM catalyst by physical mixing.

144. The catalyst composition according to claim 134, characterized in that, The OCM catalyst is a composite containing a second alkali metal element, a tungsten element, a manganese element, an oxygen element, and a fifth component element, where the fifth component element is selected from any one or more of Al, Si, Ti, Zr, C, and N, and the second alkali metal is selected from any one or more of Li, Na, and K.

145. The catalyst composition according to claim 144, characterized in that, The fifth component element is selected from any one or more of Al, Si, and Ti.

146. The catalyst composition according to claim 144, characterized in that, The fifth component element is selected from Si.

147. The catalyst composition according to claim 144, wherein The second alkali metal is selected from Na.

148. The catalyst composition according to claim 144, characterized in that, The mass percentage of the second alkali metal element in the OCM catalyst is 0.1 to 2.0 wt.%. The catalyst composition according to claim 145, wherein The mass percentage of the second alkali metal element in the OCM catalyst is 0.5 to 1.5 wt.%. The catalyst composition according to claim 144, characterized in that, The tungsten element accounts for the OCM catalyst in a mass percentage of 0.1 to 5.0 wt.%.

151. The catalyst composition according to claim 144, wherein, The tungsten element accounts for the OCM catalyst in a mass percentage of 2.0 to 4.0 wt.%.

152. The catalyst composition according to claim 144, characterized in that, The mass percentage of the manganese element in the OCM catalyst is 0.1 to 10.0 wt.%.

153. The catalyst composition according to claim 144, wherein, The mass percentage of the manganese element in the OCM catalyst is 1.0 to 4.0 wt.%. The catalyst composition according to claim 134, characterized in that, The catalyst also contains an additive, and the additive is selected from any one or more of a heat dissipation aid, a mass transfer aid, a forming aid, a wear resistance enhancer, a dispersant, and a stabilizer.

155. The catalyst composition according to claim 154, wherein, The OCM catalyst is Mn / Na2WO4 / SiO2, and the composite oxide is a composite oxide of Na, W, and Zr, NaWZr.

156. The catalyst composition according to claim 155, characterized in that, The OCM mentioned above catalyst The mass ratio to the composite oxide is 4:1 - 0.5:

1.

157. The catalyst composition according to claim 155, characterized in that, The OCM catalyst has a mass ratio to the composite oxide of 2:1 - 1:

1. The catalyst composition according to claim 154, characterized in that, The OCM catalyst is La2O3, the composite oxide is the composite oxide NaWZr of Na, W, and Zr, and the mass ratio of the OCM catalyst to the composite oxide is 4:1 - 1:

1.

159. The catalyst composition according to claim 158, wherein The OCM catalyst has a mass ratio to the composite oxide of 2:1 - 1:

1. The catalyst composition according to claim 154, wherein, The OCM catalyst is Sm2O3, and the composite oxide is the composite oxide NaWZr of Na, W, and Zr. The mass ratio of the OCM catalyst to the composite oxide is 4:1 - 1:

1.

161. The catalyst composition according to claim 160, wherein The OCM catalyst has a mass ratio to the composite oxide of 2:1 - 1:1.

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