WO2023060628A1 - 一种含有钨酸盐纳米团簇的复合氧化物、其制备方法和用途 - Google Patents

一种含有钨酸盐纳米团簇的复合氧化物、其制备方法和用途 Download PDF

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WO2023060628A1
WO2023060628A1 PCT/CN2021/124519 CN2021124519W WO2023060628A1 WO 2023060628 A1 WO2023060628 A1 WO 2023060628A1 CN 2021124519 W CN2021124519 W CN 2021124519W WO 2023060628 A1 WO2023060628 A1 WO 2023060628A1
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catalyst
ocm
tungstate
composite oxide
tungsten
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French (fr)
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范杰
周秋月
王均星
邹世辉
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浙江大学
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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    • B01J23/24—Chromium, molybdenum or tungsten
    • B01J23/30—Tungsten
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
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    • B01J23/32—Manganese, technetium or rhenium
    • B01J23/34—Manganese
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    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/85—Chromium, molybdenum or tungsten
    • B01J23/888—Tungsten
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    • B01J35/20—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state
    • B01J35/23—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state in a colloidal state
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    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
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    • B01J35/612—Surface area less than 10 m2/g
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2/00—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms
    • C07C2/76—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by condensation of hydrocarbons with partial elimination of hydrogen
    • C07C2/82—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by condensation of hydrocarbons with partial elimination of hydrogen oxidative coupling
    • C07C2/84—Preparation of hydrocarbons from hydrocarbons containing a smaller number of carbon atoms by condensation of hydrocarbons with partial elimination of hydrogen oxidative coupling catalytic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2523/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00
    • C07C2523/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • C07C2523/24—Chromium, molybdenum or tungsten
    • C07C2523/30—Tungsten
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C2523/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00
    • C07C2523/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • C07C2523/32—Manganese, technetium or rhenium
    • C07C2523/34—Manganese
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Definitions

  • the invention belongs to the field of catalysts, and in particular relates to a composite oxide containing tungstate nanoclusters, its preparation method and application.
  • Nanoclusters are ultrafine particles assembled from a few to thousands or even more atoms, and their diameter is usually less than 10nm (Journal of Molecular Catalysis A: Chemical 1999,145,1-44). In this scale range, matter undergoes the transition from microscopic atoms and molecules to macroscopic condensed matter materials, so nanoclusters often exhibit many unique properties that are different from macroscopic and microscopic. In the past few decades, nanoclusters have been widely studied, and their applications include quantum dots, sensors, biomedicine, catalysis, etc. (Nanoscale, 2021, 13, 6283-6340; Chemical Society Reviews 2020, 49, 6443-6514) .
  • WO x Due to the strong interaction between the support (such as zirconia, alumina) and WO x (the WOM bond can be formed, and M is the non-oxygen element in the support, such as Zr, Al, Si, Ti), WO x can form nano-clusters form is stable.
  • Composite oxides containing tungsten oxide nanoclusters are often used as solid acid catalysts, mainly because the W 6+ on the surface of WO x It exists in a distorted octahedral configuration (WO 6 ), which can form a Bronsted acidic site——H ⁇ + (WO 3 ) n ⁇ - (J.Catal.2004,227,479–491).
  • alkali metal tungstates such as Na 2 WO 4
  • alkali metal tungstates cannot be decomposed to form WO x by high-temperature calcination, and the presence of alkali metal ions will destroy the acidity of the compound, in order to prevent the tungsten-containing compound loaded on the carrier from containing alkali metal ions
  • the methods used in the prior art generally do not use alkali solution and alkali metal tungstate raw materials.
  • Tungsten-manganese catalysts are a class of classic OCM catalysts, and their composition includes alkali metals, tungsten, manganese and supports.
  • This type of catalyst was first developed by Li Shuben's research group at Lanzhou Institute of Chemical Physics in 1992 ("Molecular Catalysis", 1992, 6, 427-433), which usually uses sodium tungstate and manganese salt as precursors, and is loaded by impregnation and other methods On the silica gel, it is made after high-temperature roasting.
  • This type of catalyst has high OCM catalytic performance and good thermal stability, and has attracted widespread attention (ACS Catalysis 2019, 9, 5912-5928).
  • a typical tungsten-manganese catalyst composition is 1.9wt% Mn-5wt% Na2WO4/SiO2, wherein Mn element accounts for 1.9% of the catalyst mass, and Na2WO4 accounts for 5% of the catalyst mass.
  • methane space velocity 36000mL/g/h
  • CH4:O2:N2 3:1:2.6
  • the conversion rate of methane was 36.8%
  • the yield of C2 hydrocarbons reached 23.9%.
  • the OCM performance of tungsten-manganese catalysts can also be optimized by means of element doping, composition regulation, and reaction condition regulation (Applied Catalysis A: General 2012, 425, 53-61).
  • Tungsten-manganese catalysts are a class of classic OCM catalysts, and their composition includes alkali metals, tungsten, manganese and supports.
  • This type of catalyst was first developed by Li Shuben's research group at Lanzhou Institute of Chemical Physics in 1992 ("Molecular Catalysis", 1992, 6, 427-433), which usually uses sodium tungstate and manganese salt as precursors, and is loaded by impregnation and other methods On the silica gel, it is made after high-temperature roasting.
  • This type of catalyst has high OCM catalytic performance and good thermal stability, and has attracted widespread attention (ACS Catalysis 2019, 9, 5912-5928).
  • a typical tungsten-manganese catalyst composition is 1.9wt% Mn-5wt% Na 2 WO 4 /SiO 2 , where Mn accounts for 1.9% of the catalyst mass, Na 2 WO 4 accounts for 5% of the catalyst mass, and all non-oxygen elements in the catalyst
  • Mn accounts for 1.9% of the catalyst mass
  • Na 2 WO 4 accounts for 5% of the catalyst mass
  • all non-oxygen elements in the catalyst In terms of (Na, Mn, W, Si), the atomic percentage of W was 1 atomic %, and the atomic percentage of Na was 2 atomic %.
  • OCM oxidative coupling of methane
  • ethylene is one of the key technologies for the direct utilization of methane, and it is the technical basis for a new chemical route in the petrochemical industry to replace petroleum with natural gas (Energy Conversion and Management, 2019, 198, 111789; Chinese Journal of Catalysis 2021, 42, 1117-1125).
  • OCM reaction follows the "heterogeneous-homogeneous" catalytic reaction mechanism, and methane is activated on the surface of the catalyst to generate methyl radicals, which then undergo homogeneous coupling in the gas phase to produce products such as ethane and ethylene (J.Am. Chem. Soc.
  • An excellent catalyst for the controllable conversion of methyl radicals must meet the following conditions: 1) have a strong ability to adsorb methyl radicals, and be able to enrich the methyl radicals in the gas phase to the surface of the catalyst; 2) be enriched to the catalyst The methyl radicals on the surface can be converted into C 2 products with high selectivity; 3) the oxidation ability is weak (or it is difficult to activate oxygen), and the methyl radicals and C 2 products will not be converted into CO and CO 2 on the surface of the catalyst.
  • the present invention has carried out in-depth research and developed a nanocluster containing tungstate composite oxides as cocatalysts for the controllable coupling of methyl radicals.
  • the co-catalyst itself cannot be used as a catalyst alone to catalyze the OCM reaction, and does not have significant OCM activity, but when it is used as a co-catalyst in combination with traditional OCM catalysts, it can increase the C2 selectivity and C2 yield of traditional OCM catalysts by more than 1.2 times ( Figure 4).
  • the effect of the present invention is that, taking the composite oxide containing tungstate nanoclusters developed by the present invention as a cocatalyst, its cluster enrichment index reaches the necessary density, which can make the traditional OCM catalyst (such as 1.9wt% Mn-5wt%Na 2 WO 4 /SiO 2 ) has a selectivity of more than 70% and a yield of more than 30% in the oxidative coupling of methane (OCM) to ethane and ethylene.
  • OCM methane
  • the valences of the alkali metal A, the tungsten element W and the additive element M are all positive, and they are all realized by combining with the oxygen element whose valence is negative. charge balance.
  • the compound formed by alkali metal A, tungsten element W, additive element M and oxygen element can be written in oxide form.
  • Na 2 WO 4 can be written as Na 2 O ⁇ WO 3
  • ZrW 2 O 8 can be written as ZrO 2 ⁇ 2WO 3 .
  • Detection means the valence of alkali metal element A, tungsten element W, additive element M and oxygen element can be measured by X-ray photoelectron spectroscopy (XPS), and the crystal structure of the composite oxide can be measured by X-ray powder diffraction ( XRD) to confirm.
  • XPS X-ray photoelectron spectroscopy
  • XRD X-ray powder diffraction
  • the atomic percentage refers to the percentage of all elements in the catalyst measured by the atomic ratio of the dry catalyst analyzed by X-ray fluorescence spectroscopy, and the allowable test error is ⁇ 10%, preferably ⁇ 5%.
  • 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 general formula charge balance.
  • A Na
  • x 2
  • Na +1
  • W +6
  • O -2
  • all negative charges 2* y
  • A Mg
  • the particle diameter of the tungstate nanoclusters is ⁇ 10.0 nm, preferably ⁇ 5.0 nm, more preferably ⁇ 2.0 nm, and even more preferably ⁇ 1.0 nm.
  • the particle size of the tungstate nanoclusters refers to the average diameter of the nanoclusters; the detection method is: observe the composite oxide under a high-resolution transmission electron microscope, randomly select 100 tungstate nanoclusters, and The diameter is counted and the average value is taken.
  • the magnification of the high-resolution transmission electron microscope observation is 2 million to 30 million times, preferably 5 million to 10 million times.
  • the single-pass C2 selectivity refers to the C2 selectivity obtained by the feed gas passing through the catalyst bed once, and the C2 selectivity refers to the selectivity of the product ethane and ethylene, and its calculation method is:
  • C 2 selectivity (2*n C2H6 +2*n C2H4 )/(2*n C2H6 +2*n C2H4 +n CO +n CO2 +3*n C3H8 +3*n C3H6 );
  • the methane conversion rate, C2 selectivity and C2 yield mentioned in the follow-up content are all the results of a single-pass OCM reaction in a bed reactor in which methane and oxygen are fed together.
  • the invention provides a composite oxide containing tungstate nanoclusters, the composite oxide includes alkali metal element A, tungsten element W, additive element M and oxygen element O, and the alkali metal element A, tungsten Both the element W and the auxiliary element M form a complex with the oxygen element O,
  • the alkali metal element A is selected from any one or more of Li, Na, K, Mg, Ca, Sr, Ba,
  • the additive element M is selected from any one or more of Si, Zr, Ti, Al, La, Ce, Co,
  • 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%; the composite oxide
  • the content of oxygen element in the medium is the sum of the number of oxygen atoms required to meet the charge balance of alkali metal element A, tungsten element W, and M;
  • the tungstate nanocluster is composed of the alkali metal element A, the tungsten element W and the oxygen element O, and the general formula of the tungstate nanocluster is A x WO y , wherein, 0 ⁇ x ⁇ 2, y represents the number of oxygen atoms required to satisfy the general formula charge balance;
  • the number of the tungstate nanoclusters is ⁇ 3; preferably, the number of the tungstate nanoclusters is ⁇ 5, more preferably ⁇ 10, more preferably ⁇ 20;
  • the detection method of the cluster enrichment index the composite oxide is observed under a high-resolution transmission electron microscope, and the tungstate nanoparticles containing alkali metal element A, tungsten element W, and oxygen element O
  • the region of the cluster randomly select 5 regions of 10 ⁇ 10nm 2 , count the number of tungstate nanoclusters contained in the region, and take the average value; preferably, the magnification during the high-resolution transmission electron microscope observation
  • the multiple is 2 million to 30 million times, preferably 5 million to 10 million times; preferably, the particle size of the tungstate nanoclusters is ⁇ 10.0nm, preferably ⁇ 5.0nm, more preferably ⁇ 2.0nm, more preferably More preferably ⁇ 1.0nm;
  • the specific surface area of the composite oxide is 0.1-10g/m 2 , more preferably 0.5-5g/m 2 , further preferably 1-2g/m 2 ;
  • the three elements of alkali metal element A, tungsten element W, and oxygen element O in the tungstate nanocluster are uniformly distributed, and the uniform distribution means that any region in the tungstate cluster contains alkali metal element A , tungsten element W, oxygen element O;
  • the detection method of the uniform distribution is: observe the composite oxide under a high-resolution transmission electron microscope, and use X-ray energy spectrometer (EDS) surface scanning mode to scan the Tungstate nano-clusters are analyzed for composition, and 10 clusters are randomly selected, and any region in the clusters contains alkali metal element A, tungsten element W, and oxygen element O; more preferably, the high-resolution transmission electron microscope observation When the magnification is 2 million-30 million times, preferably 5 million-10 million times;
  • the tungsten element in the tungstate nanocluster exists in the form of four-coordinate tungstate, the four-coordination means that one tungsten atom has only four oxygen atoms bound to it; more preferably,
  • the detection method of the four-coordination structure is as follows: performing an X-ray fine structure spectrum test on the composite oxide, and collecting the L 1 -edge and L 3 -edge X-ray absorption near-edge structure spectra (XANES) of the tungsten element in the composite And extended X-ray absorption spectrum fine structure (EXAFS), through qualitative analysis and data fitting to get the coordination number of tungsten atoms;
  • the particle size change value of tungstate nanoclusters is ⁇ 1 ⁇ 20%, more preferably ⁇ 1 ⁇ 10%; the calculation formula is as follows:
  • the cluster enrichment index change value of tungstate nanoclusters ⁇ 2 ⁇ 20%; further preferably ⁇ 2 ⁇ 10%; the calculation formula is as follows:
  • 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 is expressed as NaWZr or NaWAl respectively
  • the tungstate Nanoclusters are composed of alkali metal elements Na, tungsten elements W and oxygen elements O.
  • the general formula of the tungstate nanoclusters is Na x WO y , 0 ⁇ x ⁇ 2, y represents the charge balance of the general formula the number of oxygen atoms required;
  • 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 additive element M is 20%-94%;
  • the atomic percentage of Na in the composite oxide is 10%-65%, more preferably 15%-50%; more preferably 10%-60% atomically, further preferably 20%-50%, further preferably is 30%-40%; the atomic percentage of the tungsten element W is 2%-55%, more preferably 5%-50%, further preferably 10%-40%, further preferably 20%-30%;
  • the atomic percentage of the agent element Zr or Al is above 22%-92%, more preferably 25%-90%, preferably 30%-80%, further preferably 40%-70%, further preferably 50%-60% ;
  • the molar ratio of W:Zr in the composite oxide ⁇ 0.1; preferably, 0.2 ⁇ W:Zr molar ratio ⁇ 100; more preferably 0.23 ⁇ W:Zr molar ratio ⁇ 10; more preferably 0.3 ⁇ W: The molar ratio of Zr ⁇ 1; more preferably 0.4 ⁇ W:Zr molar ratio ⁇ 0.5.
  • the present invention also provides a method for preparing a composite oxide containing tungstate nanoclusters, comprising the following steps:
  • the solution system 2 When the solution system 2 is stirred, the solution system 1 is completely added to the solution system 2 within 2-200 minutes until the turbid liquid appears, and the turbid liquid is continuously stirred 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, the The speed of rapid stirring is 500-1000 rpm, more preferably 750-900 rpm; preferably, the stirring time is 10 minutes-2 hours, more preferably the stirring time is 30 minutes-1 hour;
  • step 2) The product obtained in step 2) is directly removed from the solvent without any treatment, and then the obtained solid is dried to obtain a dried solid product.
  • the non-treatment refers to any washing, centrifugation, and filtration steps;
  • the method for removing the solvent is to dry the solvent.
