Composite Oxide Containing Tungstate Nanoclusters, And Preparation Method And Application Thereof

Abstract

The invention belongs to the field of catalysts, and particularly relates to a composite oxide containing tungstate nanoclusters, and a preparation method and application thereof. The tungstate nanocluster-containing composite oxide comprises an alkali metal element A, a tungsten element W, an auxiliary agent element M, and an oxygen element O, wherein the alkali metal element A, the tungsten element W and the auxiliary agent element M form a composite with the oxygen element O. The composite oxide as a cocatalyst can obviously improve the selectivity and the yield of C.sub.2 in the oxidative coupling of methane reaction with co-fed methane and oxygen.

Claims

1-19. (canceled)

20. A composite oxide containing tungstate nanoclusters, characterized by comprising an alkali metal element A, a tungsten element W, an auxiliary agent element M, and an oxygen element O; 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 percent of the auxiliary agent element M is 20-94%; the alkali metal element A is one or more selected from the group consisting of Li, Na, K, Mg, Ca, Sr and Ba; the auxiliary agent element M is one or more selected from the group consisting of Si, Zr, Ti, Al, La, Ce and Co; and the tungstate nanoclusters satisfy a cluster enrichment index, which is defined as follows: In the region that contains the tungstate nanoclusters of 1010 nm.sup.2, the number of the tungstate nanoclusters is 3.

21. The composite oxide according to claim 20, wherein the alkali metal element A is at least Na, the auxiliary element M is at least Zr or Al, the composite oxide containing tungstate nanoclusters are respectively expressed as NaWZr or NaWAl, the tungstate nanoclusters are composed of alkali metal elements Na, tungsten element W and oxygen element O, and the tungstate nanoclusters have a general formula of Na.sub.xWO.sub.y, 0<x2, y represents the number of oxygen atoms required to satisfy the charge balance of the formula; 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 percent of the auxiliary agent element M is 20-94%.

22. The composite oxide according to claim 20, wherein the atomic percentage of Na in the composite oxide is 10% to 65%; and/or the atomic percentage of the tungsten element W is 2%-55%; and/or the atomic percentage of the auxiliary element Zr or Al is 22-92%.

23. the cluster enrichment index according to claim 20, wherein the detection method comprises: observing the composite oxide under a high-resolution transmission electron microscope, randomly selecting 5 tungstate nanoclusters in a 1010 nm.sup.2 area, and counting the number of tungstate nanoclusters contained in the region, and taking an average value.

24. The tungstate nanocluster according to claim 20, wherein the particle size of the tungstate nanocluster is 10.0 nm, and/or the specific surface area of the composite oxide is 0.1 to 10.0 g/m.sup.2.

25. The tungstate nanocluster according to claim 20, wherein three elements, namely alkali metal element A, tungsten element W and oxygen element O, in the tungstate nanocluster are uniformly distributed, wherein the uniform distribution means that any region in the tungstate nanocluster contains the alkali metal element A, the tungsten element W and the oxygen element O.

26. The tungstate nanocluster according to claim 20, wherein the tungsten element in the tungstate nanocluster exists in the form of a tetracoordinate tungstate, wherein the tetracoordinate means that one tungsten atom has only four oxygen atoms bonded thereto.

27. The tetracoordinate tungstate according to claim 26, wherein the detection method of the tetracoordinate tungstate structure is as follows: performing X-ray fine structure spectrum test on the composite oxide, and collecting L1-edge and L3-edge of tungsten element in the X-ray absorption near-edge structure spectroscopy (XANES) and extended X-ray absorption spectroscopy fine structure (EXAFS), by qualitative analysis and data fitting to derive coordination numbers for tungsten atoms.

28. The composite oxide according to claim 20, wherein after the composite oxide is calcined in the air at 800 C. for 6 hours, the particle size change value 1 of the tungstate nanocluster is 20%, the calculation formula is as follows: $1=\frac{.Math.\mathrm{Cluster}{\mathrm{Size}}_{\mathrm{after}\mathrm{calcination}}-\mathrm{Cluster}{\mathrm{Size}}_{\mathrm{before}\mathrm{calcination}}.Math.}{\mathrm{Cluster}{\mathrm{Size}}_{\mathrm{before}\mathrm{calcination}}}*100\%$ and/or the cluster enrichment index change value 2 of the calcined tungstate nanoclusters is 20%; the calculation formula is as follows: $2=\frac{.Math.\mathrm{Enrichment}{\mathrm{index}}_{\mathrm{after}\mathrm{calcination}}-\mathrm{Enrichment}{\mathrm{index}}_{\mathrm{before}\mathrm{calcination}}.Math.}{\mathrm{Enrichment}{\mathrm{index}}_{\mathrm{before}\mathrm{calcination}}}*100\%.$

29. The composite oxide according to claim 22, wherein 0<the molar ratio of Na:W5; and/or the molar ratio of W to Zr in the composite oxide is 0.1.

30. A method for preparing the oxide composition of claim 20, further comprising the following steps: (1) preparing a solution system 1: dissolving an alkali metal element precursor of a compound raw material containing the element in a proper amount of water, (2) preparing a solution system 2: a) mixing and rapidly stirring a tungsten element precursor, an auxiliary agent element precursor and a proper amount of water or alcohol to form the solution; (3) reaction: adding the solution system 1 into the solution system 2, removing the solvent from the product after reaction, and drying the obtained solid to obtain a solid product; and (4) annealing the solid product obtained in the step 3) to obtain a composite oxide containing tungstate nanoclusters.

31. The method according to claim 22, further comprising: 1) respectively preparing a solution system 1 and a solution system 2, wherein the solution system 1 and the solution system 2 are both transparent solutions; the transparent solutions are solutions without obvious suspended matters; the solutions are not layered, and when light penetrates through the solutions, the Tyndall effect is not generated; and 2) adding the solution system 1 into the stirred solution system 2 within 2-200 minutes until a turbid liquid appears, and then continuously stirring the turbid liquid for more than 1 hour.

32. The method according to claim 22. wherein removing the solvent from the product obtained in the step (3) without processing, and drying the obtained solid to obtain a solid product; wherein the non-processing specifically refers to any washing, centrifuging and filtering steps.

33. The method according to claim 22, wherein the annealing temperature is 700-900 C.; the annealing time is 3-8 hours; the ramp rate of the annealing is 2-10 C./min.

