A supported composite oxide catalyst, a method for preparing the same, and an application thereof

Abstract

A supported composite oxide catalyst, its preparation method, and its application are disclosed, specifically relating to the field of heterogeneous catalysis. This invention provides a supported composite oxide catalyst for the selective oxidation of toluene in the gas phase and its preparation method. This is achieved by using MoVTeNbO... x TeO supported on composite oxide surface y To form a new TeO y / MoVTeNbO x The composite oxide significantly inhibits the over-oxidation of toluene, thereby greatly improving the selectivity of benzaldehyde, and the catalyst exhibits good stability. The catalyst preparation process is simple, reproducible, and shows promising application prospects.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis applications, and particularly relates to a supported composite oxide catalyst for the selective oxidation of toluene in the gas phase and its preparation method. Background Technology

[0002] The selective catalytic oxidation of hydrocarbon molecules to oxygen-containing products is a crucial reaction for obtaining high-end chemicals, such as the catalytic oxidation of toluene to benzaldehyde. In my country, the main methods for producing benzaldehyde are toluene chlorination hydrolysis or homogeneous oxidation of toluene. Neither of these processes is green and presents numerous problems, resulting in the complete import of high-quality benzaldehyde. The selective catalytic oxidation of toluene to benzaldehyde using air or O2 as an oxidant under completely halogen-free conditions is currently the most valuable and advanced method. However, it has never been industrialized, primarily due to the fact that the rate of further oxidation of benzaldehyde under oxygen-containing conditions is five orders of magnitude higher than that of toluene oxidation. Therefore, achieving high selectivity in obtaining benzaldehyde with high toluene conversion rates is a highly challenging topic in green chemistry research.

[0003] MoVTeNbO x Composite oxide catalysts are mainly used in reactions such as the oxidative dehydrogenation of ethane and propane to produce ethylene and propylene, and the selective (ammonia) oxidation of propane to produce acrylic acid and acrylonitrile (Bu Tingting et al. MoVTeNbO). x Research progress on catalysts applied to the oxidative dehydrogenation of ethane to ethylene [J]. Chemical Industry and Engineering Progress: 1-18.). In the gas-phase selective oxidation of toluene, Mo and V-based oxide catalysts are among the most studied. Therefore, research on MoVTeNbO... x The application of modified composite oxides in the gas-phase selective oxidation of toluene is very important for the development of novel gas-phase selective oxidation catalysts for toluene, and may also provide guidance and reference for the development of catalysts for other selective oxidation reactions. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a supported composite oxide catalyst for the gas-phase selective oxidation of toluene and a method for preparing the same, wherein the catalyst has good gas-phase selective catalytic oxidation activity of toluene and high selectivity for benzaldehyde.

[0005] The specific solution of the present invention is as follows:

[0006] A supported composite oxide catalyst for the gas-phase selective oxidation of toluene and its preparation method, wherein the catalyst has the following general formula:

[0007] TeO y / MoVTeNbO x Where x is an uncertain constant, MoVTeNbO x As a carrier, TeOy Loaded on a carrier;

[0008] The molar ratio of Mo, V, Te, and Nb in the catalyst is 1:(0.1–0.4):(0.2–0.4):(0.1–0.25), MoVTeNbO x As a carrier, TeO y / (TeO y +MoVTeNbO x The mass ratio of (1-3):25.

[0009] The preparation method of the aforementioned supported composite oxide catalyst includes the following steps:

[0010] (1) (NH4)6Mo7O 24 ·4H2O, VOSO4·xH2O and H6TeO6 were dissolved in distilled water in sequence, and the temperature of the aqueous solution was controlled at 65-95℃. This solution was labeled as solution A.

[0011] Dissolve C4H4NNbO9·xH2O in distilled water, control the temperature of the aqueous solution at 65–95℃, and label it as solution B;

[0012] (2) While stirring continuously, add solution B from step (1) to solution A. After the resulting mixture cools down, add sodium citrate while stirring continuously.

[0013] (3) Transfer the mixture obtained in step (2) to a hydrothermal reactor and hydrothermally heat it at 170-190°C for 24-60 hours;

[0014] (4) The purple substance obtained in step (3) is centrifuged and washed, dried at 60-90°C, and the resulting solid is heated from room temperature to 200-300°C at a heating rate of 4-8°C / min and calcined in air for 2-4 hours. Then, it is heated from room temperature to 550-650°C at a heating rate of 4-8°C / min and calcined in argon for 2-4 hours.