  • the method for drying is to place the product obtained in step 2) in an atmosphere with a temperature of 30-50° C. until the solution is volatilized; preferably, the temperature is 40°C;
  • the temperature for drying the solid is 60-100°C, more preferably 80-90°C; preferably, the drying time is more than 12 hours, more preferably more than 24 hours;
  • step 4) Calcining the solid product obtained in step 3) to prepare a composite oxide containing tungstate nanoclusters, preferably, the temperature of the calcination is 700-900°C, more preferably 750-850°C, more preferably is 800 selections; the roasting time is 3-8 hours, preferably 4-6 hours; the heating rate of the roasting is 2-10°C/min, more preferably 3-5°C/min;
  • the preparation method of the solution system 1 is: dissolving the alkali metal element precursor containing the compound raw material of the element in an appropriate amount of water, and fully stirring to form a transparent solution, that is, to obtain the solution system 1, and the pH of the transparent solution is greater than 7 , more preferably pH ⁇ 10;
  • the preparation method of the solution system 2 is selected from any of the following: a) mixing the tungsten element precursor, the additive element precursor and an appropriate amount of water and stirring rapidly to form a transparent solution, that is, to obtain the solution system 2-1; b) Mix the tungsten element precursor, the additive element precursor and an appropriate amount of alcohol and stir rapidly to form a transparent solution, which is the solution system 2-2;
  • the ratio of the alkali metal element precursor, tungsten element precursor, and auxiliary element precursor added in solution system 1 and solution system 2 conforms to the following formula:
  • 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%;
  • the atomic percentage of the alkali metal element A in the composite oxide is 10%-65%, more preferably 15%-50%; more preferably 10%-60%, further 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%, further preferably 20%-30% %; the atomic percentage of auxiliary element M is 22%-92%, more preferably 25%-90%, preferably 30%-80%, further preferably 40%-70%, further preferably 50%-60% %
  • 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 solution system 2-1 and 2-
  • the concentration of the tungsten element precursor in 2 is 1-30wt%, preferably 5-25wt%, more preferably 10-20wt%; preferably, the auxiliary element precursor in the solution system 2-1 and 2-2
  • the concentration is 1-50wt%, preferably 10-40wt%, more preferably 20-35wt%;
  • the alkali metal element precursor in the preparation method of the solution system 1 is selected from lithium hydroxide, sodium hydroxide, lithium carbonate, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, magnesium acetate , any one or more of calcium hydroxide, calcium acetate, strontium hydroxide and barium hydroxide;
  • the auxiliary element precursor in the preparation method of the solution system 2-1 is selected from sodium silicate, zirconyl nitrate, zirconium nitrate, zirconium oxychloride, di(acetate-O) zirconium oxide, lemon Any one or more of zirconium oxide, titanium nitrate, aluminum nitrate, lanthanum nitrate, lanthanum acetate, lanthanum chloride, cerium nitrate, cerium acetate, cerium chloride, cobalt nitrate, and cobalt acetate; Sodium tungstate, cesium tungstate, tungsten ethylate, ammonium tungstate oxide, ammonium tungstate oxide hydrate, strontium tungstate, magnesium tungstate, barium tungstate, ammonium tungstate pentahydrate, ammonium metatungstate hydrate, tungstic acid Any one or more of calcium, barium tungstate, strontium tungstate;
  • the tungsten element precursor in the preparation method of solution system 2-2 is selected from any one or both of sodium tungstate and tungsten chloride;
  • the auxiliary element precursor is selected from tetraethyl orthosilicate, zirconium nitrate, Zirconium n-butoxide, zirconium oxynitrate, zirconium oxychloride, zirconium di(acetate-O)oxyoxide, zirconium citrate, tetrabutyl titanate, aluminum sec-butoxide, aluminum isopropoxide, lanthanum nitrate, nitric acid Any one or more of aluminum, cerium nitrate, and cobalt nitrate;
  • the alcohol solution is selected from any one or more of methanol, ethanol, propanol, and butanol.
  • the alkali metal element precursor is a sodium element precursor
  • the additive element precursor is selected from a zirconium element precursor or an aluminum element precursor
  • the prepared composite oxide containing tungstate nanoclusters The substance is NaWZr or NaWAl
  • the tungstate nanocluster is composed of alkali metal element Na, tungsten element W and oxygen element O
  • the general formula of the tungstate nanocluster is Na x WO y , 0 ⁇ x ⁇ 2, y represents the number of oxygen atoms required to satisfy the general charge balance;
  • 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;
  • the auxiliary element precursor in the preparation method of the solution system 2-1 is selected from zirconyl nitrate, zirconium nitrate, zirconium oxychloride, di(acetato-O) zirconium oxyoxide, zirconium citrate, nitric acid Any one or more of aluminum;
  • the tungsten element precursor is selected from sodium tungstate, cesium tungstate, tungsten ethoxide, ammonium tungstate oxide, ammonium tungstate oxide hydrate, strontium tungstate, magnesium tungstate, barium tungstate , Any one or more of ammonium tungstate pentahydrate, ammonium metatungstate hydrate, calcium tungstate, barium tungstate, strontium tungstate;
  • the tungsten element precursor in the solution system 2-2 is selected from any one or both of sodium tungstate and tungsten chloride;
  • the auxiliary element precursor is selected from zirconium nitrate, zirconium n-butoxide, oxygen nitrate Any one or more of zirconium, zirconium oxychloride, di(acetate-O) zirconium oxyoxide, zirconium citrate, aluminum sec-butoxide, aluminum isopropoxide, aluminum nitrate;
  • the alcoholic solution is selected from methanol, Any one or more of ethanol, propanol, butanol;
  • the molar ratio of 0 ⁇ Na:W ⁇ mole, preferably, 0.1, the molar ratio of W methanol ⁇ 4, more preferably 0.8 step is preferably the molar ratio of alcohol ⁇ molar ratio; more preferably 1.0 step is preferably Molar ratio of alcohol ⁇ molar ratio; more preferably 1.5, preferably molar ratio of alcohol ⁇ molar ratio; further preferably 1.4 step, preferably molar ratio of alcohol ⁇ molar ratio;
  • the auxiliary element precursor in the preparation method of the solution system 2-2 is zirconium n-butoxide, and the tungsten element precursor is tungsten chloride; more preferably, the molar ratio of the tungsten element to the zirconium element ⁇ 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% to 60%, preferably 10% to 50% , more preferably 15% to 40%;
  • the auxiliary element precursor in the preparation method of the solution system 2-2 is aluminum isopropoxide
  • the tungsten element precursor is tungsten chloride
  • the molar ratio of the tungsten element to the aluminum element is ⁇ 1:9 , preferably ⁇ 2:9, more preferably ⁇ 3:9
  • the solution system 1 is an aqueous NaOH solution, and the mass percentage of NaOH is 1% to 60%, preferably 10% to 50%, more preferably 15% ⁇ 40%;
  • the auxiliary element precursor in the preparation method of the solution system 2-2 is zirconium n-butoxide
  • the tungsten element precursor is sodium tungstate
  • 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 1% to 60% by mass of KOH, preferably 10% to 50%, more preferably 15% to 40%;
  • the auxiliary element precursor in the preparation method of the solution system 2-2 is aluminum isopropoxide
  • the tungsten element precursor is sodium tungstate
  • 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 1% to 60% by mass of KOH, preferably 10% to 50%, more preferably 15% to 40%.
  • the present invention also provides a cocatalyst, the cocatalyst comprising the composite oxide containing tungstate nanoclusters;
  • the co-catalyst cannot be used as a catalyst alone to catalyze the oxidative coupling of methane (OCM) reaction; preferably, the co-catalyst does not have significant OCM activity; where preferably, the detection of no significant OCM activity
  • OCM oxidative coupling of methane
  • the method is as follows: in a bed reactor in which methane and oxygen are fed together, when the gas-hourly space velocity of the catalyst is greater than or equal to 20000mL/g/h, the temperature of the catalyst bed is 800°C and below, and the reaction pressure is 1 When used as a methane oxidation catalyst at atmospheric pressure, the single-pass C2 yield is not higher than 5%; preferably, the yield is quantitatively measured by gas chromatography.
  • the present invention also provides a catalyst composition, said catalyst composition comprising the composite oxide described in the right and at least one catalyst OCM catalyst with OCM activity;
  • having OCM activity means that it can be used alone as a catalyst to catalyze the OCM reaction; preferably, the meaning having OCM activity is: in a bed reactor in which methane and oxygen are fed in together, when the catalyst is in When the gas-hourly space velocity is greater than or equal to 20000mL/g/h, the catalyst bed temperature is 800°C and below, and the reaction pressure is 1 atmosphere, it is used as a methane oxidative coupling catalyst, which has a C2 single-pass yield greater than 5%;
  • the OCM catalyst has significant OCM activity, which means: in a bed reactor in which methane and oxygen are fed together, when the gas-hourly space velocity of the catalyst is greater than or equal to 20000mL/g/h, the catalyst bed When the temperature is 800°C and below and the reaction pressure is 1 atmosphere, it is used as a methane oxidative coupling catalyst, which has a C2 single-pass yield greater than 15%;
  • the mass ratio of the OCM catalyst to the composite oxide is 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 quality is 2.0 ⁇ 4.0: 1.0;
  • the yield is quantitatively measured by gas chromatography
  • 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 tungsten Manganese catalyst, lanthanum oxide, samarium oxide, Li/MgO, Ca/CeO 2 ; preferably, the tungsten manganese catalyst is Mn-Na 2 WO 4 /SiO 2 ;
  • the distance between the OCM catalyst and the composite oxide is ⁇ 3mm;
  • the catalyst composition is compounded by physically mixing the composite oxide and OCM catalyst ;
  • the OCM catalyst is a compound comprising 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 Al, Si, Any one or more of Ti, Zr, C, N, further more preferably, the fifth component element is selected from any one or more of Al, Si, Ti, more preferably, all 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;
  • 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. .%;
  • 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.%.
  • 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.%.
  • the catalyst also includes additives; more preferably, the additives are selected from any one of heat dissipation aids, mass transfer aids, molding aids, enhanced wear agents, dispersants, stabilizers, etc. or more.
  • the selectivity and yield of the OCM reaction catalyzed by the catalyst composition are all increased by more than 1.2 times compared to using OCM catalyst alone;
  • the catalyst composition can realize C2 selectivity ⁇ selectivity and C2 single-pass yield ⁇ pass yield in the OCM bed reactor with methane and oxygen co-intake; more preferably, the The catalyst composition can realize C2 selectivity ⁇ selectivity and C2 single-pass yield ⁇ 40% in the OCM bed reactor in which methane and oxygen are fed in together; more preferably, the catalyst composition is in methane and In the OCM bed reactor with oxygen co-inflow, it is possible to achieve C 2 selectivity ⁇ selectivity and C 2 single-pass yield ⁇ 45%.
  • the OCM catalyst is Mn/Na 2 WO 4 /SiO 2
  • the composite oxide is Na, W, Zr composite oxide NaWZr; preferably, the mass of the OCM catalyst and the composite oxide
  • the ratio is 4:1-0.5:1; more preferably 2:1-1:1; preferably, the catalyst composition can realize C2 selectivity in the OCM bed reactor in which methane and oxygen are fed together ⁇ 70% and C 2 single-pass yield ⁇ 35%; more preferably, the catalyst composition can realize C 2 selectivity ⁇ selectivity and C 2 Single-pass yield ⁇ 40%; more preferably, the catalyst composition can realize C2 selectivity ⁇ selectivity and C 2 single-pass yield ⁇ 45% in the OCM bed reactor where methane and oxygen are fed together ;
  • the catalyst composition is in an OCM bed reactor in which methane and oxygen are fed together, and the C2 selectivity of the catalyst composition Mn/Na 2 WO 4 /SiO 2 -NaWZr can be improved to Mn/Na 2 WO 4 /SiO 2 is 1.3 times, and its C 2 single-pass yield is 1.2 times that of Mn/Na 2 WO 4 /SiO 2 .
  • the OCM catalyst is La 2 O 3
  • the composite oxide is Na, W, and Zr composite oxide NaWZr
  • the mass ratio of the OCM catalyst to the composite oxide is 4:1-1: 1; more preferably 2:1-1:1;
  • the C 2 selectivity of La 2 O 3 -NaWZr can be increased to 1.3 times that of La 2 O 3 , and its C 2 one-way yield is 1.2 times that of La 2 O 3 .
  • the OCM catalyst is Sm 2 O 3
  • the composite oxide is Na, W, and Zr composite oxide NaWZr
  • the mass ratio of the OCM catalyst to the composite oxide is 4:1-1: 1; more preferably 2:1-1:1;
  • the C 2 selectivity of Sm 2 O 3 -NaWZr can be increased to 2.0 times that of Sm 2 O 3 , And its C 2 one-way yield is 1.8 times that of Sm 2 O 3 .
  • the OCM catalyst is Li/MgO
  • the composite oxide is Na, W, and Zr composite oxide NaWZr
  • the mass ratio of the OCM catalyst to the composite oxide is 4:1-1:1 ; More preferably 2:1-1:1;
  • the catalyst composition Li/MgO-NaWZr is in the OCM bed reactor of methane and oxygen co-intake, the C2 selectivity of Li/MgO-NaWZr can be promoted as 2.0 times of Li/MgO, and its The C 2 single pass yield is 1.45 times that of Li/MgO.
  • the OCM catalyst is Ca/CeO 2
  • the composite oxide is Na, W, Zr composite oxide NaWZr
  • the mass ratio of the OCM catalyst to the composite oxide is 4:1-1: 1; more preferably 2:1-1:1;
  • the catalyst composition Ca/CeO 2 -NaWZr is in the OCM bed reactor in which methane and oxygen are fed together, and the C 2 selectivity of Ca/CeO 2 -NaWZr can be increased to 1.3 times that of Ca/CeO 2 , and its C 2 one-way yield is 1.5 times that of Ca/CeO 2 ;
  • the catalyst composition is Mn-Na 2 WO 4 /SiO 2 -NaWAl, wherein the OCM catalyst is Mn-Na 2 WO 4 /SiO 2 , and the composite oxide is Na, W, Al Composite oxide NaWAl, the mass ratio of the OCM catalyst to the composite oxide is 4:1-1:1; more preferably 2:1-1:1;
  • the catalyst composition Mn-Na 2 WO 4 /SiO 2 -NaWAl can realize C 2 selectivity ⁇ 70% and C 2 single-pass yield ⁇ 35%; more preferably, said catalyst composition is in the OCM bed reactor of methane and oxygen co-intake, can realize C 2 selectivity ⁇ selectivity and C 2 single-pass yield ⁇ 40%; more preferably , the catalyst composition can realize C2 selectivity ⁇ selectivity and C2 single-pass yield ⁇ 45% in the OCM bed reactor in which methane and oxygen are fed together;
  • the C2 selectivity of Mn-Na 2 WO 4 -NaWAl can be increased to 1.3 times that of Mn-Na 2 WO 4 in the OCM bed reactor in which methane and oxygen are fed together by the catalyst composition, and Its C 2 yield per pass is 1.2 times that of Mn/Na 2 WO 4 /SiO 2 .
  • the OCM catalyst is La 2 O 3
  • the composite oxide is Na, W, Al composite oxide NaWAl
  • the mass ratio of the OCM catalyst to the composite oxide is 4:1-1: 1; more preferably 2:1-1:1;
  • the catalyst composition La 2 O 3 -NaWAl is in an OCM bed reactor in which methane and oxygen are fed together, the C 2 selectivity of La 2 O 3 -NaWAl can be increased to 1.3 times that of La2O3, and its The one-way yield of C 2 is 1.2 times that of La 2 O 3 .
  • the OCM catalyst is Sm 2 O 3
  • the composite oxide is Na, W, and Al composite oxide NaWAl
  • the mass ratio of the OCM catalyst to the composite oxide is 4:1-1: 1; more preferably 2:1-1:1;
  • the catalyst composition Sm 2 O 3 -NaWAl is in the OCM bed reactor in which methane and oxygen are fed together, the C 2 selectivity of Sm 2 O 3 -NaWAl can be increased to 1.2 times that of Sm 2 O 3 , And its C 2 one-way yield is 1.5 times that of Sm 2 O 3 .
  • the OCM catalyst is Li/MgO
  • the composite oxide is NaWAl
  • the mass ratio of the OCM catalyst to the composite oxide is 4:1-1:1 ; More preferably 2:1-1:1;
  • the catalyst composition Li/MgO-NaWAl is in the OCM bed reactor of methane and oxygen co-intake, the C2 selectivity of Li/MgO-NaWAl can be promoted as 1.7 times of Li/MgO, and its The C 2 single-pass yield is 1.8 times that of Li/MgO.
  • the OCM catalyst is Ca/CeO 2
  • the composite oxide is a composite oxide NaWAl of Na, W, Al
  • the mass ratio of the OCM catalyst to the composite oxide is 4:1-1: 1; more preferably 2:1-1:1;
  • the catalyst composition Ca/CeO 2 -NaWAl is in an OCM bed reactor in which methane and oxygen are fed together, the C2 selectivity of Ca/CeO 2 -NaWAl can be increased to 1.3 times that of Ca/CeO 2 , And its C 2 one-way yield is 1.6 times that of Ca/CeO 2 .
  • the present invention also provides a use of the catalyst composition in a chemical reaction; preferably, the chemical reaction is a free radical transformation reaction; more preferably, the chemical reaction is a methane oxidation coupling catalytic reaction.
  • the methane oxidative coupling catalytic reaction is a process in which under the action of a catalyst, the carbon-hydrogen bond of methane is broken, the released hydrogen reacts with oxygen to generate water, and at the same time, a carbon-carbon bond is formed to prepare hydrocarbons with carbon two or more.
  • the methane oxidative coupling catalytic reaction takes methane and oxygen as feed gas, and reacts on a bed reactor, and its products include C 2 hydrocarbons, carbon oxides and C 3 hydrocarbons;
  • the raw material gas also includes a diluent gas; more preferably, the diluent gas is selected from at least one of nitrogen, helium, and argon;
  • the ratio of methane and oxygen is 1.0-20.0, preferably 2.0-6.0, more preferably 2.0-5.0;
  • the pressure of the raw material gas is 0.1-20.0MPa, preferably 1.0-8.0MPa, more preferably 2.0-6.0MPa;
  • the reaction temperature is 600-900°C, preferably 700-850°C;
  • the space velocity of the reaction is 500-50000h -1 , preferably 1000-35000h -1 .
