Preparation method and application of gold-loaded tin dioxide catalyst

Abstract

The invention provides a preparation method and application of a gold-loaded tin dioxide catalyst, the gold-loaded tin dioxide catalyst can be used for catalyzing methane oxidation to prepare methanol, the preparation method comprises the following steps: dissolving a tin source and a gold source in water to obtain a mixed solution; drying the mixed solution, and grinding into powder; and carrying out high-temperature calcination treatment on the powder under the protection of a vacuum inert atmosphere to obtain the gold-loaded tin dioxide catalyst, which is a gold / tin dioxide catalyst and comprises a tin dioxide carrier and gold nanoparticles loaded on the carrier. In the prepared gold / tin dioxide catalyst, a gold-tin alloy layer is formed on the surfaces of gold particles loaded on tin dioxide, and under the action of water, carbon monoxide assists oxygen activation to generate hydroxyl radicals, so that oxygen-containing compounds can be prepared by efficiently oxidizing methane, and the methanol production rate and selectivity in methane oxidation reaction are improved.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a gold / tin dioxide material, a preparation method and an application thereof, including a preparation method and an application of a gold-loaded tin dioxide catalyst. Background Art

[0002] At present, the huge proven reserves of natural gas have determined that natural gas will become the main source of energy and chemicals in the future. Methane reserves are abundant and it is also one of the clean energy sources in chemical fuels, accounting for a large part of global fossil fuels. In addition to natural sources, methane can also be produced by processing renewable resources such as biomass pyrolysis. Therefore, methane plays an important role both in the current fossil fuel stage and in the future renewable energy stage. Moreover, basic chemical production has shifted from petrochemicals to the natural gas industry. In addition to being used as a fuel, methane can be used as a raw material for the manufacture of carbon materials, methanol, formaldehyde and other substances. Among them, the traditional conversion method of methane to methanol usually includes two stages: steam reforming and synthesis gas oxidation, which generally need to be carried out under high temperature and high pressure conditions.

[0003] Different from the traditional method of converting methane to methanol, the use of gold / tin dioxide materials as catalysts can directly convert methane to methanol, which optimizes the reaction conditions and simplifies the conversion route. In recent years, nanoscale gold particles loaded on metal oxides have been widely studied due to their high reactivity in various important catalytic reactions. For example, when gold is dispersed in semiconductor oxides, it has high activity for the low-temperature catalytic oxidation of carbon monoxide (CO).

[0004] Although the catalytic activity of gold catalysts in low-temperature CO oxidation has been extensively studied, the catalytic activity of gold catalysts supported on tin dioxide has been rarely studied. Due to the special physical and chemical properties of nano-tin dioxide, tin dioxide has a wide range of applications in catalysts, catalytic carriers, gas sensors, rechargeable lithium batteries, optical electronic devices, etc. However, the sintering instability of gold nanoparticles is accompanied by a corresponding loss of catalytic activity, which is a serious problem in many application fields. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing a gold-loaded tin dioxide catalyst and its application. The gold / tin dioxide catalytic material prepared by the present invention can be used in methane oxidation reactions, has high selectivity and activity, and good catalytic stability.

[0006] The present invention provides a method for preparing a gold-loaded tin dioxide catalyst, comprising:

[0007] Step S1, dissolving a tin source and a gold source in water to obtain a mixed solution;

[0008] Step S2, drying the mixed solution and grinding it into powder;

[0009] Step S3, calcining the powder at high temperature under the protection of a vacuum inert atmosphere to obtain a gold-loaded tin dioxide catalyst.

[0010] Preferably, in step S1, the tin source is tin dioxide; and the gold source is chloroauric acid.

[0011] Preferably, the step S1 comprises: stirring and mixing tin dioxide and a chloroauric acid aqueous solution to obtain a mixed solution; the concentration of the chloroauric acid aqueous solution is 23-24 mg / mL.

[0012] Preferably, in step S1, the mass ratio of gold atoms in the tin source and the gold source is 1000:1.

[0013] Preferably, in step S2, the drying is performed at 70-80° C. for 12-13 hours.

[0014] Preferably, in step S3, the temperature of the high temperature calcination treatment is 400-600° C., the heating rate is 2-5° C. / min, and the time is 3-5 h.

[0015] Preferably, in step S3, the inert atmosphere is an argon atmosphere with a flow rate of 80 to 100 mL / min.