[0015] (5) Add the powder from step (4) to a hydrogen peroxide aqueous solution with a mass fraction of 5-10%, stir at 60-70°C for 2-4 hours, filter, wash and dry;

[0016] (6) Add H6TeO6 to distilled water, then add the black powder obtained in step (5), and evaporate it while stirring under heating conditions;

[0017] (7) The black powder obtained in step (6) is heated from room temperature to 350-500°C at a heating rate of 4-8°C / min and calcined in argon for 2-4 hours to obtain the final catalyst.

[0018] Preferably, the molybdenum salt, vanadium salt, telluric acid, and niobium salt are (NH4)6Mo7O, respectively. 24 •4H2O, VOSO4·xH2O, H6TeO6, and C4H4NNbO9·xH2O. In VOSO4·xH2O and C4H4NNbO9·xH2O, x represents an indeterminate constant.

[0019] Preferably, molybdenum salt, vanadium salt, telluric acid, niobium salt and sodium citrate are added in a molar ratio of Mo, V, Te, Nb and sodium citrate of 1:(0.1~0.4):(0.2~0.4):(0.1~0.25):(0.1~0.25).

[0020] Preferably, the method used in step (6) is the over-volume impregnation method.

[0021] The catalyst of this invention is applied to the toluene-to-benzaldehyde reaction via gas-phase selective oxidation or liquid-phase selective oxidation.

[0022] The gas-phase selective oxidation method involves feeding toluene, air, and catalyst at a reaction temperature of 200–400°C and a reaction pressure of 0.05 MPa–0.15 MPa in a ratio of toluene (μL): air (mL): catalyst (g) = 1:(2–50):(0.1–0.6) to obtain benzaldehyde after the reaction is completed.

[0023] In the embodiments provided by the present invention, the catalyst is pressed into particles with a diameter of 0.25 to 0.4 mm, placed in a quartz glass U-shaped tube, and subjected to a gas-phase selective oxidation reaction at a temperature range of 200 to 400°C, at atmospheric pressure, and under continuous air and toluene vapor conditions to obtain benzaldehyde or maleic anhydride; wherein the air flow rate is 20 to 30 mL / min, and the toluene feed rate is 1 to 2 μL / min.

[0024] Beneficial effects

[0025] This invention provides a supported composite oxide catalyst for the gas-phase selective oxidation of toluene and its preparation method. The catalyst is prepared by using MoVTeNbO x TeO supported on composite oxide surface y To form a new TeO y / MoVTeNbO x The composite oxide significantly inhibits the over-oxidation of toluene, thereby greatly improving the selectivity of benzaldehyde, and the catalyst exhibits good stability. The catalyst preparation process is simple, reproducible, and shows promising application prospects. Attached Figure Description

[0026] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0027] Figure 1 The TeO prepared in Example 1 of this invention y Scanning electron microscope image of the catalyst with an 8% loading.

[0028] Figure 2 The TeO prepared in Example 1 of this invention y X-ray powder diffraction pattern of the catalyst with an 8% loading.

[0029] Figure 3 The TeO prepared in Example 1 of this invention y Results of the activity of the gas-phase selective oxidation of toluene to benzaldehyde with a catalyst loading of 8%.

[0030] Figure 4 This is the TeO prepared in Example 2 of the present invention. y Scanning electron microscope image of the catalyst with a loading of 12%.

[0031] Figure 5 This is the TeO prepared in Example 2 of the present invention. y X-ray powder diffraction pattern of the catalyst with a loading of 12%.

[0032] Figure 6 This is the TeO prepared in Example 2 of the present invention. y The activity results of the gas-phase selective oxidation of toluene to benzaldehyde with a catalyst loading of 12% are presented.

[0033] Figure 7 The TeO prepared in Example 3 of this invention y Scanning electron microscope image of the catalyst with a loading of 4%.

[0034] Figure 8 The TeO prepared in Example 3 of this invention y X-ray powder diffraction pattern of the catalyst with a loading of 4%.

[0035] Figure 9 The TeO prepared in Example 3 of this invention y The activity results of the gas-phase selective oxidation of toluene to benzaldehyde with a catalyst loading of 4% were obtained.

[0036] Figure 10 The TeO prepared in Example 4 of this invention y Scanning electron microscope image of the catalyst with zero loading.