  • the effect of the present invention is that, by adopting the composite oxide containing tungstate nanoclusters of the present invention, the cluster enrichment index reaches the necessary density, which can make methane oxidative coupling (OCM) to produce ethane and ethylene
  • OCM methane oxidative coupling
  • the inventor's research it was unexpectedly found that in the sodium tungstate-containing catalyst prepared by the co-precipitation method using an alkaline solution such as NaOH, sodium tungstate exists in the form of nano-clusters, and the sodium tungstate clusters satisfy the Cluster enrichment index (refers to the number of tungstate nanoclusters ⁇ 3 in any 10 ⁇ 10nm area containing the tungstate nanoclusters).
  • This catalyst containing sodium tungstate nanoclusters itself does not have OCM activity (in the bed reactor of methane and oxygen co-intake, when the gas-hourly space velocity of the catalyst is greater than or equal to 20000mL/g/h, the catalyst When the bed temperature is 800°C and below and the reaction pressure is 1 atmosphere, it is used as a methane oxidative coupling catalyst, and its C2 single-pass yield is not higher than 5%), but it can be used as a cocatalyst to improve the C2 selection of traditional OCM catalysts sex and yield. This prompted the inventors to further study composite oxides containing tungstate nanoclusters of different compositions as cocatalysts, and further complete the present invention. The research of the present invention is obviously different from the research of traditional tungsten-manganese catalysts, and there is no similar research reported in other literatures.
  • Figure 1 shows the OCM reaction route diagram and the corresponding Gibbs free energy diagram.
  • Fig. 2 is a schematic diagram of a bed reactor in which methane and oxygen are fed together.
  • Figure 3 (a) OCM reaction network diagram (Beck, B. et al. Catal. Today 2014, 228, 212), (b) C2 yield obtained by kinetic simulation and methyl radical formation rate (Weff/Wtherm) Correlation (literature Arutyunov, V. et al. J. Mol. Catal. A: Chem. 2017, 426, 326).
  • FIG. 4 is a graph showing the experimental results of the NaMnW-NaWZr system obtained in Example 1.
  • FIG. 4 is a graph showing the experimental results of the NaMnW-NaWZr system obtained in Example 1.
  • Figure 5 is a structural characterization diagram of NaWZr.
  • HAADF high-angle annular dark-field
  • BF bright-field
  • Example 6 is an energy dispersive spectroscopy (EDS) analysis diagram of Example 1.
  • FIG. 7 is the HAADF-STEM image of Example 1. Among them, some NaxWOy clusters are marked with green squares.
  • FIG. 8 is the EDSmapping diagram of Embodiment 1.
  • Fig. 9 is the Raman spectrogram of embodiment 1 (compared with commercially available ZrO2). Among them, the characteristic Raman band at about 925cm-1 can be attributed to the W-O-Zr bond.
  • Fig. 10 is the Zr K-edge XANES spectrogram of embodiment 1. Compared with ZrO2, the Zr K-edge of NaWZr is obviously blue-shifted, indicating that Zr transfers charge to W through the Zr-O-W bond.
  • Figure 11 shows representative BF and HAAD FSTEM images of NaWZr with a W:Zr molar ratio of 1:9. Among them, some atomically dispersed and aggregated W species are marked by red circles; NaxWOy clusters are marked by green squares.
  • Figure 12 is a representative HAADFSTEM 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.
  • Figure 13 shows representative BF and HAAD FSTEM images of NaWZr with a W:Zr molar ratio of 4:9. Among them, some NaxWOy clusters are marked with green squares.
  • Figure 14 shows representative BF and HAAD FSTEM images of NaWZr with a W:Zr molar ratio of 5:9. Among them, some NaxWOy clusters are marked with green squares.
  • Figure 15 is a typical bright-field (BF) and high-angle annular dark-field HAADF-STEM image of NaWZr with a W:Zr molar ratio of 0.5:9. Among them, some atomically dispersed species are marked by red circles.
  • Figure 16 is a typical high angle annular dark field (HAADF) STEM image of NaWAl catalyst.
  • Figure 17 is the STEM spectrum of Na2WO4 in the form of large particles.
  • the Mn/Na 2 WO 4 /SiO 2 catalyst can be purchased commercially, or can be synthesized by wet impregnation method referring to literature ("Molecular Catalysis" 1992, 6, 427-433). The specific synthesis steps are as follows: Usually, an aqueous solution of manganese (II) nitrate (50 wt.%) and hydrated sodium tungstate are dissolved in an appropriate amount of deionized water. Under constant stirring, a commercially available SiO2 support with a surface area of 200 m2 /g was added to the above solution, followed by drying at 105 °C overnight.
  • the ratio of manganese nitrate and sodium tungstate is such that the mass percentage of manganese (Mn) element in Mn/Na 2 WO 4 /SiO 2 catalyst is 2wt.%, sodium tungstate (Na 2 WO 4 ) in Mn/Na 2 WO 4 The mass percentage of SiO 2 catalyst is 5wt%. Afterwards, the dried solid was calcined at 800 °C for 4 hours to obtain the final catalyst.
  • the composition of the sample is measured by the XRF-1800 X-ray fluorescence spectrometer of Shimadzu Corporation of Japan; the specific surface area of the sample is measured by the N2 adsorption-desorption method, and the instrument used is the ASAP2020 full-automatic physicochemical adsorption of the U.S. MICROMERITICS company
  • 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 distributions were obtained on a spherical aberration-corrected Titan Chemi-STEM transmission electron microscope with an accelerating voltage of 200kV Surface scanning analysis map (EDS Mapping).
  • the Raman spectra of the catalysts were measured at room temperature on a Horiba-Jobin-Yvon with visible laser excitation (532 nm).
  • the X-ray absorption fine structure (XAFS) spectrum of the sample W L edge was measured at the 7-BM beamline of the National Synchrotron Radiation Light Source II at Brookhaven National Laboratory, USA.
  • 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 plug of quartz wool in the constant temperature 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.
  • CH 4 , O 2 and N 2 were fed into the reactor through a mass flow controller in a ratio of 3:1:2.7.
  • the total flow rate was 67 mL/min.
  • the product was analyzed by online gas chromatography equipped with FID detector and TCD detector.
  • CH4 conversion and product selectivity were calculated based on the total number of carbon atoms of the inlet and outlet gases.
  • the outlet gas was corrected for gas expansion using N2 as internal standard.
  • C2 products include C2H4 and C2H6.
  • the EDS Mapping of the catalyst is shown in Figure 8. It can be seen from the figure that Na, W, and Zr elements are evenly distributed in the catalyst.
  • the WL 3 -edge XANES spectrum of the catalyst is shown in Fig. 5 f, the WL 3 -edge XANES spectrum of the catalyst is very similar to the WL 3 -edge XANES spectrum of the commercially available Na 2 WO 4 crystal, and is similar to the WL 3 -edge XANES spectrum of WO 3
  • the XANES spectra of WL 3 -edge are quite different, indicating that W in this catalyst mainly exists in the form of four coordination.
  • the Raman of the catalyst is shown in Figure 9. Compared with pure ZrO 2 , a new characteristic peak can be observed at 925cm in the Raman spectrum of the catalyst, which can be attributed to the characteristic signal of WO-Zr .
  • the Zr K-edge XANES spectrum of this catalyst is shown in Fig. 10. Compared with ZrO2 , the Zr K-edge of NaWZr is obviously blue-shifted, indicating that Zr transfers charge to W through Zr-OW bond.
  • Embodiments 2-17 were synthesized with reference to the method described in Example 1, and the parameters in the synthesis process were slightly different from those in Example 1.
  • the specific synthesis parameters and structural parameters are shown in Table 1.
  • embodiment 2 The difference between embodiment 2 and embodiment 1 is that the additive element used in embodiment 2 is Al.
  • the high-resolution transmission electron microscope picture of the catalyst is shown in Figure 16, from which it can be clearly seen that the catalyst is rich in nano-clusters. According to the size of the nano-clusters in the statistics figure, it is found that the average particle size of the Na x WO y nano-clusters in the catalyst is 0.9nm. The number of Na x WO y nanoclusters in the 10*10nm 2 area was further counted, and it was found that there were 21 of them.
  • Example 1 By analyzing Example 1 and Example 8, it can be known that the tungsten source is chloride or sodium tungstate, and the composite oxide containing tungstate nanoclusters can be obtained, and the Na x WO y nanoclusters in these composite oxides
  • the average particle size is 0.8-0.9nm, and the number of Na x WO y nano-clusters in the area of 10* 10nm2 is ⁇ 21.
  • the solvent of system 2 is methanol, ethanol, propanol, butanol, and a composite oxide containing tungstate nanoclusters can be obtained.
  • the solvent of system 2 is methanol, ethanol, propanol, butanol, and a composite oxide containing tungstate nanoclusters can be obtained.
  • Na x WO The average particle size of the y nanocluster is 0.8-0.9nm, and the number of Na x WO y nanoclusters in the area of 10* 10nm2 is ⁇ 21.
  • the STEM pictures of Examples 9-13 correspond to Figures 11-15 respectively.
  • the difference between Examples 9-13 and Example 1 is that the molar ratio of W:Zr in the system is different.
  • the molar ratio of W:Zr is 1:9.2:9,3:9,4 :9, 5:9 and 0.5:9
  • composite oxides containing tungstate nanoclusters can be obtained.
  • W:Zr molar ratio will affect the enrichment index of Na x WO y nanoclusters.
  • the number of tungstate nanoclusters in the area of 10*10nm 2 in Examples 1 and 9-13 and its W:Zr molar ratio are plotted, as shown in Figure 5e.
  • Examples 17-36 are the catalytic tests of OCM catalyst , co-catalyst and catalyst composition.
  • Example 17 is the catalytic result after the cocatalyst synthesized by the preparation method described in Example 1 and the classic Mn/Na 2 WO 4 /SiO 2 catalyst were tested according to the above conditions. It can be seen that the catalyst composition exhibits excellent High C2 selectivity and yield.
  • Example 29 By analyzing the catalytic performance of Example 29 (Table 2), it can be concluded that when the molar ratio of W:Zr is 0.5:9, the performance of the synthesized cocatalyst is inhibited after mixing with the classic Mn/Na 2 WO 4 /SiO 2 catalyst, It is because its W content is too low to obtain nanoclusters so it shows lower performance.
  • Comparative Example 1 is WO 3 /ZrO 2 . Its preparation method is the same as that of Example 1, the only difference being that no alkali metal Na is added during the synthesis of Comparative Example 1. The results of transmission electron microscopy showed that the nanoclusters in the catalyst were tungsten oxide rather than sodium tungstate.
  • the C2 selectivity of Mn/Na 2 WO 4 /SiO 2 is 48.4%, and the C2 yield is 8.1%, while the C2 selectivity of Mn/Na 2 WO 4 /SiO 2 and the catalyst composition of Comparative Example 1 is 46.8%, C2 yield was 7.6%.
  • Comparative Example 1 not only fails to increase the selectivity and yield of Mn/Na 2 WO 4 /SiO 2 but inhibits it, which shows that the component that really acts as a cocatalyst is not the tungsten oxide nanoclusters, But tungstate nanoclusters.
  • alkali metal elements are essential.
  • the catalyst was synthesized by the same preparation method as in Example 1, the only difference being that the additive element M was not added during the synthesis of Comparative Example 2. In this case, after system 1 was added to system 2, it was still a clear solution, and the corresponding solid catalyst could not be prepared. From this result, it can be seen that auxiliary elements are crucial for the synthesis of tungstate nanoclusters.
  • the catalyst was synthesized by the same preparation method as in Example 1, the only difference being that no tungsten element was added during the synthesis of Comparative Example 3.
  • Comparative Example 3 obtained in this case does not contain NaxWOy nanoclusters.
  • Comparative Example 3 not only fails to increase the selectivity and yield of Mn/Na 2 WO 4 /SiO 2 but inhibits it, which indicates that tungsten is an indispensable active component in the cocatalyst.
  • the catalyst was synthesized by the same preparation method as in Example 1, the only difference being that the chloride was replaced by molybdenum chloride during the synthesis of Comparative Example 4, that is, the W element in Example 1 was replaced by Mo.
  • the C2 selectivity of Mn/Na 2 WO 4 /SiO 2 is 48.4%, and the C2 yield is 8.1%, while the C2 selectivity of Mn/Na 2 WO 4 /SiO 2 and the catalyst composition of Comparative Example 4 is 48.2%, C2 yield was 8.0%. It can be seen from the above results that Comparative Example 4 does not improve the selectivity and yield of Mn/Na 2 WO 4 /SiO 2 , which indicates that tungsten is an indispensable active component in the cocatalyst.
  • the catalyst was synthesized using the same preparation method as in Example 1, the only difference being that System 1 was completely added to System 2 within 1 min when Synthesizing Comparative Example 5.
  • Comparative Example 5 The high-resolution electron microscope picture of Comparative Example 5 is shown in Figure 17. It can be seen from the figure that the sodium tungstate in Comparative Example 5 mainly exists in the form of large sodium tungstate particles (>10nm) rather than nano-clusters. It shows that the addition rate of system 1 into system 2 has an important influence on the structure of the catalyst. The slow addition of system 1 (addition time ⁇ 2 minutes) to system 2 can make the tungsten element precursor and auxiliary element precursor slowly hydrolyze and cross-link under the action of alkali metal, thus contributing to the formation of tungstate nanoclusters. Adding too fast will make the auxiliary element precursor hydrolyze rapidly, so that the tungstate cannot be uniformly dispersed in the formed oxide species of the auxiliary element.
  • the C2 selectivity of Mn/Na 2 WO 4 /SiO 2 is 48.4%, and the C2 yield is 8.1%, while the C2 selectivity of Mn/Na 2 WO 4 /SiO 2 and the catalyst composition of Comparative Example 5 is 47.5%, C2 yield was 7.6%. It can be seen from the above results that Comparative Example 5 did not improve the selectivity and yield of Mn/Na 2 WO 4 /SiO 2 , which indicates that tungstate nanoclusters are the active structure of the cocatalyst, and the dropping rate of System 1 will decrease. The structure of tungstate that affects the cocatalyst species affects its reaction performance.
  • the catalyst was synthesized by the same preparation method as in Example 1, the only difference being that the solvent used in system 2 was acetone when synthesizing Comparative Example 6.
  • the catalyst was synthesized by the same preparation method as in Example 1, the only difference being that in the synthesis of Comparative Example 8, the precursor of the alkali metal element used in System 1 was sodium nitrate instead of NaOH. In this case, the pH of System 1 is neutral.