[0016] Preferably, in step S3, the loading amount of the gold-loaded tin dioxide catalyst is 0.1-1 wt%.

[0017] The present invention provides a method for direct oxidation of methane, comprising:

[0018] The gold-loaded tin dioxide catalyst obtained by the preparation method described above is used as a catalyst, and methane, carbon monoxide and oxygen are introduced for catalytic oxidation to obtain methanol and formaldehyde.

[0019] Preferably, the temperature of the catalytic oxidation is 90-130°C.

[0020] For some existing gold / oxide catalytic materials, the carrier fluidity of gold particles increases at higher temperatures, resulting in the loss of active sites. However, the structurally stable gold / tin dioxide catalyst designed in this application is conducive to improving the yield and selectivity of methane conversion to methanol.

[0021] In the method for preparing the catalyst in the embodiment of the present application, an impregnation method is first used to form a mixed solution of a tin source and a gold source, so that the gold can be uniformly and stably loaded later; then a high-temperature calcination treatment is performed in a vacuum inert atmosphere environment to obtain a tin dioxide catalyst loaded with gold, which is a gold / tin dioxide catalyst, and a specific alloy structure is formed on the surface of the gold particles. The gold / tin dioxide catalyst prepared by the present invention includes a tin dioxide carrier, and gold nanoparticles loaded on the tin dioxide carrier. In the gold / tin dioxide catalyst prepared by the present application, the gold nanoparticles and tin dioxide form a gold-tin alloy layer, which has good catalytic stability; at the same time, because carbon monoxide helps oxygen dissociate into active oxygen, the gold-tin alloy layer can directly convert methane into oxygen-containing compounds through molecular oxygen with the help of carbon monoxide, thereby improving the methanol yield and selectivity in the methane oxidation reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 is the XRD diagram of the gold / tin dioxide material prepared in Examples 1-2 and Comparative Example 1 of the present invention;

[0024] Figure 2 It is the X-ray photoelectron spectrum of the gold / tin dioxide material prepared in Examples 1-2 and Comparative Example 1 of the present invention;

[0025] Figure 3 is a fluorescence image of the gold / tin dioxide material prepared in Example 1 of the present invention;

[0026] Figure 4 1 is a graph showing the yield of methane oxidation products of gold / tin dioxide materials prepared in Examples 1-2 and Comparative Example 1 of the present invention;

[0027] Figure 5 is a graph showing the product yield of methane oxidation reaction at different reaction temperatures of the gold / tin dioxide material prepared in Example 1 of the present invention;

[0028] Figure 6 is a graph showing the product yield of methane oxidation reaction under different CO partial pressures of the gold / tin dioxide material prepared in Example 1 of the present invention;

[0029] Figure 7 This is a stability and selectivity test diagram of the gold / tin dioxide material prepared in Example 1 of the present invention under the optimal reaction conditions;

[0030] Figure 8 The catalytic performance results of different catalyst dosages in the examples of the present invention;

[0031] Fig. 9 The catalytic performance results of the catalysts with different loading amounts in the examples of the present invention are shown;

[0032] Fig.10 These are the catalytic performance results of the catalysts obtained at different calcination temperatures in the examples of the present invention. DETAILED DESCRIPTION

[0033] In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0034] In view of the performance requirements of catalysts for direct oxidation of methane to methanol in the prior art, the present invention provides a method for preparing a gold-loaded tin dioxide catalyst, comprising:

[0035] Step S1, dissolving a tin source and a gold source in water to obtain a mixed solution;

[0036] Step S2, drying the mixed solution and grinding it into powder;

[0037] Step S3, calcining the powder at high temperature under the protection of a vacuum inert atmosphere to obtain a gold-loaded tin dioxide catalyst.

[0038] The gold-loaded tin dioxide catalyst prepared by the method of the present invention can be applied to methane oxidation reaction, has high selectivity and activity, and has good catalytic stability.