34. The method according to claim 22, wherein the alkali metal element precursor in the preparation method of the solution system 1 is one or more selected from the group consisting of lithium hydroxide, sodium hydroxide, lithium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, magnesium acetate, calcium hydroxide, calcium acetate, strontium hydroxide, and barium hydroxide; the precursor of the auxiliary element is one or more selected from the group consisting of sodium silicate, zirconyl nitrate, zirconium oxychloride, zirconium di(acetate) oxide, zirconyl citrate, titanium nitrate, aluminum 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 ethoxide, ammonium tungsten oxide hydrate, strontium tungstate, magnesium tungstate, barium tungstate, ammonium tungstate pentahydrate, ammonium metatungstate hydrate, calcium tungstate, barium tungstate, and strontium tungstate; the precursor of the tungsten element is one or more selected from the group consisting of sodium tungstate and tungsten chloride; the precursor of the auxiliary element is selected from one or more of tetraethyl orthosilicate, zirconium nitrate, zirconium n-butoxide, zirconyl nitrate, zirconium oxychloride, zirconium di(acetate) oxide, zirconium citrate, tetrabutyl titanate, aluminum sec-butoxide, aluminum isopropoxide, lanthanum nitrate, aluminum nitrate, cerium nitrate and cobalt nitrate; and the alcoholic solvent is one or more selected from the group consisting of methanol, ethanol, propanol, and butanol.

35. A cocatalyst, comprising the composite oxide of claim 20.

36. A catalyst composition, comprising the composite oxide of claim 20 and at least one Oxidative Coupling of Methane OCM.sub.catalyst having OCM activity.

37. The catalyst composition, comprising the composite oxide of claim 36, wherein the mass ratio of the OCM.sub.catalyst to the composite oxide is (0.1-50.0):1.0.

38. A use of the cocatalyst of claim 36 in chemical reactions; wherein, the chemical reaction is a radical conversion reaction; the oxidative coupling of methane refers to a process that carbon-hydrogen bonds of methane are broken under the action of a catalyst, the separated hydrogen and oxygen react to generate water, and carbon-carbon bonds are formed to prepare C.sub.2+ hydrocarbon.

39. A method of oxidative coupling of methane, wherein the method of oxidative coupling of methane takes methane and oxygen as raw material gases, and the reaction is carried out on a bed reactor, and the product comprises C.sub.2 hydrocarbons, hydrocarbons and C.sub.3 hydrocarbon.

Description

BRIEF DESCRIPTION OF THE INVENTION

[0096] FIG. 1 shows the reaction pathway of OCM along with the corresponding graphical representation of Gibbs free energy.

[0097] FIG. 2 shows a schematic diagram of a co-feed bed reactor for methane and oxygen.

[0098] FIG. 3(a) shows a network diagram of the OCM reaction (reference: Beck, B. et al., Catal. Today 2014, 228, 212).

[0099] FIG. 3(b) shows the correlation between the yield of C.sub.2 products and the rate of methyl radical generation obtained through kinetic simulations (reference: Arutyunov, V. et al., J. Mol. Catal. A: Chem. 2017 426, 326).

[0100] FIG. 4 shows the experimental results of the NaMnW-NaWZr system, illustrating the outcomes of Example 1.

[0101] FIG. 5 shows structural characterization of NaWZr. In particular, (a, b) representative high-angle annular dark-field (HAADF) and bright-field (BF) scanning transmission electron microscopy (STEM) images of NaWZr are shown. Unless otherwise specified, the molar ratio of tungsten to zirconium is 3:9. (c) EDS point spectra of the region indicated by the red circle in FIG. 1(a). The Cu signal originates from the Cu grid. (d) Size distribution of NaxWOy clusters in NaWZr. (e) Coarse statistics of NaxWOy cluster density in NaWZr with different W-Zr ratios. (f) W L3-edge X-ray absorption near-edge structure (XANES) spectra of NaWZr, Na.sub.2WO.sub.4, and WO.sub.3.

[0102] FIG. 6 shows the energy-dispersive X-ray spectroscopy (EDS) analysis of Example 1.

[0103] FIG. 7 shows the high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of Example 1. Some NaxWOy clusters are highlighted with green rectangular markers.

[0104] FIG. 8 shows the EDS mapping image of Example 1.

[0105] FIG. 9 shows the Raman spectrum of Implementation 1, compared with commercially available ZrO2. The characteristic Raman band around 925 cm-1 can be attributed to the WOZr bond.

[0106] FIG. 10 shows the Zr K-edge X-ray absorption near-edge structure (XANES) spectrum of Implementation 1.Compared to ZrO.sub.2, the Zr K-edge of NaWZr shows a noticeable blue shift, indicating the charge transfer from Zr to W through the ZrOW bond.

[0107] FIG. 11 shows representative bright-field (BF) and high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) images of NaWZr with a W:Zr molar ratio of 1:9. In the images, individual dispersed and aggregated tungsten species are marked with red circles, while NaxWOy clusters are highlighted with green squares.

[0108] FIG. 12 shows representative high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) images of NaWZr with a W:Zr molar ratio of 2:9. In the images, individual dispersed and aggregated tungsten species are marked with red circles, while NaxWOy clusters are highlighted with green squares.

[0109] FIG. 13 shows representative bright-field (BF) and high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) images of NaWZr with a W:Zr molar ratio of 4:9. In the images, some NaxWOy clusters are marked with green squares.

[0110] FIG. 14 shows representative bright-field (BF) and high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) images of NaWZr with a W:Zr molar ratio of 5:9. In the images, some NaxWOy clusters are marked with green squares.

[0111] FIG. 15 shows typical bright-field (BF) and high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) images of NaWZr with a W:Zr molar ratio of 0.5:9. In the images, dispersed tungsten species are marked with red circles.

[0112] FIG. 16 shows a typical high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) image of the NaWAl catalyst.

[0113] FIG. 17 shows a STEM spectrum of Na.sub.2WO.sub.4 in the form of large particles.

[0114] FIG. 18 shows the impact of the distance between the OCM catalyst and the composite oxide on the catalytic performance of OCM.

[0115] From FIG. 18, it can be observed that the distance between the OCM catalyst and the composite oxide significantly impacts the catalytic performance of OCM. The OCM catalyst exhibits superior performance when the distance between the catalyst and the composite oxide is 3 mm. Furthermore, the catalytic effect becomes increasingly favorable as the distance decreases.