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Abstract

一种甲烷氧化偶联反应中的助催化剂及其催化剂组合物，以及在催化化学反应中的应用，属于催化剂领域。含有钨酸盐纳米团簇的复合氧化物，包含碱金属元素A、钨元素W、助剂元素M以及氧元素O，且所述碱金属元素A、钨元素W、助剂元素M均与氧元素O形成复合物。该复合氧化物作为助催化剂可显著提高在甲烷和氧气共进气的OCM床层反应器中反应的C2选择性和C2收率，具有很大应用价值。

Description

一种含有钨酸盐纳米团簇的复合氧化物、其制备方法和用途 技术领域：
本发明属于催化剂领域，具体涉及一种含有钨酸盐纳米团簇的复合氧化物、其制备方法和用途。
背景技术：
纳米团簇是几个到上千个乃至更多原子聚集而成的超微粒子，其直径通常小于10nm(Journal of Molecular Catalysis A:Chemical 1999,145,1-44)。在这一尺度范围下，物质经历着从微观原子分子向宏观凝聚态材料的转变，因此纳米团簇往往呈现出许多和宏观、微观都不相同的独特性质。过去几十年内，纳米团簇受到人们的广泛研究，其应用领域包括量子点、传感器、生物医药、催化等(Nanoscale,2021,13,6283-6340；Chemical Society Reviews 2020,49,6443-6514)。
目前绝大多数纳米团簇的合成都是针对金属纳米团簇和氧化物纳米团簇，而对于无机盐类的纳米团簇研究甚少。以含钨氧化物纳米团簇的复合氧化物为例，现有技术中(如Nature Chemistry2009,1,722-728；ACS Catal.2017,7,2181–2198)，合成钨氧化物纳米团簇的方法可以总结为：通过浸渍法或者共沉淀法将可热分解的含钨化合物(偏钨酸铵、钨酸等)负载在载体(通常为氧化物或氢氧化物)上，然后通过高温焙烧让含钨化合物(钨酸或者钨酸盐)分解形成氧化钨(WO x)。由于载体(如氧化锆、氧化铝)与WO x之间存在强相互作用(可以形成W-O-M键，M为载体中非氧元素，如Zr,Al,Si,Ti)，WO x能够以纳米团簇的形式稳定存在。含钨氧化物纳米团簇的复合氧化物(如WO 3/ZrO 2,WO 3/Al 2O 3,WO 3/SiO 2)常作为固体酸催化剂，这主要是因为WO x表面的W 6+以畸变八面体构型(WO 6)存在，可以形成Bronsted酸性位点——H δ+(WO 3) n δ-(J.Catal.2004,227,479–491)。由于碱金属钨酸盐(如Na 2WO 4)不能通过高温焙烧分解形成WO x，且碱金属离子的存在会破坏化合物的酸性，为了避免让负载到载体上的含钨化合物含有碱金属离子，现有技术所用方法通常不使用碱溶液和碱金属钨酸盐原料。在极少数采用Na 2WO 4作为钨源的合成方法中(Topics in Catalysis1998,6,87–99；Advances in Chemical Engineering and Science,2014,4,250-257)，人们也会加入HCl溶液，让钨酸根离子以不含碱金属的钨酸形式负载在载体上，从而有助于分解形成WO x。值得一提的是，碱金属钨酸盐，如Na 2WO 4中W是以WO 4四配位形式存在(J.Phys.Chem.C 2008,112,6869-6879)，这与WO x中WO 6构型截然不同，因此碱金属钨酸盐与氧化物载体之间的相互作用也必然不同于WO x与氧化物载体之间的相互作用。在此背景下，如何可控合成碱金属钨酸盐纳米团簇，特别是高浓度碱金属钨酸盐纳米团簇将充满挑战。此外，碱金属钨酸盐纳米团簇的用途也鲜有涉及。
钨锰催化剂是一类经典的OCM催化剂，其组成包括碱金属、钨、锰以及载体。该类催化剂最早于1992年由兰州化物所的李树本课题组所开发(《分子催化》1992,6，427-433)，其通常是以钨酸钠和锰盐为前驱体，通过浸渍等方法负载在到硅胶上，经高温焙烧后制得。该类催化剂具有较高的OCM催化性能和良好的热稳定性，受到人们的广泛关注(ACS Catalysis 2019,9,5912-5928)。典型的钨锰催化剂组成为1.9wt％Mn-5wt％Na2WO4/SiO2,其中Mn元素占催化剂质量的1.9％，Na2WO4占催化剂质量的5％。该催化剂在800℃,甲烷空速为36000mL/g/h,CH4:O2:N2＝3:1:2.6的实验条件下，甲烷的转化率为36.8％，C2烃的收率达到23.9％。此外，钨锰催化剂的OCM性能还可通过元素掺杂、组成调控、反应条件调控等手段来进行优化(Applied Catalysis A:General 2012,425,53-61)。
钨锰催化剂是一类经典的OCM催化剂，其组成包括碱金属、钨、锰以及载体。该类催化剂最早于1992年由兰 州化物所的李树本课题组所开发(《分子催化》1992,6，427-433)，其通常是以钨酸钠和锰盐为前驱体，通过浸渍等方法负载在到硅胶上，经高温焙烧后制得。该类催化剂具有较高的OCM催化性能和良好的热稳定性，受到人们的广泛关注(ACS Catalysis 2019,9,5912-5928)。典型的钨锰催化剂组成为1.9wt％Mn-5wt％Na 2WO 4/SiO 2,其中Mn元素占催化剂质量的1.9％，Na 2WO 4占催化剂质量的5％，以催化剂中所有非氧元素(Na、Mn、W、Si)计，W的原子百分比为1％，Na的原子百分比为2％。该催化剂在800℃,甲烷空速为36000mL/g/h,CH 4:O 2:N 2＝3:1:2.6的实验条件下，甲烷的转化率为36.8％，C2烃的收率达到23.9％。此后，人们从元素掺杂、组成调控、反应条件调控等各种手段对钨锰催化剂的性能进行了优化(Applied Catalysis A:General 2012,425,53-61；AppliedCatalysis A:General 225(2002)271–284)。在钨锰催化剂中的制备中，Na的作用主要是诱导载体SiO 2从无定形相变成方石英相，从而提高钨的分散度，Na的主要来源通常是钨源Na 2WO 4中所带的Na(Applied Catalysis A:General 2012,425,53-61；AppliedCatalysis A:General 225(2002)271–284)。在少数不采用Na2WO4作为Na源的催化剂制备方法中，人们也不会采用碱性Na盐作为Na源，这主要是因为用碱性Na盐作为Na源会使锰元素以Mn 4+的形式而不是活性Mn 2O 3的形式存在，这会显著降低钨锰催化剂的OCM催化活性(Ind.Eng.Chem.Res.2006,45,7077-7083)。
甲烷氧化偶联(OCM)制乙烷和乙烯是甲烷直接利用的关键技术之一，是石化工业中实现天然气取代石油为原料新化工路线的技术基础(Energy Conversion and Management,2019,198,111789；Chinese Journal of Catalysis2021,42,1117-1125)。传统研究一般认为OCM反应遵循“多相-均相”催化反应机理，甲烷在催化剂表面活化产生甲基自由基后，在气相中发生均相偶联生成乙烷和乙烯等产物(J.Am.Chem.Soc.1987,109,7900-7901；J.Mol.Catal.A:Chem.2017,426,326-342)。这一反应机理的挑战在于催化剂仅在产生甲基自由基时发挥作用，而气相中甲基自由基的均相偶联无法通过催化剂优化来进行调控(ACS Catal.2016,6,4340–4346)。受热力学驱动，甲基自由基和C 2物种倾向于与气相中的氧气发生反应，生成CO 2等完全氧化产物，因此传统OCM催化体系中C 2的选择性和收率很难实现突破(图1)。Arutyunov等人(J.Mol.Catal.A:Chem.2017,426,326)采用气相反应的动力学模拟得出了C 2物种产率的上限，他们指出只有当催化剂能够在甲基自由基偶联这一步发挥作用时，C 2物种的收率才有可能超过25％(图3)。在过去几十年内，人们开发了1000多种催化剂，涉及68种元素，但其反应机制都未有突破(ChemCatChem,2011,3,1935-1947)。现有技术中(Appl.Catal.A 2012,425-426,53-61)对OCM催化剂的优化方法可以总结为：通过元素替换/掺杂、助剂添加、催化剂形貌控制、载体调控等手段来调节催化剂表面氧气/甲烷的活化，进而优化甲基自由基生成、提高OCM反应性能。这些手段都是从甲烷活化催化剂的组成和结构入手，其最终调控的都是甲烷活化产生甲基自由基这一步，并没有实现甲基自由基的可控转化。理论上来说，如果能够开发出一种能够可控偶联甲基自由基的催化剂，将其与甲烷活化产生甲基自由基的催化剂耦合，就有望打破传统OCM反应机制的限制，实现其性能的突破。优异的甲基自由基可控转化催化剂必须满足以下条件：1)具有较强的吸附甲基自由基的能力，能够将气相中的甲基自由基富集到催化剂表面；2)富集到催化剂表面的甲基自由基能够高选择性转化为C 2产物；3)氧化能力弱(或难以活化氧气)，不会在催化剂表面将甲基自由基和C 2产物转化为CO和CO 2。从上述条件可以看出，优异的甲基自由基偶联催化剂本身必定不具备显著的OCM活性，因为它氧化能力弱，难以活化甲烷产生甲基自由基；同时由于它对甲基自由基具有较强的吸附作用，甲基自由基很难脱附到气相中，也不满足传统OCM反应机制对OCM催化剂的要求。在现有技术中，人们通常认为甲基自由基在OCM反应条件下(高温且有氧气存在)太过活泼，要实现甲基自由基在催化剂表面的可控偶联几乎是一个不可能完成的奇迹(ACS Catal.2016,6,4340–4346)。因此，目前尚未有技术从甲基自由基可控表面偶联的角度来对设计和优化催化剂，也没有人通过往传统OCM催化剂中物理混合一种没有显著OCM性能的助催化剂来提升反应的C 2选择性和收率。
发明内容：
为了打破传统甲烷氧化偶联(OCM)反应机制的限制，实现其性能(C 2选择性和C 2收率)的突破，本发明进行了深入研究，开发出一种含有钨酸盐纳米团簇的复合氧化物，将其作为助催化剂用于可控偶联甲基自由基。该助催化剂本身不能单独作为催化剂催化OCM反应，不显著具有OCM活性，但其作为助催化剂与传统OCM催化剂复合在一起时，可将传统OCM催化剂的C2选择性和C2收率都提高1.2倍以上(图4)。因此，本发明的效果在于，采取本发明开发的含有钨酸盐纳米团簇的复合氧化物作为助催化剂，其团簇富集指数达到必要的密度，则能够使得传统OCM催化剂(如1.9wt％Mn-5wt％Na 2WO 4/SiO 2)在甲烷氧化偶联(OCM)制乙烷和乙烯中的选择性达到70％以上，同时收率达到30％以上。
采取本发明开发的含有钨酸盐纳米团簇的复合氧化物与经典OCM催化剂1.9wt％Mn-5wt％Na 2WO 4/SiO 2作为催化剂组合物，在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥70％且C 2单程收率≥35％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥70％且C 2单程收率≥40％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥70％且C 2单程收率≥45％。
其中所述的复合物的解释：在所述复合氧化物中，碱金属A、钨元素W和助剂元素M的化合价均为正价，它们都通过与化合价为负价的氧元素结合来实现电荷平衡。碱金属A、钨元素W和助剂元素M与氧元素形成的化合物均可写成氧化物形式。例如，Na 2WO 4可以写成Na 2O·WO 3；ZrW 2O 8可以写成ZrO 2·2WO 3。检测手段：碱金属元素A、钨元素W、助剂元素M以及氧元素的化合价可以通过X射线光电子能谱(XPS)进行测定，所述复合氧化物的晶型结构可通过X射线粉末衍射(XRD)来确定。
其中，此处所述原子百分比(包括A，W以及M)，原子百分比不包含氧，所述复合氧化物中某元素的原子百分比定义如下：
Figure PCTCN2021124519-appb-000001
所述原子百分比是指采用X射线荧光光谱分析干燥催化剂，测得的该催化剂中所有元素按照原子比的百分比例，允许的测试误差为±10％，优选为±5％。
其中，所述钨酸盐纳米团簇的通式为A xWO y，其中，0<x≤2，y代表满足通式电荷平衡所需的氧原子的数目。例如：当A为Na,x＝2时，Na为+1价，W为+6价，O为-2价，所有正电荷为2*1+1*6＝8，所有负电荷为2*y,根据电荷平衡，正电荷＝负电荷，因此2*y＝8,得出y＝4；当A为Mg,x＝1时，Mg为+2价，W为+6价，O为-2价，所有正电荷为1*2+1*6＝8，所有负电荷为2*y,根据电荷平衡，正电荷＝负电荷，因此2*y＝8,得出y＝4。
更优选的，所述钨酸盐纳米团簇的粒径≤10.0nm，优选为≤5.0nm，进一步优选为≤2.0nm，更进一步优选为≤1.0nm。所述钨酸盐纳米团簇的粒径是指纳米团簇的平均直径；检测方法为：将该复合氧化物在高分辨透射电镜下进行观察，随机选取100个钨酸盐纳米团簇，对其直径进行统计，取平均值。所述高分辨透射电镜观察时的放大倍数为200万-3000万倍,优选为500万-1000万倍。
所述单程C 2选择性是指原料气单次经过催化剂床层所获的C 2选择性，所述C 2选择性指的是产物乙烷和乙烯的 选择性，其计算方法：
C 2选择性＝(2*n C2H6+2*n C2H4)/(2*n C2H6+2*n C2H4+n CO+n CO2+3*n C3H8+3*n C3H6)；
C 2收率＝C 2选择性*CH 4转化率得到，所述CH 4转化率指的是甲烷转化效率，其计算方法为：
Figure PCTCN2021124519-appb-000002
如果没有特别说明，后续内容中所提到的甲烷转化率、C2选择性和C2收率均为在甲烷和氧气共进气的床层反应器中单程OCM反应的结果。
本发明提供一种含有钨酸盐纳米团簇的复合氧化物，所述复合氧化物包含碱金属元素A、钨元素W、助剂元素M以及氧元素O，且所述碱金属元素A、钨元素W、助剂元素M均与氧元素O形成复合物，
所述碱金属元素A选自Li、Na、K、Mg、Ca、Sr、Ba中的任意一种或多种，
所述助剂元素M选自Si、Zr、Ti、Al、La、Ce、Co中的任意一种或多种，
所述碱金属元素A的原子百分比为5％-67％；所述钨元素W的原子百分比为1％-60％；助剂元素M的原子百分比为20％-94％；所述复合氧化物中氧元素的含量为满足碱金属元素A、钨元素W、M电荷平衡所需的氧原子数的总和；
所述某元素的原子百分比按照以下公式计算，
Figure PCTCN2021124519-appb-000003
其中，所述钨酸盐纳米团簇由所述碱金属元素A、钨元素W和氧元素O所组成，所述钨酸盐纳米团簇的通式为A xWO y，其中，0<x≤2，y代表满足通式电荷平衡所需的氧原子的数目；且所述钨酸盐纳米团簇满足团簇富集指数，所述团簇富集指数是指在任意一个包含所述钨酸盐纳米团簇的10×10nm 2的区域内，所述钨酸盐纳米团簇的个数≥3个；优选的，所述钨酸盐纳米团簇的个数≥5个，进一步优选≥10个，进一步优选≥20个；
优选的，所述团簇富集指数检测方法：将所述复合氧化物在高分辨透射电镜下进行观察，在含有碱金属元素A、钨元素W和氧元素O三种元素的钨酸盐纳米团簇的区域内，随机选取5个10×10nm 2的区域，统计该区域所含的钨酸盐纳米团簇的个数，取平均值；优选的，所述高分辨透射电镜观察时的放大倍数为200万-3000万倍，优选为500万-1000万倍；优选的，所述钨酸盐纳米团簇的粒径≤10.0nm，优选为≤5.0nm，进一步优选为≤2.0nm，更进一步优选为≤1.0nm；
优选的，所述复合氧化物的比表面积为0.1-10g/m 2，进一步优选为0.5-5g/m 2，进一步优选1-2g/m 2；
优选的，所述钨酸盐纳米团簇中碱金属元素A、钨元素W、氧元素O三种元素均匀分布，所述均匀分布是指钨酸盐团簇中任意区域均含有碱金属元素A、钨元素W、氧元素O；优选的，所述均匀分布的检测方法为：将所述复合氧化物在高分辨透射电镜下观察，采用X射线能谱仪(EDS)面扫模式对所述钨酸盐纳米团簇进行成分分析，随机选取10个团簇，所述团簇中任意区域均含有碱金属元素A、钨元素W、氧元素O；更优选的，所述高分辨透射电镜观察时的放大倍数为200万-3000万倍,优选为500万-1000万倍；
优选的，所述复合氧化物中碱金属元素A的原子百分比为10％-65％，进一步优选为15％-50％；进一步优选为原子10％-60％，进一步优选为20％-50％，进一步优选为30％-40％；所述钨元素W的原子百分比为2％-55％，进一步优选为5％-50％，进一步优选为10％-40％，进一步优选为20％-30％；助剂元素M的原子百分比为22％-92％上，进一步优选为25％-90％，优选为30％-80％，进一步优选为40％-70％，进一步优选为50％-60％；
优选的，所述钨酸盐纳米团簇中钨元素以四配位钨酸盐的形式存在，所述四配位是指一个钨原子有且仅有四个氧原子与其结合；更优选的，所述四配位结构的检测方法为：对所述复合氧化物进行X射线精细结构谱测试，采集复合物中钨元素的L 1-edge和L 3-edgeX射线吸收近边结构谱(XANES)和扩展X射线吸收谱精细结构(EXAFS)，通过定性分析和数据拟合得出钨原子的配位数；
优选的，所述复合氧化物在800℃下空气中焙烧6h之后，钨酸盐纳米团簇的粒径变化值Δ1≤20％，进一步优选为Δ1≤10％；计算公式如下：
Figure PCTCN2021124519-appb-000004
焙烧后钨酸盐纳米团簇的团簇富集指数变化值Δ2≤20％；进一步优选为Δ2≤10％；计算公式如下：
Figure PCTCN2021124519-appb-000005
进一步的，所述碱金属元素A至少是Na，所述助剂元素M至少是Zr或者Al，所述含有钨酸盐纳米团簇的复合氧化物分别表述为NaWZr或NaWAl，所述钨酸盐纳米团簇由碱金属元素Na、钨元素W和氧元素O所组成，所述钨酸盐纳米团簇的通式为Na xWO y，0<x≤2，y代表满足通式电荷平衡所需的氧原子的数目；