[0039] In the preparation method of the gold-loaded tin dioxide catalyst described in the embodiment of the present application, tin dioxide (SnO2) is preferably used as the tin source and chloroauric acid is used as the gold source; the chemical formula of chloroauric acid is HAuCl4·4H2O, and the molecular weight is 411.85. For example, it includes the following specific steps:

[0040] Take appropriate amounts of tin dioxide powder and gold source aqueous solution, place them in a beaker and mix them. The mixture can be evenly mixed under the stirring of a glass rod so that the mixed solution can fully adhere to the wall. After that, the obtained mixed solution is preferably placed in an oven for drying, and the solid is collected and ground into powder. Finally, it is loaded into a porcelain boat and calcined in a vacuum inert protective atmosphere using a tubular furnace. The obtained gold / tin dioxide catalyst is a gold-loaded tin dioxide catalyst.

[0041] Specifically, the embodiment of the present application first mixes tin dioxide powder with a gold source solution (chloroauric acid aqueous solution); in this process, the mass ratio of the tin dioxide powder to the gold atoms in the gold source is preferably 1000:1, and the maximum should not exceed 1%, otherwise it is not suitable for preparation. Specifically, the gold source containing gold atoms is chloroauric acid; the concentration of the chloroauric acid aqueous solution is preferably 23-24 mg / mL, and more preferably 23.21 mg / mL. The mass ratio of the raw materials and the gold atoms is reflected in the feed ratio. For example, in this case, 500 mg SnO2 is fed. According to the mass ratio of 1000:1, 0.5 mg of gold atoms need to be added, and then divided by the concentration of chloroauric acid 23.21 mg / ml, the volume of chloroauric acid to be added is 21.5 microliters. The present application preferably adopts an equal volume impregnation method, which is conducive to more uniform and stable loading of gold on SnO2.

[0042] In the embodiment of the present invention, the uniformly stirred mixed liquid can be dried in an oven, and the drying is preferably carried out at 70 to 80° C., and the drying time can be 12 to 13 hours to obtain a solid sample.

[0043] After the solid sample is collected, the embodiment of the present invention grinds it into fine powder, transfers it into a porcelain boat and puts it into a tube furnace, and performs high-temperature calcination treatment in a vacuum environment in the tube furnace.

[0044] After evacuation, the vacuum degree is evacuated to -0.1MPa, and the calcination treatment described in the embodiment of the present invention is carried out under an inert protective atmosphere, especially in an argon atmosphere, which is beneficial to improve the catalytic activity of the catalytic material. Specifically, the flow rate of the argon gas is preferably 80-100ml / min; the calcination temperature is preferably 400-600°C, the heating rate can be 2-5°C / min, and the time is 3-5h. Further specifically, the calcination temperature is 400°C, the heating rate is 2°C / min, and the time is 4h. The preparation method of the embodiment of the present invention is simple and easy, and is suitable for large-scale promotion and application.

[0045] Accordingly, an embodiment of the present application provides a gold-loaded tin dioxide catalyst, and this gold / tin dioxide material is prepared by the method described above; the gold / tin dioxide material includes a tin dioxide carrier and gold particles loaded on the tin dioxide carrier, and a specific alloy structure is formed on the surface of the gold particles. The introduction of gold is conducive to the adsorption of carbon monoxide and further combines with molecular oxygen to promote methane conversion, thereby improving the catalytic activity, selectivity and stability of the methane oxidation reaction.

[0046] In the gold / tin dioxide material described in the embodiment of the present application, the gold loading in the tin dioxide carrier is 0.1-1.0wt%; the gold loading is preferably 0.1-0.5wt%, specifically 0.1wt%, 0.2wt%, etc., which has an important influence on the catalytic activity, etc. Among them, if the gold loading is too low, it will not promote the adsorption of carbon monoxide in the catalytic reaction system of methane oxidation, and if the loading is too high, it will hinder the adsorption of carbon monoxide by the gold-tin alloy site.

[0047] The present application also provides the use of the above-mentioned gold / tin dioxide material in the reaction of methane oxidation to methanol; that is, the present invention provides a method for direct oxidation of methane, comprising: using the gold-loaded tin dioxide catalyst obtained by the preparation method described above as a catalyst, introducing methane, carbon monoxide and oxygen for catalytic oxidation to obtain methanol and formaldehyde.

[0048] In some embodiments of the present invention, 10-50 mg of gold / tin dioxide catalyst powder and a certain amount of water can be added to a 50 ml batch reactor; after the batch reactor is assembled and reinforced, 5 bar of oxygen, 5 bar of carbon monoxide, and 20 bar of methane are sequentially filled as reaction gases. The methane oxidation to methanol reaction occurs in a batch reactor, wherein the temperature of the catalytic oxidation is preferably 90-130°C, and further 100-120°C. Specifically, the CO partial pressure can be 1 bar, 3 bar, 5 bar, 7 bar, 9 bar, etc.