[0037] Figure 11 The TeO prepared in Example 4 of this invention y X-ray powder diffraction pattern of a catalyst with zero loading.

[0038] Figure 12 The TeO prepared in Example 4 of this inventiony The activity results of selective oxidation of toluene to benzaldehyde in the gas phase with a catalyst of 0 loading. Detailed Implementation

[0039] The present invention can be further illustrated by the following embodiments, which are for illustrative purposes only and not for limiting the invention. Any person skilled in the art will understand that these embodiments do not limit the invention in any way, and that appropriate modifications and data transformations can be made thereto without departing from the spirit and scope of the invention.

[0040] Unless otherwise stated, all chemicals were purchased as commercial products.

[0041] Example 1

[0042] Step 1: Weigh out 0.01 mol, 0.0175 mol, 0.0161 mol, and 0.0084 mol of (NH4)6Mo7O according to the molar ratio of Mo, V, Te, and Nb of 1:0.25:0.23:0.12. 24 ·4H2O, VOSO4·xH2O, H6TeO6, C4H4NNbO9·xH2O. Dissolve the first three in 90mL of distilled water and heat to 80℃ with constant stirring. This solution is called solution A.

[0043] Step 2: Dissolve C4H4NNbO9·xH2O in 40mL of distilled water and heat to 80℃ with constant stirring; this is called solution B.

[0044] Step 3: Once the temperatures of solutions A and B have both dropped to 40°C, slowly add solution B to solution A while stirring continuously for 0.5 hours.

[0045] Step 4: After the mixed emulsion obtained in Step 3 has cooled, add 10 mL of 0.84 mol / L sodium citrate aqueous solution and stir until homogeneous.

[0046] Step 5: Transfer the mixture obtained in Step 4 to a 200 mL hydrothermal reactor and hydrothermally heat it at 175 °C for 48 h.

[0047] Step six: Wash the mixture obtained in step five by centrifugation three times with distilled water, then by centrifugation once with ethanol, and dry it at 70°C.

[0048] Step 7: The solid obtained in Step 6 is heated from room temperature to 250°C at a heating rate of 5°C / min and calcined in air for 2 hours. After it is cooled to room temperature, it is then heated from room temperature to 600°C at a heating rate of 5°C / min and calcined in argon for 2 hours to obtain a black powder.

[0049] Step 8: The black powder obtained in Step 7 is added to a 7.5% (w / w) aqueous solution of hydrogen peroxide, stirred at 60°C for 3 hours, filtered, washed, and dried to obtain MoVTeNbO. x ;

[0050] Step nine, according to TeO y / (TeO y +MoVTeNbO x Add 0.091 g of H6TeO6 and 0.8 g of MoVTeNbO to 20 mL of distilled water at a mass ratio of 8%. x The mixture was stirred and evaporated at 80°C to obtain a black powder.

[0051] Step 10: The black powder obtained in Step 9 is calcined in argon gas at a heating rate of 5℃ / min from room temperature to 450℃ for 2 hours to obtain the final catalyst.

[0052] Test Example 1: Physicochemical Properties of the Catalyst Prepared in Example 1

[0053] 1. Characterization Test

[0054] The catalyst prepared in Example 1 had a specific surface area of ​​16.7 m², as determined by testing. 2 / g (The specific surface area of ​​the catalyst is tested using the BET method. The principle is to determine the absolute amount of nitrogen adsorbed by the sample under different partial pressures, and then calculate the monolayer adsorption amount through BET theory to obtain the specific surface area).

[0055] The morphology of the catalyst was characterized by scanning electron microscopy, such as... Figure 1 As shown;

[0056] The prepared catalyst was analyzed by XRD, and the results are as follows: Figure 2 As shown, its structure is mainly in the M1 phase.

[0057] 2. Catalytic performance test

[0058] The obtained catalyst was pressed into 40-60 mesh particles, and 0.3 g was placed in a quartz glass U-tube. The catalytic reaction was carried out in the range of 300-450℃, at atmospheric pressure, and under continuous air and toluene vapor conditions. The liquid toluene injection rate was 1 μL / min, and the air flow rate was 25 mL / min.

[0059] Qualitative and quantitative analysis of the product was performed using gas chromatography, and its specific catalytic activity was as follows: Figure 3 As shown, the main product of this catalyst is benzaldehyde. At 400℃, the toluene conversion rate is 14.27%, and the benzaldehyde selectivity is 92.77%.