所述复合氧化物中Na的原子百分比为5％-67％；所述钨元素W的原子百分比为1％-60％；助剂元素M的原子百分比为20％-94％；
优选的，所述复合氧化物中Na的原子百分比为10％-65％，进一步优选为15％-50％；进一步优选为原子10％-60％，进一步优选为20％-50％，进一步优选为30％-40％；所述钨元素W的原子百分比为2％-55％，进一步优选为5％-50％，进一步优选为10％-40％，进一步优选为20％-30％；助剂元素Zr或者Al的原子百分比为22％-92％上，进一步优选为25％-90％，优选为30％-80％，进一步优选为40％-70％，进一步优选为50％-60％；
所述复合氧化物中0<Na:W的摩尔比≤5，优选的，0.1≤Na:W的摩尔比≤4，进一步优选为0.8≤Na:W的摩尔比≤3.5；进一步优选为1.0≤Na:W的摩尔比≤3.0；进一步优选为1.5≤Na:W的摩尔比≤2.0；进一步优选为1.4≤Na:W的摩尔比≤1.6；
所述复合氧化物中W:Zr的摩尔比≥0.1；优选的，0.2≤W:Zr的摩尔比≤100；进一步优选为0.23≤W:Zr的摩尔比≤10；进一步优选为0.3≤W:Zr的摩尔比≤1；进一步优选为0.4≤W:Zr的摩尔比≤0.5。
本发明还提供一种含有钨酸盐纳米团簇的复合氧化物的制备方法，包含如下步骤：
1)分别制备溶液体系1和溶液体系2，所述溶液体系1和溶液体系2均为透明溶液，其中所述透明溶液是指溶液中没有显在的悬浊物，且溶液不会分层，当光线透过该溶液时，不会产生丁达尔效应；
2)对溶液体系2进行搅拌的情况下，将溶液体系1在2-200分钟内完全加入到溶液体系2中，直至呈现浊液，将所述浊液继续搅拌1小时以上，优选2小时以上，更优选为3小时以上；优选的，所述滴加时间为2-200分钟，优选为10-100分钟，更优选为20-60分钟；优选的，所述的搅拌为快速搅拌，所述快速搅拌的转速为500-1000转/分钟，更优选为750-900转/分钟；优选的，所述搅拌的时间为10分钟-2小时，更优选的搅拌时间为30分钟-1小时；
3)将步骤2)所得产物不经处理，直接去除溶剂后，将得到的固体进行干燥，得到干燥的固体产物，具体地所述不经处理是指任何洗涤、离心、过滤步骤；
优选的，去除溶剂的方法为将溶剂烘干，优选的，烘干的方法为将步骤2)所得产物置于温度为30-50℃的氛围中烘至溶液挥发；优选的，所述温度为40℃；
优选的，将固体进行干燥的温度为60-100℃，更优选为80-90℃；优选的，所述干燥的时间为12小时以上，更优选的时间为24小时以上；
4)将步骤3)得到的固体产物焙烧后制得含有钨酸盐纳米团簇的复合氧化物，优选的，所述焙烧的温度为700-900℃，更优选为750-850℃，更优选为800选；所焙烧的时间为3-8小时，优选为4-6小时；所述焙烧的升温速率为2-10℃/分钟，更优选为3-5℃/分钟；
所述溶液体系1的制备方法为：将含有该元素的化合物原料的碱金属元素前驱体溶于适量水中，充分搅拌下使其形成透明溶液，即得到溶液体系1，所述透明溶液pH大于7，更优选为pH≥10；
所述溶液体系2的制备方法选自以下任意一种：a)将钨元素前驱体、助剂元素前驱体和适量水混合并快速搅拌，形成透明溶液，即得到溶液体系2-1；b)将钨元素前驱体、助剂元素前驱体和适量醇混合并快速搅拌，形成透明溶液，即得到溶液体系2-2；
其中，溶液体系1和溶液体系2中加入的碱金属元素前驱体、钨元素前驱体、助剂元素前驱体的配比符合以下公式：
溶液体系1和溶液体系2中，按下述公式计算某元素的原子百分比，
Figure PCTCN2021124519-appb-000006
所述碱金属元素A的原子百分比为5％-67％；所述钨元素W的原子百分比为1％-60％；助剂元素M的原子百分比为20％-94％；
优选的，所述复合氧化物中碱金属元素A的原子百分比为10％-65％，进一步优选为15％-50％；进一步优选为原子10％-60％，进一步优选为20％-50％，进一步优选为30％-40％；所述钨元素W的原子百分比为2％-55％，进一步优选为5％-50％，进一步优选为10％-40％，进一步优选为20％-30％；助剂元素M的原子百分比为22％-92％上，进一步优选为25％-90％，优选为30％-80％，进一步优选为40％-70％，进一步优选为50％-60％
优选的，所述溶液体系1中碱金属元素前驱体的浓度为1-40wt％,优选为10-30wt％,更优选为15-25wt％；优选的，所述溶液体系2-1和2-2中钨元素前驱体的浓度为1-30wt％,优选为5-25wt％,更优选为10-20wt％；优选的，所述溶液体系2-1和2-2中助剂元素前驱体的浓度为1-50wt％,优选为10-40wt％,更优选为20-35wt％；
优选的，所述溶液体系1制备方法中的碱金属元素前驱体选自氢氧化锂、氢氧化钠、碳酸锂、碳酸钠、碳酸氢钠、氢氧化钾、碳酸钾、碳酸氢钾、乙酸镁、氢氧化钙、乙酸钙、氢氧化锶和氢氧化钡任意一种或多种；
优选的，所述溶液体系2-1制备方法中的助剂元素前驱体选自硅酸钠、硝酸氧锆、硝酸锆、氧氯化锆、二(乙酸根合-O)氧合锆、柠檬酸锆、硝酸钛、硝酸铝、硝酸镧、乙酸镧、氯化镧、硝酸铈、乙酸铈、氯化铈、硝酸钴、乙酸钴中的任意一种或多种；所述钨元素前驱体选自钨酸钠、钨酸铯、乙醇钨、氧化钨铵、氧化钨铵水合物、钨酸锶、钨酸镁、钨酸钡、对五水合钨酸铵、偏钨酸铵水合物、钨酸钙、钨酸钡、钨酸锶的任意一种或多种；
优选的，溶液体系2-2制备方法中的钨元素前驱体选自钨酸钠、氯化钨的任意一种或两种；助剂元素前驱体选自正硅酸四乙酯、硝酸锆、正丁醇锆、硝酸氧锆、氧氯化锆、二(乙酸根合-O)氧合锆、柠檬酸锆、钛酸四丁酯、仲丁醇铝、异丙醇铝、硝酸镧、硝酸铝、硝酸铈、硝酸钴中的任意一种或多种；醇溶液选自甲醇、乙醇、丙醇、丁醇中的任意一种或多种。
进一步的，所述碱金属元素前驱体为钠元素前驱体，所述助剂元素前驱体选自锆元素前驱体或者铝元素前驱体，制得的所述含有钨酸盐纳米团簇的复合氧化物为NaWZr或NaWAl，所述钨酸盐纳米团簇由碱金属元素Na、钨元素 W和氧元素O所组成，所述钨酸盐纳米团簇的通式为Na xWO y，0<x≤2，y代表满足通式电荷平衡所需的氧原子的数目；
优选的，所述溶液体系1制备方法中的碱金属前驱体选自氢氧化钠、碳酸钠、碳酸氢钠中的任意一种或多种；
优选的，所述溶液体系2-1制备方法中的助剂元素前驱体选自硝酸氧锆、硝酸锆、氧氯化锆、二(乙酸根合-O)氧合锆、柠檬酸锆、硝酸铝中的任意一种或多种；所述钨元素前驱体选自钨酸钠、钨酸铯、乙醇钨、氧化钨铵、氧化钨铵水合物、钨酸锶、钨酸镁、钨酸钡、对五水合钨酸铵、偏钨酸铵水合物、钨酸钙、钨酸钡、钨酸锶的任意一种或多种；
优选的，所述溶液体系2-2中的钨元素前驱体选自钨酸钠、氯化钨的任意一种或两种；助剂元素前驱体选自硝酸锆、正丁醇锆、硝酸氧锆、氧氯化锆、二(乙酸根合-O)氧合锆、柠檬酸锆、仲丁醇铝、异丙醇铝、硝酸铝中的任意一种或多种；醇溶液选自甲醇、乙醇、丙醇、丁醇中的任意一种或多种；
优选的，0<Na:W的摩尔比≤摩，优选的，0.1的，W甲醇的摩尔比≤4，进一步优选为0.8步优选为醇的摩尔比≤摩尔比；进一步优选为1.0步优选为醇的摩尔比≤摩尔比；进一步优选为1.5优选为为醇的摩尔比≤摩尔比；进一步优选为1.4步优选为醇的摩尔比≤摩尔比；
W:Zr的摩尔比≥摩尔1；优选的，0.2≤W:Zr的摩尔比≤摩尔比；进一步优选为0.23≤W:Zr的摩尔比≤摩尔；进一步优选为0.3步优选为Z的摩尔比≤摩；进一步优选为0.4步优选为Z的摩尔比≤摩尔比；
优选的，所述溶液体系2-2制备方法中的助剂元素前驱体为正丁醇锆，所述钨元素前驱体为氯化钨；更优选的，所述钨元素和锆元素的摩尔比≥1∶9，优选为≥2∶9，更优选为≥3∶9；更优选的，所述溶液体系1为NaOH水溶液，NaOH质量百分数为1％～60％，优选为10％～50％，更优选为15％～40％；
优选的，所述溶液体系2-2制备方法中的助剂元素前驱体为异丙醇铝，所述钨元素前驱体为氯化钨，所述钨元素和铝元素的摩尔比≥1∶9，优选为≥2∶9，更优选为≥3∶9；更优选的，所述溶液体系1为NaOH水溶液，NaOH质量百分数为1％～60％，优选为10％～50％，更优选为15％～40％；
优选的，所述溶液体系2-2制备方法中的助剂元素前驱体为正丁醇锆，所述钨元素前驱体为钨酸钠，所述钨元素和锆元素的摩尔比≥1∶9，优选为≥2∶9，更优选为≥3∶9；更优选的，所述溶液体系1为KOH质量百分数为1％～60％，优选为10％～50％，更优选为15％～40％；
优选的，所述溶液体系2-2制备方法中的助剂元素前驱体为异丙醇铝，所述钨元素前驱体为钨酸钠，所述钨元素和铝元素的摩尔比≥1∶9，优选为≥2∶9，更优选为≥3∶9；更优选的，所述溶液体系1为KOH质量百分数为1％～60％，优选为10％～50％，更优选为15％～40％。
本发明还提供一种助催化剂，所述的助催化剂包含所述的含有钨酸盐纳米团簇的复合氧化物；
优选的，所述的助催化剂不能单独用作催化剂催化甲烷氧化偶联(OCM)反应；优选的，所述的助催化剂不具有显著OCM活性；其中优选的，所述不具有显著OCM活性的检测方法为：在甲烷和氧气共进气的床层反应器中，当所述催化剂在气体-时空速度为大于等于20000mL/g/h、催化剂床层温度为800℃及以下、反应压力为1个大气压时用作甲烷氧化催化剂，其单程C2收率不高于5％；优选的，所述收率采用气相色谱法定量测得。
本发明还提供一种催化剂组合物，所述的催化剂组合物包含权利所述的复合氧化物和至少一种具有OCM活性的催化剂OCM catalyst；
优选的，所述具有OCM活性是指能够单独用作催化剂催化OCM反应；优选的，所述具有OCM活性的含义是：在甲烷和氧气共进气的床层反应器中，当所述催化剂在气体-时空速度为大于等于20000mL/g/h、催化剂床层温度为 800℃及以下、反应压力为1个大气压时用作甲烷氧化偶联催化剂，其具有大于5％的C 2单程收率；
优选的，所述OCM catalyst具有显著OCM活性，其含义：在甲烷和氧气共进气的床层反应器中，当所述催化剂在气体-时空速度为大于等于20000mL/g/h、催化剂床层温度为800℃及以下、反应压力为1个大气压时用作甲烷氧化偶联催化剂，其具有大于15％的C 2单程收率；
优选的，所述OCM catalyst与所述复合氧化物的质量比为0.1-50.0；更优选的，所述的质量比为0.5～20.0∶1.0；更优选的，所述的质量比为1.0～10.0∶1.0；更优选的，所述的质量为2.0～4.0∶1.0；
优选的，所述收率采用气相色谱法定量测得；
优选的，所述OCM catalyst选自钨锰催化剂、稀土金属氧化物、钙钛矿类化合物、碱金属和碱土金属氧化物以及上述催化剂的衍生物中的任意一种或多种；更优选为钨锰催化剂、氧化镧、氧化钐、Li/MgO、Ca/CeO 2；优选的，所述钨锰催化剂为Mn-Na 2WO 4/SiO 2；
优选的，所述OCM catalyst与所述复合氧化物之间的距离≤3mm；
优选的，所述的催化剂组合物是将所述复合氧化物和OCM catalyst通过物理混合的方式复合而成；
优选的，所述OCM catalyst为包含第二碱金属元素、钨元素、锰元素、氧元素以及第五组分元素的复合物；更优选的，所述第五组分元素选自Al、Si、Ti、Zr、C、N中的任意一种或多种，进一步更优选的，所述第五组分元素选自Al,、Si、Ti中的任意一种或多种，更优选的，所述第五组分元素选自Si；更优选的，所述第二碱金属选自Li、Na、K中的任意一种或多种；更优选的，所述第二碱金属选自Na；
优选的，所述第二碱金属元素占所述OCM catalyst的质量百分比为0.1～2.0wt.％；更优选的，所述第二碱金属元素占所述OCM catalyst的质量百分比为0.5～1.5wt.％；
优选的，所述钨元素占所述OCM catalyst的质量百分比为0.1～5.0wt.％，优选的，所述钨元素占所述OCM catalyst的质量百分比为2.0～4.0wt.％；
优选的，所述锰元素的占所述OCM catalyst的质量百分比为0.1～10.0wt.％，优选的，所述锰元素的占所述OCM catalyst的质量百分比为1.0～4.0wt.％。
优选的，所述的催化剂还包含添加剂；更优选的，所述的添加剂选自散热助剂、传质助剂、成型助剂、增强耐磨剂、分散剂、稳定剂等中的任意一种或多种。
优选的，在相同的反应条件下，所述催化剂组合物催化OCM反应的选择性和收率比单独使用OCM catalyst均提高1.2倍以上；
优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥程收率；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥40％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥45％。
进一步的，所述OCM catalyst为Mn/Na 2WO 4/SiO 2，所述复合氧化物为Na、W、Zr的复合氧化物NaWZr；优选地，所述OCM catalyst与所述复合氧化物的质量比为4:1-0.5:1；更优选为2:1-1:1；优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥70％且C 2单程收率≥35％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥40％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥45％；
优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，所述催化剂组合物 Mn/Na 2WO 4/SiO 2-NaWZr的C 2选择性可以提升为Mn/Na 2WO 4/SiO 2的1.3倍，且其C 2单程收率为Mn/Na 2WO 4/SiO 2的1.2倍。
进一步的，所述OCM catalyst为La 2O 3，所述复合氧化物为Na、W、Zr的复合氧化物NaWZr，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
优选的，所述催化剂组合物La 2O 3-NaWZr在甲烷和氧气共进气的OCM床层反应器中，La 2O 3-NaWZr的C 2选择性可以提升为La 2O 3的1.3倍，且其C 2单程收率为La 2O 3的1.2倍。
进一步的，所述OCM catalyst为Sm 2O 3，所述复合氧化物为Na、W、Zr的复合氧化物NaWZr，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
优选的，所述催化剂组合物Sm 2O 3-NaWZr在甲烷和氧气共进气的OCM床层反应器中，Sm 2O3-NaWZr的C 2选择性可以提升为Sm 2O 3的2.0倍，且其C 2单程收率为Sm 2O 3的1.8倍。
进一步的，所述OCM catalyst为Li/MgO，所述复合氧化物为Na、W、Zr的复合氧化物NaWZr，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
优选的，所述催化剂组合物Li/MgO-NaWZr在甲烷和氧气共进气的OCM床层反应器中，Li/MgO-NaWZr的C 2选择性可以提升为Li/MgO的2.0倍，且其C 2单程收率为Li/MgO的1.45倍。
进一步的，所述OCM catalyst为Ca/CeO 2，所述复合氧化物为Na、W、Zr的复合氧化物NaWZr，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
优选的，所述催化剂组合物Ca/CeO 2-NaWZr在甲烷和氧气共进气的OCM床层反应器中，Ca/CeO 2-NaWZr的C 2选择性可以提升为Ca/CeO 2的1.3倍，且其C 2单程收率为Ca/CeO 2的1.5倍；
进一步的，所述催化剂组合物为Mn-Na 2WO 4/SiO 2-NaWAl，其中，所述OCM catalyst为Mn-Na 2WO 4/SiO 2，所述复合氧化物为Na、W、Al的复合氧化物NaWAl，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
优选的，所述催化剂组合物Mn-Na 2WO 4/SiO 2-NaWAl在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥70％且C 2单程收率≥35％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥40％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥45％；
优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，Mn-Na 2WO 4-NaWAl的C 2选择性可以提升为Mn-Na 2WO 4的1.3倍，且其C 2单程收率为Mn/Na 2WO 4/SiO 2的1.2倍。
进一步的，所述OCM catalyst为La 2O 3，所述复合氧化物为Na、W、Al的复合氧化物NaWAl，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
优选的，所述催化剂组合物La 2O 3-NaWAl在甲烷和氧气共进气的OCM床层反应器中，La 2O 3-NaWAl的C 2选择性可以提升为La2O3的1.3倍，且其C 2单程收率为La 2O 3的1.2倍。
进一步的，所述OCM catalyst为Sm 2O 3，所述复合氧化物为Na、W、Al的复合氧化物NaWAl，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
优选的，所述催化剂组合物Sm 2O 3-NaWAl在甲烷和氧气共进气的OCM床层反应器中，Sm 2O3-NaWAl的C 2选择性可以提升为Sm 2O 3的1.2倍，且其C 2单程收率为Sm 2O 3的1.5倍。