DETAILED DESCRIPTION OF THE INVENTION

[0116] The following description of the embodiments is provided for a better understanding of the invention and should not be taken as limiting the invention.

[0117] Wherein the following examples are described using the relevant methods: [0118] 1. The Mn/Na.sub.2WO.sub.4/SiO.sub.2 catalysts are commercially available or can be synthesized by wet impregnation methods, as described in the literature (Journal of Molecular Catalysis (China) 1992, 6, 427-433). The specific synthesis steps are as follows: typically, an aqueous manganese (II) nitrate solution (50 wt %) and sodium tungstate hydrate were dissolved in an appropriate amount of deionized water. A commercially available SiO.sub.2 carrier with a surface area of 200 m.sup.2/g is added to the above solution with continuous agitation and then dried overnight at 105 C. The ratio of manganese nitrate and sodium tungstate satisfies that the mass percentage of manganese (Mn) element to Mn/Na.sub.2WO.sub.4/SiO.sub.2 catalyst is 2 wt %, and sodium tungstate (Na.sub.2WO.sub.4) is 5 wt % of Mn/Na.sub.2WO.sub.4/SiO.sub.2 catalyst. Thereafter, the dried solid was calcined at 800 C. for 4 hours to obtain the final catalyst. [0119] 2. In the following examples, the composition of the samples was measured using an XRF-1800 X-ray fluorescence spectrometer from Shimadzu corporation, Japan; the specific surface area of the sample is determined by N.sub.2 absorption and desorption method using an MICROMERICS ASAP2020 (USA), and the measured specific surface area refers to BET specific surface area; High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images and elemental mapping were acquired ex-situ on a Cs-corrected Titan Chemi-STEM operating at an accelerating voltage of 200 kV. The Raman spectrum of the catalyst was measured at room temperature with visible laser excitation (532 nm) on a Horiba-Jobin-Yvon. In situ X-ray absorption fine structure (XAFS) spectra were measured on beamline 14 W at the Shanghai Synchrotron Radiation Facility (SSRF) in China, using a Si(111) double crystal monochromator and an in situ cell (HTC-MSXAS-500, Beijing Scistar Technology Co., Ltd., maximum working temperature: 1000 K). [0120] 3. The OCM tests were performed in a quartz fix-bed reactor tube with an inner diameter of 8 mm under atmospheric pressure. The catalyst bed was placed on a quartz wool plug in the constant-temperature zone of the furnace. A thermocouple well with an outer diameter of 6 mm was inserted into the quartz reactor to monitor the bed temperature and to further reduce the free space volume. CH.sub.4, O.sub.2, and N.sub.2 in a ratio of 3:1:2.7 were cofed into the reactor through mass flow controllers. The total flow rate was 67 mL min.sup.1. The products were analyzed by an online gas chromatograph equipped with an FID detector and a TCD detector. Molecular sieve 5 A column was coupled with Porapak N column to separate CO.sub.2, CH.sub.4, O.sub.2 and N.sub.2 while aluminum trioxide capillary column was used to separate hydrocarbon products (CH.sub.4, C.sub.2H.sub.4, C.sub.2H.sub.6, C.sub.3H.sub.6 and C.sub.3H.sub.8). All the carbon-containing products except C.sub.3 species were quantified by TCD. The trace C.sub.3 species were quantified by FID. In order to eliminate the error associated with the different detection methods, FID signals were calibrated to make sure the quantification of methane, ethane, and ethylene by FID was exactly the same as that quantified by TCD. All the catalysts were calcined in air at 800 C. for 5 h before catalytic test. For testing OCM.sub.catalyst (e.g. Mn/Na.sub.2WO.sub.4/SiO.sub.2, La.sub.2O.sub.3, etc.) and cocatalyst (e.g., NaWZr) alone, 200 and 100 mg of catalyst was loaded, specifically.

[0121] When testing the catalyst composition formed by OCM.sub.catalyst and cocatalyst, unless otherwise specified, the dosage of OCM.sub.catalyst is 200 mg, and the dosage of cocatalyst is 100 mg.

[0122] The CH.sub.4 conversion and product selectivity were calculated based on a carbon atom basis of the inlet and outlet gases. The outlet gases were corrected for gas expansion by using N.sub.2 as an internal standard.

[00008]$\begin{array}{cc}{\mathrm{CH}}_4\mathrm{Conv}.=\left(1-\frac{{n\mathrm{CH}}_{4_{\mathrm{outlet}}}}{{n\mathrm{CH}}_{4_{\mathrm{outlet}}}+.Math.x{n\left[\mathrm{products}\right]}_{\mathrm{outlet}}}\right)100\%& \left(3\right)\end{array}$

where x is the number of carbon atom in the products.

[0123] The products selectivity was calculated on a carbon atom basis of the outlet products (i.e., C.sub.2H.sub.4, C.sub.2H.sub.6, CO, CO.sub.2, C.sub.3H.sub.6 and C.sub.3H.sub.8). C.sub.2 products include both C.sub.2H.sub.4 and C.sub.2H.sub.6.

[00009]$\begin{array}{cc}{C}_2\mathrm{Sel}.=\frac{2{nC}_2{H}_4+2{nC}_2{H}_6}{\begin{array}{c}2{nC}_2{H}_4+2{nC}_2{H}_6+1n\mathrm{CO}+\\ 1{n\mathrm{CO}}_2+3{nC}_3{H}_6+3{nC}_3{H}_8\end{array}}100\%& \left(4\right)\end{array}$$\begin{array}{cc}\mathrm{CO}\mathrm{Sel}.=\frac{1n\mathrm{CO}}{\begin{array}{c}2{nC}_2{H}_4+2{nC}_2{H}_6+1n\mathrm{CO}+\\ 1{n\mathrm{CO}}_2+3{nC}_3{H}_6+3{nC}_3{H}_8\end{array}}100\%& \left(5\right)\end{array}$$\begin{array}{cc}{C}_2\mathrm{Sel}.=\frac{1{n\mathrm{CO}}_2}{\begin{array}{c}2{nC}_2{H}_4+2{nC}_2{H}_6+1n\mathrm{CO}+\\ 1{n\mathrm{CO}}_2+3{nC}_3{H}_6+3{nC}_3{H}_8\end{array}}100\%& \left(6\right)\end{array}$$\begin{array}{cc}{C}_2\mathrm{Yield}={\mathrm{CH}}_4\mathrm{Conv}.*C_2\mathrm{Sel}.*100\%& \left(7\right)\end{array}$

[0124] The carbon balance was calculated according to:

[00010]$\begin{array}{cc}\mathrm{Carbon}\mathrm{balance}=\frac{{n\mathrm{CH}}_{4_{\mathrm{outlet}}}+.Math.x{n\left[\mathrm{products}\right]}_{\mathrm{outlet}}}{{n\mathrm{CH}}_{4_{\mathrm{inlet}}}}100\%& \left(8\right)\end{array}$

where x is the number of carbon atom in the products. Generally, the carbon balance was higher than 95%.