[0060] Example 2

[0061] Step 1: Weigh out 0.01 mol, 0.0175 mol, 0.0161 mol, and 0.0084 mol of (NH4)6Mo7O according to the molar ratio of Mo, V, Te, and Nb of 1:0.25:0.23:0.12. 24 ·4H2O, VOSO4·xH2O, H6TeO6, C4H4NNbO9·xH2O. Dissolve the first three in 90mL of distilled water and heat to 80℃ with constant stirring. This solution is called solution A.

[0062] Step 2: Dissolve C4H4NNbO9·xH2O in 40mL of distilled water and heat to 80℃ with constant stirring; this is called solution B.

[0063] Step 3: Once the temperatures of solutions A and B have both dropped to 40°C, slowly add solution B to solution A while stirring continuously for 0.5 hours.

[0064] Step 4: After the mixed emulsion obtained in Step 3 has cooled, add 10 mL of 0.84 mol / L sodium citrate aqueous solution and stir until homogeneous.

[0065] Step 5: Transfer the mixture obtained in Step 4 to a 200 mL hydrothermal reactor and hydrothermally heat it at 175 °C for 48 h.

[0066] Step six: Wash the mixture obtained in step five by centrifugation three times with distilled water, then by centrifugation once with ethanol, and dry it at 70°C.

[0067] Step 7: The solid obtained in Step 6 is heated from room temperature to 250°C at a heating rate of 5°C / min and calcined in air for 2 hours. After it is cooled to room temperature, it is then heated from room temperature to 600°C at a heating rate of 5°C / min and calcined in argon for 2 hours to obtain a black powder.

[0068] Step 8: The black powder obtained in Step 7 is added to a 7.5% (w / w) aqueous solution of hydrogen peroxide, stirred at 60°C for 3 hours, filtered, washed, and dried to obtain MoVTeNbO. x .

[0069] Step nine, according to TeO y / (TeO y +MoVTeNbO x Add 0.136 g of H6TeO6 and 0.8 g of MoVTeNbO to 20 mL of distilled water at a mass ratio of 12%. x The mixture was stirred and evaporated at 80°C to obtain a black powder.

[0070] Step 10: The black powder obtained in Step 9 is calcined in argon gas at a heating rate of 5℃ / min from room temperature to 450℃ for 2 hours to obtain the final catalyst.

[0071] Test Example 2: Physicochemical Properties of the Catalyst Prepared in Example 2

[0072] 1. Characterization Test

[0073] The catalyst prepared in Example 2 was found to have a specific surface area of ​​13.8 m². 2 / g (The specific surface area of ​​the catalyst is tested using the BET method. The principle is to determine the absolute amount of nitrogen adsorbed by the sample under different partial pressures, and then calculate the monolayer adsorption amount through BET theory to obtain the specific surface area).

[0074] The morphology of the catalyst was characterized by scanning electron microscopy, such as... Figure 4 As shown, it can be seen that in MoVTeNbO x Surface loaded with 4% more TeO y It has little effect on the catalyst morphology;

[0075] The prepared catalyst was analyzed by XRD, and the results are as follows: Figure 5 As shown, its structure mainly exhibits the M1 phase in MoVTeNbO x Surface loaded with 4% more TeO y It has little effect on the catalyst structure.

[0076] 2. Catalytic performance test

[0077] The obtained catalyst was pressed into 40-60 mesh particles, and 0.3 g was placed in a quartz glass U-tube. The catalytic reaction was carried out in the range of 300-450℃, at atmospheric pressure, and under continuous air and toluene vapor conditions. The liquid toluene injection rate was 1 μL / min, and the air flow rate was 25 mL / min.

[0078] Qualitative and quantitative analysis of the product was performed using gas chromatography, and its specific catalytic activity was as follows: Figure 6 As shown. The main product of this catalyst is benzaldehyde. At 400℃, the toluene conversion rate is 11.13%, and the benzaldehyde selectivity is 93.66%. This indicates that MoVTeNbO x Excessive TeO on the surface y It will cover the active sites, leading to a decrease in toluene conversion, but it will further improve the selectivity of benzaldehyde.

[0079] Example 3

[0080] Step 1: Weigh out 0.01 mol, 0.0175 mol, 0.0161 mol, and 0.0084 mol of (NH4)6Mo7O according to the molar ratio of Mo, V, Te, and Nb of 1:0.25:0.23:0.12. 24 ·4H2O, VOSO4·xH2O, H6TeO6, C4H4NNbO9·xH2O. Dissolve the first three in 90mL of distilled water and heat to 80℃ with constant stirring. This solution is called solution A.