进一步的，所述OCM catalyst为Li/MgO，所述复合氧化物为Na、W、Al的复合氧化物NaWAl，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
优选的，所述催化剂组合物Li/MgO-NaWAl在甲烷和氧气共进气的OCM床层反应器中，Li/MgO-NaWAl的C 2选择性可以提升为Li/MgO的1.7倍，且其C 2单程收率为Li/MgO的1.8倍。
进一步的，所述OCM catalyst为Ca/CeO 2，所述复合氧化物为Na、W、Al的复合氧化物NaWAl，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
优选的，所述催化剂组合物Ca/CeO 2-NaWAl在甲烷和氧气共进气的OCM床层反应器中，Ca/CeO 2-NaWAl的C2选择性可以提升为Ca/CeO 2的1.3倍，且其C 2单程收率为Ca/CeO 2的1.6倍。
本发明还提供一种所述的催化剂组合物在化学反应中的用途；优选的，所述的化学反应是自由基转化反应；更优选的，所述的化学反应是甲烷氧化偶联催化反应。所述甲烷氧化偶联催化反应指甲烷在催化剂作用下，碳氢键断裂，脱出的氢与氧作用生成水，同时形成碳碳键制取碳二及以上烃的过程。
进一步的，所述甲烷氧化偶联催化反应以甲烷和氧气为原料气，在床层反应器上进行反应，其产物包括C 2烃、碳氧化合物和C 3烃；
优选的，所述原料气还包含稀释气；更优选的，所述稀释气选自氮气、氦气、氩气的至少一种；
所述甲烷和氧气的比例为1.0-20.0，优选为2.0-6.0，更优选为2.0-5.0；
优选的，所述原料气的压力为0.1-20.0MPa，优选为1.0-8.0MPa，更优选为2.0-6.0MPa；
优选的，所述反应的温度为600-900℃，优选为700-850℃；
优选的，所述反应的空速为500-50000h -1，优选为1000-35000h -1。
本发明的效果在于，采取本发明的含有钨酸盐纳米团簇的复合氧化物，其团簇富集指数达到必要的密度，则能够使得甲烷氧化偶联(OCM)制乙烷和乙烯中的选择性选择性达到70％以上，同时收率达到30％以上。
其中特别提到的是，由于传统钨锰OCM催化剂的研究人员都是从提升OCM性能的角度来优化催化剂合成，因此本领域技术人员没有动机采用碱性钠盐(Na2CO3、Na2SiO3)或者NaOH等Na的碱性溶液(pH>7)来制备钨锰催化剂。在此背景下，绝大数钨锰催化剂都是采用Na2WO4和锰盐为前驱体通过浸渍法合成的，几乎没有研究人员以Na的碱性溶液采用共沉淀法来制备钨锰催化剂。在本发明人的研究中，意外发现利用NaOH等Na的碱性溶液进行共沉淀法制备的含钨酸钠催化剂中，钨酸钠以纳米团簇的形式存在，且钨酸钠团簇满足团簇富集指数(指在任意一个包含所述钨酸盐纳米团簇的10×10nm 2的区域内，所述钨酸盐纳米团簇的个数≥3个)。这种含钨酸钠纳米团簇的催化剂本身不具备OCM活性(在甲烷和氧气共进气的床层反应器中，当所述催化剂在气体-时空速度为大于等于20000mL/g/h、催化剂床层温度为800℃及以下、反应压力为1个大气压时用作甲烷氧化偶联催化剂，其C2单程收率不高于5％)，但其可以作为助催化剂来提升传统OCM催化剂的C2选择性和收率。这促使着本发明人进一步研究不同组成的含有钨酸盐纳米团簇的复合氧化物作为助催化剂，进一步完成本发明。本发明的研究明显有别于传统钨锰催化剂的研究，目前未有其它文献报道类似研究。
附图说明：
图1为OCM反应路线图以及相应的吉布斯自由能示意图。
图2为甲烷和氧气共进气的床层反应器示意图。
图3(a)OCM反应网络图(文献Beck,B.et al.Catal.Today 2014,228,212)，(b)动力学模拟得到的C2收率与甲基自由基生成速率(Weff/Wtherm)的相关性(文献Arutyunov,V.et al.J.Mol.Catal.A:Chem.2017,426,326)。
图4为实施例1的结果NaMnW-NaWZr体系的实验结果图。
图5为NaWZr的结构表征图。其中，(a，b)NaWZr的代表性高角度环形暗场(HAADF)和亮场(BF)STEM图像。如果没有其他规定，钨锆摩尔比为3:9。(c)图1a中红色圆圈所示区域的EDS点光谱。Cu信号来自Cu栅网。(d)NaWZr中NaxWOy团簇的尺寸分布。(e)不同W-Zr比的NaWZr中NaxWOy团簇密度的粗略统计。(f)NaWZr、Na2WO4和WO3的W L3边XANES光谱。
图6为实施例1的能量色散光谱(EDS)分析图。
图7为实施例1的HAADF-STEM图。其中，一些NaxWOy团簇采用绿色方块标记。
图8为实施例1的EDSmapping图。
图9为实施例1的拉曼光谱图(与市售ZrO2进行对比)。其中，约925cm–1处的特征拉曼谱带可归属于W-O-Zr键。
图10为实施例1的Zr K-edge XANES谱图。与ZrO2相比，NaWZr的Zr K-edge明显蓝移，表明Zr通过Zr-O-W键向W转移电荷。
图11为W:Zr摩尔比为1:9的NaWZr的代表性BF和HAADFSTEM图。其中，一些原子分散和聚合的W物种用红色圆圈标记；NaxWOy簇用绿色正方形标记。
图12为W:Zr摩尔比为2:9的NaWZr的代表性HAADFSTEM图。其中，一些原子分散和聚合的W物种用红色圆圈标记。NaxWOy簇用绿色正方形标记。
图13为W:Zr摩尔比为4:9的NaWZr的代表性BF和HAADFSTEM图。其中，一些NaxWOy团簇用绿色方块标记。
图14为W:Zr摩尔比为5:9的NaWZr的代表性BF和HAADFSTEM图。其中，一些NaxWOy团簇用绿色方块标记。
图15为W:Zr摩尔比为0.5:9的NaWZr的典型亮场(BF)和高角度环形暗场HAADF-STEM图。其中，一些原子分散的物种以红色圆圈为标志。
图16为NaWAl催化剂的典型高角度环形暗场(HAADF)STEM图。
图17为Na2WO4以大颗粒形式存在的STEM谱图。
图18 OCMcatalyst与所述复合氧化物之间的距离对OCM催化性能的影响。
OCMcatalyst与所述复合氧化物之间的距离对OCM催化性能的影响。从图18可以看出，OCMcatalyst与所述复合氧化物之间的距离≤3mm才表现出比OCMcatalyst更优的效果，具体越小，效果越好。
具体实施方式：
下面通过具体实施方式的描述以便好的理解本发明，但不构成对本发明的限制。
其中下述实施例中采用相关方法描述如下：
1、Mn/Na 2WO 4/SiO 2催化剂可以来自商购，也可以参照文献(《分子催化》1992，6，427-433)利用湿法浸渍法来合成。具体合成步骤如下：通常，将硝酸锰(II)水溶液(50wt.％)和水合钨酸钠溶解到适量的去离子水中。在持续搅拌下，将表面积为200m 2/g的市售SiO 2载体添加到上述溶液中，然后在105℃下干燥过夜。硝酸锰和钨酸钠的配比满足锰(Mn)元素占Mn/Na 2WO 4/SiO 2催化剂的质量百分比为2wt.％,钨酸钠(Na 2WO 4)占Mn/Na 2WO 4/SiO 2催化剂的质量百分比为5wt％。之后，将干燥固体在800℃下煅烧4小时，以获得最终催化剂。
2、以下实施例中，样品的组成采用日本岛津公司的XRF-1800X射线荧光光谱仪进行测定；样品的比表面积采用N 2吸脱附方法进行测定，所用仪器为美国MICROMERITICS公司ASAP2020全自动物化吸附仪，所测比表面积指的是BET比表面积；在加速电压为200kV的球差校正Titan Chemi-STEM透射电镜上获得了高角度环形暗场扫描透射电子显微镜(HAADF-STEM)图像和元素能量分布面扫描分析图谱(EDS Mapping)。在Horiba-Jobin-Yvon 上用可见光激光激发(532nm)在室温下测量了催化剂的拉曼光谱。在美国布鲁克海文国家实验室国家同步辐射光源II的7-BM光束线上测量了样品W L 3边缘的X射线吸收精细结构(XAFS)光谱。
3、OCM试验在内径为8mm的石英固定床反应器管中在1个大气压力下进行。催化剂床放置在炉恒温区的石英棉塞上。将外径为6mm的热电偶插入石英反应器，以监测床层温度并进一步减小自由空间体积。CH 4、O 2和N 2以3:1:2.7的比例通过质量流量控制器加入反应器。总流速为67mL/min.产品通过配备FID检测器和TCD检测器的在线气相色谱进行分析。分子筛5A柱和Porapak N柱与TCD耦合以分离CO 2、CH 4、O 2和N 2，而三氧化铝毛细管柱与FID耦合以分离CO 2和碳氢化合物产物(CH 4、C 2H 4、C 2H 6、C 3H 6和C 3H 8)。CH 4、C 2H 4和C 2H 6被用作FID和TCD之间的参考桥梁。单独测试OCM catalyst(如Mn/Na 2WO 4/SiO 2、La 2O 3等)时，催化剂用量为200mg，单独测试助催化剂(如NaWZr)时，催化剂yongl为100mg，测试OCM catalyst与助催化剂形成的催化剂组合物时，如果未另行规定，OCM catalyst的用量为200mg，助催化剂的用量为100mg。
根据入口和出口气体的碳原子总数计算CH 4转化率和产物选择性。使用N 2作为内标，对出口气体进行气体膨胀校正。
Figure PCTCN2021124519-appb-000007
其中x是产物中的碳原子数。
根据出口产物(即C 2H 4、C 2H 6、CO、CO 2、C 3H 6和C 3H 8)的碳原子计算产物选择性。C 2产品包括C2H4和C2H6。
Figure PCTCN2021124519-appb-000008
Figure PCTCN2021124519-appb-000009
Figure PCTCN2021124519-appb-000010
C 2Yield＝CH 4Conv.*C 2Sel.*100％     (6)
根据以下公式计算碳平衡：
Figure PCTCN2021124519-appb-000011
其中，x是产物中的碳原子数。一般来说，碳平衡高于95％。
实施例1：
称取一定量NaOH溶解于水中，得到质量浓度为23wt％的澄清NaOH水溶液1；称取3.453g的正丁醇锆(80wt.％)和1.188g的六氯化钨加入到30mL乙醇，充分搅拌溶解，得到澄清溶液2；在快速搅拌下(搅拌速度为800转/分钟)将2mL NaOH水溶液1于10分钟内加入到溶液2中并持续搅拌3小时得到浊液，将所得的浊液在40℃下烘干溶剂后置于80℃烘箱内干燥12小时，随后将所得固体在800℃空气条件下焙烧5小时，即得到催化剂。该催化剂中W原子和锆原子的原子比为3:9。
该催化剂的高分辨透射电镜图片如图5中a和5中b所示，从图中可以明显看到该催化剂富含纳米团簇。分别对图中白色团簇和深色的非团簇区域进行元素点扫分析(图5中c和图6)，发现白色团簇为富含Na、W和O元素的NaxWOy团簇，而非团簇区域主要是助剂元素Zr形成的氧化物ZrO 2。通过统计图5中a和图7中纳米团簇的尺 寸，发现该催化剂中Na xWO y纳米团簇的平均粒径为0.8nm(如图5中d所示)。更进一步统计10*10nm 2区域内Na xWO y纳米团簇的个数，发现其个数为21个(图5中e)。
该催化剂的EDS Mapping如图8所示，从图中可以看出Na，W，Zr元素均匀分布分布在催化剂中。
该催化剂的WL 3-edge XANES如图5中f所示，该催化剂的WL 3-edge XANES谱图与市售Na 2WO 4晶体的WL 3-edge XANES谱图非常类似，而与WO 3的WL 3-edge XANES谱图截然不同，表明该催化剂中的W主要以四配位的形式存在。
该催化剂的Raman如图9所示，与纯的ZrO 2相比，该催化剂的Raman谱图中可以在925cm -1处观察到一个新的特征峰，该峰可以归属于W-O-Zr的特征信号。此外，该催化剂的Zr K-edge XANES谱图如图10所示，与ZrO 2相比，NaWZr的Zr K-edge明显蓝移，表明Zr通过Zr-O-W键向W转移电荷。Zr-O-W键的存在以及Zr与W之间的强相互作用是实现Na xWO y纳米团簇富集指数的关键，它一方面可以稳定Na xWO y纳米团簇，让其能以纳米团簇的形式存在；另一方面也避免了相邻Na xWO y纳米团簇的烧结团聚，从而可以在10*10nm 2的区域内存在多个Na xWO y纳米团簇。
实施例2-17参照实施例1所述的方法进行合成，合成过程中与实施例1的参数略有不同，具体合成参数和结构参数见表1.
实施例2与实施例1的区别在于实施例2所用助剂元素为Al。该催化剂的高分辨透射电镜图片如图16所示，从图中可以明显看到该催化剂富含纳米团簇。通过统计图中纳米团簇的尺寸，发现该催化剂中Na xWO y纳米团簇的平均粒径为0.9nm。更进一步统计10*10nm 2区域内Na xWO y纳米团簇的个数，发现其个数为21个。
通过分析实施例1-7的结构参数(表1)可以得出结论，当碱金属元素为Na、K、Li，助剂元素为Zr或者Al时，均可以得到含有钨酸盐纳米团簇的复合氧化物，这些复合氧化物中Na xWO y纳米团簇的平均粒径为0.8-0.9nm，10*10nm 2区域内Na xWO y纳米团簇的个数～21个。
通过分析实施例1和实施例8，可以得知钨源为氯化物或钨酸钠均可得到含有钨酸盐纳米团簇的复合氧化物，这些复合氧化物中Na xWO y纳米团簇的平均粒径为0.8-0.9nm，10*10nm 2区域内Na xWO y纳米团簇的个数～21个。
通过分析实施例1和实施例13，可以得知体系2的溶剂为甲醇、乙醇、丙醇、丁醇均可得到含有钨酸盐纳米团簇的复合氧化物，这些复合氧化物中Na xWO y纳米团簇的平均粒径为0.8-0.9nm，10*10nm 2区域内Na xWO y纳米团簇的个数～21个。
实施例9-13STEM图片分别对应图11-15。实施例9-13与实施例1的区别在于体系中W:Zr的摩尔比不同，从图11-15可以看出，当W:Zr的摩尔比为1:9.2:9,3:9,4:9,5:9和0.5:9时，均可以得到含有钨酸盐纳米团簇的复合氧化物。但W:Zr摩尔比会影响到Na xWO y纳米团簇的富集指数。将实施例1以及9-13中10*10nm 2区域内钨酸盐纳米团簇的个数与其W:Zr摩尔比作图，如图5e所示。实施例13(W:Zr＝0.5:9)的STEM图片如图15所示，从图中可以看出当W:Zr的摩尔比为0.5:9时，复合氧化物中的Na xWO y不能形成纳米团簇，这表明钨酸盐纳米团簇的合成需要满足W元素百分比含量的要求，W含量太低得不到纳米团簇。随着W:Zr摩尔比的增加，Na xWO y纳米团簇的个数逐渐增加，最后达到饱和。
实施例17-36是将OCM catalyst、助催化剂以及催化剂组合物进行催化测试。
所有反应条件、参数以及产物参数如表2所示，反应步骤如下总述：按照Q/P质量比为2/1取0.3g催化剂装入内径4mm的石英反应器中，将特定比例的CH 4、N 2、O 2的混合气体连续通过催化剂床层，反应气空速(GHSV)为13400小时 -1克 -1，反应在常压下进行，由气相色谱进行在线检测反应产物(图2)。催化反应结果如表2所示。
实施例17是由实施例1所述的制备方法合成的助催化剂与经典的Mn/Na 2WO 4/SiO 2催化剂按照上述条件进行测试后的催化结果，可以看出该催化剂组合物表现出极高的C2选择性和收率。
通过分析实施例18-23的催化性能(表2)可以得出结论，当碱金属元素为Na、K、Li，助剂元素为Zr或者Al时所制备的助催化剂在与经典的Mn/Na 2WO 4/SiO 2催化剂混合后均表现出了与实施例17相近的催化性能。
通过分析实施例17和24的催化性能(表2)可以得出结论，钨源为钨酸钠均得到含有钨酸盐纳米团簇的复合氧化物在与经典Mn/Na 2WO 4/SiO 2催化剂混合后的催化性能虽不及钨源为氯化钨的催化性能，但其对经典Mn/Na 2WO 4/SiO 2催化剂的提升仍是十分显著的。
通过分析实施例17和25-28的催化性能(表2)可以得出结论当W:Zr的摩尔比为1:9.2:9,3:9,4:9和5:9时合成的助催化剂在与经典Mn/Na 2WO 4/SiO 2催化剂混合后性能提升均十分明显，且表现出了“火山型”的性能趋势。
通过分析实施例29的催化性能(表2)可以得出结论当W:Zr的摩尔比0.5:9时合成的助催化剂在与经典Mn/Na 2WO 4/SiO 2催化剂混合后性能受到抑制，是由于其W含量太低得不到纳米团簇所以表现出了较低的性能。
通过分析实施例17和30-32的催化性能(表2)可以得出结论当使用不同醇溶液所制备的助催化剂在与经典Mn/Na 2WO 4/SiO 2催化剂混合后性能提升均十分明显。
通过分析实施例33-36的催化性能(表2)可以得出结论当使用不同的经典OCM催化剂与由实施例1所述的制备方法合成的助催化剂混合后均表现出了不同的性能提升。
表1-1
Figure PCTCN2021124519-appb-000012
Figure PCTCN2021124519-appb-000013
表1-2
Figure PCTCN2021124519-appb-000014
表1-3
Figure PCTCN2021124519-appb-000015
Figure PCTCN2021124519-appb-000016
表1-4
Figure PCTCN2021124519-appb-000017
Figure PCTCN2021124519-appb-000018
表2-1
Figure PCTCN2021124519-appb-000019
表2-2
Figure PCTCN2021124519-appb-000020
Figure PCTCN2021124519-appb-000021
表2-3
Figure PCTCN2021124519-appb-000022
对比例1：
对比例1为WO 3/ZrO 2.其制备方法与实施例1一致，唯一的区别是对比例1的合成过程中不加入碱金属Na。透射电镜结果表明该催化剂中的纳米团簇为氧化钨而不是钨酸钠.