Example 1

[0125] Weighing a certain amount of NaOH and dissolving the NaOH in water to obtain a clear NaOH aqueous solution 1 with the mass concentration of 23 wt %; 3.453 g of zirconium n-butoxide (80 wt %) and 1.188 g of tungsten hexachloride are weighed and added into 30 mL of ethanol, and the mixture is fully stirred and dissolved to obtain a clear solution 2; adding 2 mL of NaOH aqueous solution 1 into the solution 2 within 10 minutes under rapid stirring (the stirring speed is 800 rpm) and continuously stirring for 3 hours to obtain a turbid solution. The obtained turbid solution was dried at 40 C. and aged in an 80 C. oven for 12 hours. The obtained solid was calcined at 800 C. in the air for 5 hours to obtain the catalyst. The atomic ratio of W atoms to zirconium atoms in the catalyst was 3:9.

[0126] The high-resolution transmission electron microscope images of the catalyst are shown in FIGS. 5a, 5b, and 7, and the catalyst is obviously rich in nanoclusters. The white clusters and the dark non-cluster regions in the graph were subjected to element scanning analysis (FIGS. 5c and 6), respectively, and it was found that the white clusters were Na.sub.xWO.sub.y clusters rich in Na, W and O elements, while the non-cluster regions were mainly ZrO.sub.2 formed from the auxiliary element Zr. The average particle size of the Na.sub.xWO.sub.y nanoclusters in this catalyst was found to be 0.8 nm (as shown in d in FIG. 5). Further counting the number of Na.sub.xWO.sub.y nanoclusters in the 10*10 nm.sup.2 region, it was found that the number was 21 (e in FIG. 5).

[0127] EDS Mapping of the catalyst is shown in FIG. 8, and Na, W and Zr elements are uniformly distributed in the catalyst.

[0128] W L.sub.1 edge XANES spectra of NaWZr shown in FIG. 5f exhibit characteristic pre-edge peaks at 12117 eV, which is similar to that of Na.sub.2WO.sub.4 and different from WO.sub.3. These results suggest that W species in the catalyst feature tetrahedral WO.sub.4 (i.e., tungstate) rather than octahedral WO.sub.6 (i.e., tungsten oxide) structures. The Raman spectra of the catalyst was shown in FIG. 9. Comparing to ZrO.sub.2, the catalyst exhibits a characteristic peak at 925 cm.sup.1, which could be attributed to Na.sub.2WO.sub.4. In addition, the Zr K-edge XANES spectrum of the catalyst is shown in FIG. 10. Compared with ZrO.sub.2, the Zr K-edge of NaWZr is significantly blue shifted, indicating that Zr transfers charge to W. The existence of strong interaction between Zr and W is the key to achieve the high enrichment index of Na.sub.xWO.sub.y nanoclusters. On the one hand, it can stabilize Na.sub.xWO.sub.y nanoclusters and allow them to exist in the form of nanoclusters. On the other hand, the sintering agglomeration of adjacent Na.sub.xWO.sub.y nanoclusters is avoided, so that multiple Na.sub.xWO.sub.y nanoclusters can exist in the region of 10*10 nm.sup.2.

[0129] Examples 2-16 were synthesized according to the method described in example 1, with slightly different parameters from example 1. and the specific synthesis parameters and structural parameters are shown in (table 1-1-1-4).

[0130] Example 2 differs from example 1 in that the auxiliary element used in example 2 is Al. The high-resolution transmission electron microscopy image of the catalyst is shown in FIG. 16, from which it can be clearly seen that the catalyst is rich in nanoclusters. It was found that the average particle size of Na.sub.xWO.sub.y nanoclusters in the catalyst was 0.9 nm. Further statistics of the number of Na.sub.xWO.sub.y nanoclusters in the 1010 nm.sup.2 region showed that the number was 21.

[0131] By analyzing the structural parameters (Table 1-1) of examples 1 to 7, it was concluded that when the alkali metal element was Na, K, or Li and the auxiliary element was Zr or Al, composite, oxides containing tungstate nanoclusters can be obtained. The nanoclusters have an average particle size of 0.8-0.9 nm, the number of Na.sub.xWO.sub.y nanoclusters is 21 in the 1010 nm.sup.2 region.

[0132] By analyzing examples 1 and 8, the compound oxide containing tungstate nanoclusters can be obtained if the tungsten source is chloride or sodium tungstate, and the nanoclusters have an average particle size of 0.8-0.9 nm, the number of Na.sub.xWO.sub.y nanoclusters is 21 in the 1010 nm.sup.2 region.

[0133] STEM images of Examples 9-13 are shown in FIG. 11-15, respectively. Examples 9 to 13 differ from example 1 in the molar ratio of W to Zr. As can be seen from FIGS. 11 to 15, composite oxides containing tungstate nanoclusters were obtained when the molar ratio of W to Zr was 1:9, 2:9, 3:9, 4:9, 5:9, and 0.5:9. However, the molar ratio of W to Zr influences Na.sub.xWO.sub.y enrichment index of nanoclusters. The number of tungstate nanoclusters in the 1010 nm.sup.2 region in Examples 1 and 9-13 are summarized in FIG. 5e. Clearly, the high feeding molar ratio of W:Zr is critical for the formation of high-concentration tungstate clusters. The number of tungstate clusters per 1010 nm.sup.2 of ZrO.sub.2 matrix increases from 0 (W:Zr=0.5:9) to 20 (W:Zr=3:9). By analyzing Examples 14 to 16 show that when the solvent of system 2 is methanol, ethanol, propanol, or butanol, the tungstate nanocluster-containing composite oxide can be obtained. The nanoclusters have an average particle size of 0.8-0.9 nm, the number of Na.sub.xWO.sub.y nanoclusters is 21 in the 1010 nm.sup.2 region. By analyzing Examples 17 to 20 show that when using different types of alkane metals of precursors A, the tungstate nanocluster-containing composite oxide can be obtained. The nanoclusters have an average particle size of 0.7-1.1 nm, the number of Na.sub.xWO.sub.y nanoclusters is 3-12 in the 1010 nm.sup.2 region. By analyzing Examples 21 to 29 show that when using the synthetical parameters described in claim, the tungstate nanocluster-containing composite oxide can be obtained. The nanoclusters have an average particle size of 0.7-1.4 nm, the number of Na.sub.xWO.sub.y nanoclusters range from 1 to 18 in the 1010 nm.sup.2 region. Examples 30 to 62 present the catalytic results of OCM.sub.catalyst, cocatalyst and the catalyst composition.