[0049] After the reaction is completed, the embodiment of the present invention immediately places the reactor in cold water and cools for more than 0.5 hours; then the reactor is opened, and the reaction liquid can be collected with a syringe and filtered into a vial. Specifically, the reaction liquid is taken into a nuclear magnetic resonance tube, an appropriate amount of deuterated water is added and mixed evenly, and then the methanol yield is detected by nuclear magnetic resonance.

[0050] The oxidation of methane to methanol is a cascade catalytic process. On the gold / tin dioxide catalyst of the present invention, in the presence of water, CO assists O2 activation to form active oxygen species (hydroxyl radicals), which further activate methane to generate methanol. In the gold / tin dioxide catalytic material provided in the embodiment of the present application, by constructing a gold-tin alloy layer and taking the metal alloy layer as the active center, the effect of promoting the oxidation of methane to methanol can be achieved.

[0051] In order to better illustrate the present invention, the following examples are further illustrated. In the examples, all raw reagents and materials are commercially available, and the experimental methods without specific experimental conditions are conventional methods and conditions well known in the art.

[0052] Example 1

[0053] The present invention prepares a gold / tin dioxide material (tin dioxide catalyst loaded with gold), and the synthesis method thereof is as follows:

[0054] Take 500 mg of tin dioxide powder and place it in a beaker, add 21.5 μl of freshly prepared 23.21 mg / ml chloroauric acid solution, stir evenly with a glass rod to allow the sample to fully adhere to the wall. Then, place the sample in an oven and dry it at 80°C for 12 hours to obtain a solid sample.

[0055] The solid sample was collected, ground into a uniform fine powder, transferred to a porcelain boat and placed in a tube furnace, evacuated to -0.1 MPa, and calcined in the tube furnace with an argon flow rate of 100 ml / min, a heating rate of 2°C / min, a calcination temperature of 400°C, and a calcination time of 4 hours. After the cooling was completed, the sample was taken out and the powder was ground uniformly to obtain a gold / tin dioxide catalyst with a loading of 0.1%; recorded as 0.1% Au / SnO2-Ar.

[0056] Example 2

[0057] The preparation method is basically the same as that in Example 1, except that the mass of the loaded gold is different; thus, a high-loaded gold / tin dioxide catalyst is obtained, with a loading of 1%, recorded as 1% Au / SnO2-Ar.

[0058] Comparative Example 1

[0059] The preparation method is basically the same as that in Example 1, except that the calcination atmosphere is air and the calcination is carried out in a muffle furnace; thus, gold / tin dioxide catalysts with different calcination atmospheres are obtained, which are recorded as 0.1% Au / SnO2-O2.

[0060] The catalyst prepared in the embodiment of the present invention was structurally characterized:

[0061] Figure 1 X-ray diffraction (XRD) diagram of the catalyst prepared for Example 1-2 and Comparative Example 1. Compared with the JCPDS standard diagram, these peaks are very consistent with the tetragonal rutile crystal structure of the crystal, and in any X-ray diffraction diagram, no additional spectral lines belonging to other phases such as SnO are observed. This shows that the change of the calcining atmosphere and the increase of the gold loading do not cause the transformation of the SnO2 lattice structure, indicating that the crystal structure of SnO2 tends to be complete. As can be seen from the XRD diagram, under the low loading of gold, the characterization diffraction peaks of the sample are obviously broad, indicating that small-sized SnO2 nanocrystals are obtained. At the same time, as the loading increases, the characteristic peaks of gold gradually become sharp, indicating that gold nanoparticles have been successfully loaded on the tin dioxide carrier.

[0062] Figure 2XPS graphs of catalysts prepared in Examples 1-2 and Comparative Example 1. It is generally believed that when an atom loses an electron (i.e., the element is in a high-valence state), the binding energy of the electrons in the orbit will increase. When the gold / tin dioxide material is calcined with argon gas, a gold-tin alloy layer is formed, the oxygen defects in the material increase, and the number of oxygen atoms on the surface decreases, resulting in a change in the binding energy between the oxygen atoms and the surrounding atoms. Due to the lack of oxygen atoms, the interaction between the surrounding atoms and the remaining oxygen atoms will change, causing the binding energy to shift toward the high binding energy direction.