将对比例1与Mn/Na 2WO 4/SiO 2按照实施例17所示的方式进行测试，其结果如下：
Mn/Na 2WO 4/SiO 2的C2选择性为48.4％,C2收率为8.1％，而Mn/Na 2WO 4/SiO 2与对比例1的催化剂组合物的C2选择性为46.8％,C2收率为7.6％。
从上述结果可以看出，对比例1不仅不能提高Mn/Na 2WO 4/SiO 2的选择性与收率反而起抑制作用，这表明真正起助催化剂作用的组分不是氧化钨纳米团簇，而是钨酸盐纳米团簇。在助催化剂的合成中，碱金属元素必不可少。
对比例2：
采用与实施例1相同的制备方法来合成催化剂，其唯一的区别在于合成对比例2时不加入助剂元素M。在这种情况下，体系1加入体系2之后，依然为澄清溶液，无法制得相应的固体催化剂。从这一结果可以看出，助剂元素 对于合成钨酸盐纳米团簇至关重要。
对比例3：
采用与实施例1相同的制备方法来合成催化剂，其唯一的区别在于合成对比例3时不加入钨元素。在这种情况下所得的对比例3不含NaxWOy纳米团簇。
将对比例3与Mn/Na 2WO 4/SiO 2按照实施例17所示的方式进行测试，其结果如下：
Mn/Na 2WO 4/SiO 2的C2选择性为48.4％,C2收率为8.1％，而Mn/Na 2WO 4/SiO 2与对比例3的催化剂组合物的C2选择性为45.4％,C2收率为6.8％。从上述结果可以看出，对比例3不仅不能提高Mn/Na 2WO 4/SiO 2的选择性与收率反而起抑制作用，这表明钨元素是助催化剂中不可缺少的活性组分。
对比例4：
采用与实施例1相同的制备方法来合成催化剂，其唯一的区别在于合成对比例4时将氯化物换成氯化钼，即将实施例1中的W元素换成Mo元素。
将对比例4与Mn/Na 2WO 4/SiO 2按照实施例17所示的方式进行测试，其结果如下：
Mn/Na 2WO 4/SiO 2的C2选择性为48.4％,C2收率为8.1％，而Mn/Na 2WO 4/SiO 2与对比例4的催化剂组合物的C2选择性为48.2％,C2收率为8.0％。从上述结果可以看出，对比例4没有提高Mn/Na 2WO 4/SiO 2的选择性与收率，这表明钨元素是助催化剂中不可缺少的活性组分。
对比例5：
采用与实施例1相同的制备方法合成催化剂，唯一的区别在于合成对比例5时体系1在1min内就全部加入到了体系2中。
对比例5的高分辨电镜图片如图17所示，从图中可以看出，对比例5中的钨酸钠主要以钨酸钠大颗粒(>10nm)而不是纳米团簇的形式存在，这表明体系1加入体系2中的滴加速度对于催化剂的结构具有重要影响。体系1缓慢加入(加入时间≥2分钟)体系2可以使钨元素前驱体和助剂元素前驱体在碱金属作用下缓慢水解交联，从而有助于钨酸盐纳米团簇的形成。太快的加入将使得助剂元素前驱体迅速水解，从而无法让钨酸盐均匀分散在所形成的助剂元素的氧化物种。
将对比例5与Mn/Na 2WO 4/SiO 2按照实施例17所示的方式进行测试，其结果如下：
Mn/Na 2WO 4/SiO 2的C2选择性为48.4％,C2收率为8.1％，而Mn/Na 2WO 4/SiO 2与对比例5的催化剂组合物的C2选择性为47.5％,C2收率为7.6％。从上述结果可以看出，对比例5没有提高Mn/Na 2WO 4/SiO 2的选择性与收率，这表明钨酸盐纳米团簇才是助催化剂的活性结构，体系1的滴加速度会影响助催化剂种的钨酸盐结构进而影响其反应性能。
对比例6：
采用与实施例1相同的制备方法合成催化剂，唯一的区别在于合成对比例6时体系2所用的溶剂为丙酮。
将对比例6与Mn/Na 2WO 4/SiO 2按照实施例17所示的方式进行测试，其结果如下：
Mn/Na 2WO 4/SiO 2的C2选择性为48.4％,C2收率为8.1％，而Mn/Na 2WO 4/SiO 2与对比例6的催化剂组合物的C2选择性为40.3％,C2收率为6.3％。从上述结果可以看出，对比例6没有提高Mn/Na 2WO 4/SiO 2的选择性与收率，这表明助催化剂合成种必须使用合适的溶剂。
对比例7：
采用与实施例1相同的制备方法合成催化剂，唯一的区别在于在合成对比例7时，第3)步采用的是离心洗涤的方法而不是不经处理，直接烘干去除溶剂(即40℃下烘干溶剂后置于80℃烘箱内干燥12小时)。XRF测得对比例7中的钨元素wt％小于0.1％。这表明离心洗涤步骤会使催化剂中的钨元素流失。
将对比例7与Mn/Na 2WO 4/SiO 2按照实施例17所示的方式进行测试，其结果如下：
Mn/Na 2WO 4/SiO 2的C2选择性为48.4％,C2收率为8.1％，而Mn/Na 2WO 4/SiO 2与对比例7的催化剂组合物的C2选择性为44.2％,C2收率为6.9％。从上述结果可以看出，对比例7没有提高Mn/Na 2WO 4/SiO 2的选择性与收率。
上述结果表明，合成方法中步骤3)所述不经处理，直接烘干去除溶剂是非常重要的技术特征。
对比例8：
采用与实施例1相同的制备方法合成催化剂，唯一的区别在于在合成对比例8时，体系1所用的碱金属元素前驱体为硝酸钠，而不是NaOH。在这种情况下，体系1的pH为中性。
将对比例8与Mn/Na 2WO 4/SiO 2按照实施例17所示的方式进行测试，其结果如下：
Mn/Na 2WO 4/SiO 2的C2选择性为48.4％,C2收率为8.1％，而Mn/Na 2WO 4/SiO 2与对比例8的催化剂组合物的C2选择性为39.5％,C2收率为5.9％。从上述结果可以看出，对比例8不能提高Mn/Na 2WO 4/SiO 2的选择性与收率，这表明合成方法中体系1中碱金属前驱体的选取以及体系pH是非常重要的技术参数。

Claims (19)

  1. 一种含有钨酸盐纳米团簇的复合氧化物，其特征在于：所述复合氧化物包含碱金属元素A、钨元素W、助剂元素M以及氧元素O，且所述碱金属元素A、钨元素W、助剂元素M均与氧元素O形成复合物，
    所述碱金属元素A、钨元素W、助剂元素M均与氧元素O形成化合物是指该复合氧化物可以写成如下通式：：aAOx bWO3 cMOy,其中x,y分别为满足碱金属元素A和助剂元素M所形成氧化物电荷平衡所需的氧原子个数；a,b,c分别为碱金属元素A、钨元素W和助剂元素M占复合氧化物中所有非氧元素的原子百分比，5％≤a≤67％,1％≤b≤60％,20％≤c≤94％，
    所述碱金属元素A选自Li、Na、K、Mg、Ca、Sr、Ba中的任意一种或多种，
    所述助剂元素M选自Si、Zr、Ti、Al、La、Ce、Co中的任意一种或多种，
    所述碱金属元素A的原子百分比为5％-67％；所述钨元素W的原子百分比为1％-60％；助剂元素M的原子百分比为20％-94％；所述复合氧化物中氧元素的含量为满足碱金属元素A、钨元素W、M电荷平衡所需的氧原子数的总和；
    所述某元素的原子百分比按照以下公式计算，
    Figure PCTCN2021124519-appb-100001
    其中，所述钨酸盐纳米团簇由所述碱金属元素A、钨元素W和氧元素O所组成，所述钨酸盐纳米团簇的通式为A xWO y，其中，0<x≤2，y代表满足通式电荷平衡所需的氧原子的数目；且所述钨酸盐纳米团簇满足团簇富集指数，所述团簇富集指数是指在任意一个包含所述钨酸盐纳米团簇的10×10nm 2的区域内，所述钨酸盐纳米团簇的个数≥3个；优选的，所述钨酸盐纳米团簇的个数≥5个，进一步优选≥10个，进一步优选≥20个；
    优选的，所述团簇富集指数检测方法：将所述复合氧化物在高分辨透射电镜下进行观察，在含有碱金属元素A、钨元素W和氧元素O三种元素的钨酸盐纳米团簇的区域内，随机选取5个10×10nm 2的区域，统计该区域所含的钨酸盐纳米团簇的个数，取平均值；优选的，所述高分辨透射电镜观察时的放大倍数为200万-3000万倍，优选为500万-1000万倍；优选的，所述钨酸盐纳米团簇的粒径≤10.0nm，优选为≤5.0nm，进一步优选为≤2.0nm，更进一步优选为≤1.0nm；
    优选的，所述复合氧化物的比表面积为0.1-10g/m 2，进一步优选为0.5-5g/m 2，进一步优选1-2g/m 2；
    优选的，所述钨酸盐纳米团簇中碱金属元素A、钨元素W、氧元素O三种元素均匀分布，所述均匀分布是指钨酸盐团簇中任意区域均含有碱金属元素A、钨元素W、氧元素O；优选的，所述均匀分布的检测方法为：将所述复合氧化物在高分辨透射电镜下观察，采用X射线能谱仪(EDS)面扫模式对所述钨酸盐纳米团簇进行成分分析，随机选取10个团簇，所述团簇中任意区域均含有碱金属元素A、钨元素W、氧元素O；更优选的，所述高分辨透射电镜观察时的放大倍数为200万-3000万倍,优选为500万-1000万倍；
    优选的，所述复合氧化物中碱金属元素A的原子百分比为10％-65％，进一步优选为15％-50％；进一步优选为原子10％-60％，进一步优选为20％-50％，进一步优选为30％-40％；所述钨元素W的原子百分比为2％-55％，进一步优选为5％-50％，进一步优选为10％-40％，进一步优选为20％-30％；助剂元素M的原子百分比为22％-92％上，进一步优选为25％-90％，优选为30％-80％，进一步优选为40％-70％，进一步优选为50％-60％；
    优选的，所述钨酸盐纳米团簇中钨元素以四配位钨酸盐的形式存在，所述四配位是指一个钨原子有且仅有四个氧原子与其结合；更优选的，所述四配位结构的检测方法为：对所述复合氧化物进行X射线精细结构谱测试，采集复合物中钨元素的L 1-edge和L 3-edgeX射线吸收近边结构谱(XANES)和扩展X射线吸收谱精细结构(EXAFS)，通过定性分析和数据拟合得出钨原子的配位数；
    优选的，所述复合氧化物在800℃下空气中焙烧6h之后，钨酸盐纳米团簇的粒径变化值Δ1≤20％，进一步优选为Δ1≤10％；计算公式如下：
    Figure PCTCN2021124519-appb-100002
    焙烧后钨酸盐纳米团簇的团簇富集指数变化值Δ2≤20％；进一步优选为Δ2≤10％；计算公式如下：
    Figure PCTCN2021124519-appb-100003
  2. 根据权利要求1所述的复合氧化物，其特征在于：所述碱金属元素A至少是Na，所述助剂元素M至少是Zr或者Al，所述含有钨酸盐纳米团簇的复合氧化物分别表述为NaWZr或NaWAl，所述钨酸盐纳米团簇由碱金属元素Na、钨元素W和氧元素O所组成，所述钨酸盐纳米团簇的通式为Na xWO y，0<x≤2，y代表满足通式电荷平衡所需的氧原子的数目；
    所述复合氧化物中Na的原子百分比为5％-67％；所述钨元素W的原子百分比为1％-60％；助剂元素M的原子百分比为20％-94％；
    优选的，所述复合氧化物中Na的原子百分比为10％-65％，进一步优选为15％-50％；进一步优选为原子10％-60％，进一步优选为20％-50％，进一步优选为30％-40％；所述钨元素W的原子百分比为2％-55％，进一步优选为5％-50％，进一步优选为10％-40％，进一步优选为20％-30％；助剂元素Zr或者Al的原子百分比为22％-92％上，进一步优选为25％-90％，优选为30％-80％，进一步优选为40％-70％，进一步优选为50％-60％；
    所述复合氧化物中0<Na:W的摩尔比≤5，优选的，0.1≤Na:W的摩尔比≤4，进一步优选为0.8≤Na:W的摩尔比≤3.5；进一步优选为1.0≤Na:W的摩尔比≤3.0；进一步优选为1.5≤Na:W的摩尔比≤2.0；进一步优选为1.4≤Na:W的摩尔比≤1.6；
    所述复合氧化物中W:Zr的摩尔比≥0.1；优选的，0.2≤W:Zr的摩尔比≤100；进一步优选为0.23≤W:Zr的摩尔比≤10；进一步优选为0.3≤W:Zr的摩尔比≤1；进一步优选为0.4 ≤W:Zr的摩尔比≤0.5。
  3. 权利要求1或2所述含有钨酸盐纳米团簇的复合氧化物的制备方法，其特征在于，包含如下步骤：
    1)分别制备溶液体系1和溶液体系2，所述溶液体系1和溶液体系2均为透明溶液，其中所述透明溶液是指溶液中没有显在的悬浊物，且溶液不会分层，当光线透过该溶液时，不会产生丁达尔效应；
    2)对溶液体系2进行搅拌的情况下，将溶液体系1在2-200分钟内完全加入到溶液体系2中，直至呈现浊液，将所述浊液继续搅拌1小时以上，优选2小时以上，更优选为3小时以上；优选的，所述滴加时间为2-200分钟，优选为10-100分钟，更优选为20-60分钟；优选的，所述的搅拌为快速搅拌，所述快速搅拌的转速为500-1000转/分钟，更优选为750-900转/分钟；优选的，所述搅拌的时间为10分钟-2小时，更优选的搅拌时间为30分钟-1小时；
    3)将步骤2)所得产物不经处理，直接去除溶剂后，将得到的固体进行干燥，得到干燥的固体产物，具体地所述不经处理是指任何洗涤、离心、过滤步骤；
    优选的，去除溶剂的方法为将溶剂烘干，更具体地，烘干的方法为将步骤2)所得产物置于温度为30-50℃的氛围中烘至溶液挥发；优选的，所述温度为40℃；
    优选的，将固体进行干燥的温度为60-100℃，更优选为80-90℃；优选的，所述干燥的时间为12小时以上，更优选的时间为24小时以上；
    4)将步骤3)得到的固体产物焙烧后制得含有钨酸盐纳米团簇的复合氧化物，优选的，所述焙烧的温度为700-900℃，更优选为750-850℃，更优选为800选；所焙烧的时间为3-8小时，优选为4-6小时；所述焙烧的升温速率为2-10℃/分钟，更优选为3-5℃/分钟；
    所述溶液体系1的制备方法为：将含有该元素的化合物原料的碱金属元素前驱体溶于适量水中，充分搅拌下使其形成透明溶液，即得到溶液体系1，所述透明溶液pH大于7，更优选为pH≥10；
    所述溶液体系2的制备方法选自以下任意一种：a)将钨元素前驱体、助剂元素前驱体和适量水混合并快速搅拌，形成透明溶液，即得到溶液体系2-1；b)将钨元素前驱体、助剂元素前驱体和适量醇混合并快速搅拌，形成透明溶液，即得到溶液体系2-2；
    其中，溶液体系1和溶液体系2中加入的碱金属元素前驱体、钨元素前驱体、助剂元素前驱体的配比符合以下公式：
    溶液体系1和溶液体系2中，按下述公式计算某元素的原子百分比，
    Figure PCTCN2021124519-appb-100004
    所述碱金属元素A的原子百分比为5％-67％；所述钨元素W的原子百分比为1％-60％；助剂元素M的原子百分比为20％-94％；
    优选的，所述复合氧化物中碱金属元素A的原子百分比为10％-65％，进一步优选为15％-50％；进一步优选为原子10％-60％，进一步优选为20％-50％，进一步优选为30％-40％；所述钨元素W的原子百分比为2％-55％，进一步优选为5％-50％，进一步优选为10％-40％，进一步优选为20％-30％；助剂元素M的原子百分比为22％-92％上，进一步优选为25％-90％，优选为30％-80％，进一步优选为40％-70％，进一步优选为50％-60％
    优选的，所述溶液体系1中碱金属元素前驱体的浓度为1-40wt％,优选为10-30wt％,更优选为15-25wt％；优选的，所述溶液体系2-1和2-2中钨元素前驱体的浓度为1-30wt％,优选为5-25wt％,更优选为10-20wt％；优选的，所述溶液体系2-1和2-2中助剂元素前驱体的浓度为1-50wt％,优选为10-40wt％,更优选为20-35wt％；
    优选的，所述溶液体系1制备方法中的碱金属元素前驱体选自氢氧化锂、氢氧化钠、碳酸锂、碳酸钠、碳酸氢钠、氢氧化钾、碳酸钾、碳酸氢钾、乙酸镁、氢氧化钙、乙酸钙、氢氧化锶和氢氧化钡任意一种或多种；
    优选的，所述溶液体系2-1制备方法中的助剂元素前驱体选自硅酸钠、硝酸氧锆、硝酸锆、氧氯化锆、二(乙酸根合-O)氧合锆、柠檬酸锆、硝酸钛、硝酸铝、硝酸镧、乙酸镧、氯化镧、硝酸铈、乙酸铈、氯化铈、硝酸钴、乙酸钴中的任意一种或多种；所述钨元素前驱体选自钨酸钠、钨酸铯、乙醇钨、氧化钨铵、氧化钨铵水合物、钨酸锶、钨酸镁、钨酸钡、对五水合钨酸铵、偏钨酸铵水合物、钨酸钙、钨酸钡、钨酸锶的任意一种或多种；