[0134] All reaction conditions, parameters, and catalytic performance are shown in table 2. Typically, 0.2 g of catalyst (Q) and 0.1 g of cocatalyst (P) were physically mixed and then loaded in the quartz reactor. CH.sub.4, O.sub.2, and N.sub.2 in a certain ratio were cofed into the reactor through mass flow controllers. The reaction was carried out at ambient pressure and the reaction products were detected by on-line gas chromatography (FIG. 2).

[0135] Example 30 shows the catalytic performance of a cocatalyst synthesized by the preparation method described in example 1 mixed with classical Mn/Na.sub.2WO.sub.4/SiO.sub.2. The catalytic results of the catalysts tested under the above conditions show that the catalyst composition exhibits very high selectivity and yield of C.sub.2.

[0136] By analyzing the catalytic performance of examples 31-46 (Table 2), 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 are compatible with the classical Mn/Na.sub.2WO.sub.4/SiO.sub.2. The catalyst showed similar catalytic performance to example 17.

[0137] By analyzing the catalytic performance of examples 30 and 37 (Table 2), it can be concluded that sodium tungstate can also be used as the tungsten source to synthesize tungstate nanocluster-containing composite oxide. The mixture with as-synthesized composite oxide significantly improves the OCM performance of Mn/Na.sub.2WO.sub.4/SiO.sub.2.

[0138] By analyzing the catalytic performances of examples 30 and 38-41 (Table 2), it can be concluded that composite oxides with W:Zr molar ratios of 1:9, 2:9, 3:9, 4:9 and 5:9 are all good cocatalysts to improve the OCM performance of classical Mn/Na.sub.2WO.sub.4/SiO.sub.2. The volcano plot of C.sub.2 yield versus W:Zr ratio is similar to that of tungstate nanoclusters concentration versus W:Zr ratio, suggesting a high concentration of tungstate sub-nanometer clusters is beneficial for the catalytic performance with a volcano-type trend.

[0139] By analyzing the catalytic performance of example 42 (Table 2) it can be concluded that the NaWZr with a W:Zr ratio of 0.5:9 cannot improve the OCM performance of Mn/Na.sub.2WO.sub.4/SiO.sub.2, likely because the W content thereof is too low to obtain nanoclusters.

[0140] By analyzing the catalytic performance of examples 30 and 43-45 (Table 2) it can be concluded that the co-catalyst prepared when using different alcohol solutions is comparable to the classical Mn/Na.sub.2WO.sub.4/SiO.sub.2. The performance of the mixed catalyst is obviously improved.

[0141] By analyzing the catalytic performance of examples 46-49 (Table 2), it can be concluded that different performance enhancements are exhibited when different classical OCM catalysts are used in combination with the co-catalyst synthesized by the preparation method described in example 1.

[0142] By analyzing the catalytic performance of examples 50-62 (Table 2), it can be concluded that different performance enhancements are exhibited when different classical OCM catalysts are used in combination with the co-catalyst synthesized by the preparation method described in example 17-29.

TABLE-US-00001 TABLE 1-1 Parameters Example1 Example2 Example3 Example4 Example5 Example6 Example7 Example8 Alkali metal species of A Na Na K K Na, K Li Na Na Precursor of A NaOH NaOH KOH KOH NaOH, LiOH NaOH NaOH KOH Atom % in A 40 40 40 40 40 35 40 40 Additive element of M Zr Al Zr Al Zr Zr Zr, Al Zr Precursor of M Zr(n-BuO).sub.4 Al(i-PrO).sub.3 Zr(n-BuO).sub.4 Al(i-PrO).sub.3 Zr(n-BuO).sub.4 Zr(n-BuO).sub.4 Zr(n-BuO).sub.4, Zr(n-BuO).sub.4 Al(i-PrO).sub.3 Atom % in M 45 45 45 45 45 48.8 45 45 Precursor of tungsten WCl.sub.6 WCl.sub.6 WCl.sub.6 WCl.sub.6 WCl.sub.6 WCl.sub.6 WCl.sub.6 Na.sub.2WO.sub.4 Atom % of tungsten 15 15 15 15 15 16.2 15 15 Mole ration of 2.7 2.7 2.7 2.7 2.7 2.2 2.7 2.7 A/tungsten Mole ration of tungsten/M 3:9 3:9 3:9 3:9 3:9 3:9 3:9 3:9 Type of alcohol in System 2 ethanol ethanol ethanol ethanol ethanol ethanol ethanol ethanol Dip time (min) 10 10 10 10 10 10 10 10 Number of Na.sub.xWO.sub.y 21 21 21 21 21 21 21 21 nanoclusters (per 100 nm.sup.2) Size of Na.sub.xWO.sub.y nanoclusters 0.8 0.9 0.9 0.9 0.9 0.9 0.9 0.9 (nm) Specific surface area (m.sup.2/g) 0.7 0.8 0.7 0.8 1.0 0.9 0.7 0.5