[0063] Figure 3 This is a fluorescence image of the catalyst prepared in Example 1. When methane is not introduced, the hydroxyl signal is very obvious, indicating that carbon monoxide can react with oxygen to generate hydroxyl radicals under the action of water during the reaction. After methane is introduced, the hydroxyl radical signal is significantly weakened, indicating that part of the hydroxyl radicals are consumed in the reaction process to activate methane.

[0064] Example 3

[0065] Test conditions for the oxidation of methane to methanol using gold / tin dioxide as catalyst

[0066] 10 mg of gold / tin dioxide catalyst powder and 20 ml of water were added to a 50 ml batch reactor. After the batch reactor was assembled and reinforced, 5 bar of oxygen, 5 bar of carbon monoxide, and 20 bar of methane were filled in turn as reaction gases. The methane oxidation to methanol reaction occurred in the batch reactor, and the reaction conditions were set to 110 degrees, 1 hour, and a magnetic speed of 1000 revolutions per minute. After the reaction was completed, the reactor was immediately placed in cold water to cool for more than 0.5 hours.

[0067] Afterwards, open the kettle and collect the reaction solution with a syringe, and filter it into a vial. Take 600 microliters of the reaction solution into a nuclear magnetic tube and add 100 microliters of deuterated water. After mixing evenly, perform nuclear magnetic resonance to detect the methanol yield. The formaldehyde content in the liquid product was tested by ultraviolet-visible light. Specifically, 1.5 ml of the reaction solution was mixed evenly with 1 ml of formaldehyde detection solution, reacted for 3 minutes in an 80-degree water bath, and then tested. The preparation method of formaldehyde detection solution is specifically as follows: take 25g of ammonium acetate and place it in a beaker, add about 20ml of deionized water, then add 3ml of acetic acid and 0.25ml of acetylacetone, dilute to 100ml, ultrasonically evenly, and transfer to a volumetric flask with a glass rod.

[0068] From this we get Figure 4 , Figure 4 It is a graph of the methane oxidation product yield of the gold / tin dioxide materials prepared in Examples 1-2 of the present invention and Comparative Example 1; after the catalyst prepared in Example 1 of the present invention is used, the methanol product yield is the highest.

[0069] Example 4

[0070] Optimal temperature and optimal carbon monoxide partial pressure test conditions for gold / tin dioxide catalyst in methane oxidation to methanol reaction

[0071] Ensure that other reaction conditions are consistent with Example 3, change the reaction temperature to 90°C, 100°C, 110°C, 120°C, and 130°C, respectively, to obtain Figure 5 .

[0072] Figure 5 This is a graph showing the product yields of methane oxidation reaction at different reaction temperatures for the gold / tin dioxide material prepared in Example 1 of the present invention. When the catalytic oxidation temperature is 110° C., the methanol product yield is the highest.

[0073] Example 5

[0074] Keeping other reaction conditions consistent with those in Example 3, the CO partial pressure was changed to 1 bar, 3 bar, 5 bar, 7 bar, and 9 bar, respectively, to obtain Figure 6 .

[0075] Figure 6 This is a graph of the product yields of methane oxidation reaction under different CO partial pressures of the gold / tin dioxide material prepared in Example 1 of the present invention. When the CO partial pressure is 5 bar, the methanol product yield is the highest.

[0076] Example 6

[0077] Stability test conditions of gold / tin dioxide materials as catalysts for methane oxidation to methanol

[0078] Under the reaction conditions of Example 3, after one reaction, the reaction solution obtained was divided into small centrifuge tubes, and the supernatant and precipitate were collected after centrifugation. The centrifugal speed was 13000 rpm, and the centrifugation time was 3 minutes. The supernatant after centrifugation was used to detect the liquid phase product, wherein the nuclear magnetic resonance can detect the methanol yield; after the precipitate was collected, a second cycle test was performed. The steps of the third cycle test were the same as the second.

[0079] The stability test results of methane oxidation to methanol with 0.1% Au / SnO2 are shown in Figure 7 ;Depend on Figure 7 It can be seen that after three cycles, the conversion rate and selectivity of the catalyst remain basically unchanged.