    优选的，溶液体系2-2制备方法中的钨元素前驱体选自钨酸钠、氯化钨的任意一种或两种；助剂元素前驱体选自正硅酸四乙酯、硝酸锆、正丁醇锆、硝酸氧锆、氧氯化锆、二(乙酸根合-O)氧合锆、柠檬酸锆、钛酸四丁酯、仲丁醇铝、异丙醇铝、硝酸镧、硝酸铝、硝酸铈、硝酸钴中的任意一种或多种；醇溶液选自甲醇、乙醇、丙醇、丁醇中的任意一种或多种。
  4. 根据权利要求3所述的制备方法，其特征在于，所述碱金属元素前驱体为钠元素前驱体，所述助剂元素前驱体选自锆元素前驱体或者铝元素前驱体，制得的所述含有钨酸盐纳米团簇的复合氧化物为NaWZr或NaWAl，所述钨酸盐纳米团簇由碱金属元素Na、钨元素W和氧元素O所组成，所述钨酸盐纳米团簇的通式为Na xWO y，0<x≤2，y代表满足通式电荷平衡所需的氧原子的数目；
    优选的，所述溶液体系1制备方法中的碱金属前驱体选自氢氧化钠、碳酸钠、碳酸氢钠中的任意一种或多种；
    优选的，所述溶液体系2-1制备方法中的助剂元素前驱体选自硝酸氧锆、硝酸锆、氧氯化锆、二(乙酸根合-O)氧合锆、柠檬酸锆、硝酸铝中的任意一种或多种；所述钨元素前驱体选自钨酸钠、钨酸铯、乙醇钨、氧化钨铵、氧化钨铵水合物、钨酸锶、钨酸镁、钨酸钡、对五水合钨酸铵、偏钨酸铵水合物、钨酸钙、钨酸钡、钨酸锶的任意一种或多种；
    优选的，所述溶液体系2-2中的钨元素前驱体选自钨酸钠、氯化钨的任意一种或两种；助剂元素前驱体选自硝酸锆、正丁醇锆、硝酸氧锆、氧氯化锆、二(乙酸根合-O)氧合锆、柠 檬酸锆、仲丁醇铝、异丙醇铝、硝酸铝中的任意一种或多种；醇溶液选自甲醇、乙醇、丙醇、丁醇中的任意一种或多种；
    优选的，0<Na:W的摩尔比≤摩，优选的，0.1的，W甲醇的摩尔比≤4，进一步优选为0.8步优选为醇的摩尔比≤摩尔比；进一步优选为1.0步优选为醇的摩尔比≤摩尔比；进一步优选为1.5优选为为醇的摩尔比≤摩尔比；进一步优选为1.4步优选为醇的摩尔比≤摩尔比；
    W:Zr的摩尔比≥摩尔1；优选的，0.2≤W:Zr的摩尔比≤摩尔比；进一步优选为0.23≤W:Zr的摩尔比≤摩尔；进一步优选为0.3步优选为Z的摩尔比≤摩；进一步优选为0.4步优选为Z的摩尔比≤摩尔比；
    优选的，所述溶液体系2-2制备方法中的助剂元素前驱体为正丁醇锆，所述钨元素前驱体为氯化钨；更优选的，所述钨元素和锆元素的摩尔比≥1∶9，优选为≥2∶9，更优选为≥3∶9；更优选的，所述溶液体系1为NaOH水溶液，NaOH质量百分数为1％～60％，优选为10％～50％，更优选为15％～40％；
    优选的，所述溶液体系2-2制备方法中的助剂元素前驱体为异丙醇铝，所述钨元素前驱体为氯化钨，所述钨元素和铝元素的摩尔比≥1∶9，优选为≥2∶9，更优选为≥3∶9；更优选的，所述溶液体系1为NaOH水溶液，NaOH质量百分数为1％～60％，优选为10％～50％，更优选为15％～40％；
    优选的，所述溶液体系2-2制备方法中的助剂元素前驱体为正丁醇锆，所述钨元素前驱体为钨酸钠，所述钨元素和锆元素的摩尔比≥1∶9，优选为≥2∶9，更优选为≥3∶9；更优选的，所述溶液体系1为KOH质量百分数为1％～60％，优选为10％～50％，更优选为15％～40％；
    优选的，所述溶液体系2-2制备方法中的助剂元素前驱体为异丙醇铝，所述钨元素前驱体为钨酸钠，所述钨元素和铝元素的摩尔比≥1∶9，优选为≥2∶9，更优选为≥3∶9；更优选的，所述溶液体系1为KOH质量百分数为1％～60％，优选为10％～50％，更优选为15％～40％。
  5. 一种助催化剂，其特征在于，所述的助催化剂包含权利要求1或2所述的含有钨酸盐纳米团簇的复合氧化物；
    优选的，所述的助催化剂不能单独用作催化剂催化甲烷氧化偶联(OCM)反应；优选的，所述的助催化剂不具有显著OCM活性；其中优选的，所述不具有显著OCM活性的检测方法为：在甲烷和氧气共进气的床层反应器中，当所述催化剂在气体-时空速度为大于等于20000mL/g/h、催化剂床层温度为800℃及以下、反应压力为1个大气压时用作甲烷氧化催化剂，其单程C2收率不高于5％；优选的，所述收率采用气相色谱法定量测得。
  6. 一种催化剂组合物，其特征在于，所述的催化剂组合物包含权利要求1或2所述复合氧化物和至少一种具有或显著具有OCM活性的催化剂OCM catalyst；
    优选的，所述具有OCM活性是指能够单独用作催化剂催化OCM反应；优选的，所述具有OCM活性的含义是：在甲烷和氧气共进气的床层反应器中，当所述催化剂在气体-时空速度为大于等于20000mL/g/h、催化剂床层温度为800℃及以下、反应压力为1个大气压 时用作甲烷氧化偶联催化剂，其具有大于5％的C 2单程收率；
    优选的，所述OCM catalyst具有显著OCM活性的含义：在甲烷和氧气共进气的床层反应器中，当所述催化剂在气体-时空速度为大于等于20000mL/g/h、催化剂床层温度为800℃及以下、反应压力为1个大气压时用作甲烷氧化偶联催化剂，其具有大于15％的C 2单程收率；
    优选的，所述OCM catalyst与所述复合氧化物的质量比为0.1-50.0；更优选的，所述的质量比为0.5～20.0∶1.0；更优选的，所述的质量比为1.0～10.0∶1.0；更优选的，所述的质量为2.0～4.0∶1.0；
    优选的，所述收率采用气相色谱法定量测得；
    优选的，所述OCM catalyst选自钨锰催化剂、稀土金属氧化物、钙钛矿类化合物、碱金属和碱土金属氧化物以及上述催化剂的衍生物中的任意一种或多种；更优选为钨锰催化剂、氧化镧、氧化钐、Li/MgO、Ca/CeO 2；优选的，所述钨锰催化剂为Mn-Na 2WO 4/SiO 2；
    优选的，所述OCM catalyst与所述复合氧化物之间的距离≤3mm；
    优选的，所述的催化剂组合物是将所述复合氧化物和OCM catalyst通过物理混合的方式复合而成；
    优选的，所述OCM catalyst为包含第二碱金属元素、钨元素、锰元素、氧元素以及第五组分元素的复合物；更优选的，所述第五组分元素选自Al、Si、Ti、Zr、C、N中的任意一种或多种，进一步更优选的，所述第五组分元素选自Al,、Si、Ti中的任意一种或多种，更优选的，所述第五组分元素选自Si；更优选的，所述第二碱金属选自Li、Na、K中的任意一种或多种；更优选的，所述第二碱金属选自Na；
    优选的，所述第二碱金属元素占所述OCM catalyst的质量百分比为0.1～2.0wt.％；更优选的，所述第二碱金属元素占所述OCM catalyst的质量百分比为0.5～1.5wt.％；
    优选的，所述钨元素占所述OCM catalyst的质量百分比为0.1～5.0wt.％，优选的，所述钨元素占所述OCM catalyst的质量百分比为2.0～4.0wt.％；
    优选的，所述锰元素的占所述OCM catalyst的质量百分比为0.1～10.0wt.％，优选的，所述锰元素的占所述OCM catalyst的质量百分比为1.0～4.0wt.％。
    优选的，所述的催化剂还包含添加剂；更优选的，所述的添加剂选自散热助剂、传质助剂、成型助剂、增强耐磨剂、分散剂、稳定剂等中的任意一种或多种。
  7. 如权利要6所述的催化剂组合物，其特征在于，在相同的反应条件下，所述催化剂组合物催化OCM反应的选择性和收率比单独使用OCM catalyst均提高1.2倍以上；
    优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥程收率；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥40％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥45％。
  8. 如权利要7所述的催化剂组合物，其特征在于，所述OCM catalyst为Mn/Na 2WO 4/SiO 2，所述复合氧化物为Na、W、Zr的复合氧化物NaWZr；优选地，所述OCM catalyst与所述复合氧化物的质量比为4:1-0.5:1；更优选为2:1-1:1；优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥70％且C 2单程收率≥35％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥40％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥45％；
    优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，所述催化剂组合物Mn/Na 2WO 4/SiO 2-NaWZr的C 2选择性可以提升为Mn/Na 2WO 4/SiO 2的1.3倍，且其C 2单程收率为Mn/Na 2WO 4/SiO 2的1.2倍。
  9. 根据权利要求7所述的催化剂组合物，其特征在于：所述OCM catalyst为La 2O 3，所述复合氧化物为Na、W、Zr的复合氧化物NaWZr，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
    优选的，所述催化剂组合物La 2O 3-NaWZr在甲烷和氧气共进气的OCM床层反应器中，La 2O 3-NaWZr的C 2选择性可以提升为La 2O 3的1.3倍，且其C 2单程收率为La 2O 3的1.2倍。
  10. 根据权利要求7所述的催化剂组合物，其特征在于：所述OCM catalyst为Sm 2O 3，所述复合氧化物为Na、W、Zr的复合氧化物NaWZr，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
    优选的，所述催化剂组合物Sm 2O 3-NaWZr在甲烷和氧气共进气的OCM床层反应器中，Sm 2O3-NaWZr的C 2选择性可以提升为Sm 2O 3的2.0倍，且其C 2单程收率为Sm 2O 3的1.8倍。
  11. 根据权利要求7所述的催化剂组合物，其特征在于：所述OCM catalyst为Li/MgO，所述复合氧化物为Na、W、Zr的复合氧化物NaWZr，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
    优选的，所述催化剂组合物Li/MgO-NaWZr在甲烷和氧气共进气的OCM床层反应器中，Li/MgO-NaWZr的C 2选择性可以提升为Li/MgO的2.0倍，且其C 2单程收率为Li/MgO的1.45倍。
  12. 根据权利要求7所述的催化剂组合物，其特征在于：所述OCM catalyst为Ca/CeO 2，所述复合氧化物为Na、W、Zr的复合氧化物NaWZr，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
    优选的，所述催化剂组合物Ca/CeO 2-NaWZr在甲烷和氧气共进气的OCM床层反应器中，Ca/CeO 2-NaWZr的C 2选择性可以提升为Ca/CeO 2的1.3倍，且其C 2单程收率为Ca/CeO 2的1.5倍；
  13. 根据权利要求7所述的催化剂组合物，其特征在于：所述催化剂组合物为 Mn-Na 2WO 4/SiO 2-NaWAl，其中，所述OCM catalyst为Mn-Na 2WO 4/SiO 2，所述复合氧化物为Na、W、Al的复合氧化物NaWAl，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
    优选的，所述催化剂组合物Mn-Na 2WO 4/SiO 2-NaWAl在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥70％且C 2单程收率≥35％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥40％；更优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，能够实现C 2选择性≥择性应且C 2单程收率≥45％；
    优选的，所述催化剂组合物在甲烷和氧气共进气的OCM床层反应器中，Mn-Na 2WO 4-NaWAl的C 2选择性可以提升为Mn-Na 2WO 4的1.3倍，且其C 2单程收率为Mn/Na 2WO 4/SiO 2的1.2倍。
  14. 根据权利要求7所述的催化剂组合物，其特征在于：所述OCM catalyst为La 2O 3，所述复合氧化物为Na、W、Al的复合氧化物NaWAl，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
    优选的，所述催化剂组合物La 2O 3-NaWAl在甲烷和氧气共进气的OCM床层反应器中，La 2O 3-NaWAl的C 2选择性可以提升为La2O3的1.3倍，且其C 2单程收率为La 2O 3的1.2倍。
  15. 根据权利要求7所述的催化剂组合物，其特征在于：所述OCM catalyst为Sm 2O 3，所述复合氧化物为Na、W、Al的复合氧化物NaWAl，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
    优选的，所述催化剂组合物Sm 2O 3-NaWAl在甲烷和氧气共进气的OCM床层反应器中，Sm 2O3-NaWAl的C 2选择性可以提升为Sm 2O 3的1.2倍，且其C 2单程收率为Sm 2O 3的1.5倍。
  16. 根据权利要求7所述的催化剂组合物，其特征在于：所述OCM catalyst为Li/MgO，所述复合氧化物为Na、W、Al的复合氧化物NaWAl，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
    优选的，所述催化剂组合物Li/MgO-NaWAl在甲烷和氧气共进气的OCM床层反应器中，Li/MgO-NaWAl的C 2选择性可以提升为Li/MgO的1.7倍，且其C 2单程收率为Li/MgO的1.8倍。
  17. 根据权利要求7所述的催化剂组合物，其特征在于：所述OCM catalyst为Ca/CeO 2，所述复合氧化物为Na、W、Al的复合氧化物NaWAl，所述OCM catalyst与所述复合氧化物的质量比为4:1-1:1；更优选为2:1-1:1；
    优选的，所述催化剂组合物Ca/CeO 2-NaWAl在甲烷和氧气共进气的OCM床层反应器中，Ca/CeO 2-NaWAl的C2选择性可以提升为Ca/CeO 2的1.3倍，且其C 2单程收率为Ca/CeO 2的1.6倍。
  18. 权利要求5所述的助催化剂和权利要求6-17任一项所述的催化剂组合物在化学反应中的用途；优选的，所述的化学反应是自由基转化反应；更优选的，所述的化学反应是甲烷氧化偶联催化反应。所述甲烷氧化偶联催化反应指甲烷在催化剂作用下，碳氢键断裂，脱出的氢与氧作用生成水，同时形成碳碳键制取碳二及以上烃的过程。
  19. 根据权利要求18所述的用途，其特征在于：所述甲烷氧化偶联催化反应以甲烷和氧气为原料气，在床层反应器上进行反应，其产物包括C 2烃、碳氧化合物和C 3烃；
    优选的，所述原料气还包含稀释气；更优选的，所述稀释气选自氮气、氦气、氩气的至少一种；
    所述甲烷和氧气的比例为1.0-20.0，优选为2.0-6.0，更优选为2.0-5.0；
    优选的，所述原料气的压力为0.1-20.0MPa，优选为1.0-8.0MPa，更优选为2.0-6.0MPa；
    优选的，所述反应的温度为600-900℃，优选为700-850℃；
    优选的，所述反应的空速为500-50000h -1，优选为1000-35000h -1。
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