TABLE-US-00002 TABLE 1-2 Parameters Example 9 Example10 Example11 Example12 Example13 Example14 Example15 Example16 Alkali metal species of A Na Na Na Na Na Na Na Na Precursor of A NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH Atom % in A 50 45 35 30 53.5 40 40 40 Additive element of M Zr Zr Zr Zr Zr Zr Zr Zr Precursor of M Zr(n-BuO).sub.4 Zr(n-BuO).sub.4 Zr(n-BuO).sub.4 Zr(n-BuO).sub.4 Zr(n-BuO).sub.4 Zr(n-BuO).sub.4 Zr(n-BuO).sub.4 Zr(n-BuO).sub.4 Atom % in M 45 45 45 45 45 45 45 45 Precursor of tungsten WCl.sub.6 WCl.sub.6 WCl.sub.6 WCl.sub.6 WCl.sub.6 WCl.sub.6 WCl.sub.6 WCl.sub.6 Atom % of tungsten 5 10 20 25 2.5 15 15 15 Mole ration of 10 4.5 1.8 1.2 2.7 2.7 2.7 2.7 A/tungsten Mole ration of tungsten/M 1:9 2:9 4:9 5:9 0.5:9 3:9 3:9 3:9 Type of alcohol in System 2 ethanol Ethanol ethanol ethanol ethanol methanol n-propanol n-butanol Dip time (min) 10 10 10 10 10 10 10 10 Number of Na.sub.xWO.sub.y ~3 ~11 ~22 ~22 ~21 ~21 ~21 ~21 nanoclusters (per 100 nm.sup.2) Size of Na.sub.xWO.sub.y nanoclusters 0.7 0.8 1.1 1.1 0.5 0.9 0.8 0.8 (nm) Specific surface area (m.sup.2/g) 0.6 0.9 1.3 1.5 0.9 0.8 1.0 1.2

TABLE-US-00003 TABLE 1-3 Parameters Example17 Example18 Example19 Example20 Example21 Example22 Example23 Alkali metal species of A Mg Ca Ba Sr Na Na Na Precursor of A Mg(OH).sub.2 Ca(OH).sub.2 Ba(OH).sub.2 Sr(OH).sub.2 NaOH NaHCO.sub.3 NaOH, NaNO.sub.3 Atom % in A 10 65 18 2 53.5 40 40 Additive element of M Si Ti La, Ce Zr, Co Zr Zr Zr Precursor of M Si(C.sub.2H.sub.3O.sub.2).sub.4 Ti(n-BuO).sub.4 La(NO.sub.3).sub.3, ZrO(NO.sub.3).sub.2, Zr(n-BuO).sub.4 Zr(n-BuO).sub.4 Zr(n-BuO).sub.4 Sm(NO.sub.3).sub.3 Co(OAc).sub.2 Atom % in M 81 26.2 27 90 45 45 45 Precursor of tungsten WCl.sub.6 WCl.sub.6 WCl.sub.6 WCl.sub.6 Sr.sub.2WO.sub.4, WCl.sub.6 NH.sub.3WO.sub.3, CaWO.sub.4 NH.sub.3WO.sub.3 .Math. H.sub.2O Atom % of tungsten 9 8.8 55 8 2.5 15 15 Mole ration of 1.1 7.4 0.3 0.25 2.7 2.7 2.7 A/tungsten Mole ration of tungsten/M 1:9 3:9 2:1 1:11 0.5:9 3:9 3:9 Type of alcohol in System 2 ethanol ethanol ethanol ethanol ethanol methanol, ethanol, n-propanol n-propanol Dip time (min) 10 10 10 10 10 10 10 Number of Na.sub.xWO.sub.y ~3 ~12 ~3 ~5 ~3 ~18 ~11 nanoclusters (per 100 nm.sup.2) Size of Na.sub.xWO.sub.y nanoclusters 0.7 0.8 1.1 0.8 1.4 1.2 1.1 (nm) Specific surface area (m.sup.2/g) 0.9 0.8 1.0 1.2 1.1 0.5 0.9

TABLE-US-00004 TABLE 1-4 Parameters Example24 Example25 Example26 Example27 Example27 Example29 Alkali metal species of A K Li, Ca Ba Na, Sr Na Sr, Ba Precursor of A KHCO.sub.3 LiOH, Ba(OH).sub.2 Na.sub.2CO.sub.3, NaOH Sr(OH).sub.2, Ca(OH).sub.2 Sr(OH).sub.2 Ba(OH).sub.2 Atom % in A 27 40 2 15 20 40 Additive element of M Zr, La Ce La, Zr Zr, Co Zr Zr Precursor of M ZrOCl.sub.2, LaCl.sub.3 CeAc.sub.2, La(NO.sub.3).sub.3, ZrO(NO.sub.3) ZrO(NO.sub.3), Zr(n-BuO).sub.4 citric acid CeCl.sub.2 Co(OAc).sub.2 zirconium salt Atom % in M 22 30 92 70 60 45 Precursor of tungsten WCl.sub.6 NH.sub.4WO.sub.3 .Math. H.sub.2O WCl.sub.6 WCl.sub.6 Sr.sub.2WO.sub.4, (NH.sub.4).sub.2WO.sub.4 .Math. 5H.sub.2O CaWO.sub.4 Atom % of tungsten 50 30 6 15 20 15 Mole ration of 1.2 1.3 0.3 1 1 2.7 A/tungsten Mole ration of tungsten/M 1:2.3 1:1 1:15 1:4.6 3:9 3:9 Type of alcohol in System 2 n-propanol ethanol ethanol ethanol methanol, methanol, ethanol, n-propanol n-propanol Dip time (min) 10 10 10 10 10 10 Number of Na.sub.xWO.sub.y nanoclusters ~11 ~17 ~1 ~5 ~15 ~18 (per 100 nm.sup.2) Size of Na.sub.xWO.sub.y nanoclusters (nm) 1.4 1.2 1.0 0.8 1.4 1.2 Specific surface area (m.sup.2/g) 1.5 0.9 1.7 1.2 1.1 0.5