[0080] Example 7

[0081] According to the reaction conditions of Example 3: 110°C, reaction gas 5bar O2+5bar CO+20bar CH4, 20mlH2O; gold / tin dioxide material is used as a catalyst for methane oxidation to methanol, the difference is that the catalyst masses are 30 mg and 50 mg respectively.

[0082] Test results see Figure 8 It can be seen that the catalytic performance changes to a certain extent when the catalyst dosage is 10 mg, 30 mg, and 50 mg.

[0083] Example 8

[0084] According to the reaction conditions of Example 3: 110°C, reaction gas 5bar O2+5bar CO+20bar CH4, 20mlH2O, 10mg catalyst; gold / tin dioxide material is used as a catalyst for methane oxidation to methanol, except that the catalyst loadings are 0.2wt% and 0.5wt% respectively (the other preparation conditions are the same as those in Example 1).

[0085] Test results see Fig. 9 It can be seen that different catalysts with loading amounts of 0.1wt%, 0.2wt%, 0.5wt% and 1wt% have different corresponding specific catalytic properties.

[0086] Example 9

[0087] According to the reaction conditions of Example 3: 110°C, reaction gas 5bar O2+5bar CO+20bar CH4, 20mlH2O, 10mg catalyst, and control the argon flow rate and calcination time unchanged; gold / tin dioxide material is used as a catalyst for methane oxidation to methanol, except that the calcination temperatures are 500°C and 600°C respectively. Test results are shown in Fig.10 ; It can be seen that different calcination temperatures have a certain influence on the specific catalytic performance.

[0088] It can be seen from the above embodiments that in the gold / tin dioxide catalyst prepared by the method of the embodiment of the present application, uniform gold nanoparticles are loaded on the tin dioxide carrier, and a specific gold-tin alloy layer is formed on its surface; the catalyst is used for methanol oxidation to produce methanol, and under the action of water, carbon monoxide assists oxygen activation to generate hydroxyl radicals, thereby efficiently oxidizing methane to prepare oxygen-containing compounds, thereby improving the methanol production rate and selectivity in the methane oxidation reaction.

[0089] The description of the above embodiments is only used to help understand the method of the present invention and its core idea. It should be noted that for those of ordinary skill in the art, without departing from the principles of the present invention, several improvements and modifications may be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The above description of the disclosed embodiments enables professionals and technicians in this field to implement or use the present invention. The various modifications to these embodiments will be obvious to professionals and technicians in this field, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a gold-loaded tin dioxide catalyst, characterized in that: include: Step S1, dissolving a tin source and a gold source in water to obtain a mixed solution; Step S2, drying the mixed solution and grinding it into powder; Step S3, calcining the powder at high temperature under the protection of a vacuum inert atmosphere to obtain a gold-loaded tin dioxide catalyst.

2. The preparation method according to claim 1, characterized in that: In the step S1, the tin source is tin dioxide; and the gold source is chloroauric acid.

3. The preparation method according to claim 2, characterized in that: The step S1 comprises: stirring and mixing tin dioxide and chloroauric acid aqueous solution to obtain a mixed solution; the concentration of the chloroauric acid aqueous solution is 23-24 mg / mL.

4. The preparation method according to claim 2, characterized in that: In the step S1, the mass ratio of gold atoms in the tin source and the gold source is 1000:

1.

5. The preparation method according to claim 2, characterized in that: In the step S2, the drying is performed at 70-80° C. for 12-13 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In the step S3, the temperature of the high temperature calcination treatment is 400-600°C, the heating rate is 2-5°C / min, and the time is 3-5h.

7. The preparation method according to claim 6, characterized in that: In the step S3, the inert atmosphere is an argon atmosphere with a flow rate of 80 to 100 mL / min.

8. The preparation method according to any one of claims 1 to 5, characterized in that: In the step S3, the loading amount of the gold-loaded tin dioxide catalyst is 0.1-1 wt%.

9. A method for direct oxidation of methane, characterized in that: include: The gold-loaded tin dioxide catalyst obtained by the preparation method according to any one of claims 1 to 8 is used as a catalyst, and methane, carbon monoxide and oxygen are introduced for catalytic oxidation to obtain methanol and formaldehyde.

10. The method for direct oxidation of methane according to claim 9, characterized in that: The temperature of the catalytic oxidation is 90-130°C.

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