TABLE-US-00005 TABLE 2-1 Parameters Example30 Example31 Example32 Example33 Example34 Source of Example1 Example2 Example3 Example4 Example5 catalyst (P) Traditional Mn/ Mn/ Mn/ Mn/ Mn/ OCM Na.sub.2WO.sub.4/SiO.sub.2 Na.sub.2WO.sub.4/SiO.sub.2 Na.sub.2WO.sub.4/SiO.sub.2 Na.sub.2WO.sub.4/SiO.sub.2 Na.sub.2WO.sub.4/SiO.sub.2 catalyst (Q) Feeding 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 gas (CH.sub.4/O.sub.2/N.sub.2) Temperature 750 750 750 750 750 ( C.) Selectivity 48.4 48.4 48.4 48.4 48.4 of Q (%) Yield of Q 8.1 8.1 8.1 8.1 8.1 (%) Yield of P 0.5 0.8 0.5 0.5 0.9 (%) Selectivity 73.9 70.1 67.2 65.2 75.4 of mixed catalysts (%) Yield of 30.9 30.5 28.5 27.7 31.2 mixed catalysts (%) Parameters Example35 Example36 Example37 Example38 Example39 Source of Example6 Example7 Example8 Example9 Example10 catalyst (P) Traditional Mn/ Mn/ Mn/ Mn/ Mn/ OCM Na.sub.2WO.sub.4/SiO.sub.2 Na.sub.2WO.sub.4/SiO.sub.2 Na.sub.2WO.sub.4/SiO.sub.2 Na.sub.2WO.sub.4/SiO.sub.2 Na.sub.2WO.sub.4/SiO.sub.2 catalyst (Q) Feeding 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 gas (CH.sub.4/O.sub.2/N.sub.2) Temperature 750 750 750 750 750 ( C.) Selectivity 48.4 48.4 48.4 48.4 48.4 of Q (%) Yield of Q 8.1 8.1 8.1 8.1 8.1 (%) Yield of P 0.6 1.0 0.8 0.3 0.5 (%) Selectivity 63.7 77.2 65.8 77.2 72.4 of mixed catalysts (%) Yield of 27.5 29.4 23.9 25.3 26.5 mixed catalysts (%)

TABLE-US-00006 TABLE 2-2 Parameters Example40 Example41 Example42 Example43 Example44 Source of Example11 Example12 Example13 Example14 Example15 catalyst (P) Traditional Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 OCM catalyst (Q) Feeding 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 gas (CH.sub.4/O.sub.2/N.sub.2) Temperature 750 750 800 750 750 ( C.) Selectivity 48.4 48.4 60.1 48.4 48.4 of Q (%) Yield of Q 8.1 8.1 23.3 8.1 8.1 (%) Yield of P 0.6 0.7 1.1 1.1 0.8 (%) Selectivity 74.2 65.9 80.1 68.9 70.1 of mixed catalysts (%) Yield of 29.7 27.8 20.5 24.8 28.5 mixed catalysts (%) Parameters Example45 Example46 Example47 Example48 Example49 Source of Example16 Example1 Example1 Example1 Example1 catalyst (P) Traditional Mn/Na.sub.2WO.sub.4/SiO.sub.2 La.sub.2O.sub.3 Sm.sub.2O.sub.3 Li/MgO Ca/CeO.sub.2 OCM catalyst (Q) Feeding 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 gas (CH.sub.4/O.sub.2/N.sub.2) Temperature 750 800 800 800 800 ( C.) Selectivity 48.4 47.2 33.6 45.1 52.6 of Q (%) Yield of Q 8.1 16.3 9.0 11.3 8.2 (%) Yield of P 0.9 0.5 0.5 0.5 0.5 (%) Selectivity 67.7 56.1 60.0 56.5 64.7 of mixed catalysts (%) Yield of 28.8 20.4 16.1 16.0 12.2 mixed catalysts (%)

TABLE-US-00007 TABLE 2-3 Parameters Example50 Example51 Example52 Example53 Source of Example17 Example18 Example19 Example20 catalyst (P) Traditional Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 OCM catalyst (Q) Feeding gas 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 (CH.sub.4/O.sub.2/N.sub.2) Temperature ( C.) 750 750 750 750 Selectivity of Q (%) 48.4 48.4 48.4 48.4 Yield of Q (%) 8.1 8.1 8.1 8.1 Yield of P (%) 1.1 1.2 2.0 2.1 Selectivity of 44.2 55.9 50.1 47.9 mixed catalysts (%) Yield of mixed 12.5 14.2 12.8 17.6 catalysts (%) Parameters Example54 Example55 Example56 Source of Example21 Example22 Example23 catalyst (P) Traditional Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 OCM catalyst (Q) Feeding gas 3/1/2.7 3/1/2.7 3/1/2.7 (CH.sub.4/O.sub.2/N.sub.2) Temperature ( C.) 750 750 750 Selectivity of Q (%) 48.4 48.4 48.4 Yield of Q (%) 8.1 8.1 8.1 Yield of P (%) 2.2 1.9 0.3 Selectivity of 53.1 63.7 51.1 mixed catalysts (%) Yield of mixed 19.4 24.2 19.5 catalysts (%)

TABLE-US-00008 TABLE 2-4 Parameters Example57 Example58 Example59 Example60 Example61 Example62 Source of Example24 Example25 Example26 Example27 Example28 Example29 catalyst (P) Traditional Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 Mn/Na.sub.2WO.sub.4/SiO.sub.2 OCM catalyst (Q) Feeding gas 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 3/1/2.7 (CH.sub.4/O.sub.2/N.sub.2) Temperature ( C.) 750 750 750 750 750 750 Selectivity of Q (%) 48.4 48.4 48.4 48.4 48.4 48.4 Yield of Q (%) 8.1 8.1 8.1 8.1 8.1 8.1 Yield of P (%) 1.1 0.8 0.9 0.9 0.6 1.0 Selectivity of 45.8 57.5 51.7 49.5 54.7 65.3 mixed catalysts (%) Yield of mixed 13.8 15.5 14.1 18.9 20.7 25.5 catalysts (%)

Comparative Example 1

[0143] WO.sub.3/ZrO.sub.2 is the comparison example 1. The preparation process of WO.sub.3/ZrO.sub.2 is the same as that of example 1, except that no alkali metal Na was added during the synthesis of comparative example 1. The transmission electron microscope result shows that the nanoclusters in the WO.sub.3/ZrO.sub.2 catalyst were tungsten oxide instead of sodium tungstate.

[0144] Comparative example 1 was tested with Mn/Na.sub.2WO.sub.4/SiO.sub.2 in the manner shown in Example 17, with the following results: [0145] The C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 was 48.4% and the C.sub.2 yield was 8.1%, while the C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO and WO.sub.3/ZrO.sub.2 was 46.8% and the C.sub.2 yield was 7.6%. From the above results, it can be seen that the comparative example 1 not only failed to improve the selectivity and yield of Mn/Na.sub.2WO.sub.4/SiO.sub.2, but also inhibited it. It indicates that the real component of the co-catalyst is not the tungsten oxide nanoclusters, but the tungstate nanoclusters. In the synthesis of the cocatalyst, an alkali metal element is indispensable.

Comparative Example 2

[0146] 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 in the synthesis of comparative example 2. In this case, after the addition of system 1 to system 2, the solution remains clarified, and the corresponding solid catalyst cannot be produced. From this result, it can be seen that the additive element is essential for the synthesis of tungstate nanoclusters.

Comparative example 3

[0147] The catalyst was synthesized by the same preparation method as example 1, with the only difference being that the tungsten element was not added in synthesizing comparative example 3. In this case, the resulting comparative example 3 does not contain Na.sub.xWO.sub.y nanoclusters.

[0148] Comparative example 3 was tested with Mn/Na.sub.2WO.sub.4/SiO.sub.2 in the manner shown in Example 17 with the following results: [0149] The C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 was 48.4% and the C.sub.2 yield was 8.1%, while the C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 with the catalyst composition in comparative example 3 was 45.4% and the C.sub.2 yield was 6.8%. From the above results, it can be seen that the comparative example 3 not only failed to improve the selectivity and yield of Mn/Na.sub.2WO.sub.4/SiO.sub.2, but also inhibited it. It indicates that elemental tungsten is an indispensable active component of the co-catalyst.

Comparative Example 4

[0150] The catalyst was synthesized using the same preparation method as in example 1, with the only difference being the replacement of chloride with molybdenum chloride in the synthesis of Comparative example 4, that is the element W in example 1 was changed to the element Mo.

[0151] Comparative example 4 was tested with Mn/Na.sub.2WO.sub.4/SiO.sub.2 in the manner shown in Example 17 with the following results: [0152] The C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 was 48.4% and the C.sub.2 yield was 8.1%, while the C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 with the catalyst composition in comparative example 4 was 48.2% and the C.sub.2 yield was 8.0%. From the above results, it can be seen that the comparative example 4 not only failed to improve the selectivity and yield of Mn/Na.sub.2WO.sub.4/SiO.sub.2, but also inhibited it. It indicates that elemental tungsten is an indispensable active component of the co-catalyst.

Comparative Example 5

[0153] The catalyst was synthesized using the same preparation method as in example 1, with the only difference being that in the synthesis of Comparative example 5, all of system 1 was added to system 2 within 1 min.

[0154] The high-resolution electron microscopy images of comparative example 5 are shown in FIG. 17, where it can be seen that the sodium tungstate in comparative example 5 is mainly in the form of large sodium tungstate particles (>10 nm) rather than nanoclusters, indicating that the dropping of acceleration from system 1 into system 2 has an important effect on the structure of the catalyst. The slow addition of system 1 (addition time 2 min) to system 2 allows for the slow hydrolytic crosslinking of the tungsten precursor and the auxiliary element precursor by the alkali metal, thus facilitating the formation of tungstate nanoclusters. Too rapid an addition will result in rapid hydrolysis of the auxiliary element precursors, which will not allow the tungstate to be uniformly dispersed in the nanoclusters.

[0155] Comparative example 5 was tested with Mn/Na.sub.2WO.sub.4/SiO.sub.2 in the manner shown in Example 17 with the following results: [0156] The C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 was 48.4% and the C.sub.2 yield was 8.1%, while the C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 with the catalyst composition in comparative example 5 was 47.5% and the C.sub.2 yield was 7.6%. From the above results, it can be seen that the comparative example 5 failed to improve the selectivity and yield of Mn/Na.sub.2WO.sub.4/SiO.sub.2. It indicates that the tungstate nanocluster is the active structure of the cocatalyst, and the dropping speed of the system 1 can influence the tungstate structure of the cocatalyst species and further influence the reaction performance of the cocatalyst species.

Comparative Example 6

[0157] The catalyst was synthesized using the same preparation method as in example 1, with the only difference being that the solvent used in the system 2 in the synthesis of comparative example 6 was acetone.

[0158] Comparative example 6 was tested with Mn/Na.sub.2WO.sub.2/SiO.sub.2 in the manner shown in Example 17 with the following results: [0159] The C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 was 48.4% and the C.sub.2 yield was 8.1%, while the C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 with the catalyst composition in comparative example 6 was 40.3% and the C.sub.2 yield was 6.3%. From the above results, it can be seen that the comparative example 6 failed to improve the selectivity and yield of Mn/Na.sub.2WO.sub.4/SiO.sub.2. It indicates that a suitable solvent must be used for the cocatalyst synthesis.

Comparative Example 7

[0160] The catalyst was synthesized by the same preparation method as in example 1, the only difference is that in the synthesis of Comparative example 7, step 3) was performed by centrifugal washing instead of drying without treatment (i.e., drying the solvent at 40 C. for 12 hours in an oven at 80 C.). The wt % of tungsten in Proportion 7 was measured by XRF to be less than 0.1%. This indicates that the centrifugal washing step caused the loss of elemental tungsten from the catalyst.

[0161] Comparative example 7 was tested with Mn/Na.sub.2WO.sub.4/SiO.sub.2 in the manner shown in Example 17 with the following results: [0162] The C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 was 48.4% and the C.sub.2 yield was 8.1%, while the C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 with the catalyst composition in comparative example 7 was 44.2% and the C.sub.2 yield was 6.9%. From the above results, it can be seen that the comparative example 7 failed to improve the selectivity and yield of Mn/Na.sub.2WO.sub.4/SiO.sub.2. The above results show that the direct drying of the solvent without treatment as described in step 3) is a very important technical feature of the synthesis method.

Comparative Example 8

[0163] The catalyst was synthesized using the same preparation method as in example 1, the only difference being that in the synthesis of comparative example 8, the alkali metal precursor used in system 1 was sodium nitrate instead of NaOH. In this case, the pH of system 1 is neutral.

[0164] Comparative example 8 was tested with Mn/Na.sub.2WO.sub.4/SiO.sub.2 in the manner shown in Example 17 with the following results: [0165] The C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 was 48.4% and the C.sub.2 yield was 8.1%, while the C.sub.2 selectivity of Mn/Na.sub.2WO.sub.4/SiO.sub.2 with the catalyst composition in comparative example 8 was 39.5% and the C.sub.2 yield was 5.9%. From the above results, it can be seen that the comparative example 8 failed to improve the selectivity and yield of Mn/Na.sub.2WO.sub.4/SiO.sub.2. It indicates that the selection of the alkali metal precursor in the system 1 and the pH value of the system in the synthesis method are very important t technical parameters in the synthesis method.