[0081] Step 2: Dissolve C4H4NNbO9·xH2O in 40mL of distilled water and heat to 80℃ with constant stirring; this is called solution B.

[0082] Step 3: Once the temperatures of solutions A and B have both dropped to 40°C, slowly add solution B to solution A while stirring continuously for 0.5 hours.

[0083] Step 4: After the mixed emulsion obtained in Step 3 has cooled, add 10 mL of 0.84 mol / L sodium citrate aqueous solution and stir until homogeneous.

[0084] Step 5: Transfer the mixture obtained in Step 4 to a 200 mL hydrothermal reactor and hydrothermally heat it at 175 °C for 48 h.

[0085] Step six: Wash the mixture obtained in step five by centrifugation three times with distilled water, then by centrifugation once with ethanol, and dry it at 70°C.

[0086] Step 7: The solid obtained in Step 6 is heated from room temperature to 250°C at a heating rate of 5°C / min and calcined in air for 2 hours. After it is cooled to room temperature, it is then heated from room temperature to 600°C at a heating rate of 5°C / min and calcined in argon for 2 hours to obtain a black powder.

[0087] Step 8: The black powder obtained in step 7 is added to a 7.5% hydrogen peroxide aqueous solution, stirred at 60°C for 3 hours, filtered, washed and dried to obtain MoVTeNbOx.

[0088] Step nine, according to TeO y / (TeO y +MoVTeNbO x Add 0.041 g of H6TeO6 and 0.8 g of MoVTeNbO to 20 mL of distilled water at a mass ratio of 4%. x The mixture was stirred and evaporated at 80°C to obtain a black powder.

[0089] Step 10: The black powder obtained in Step 9 is calcined in argon gas at a heating rate of 5℃ / min from room temperature to 450℃ for 2 hours to obtain the final catalyst.

[0090] Test Example 3: Physicochemical Properties of the Catalyst Prepared in Example 3

[0091] 1. Characterization Test

[0092] The catalyst prepared in Example 3 was found to have a specific surface area of ​​18.1 m². 2 / g (The specific surface area of ​​the catalyst is tested using the BET method. The principle is to determine the absolute amount of nitrogen adsorbed by the sample under different partial pressures, and then calculate the monolayer adsorption amount through BET theory to obtain the specific surface area).

[0093] The morphology of the catalyst was characterized by scanning electron microscopy, such as... Figure 7 As shown;

[0094] The prepared catalyst was analyzed by XRD, and the results are as follows: Figure 8 As shown, its structure is mainly in the M1 phase.

[0095] 2. Catalytic performance test

[0096] The obtained catalyst was pressed into 40-60 mesh particles, and 0.3 g was placed in a quartz glass U-tube. The catalytic reaction was carried out in the range of 300-450℃, at atmospheric pressure, and under continuous air and toluene vapor conditions. The liquid toluene injection rate was 1 μL / min, and the air flow rate was 25 mL / min.

[0097] Qualitative and quantitative analysis of the product was performed using gas chromatography, and its specific catalytic activity was as follows: Figure 9 As shown. The main product of this catalyst is not benzaldehyde. At 400℃, the toluene conversion rate is 29.44%, the benzaldehyde selectivity is 23.94%, and the rest are over-oxidation products. This indicates that when MoVTeNbO x Surface-loaded TeO y When the amount is insufficient, the active sites on the catalyst surface that are partially over-oxidized are not covered, resulting in low selectivity of benzaldehyde.

[0098] Example 4

[0099] Step 1: Weigh out 0.01 mol, 0.0175 mol, 0.0161 mol, and 0.0084 mol of (NH4)6Mo7O according to the molar ratio of Mo, V, Te, and Nb of 1:0.25:0.23:0.12. 24·4H2O, VOSO4·xH2O, H6TeO6, C4H4NNbO9·xH2O. Dissolve the first three in 90mL of distilled water and heat to 80℃ with constant stirring. This solution is called solution A.

[0100] Step 2: Dissolve C4H4NNbO9·xH2O in 40mL of distilled water and heat to 80℃ with constant stirring; this is called solution B.

[0101] Step 3: Once the temperatures of solutions A and B have both dropped to 40°C, slowly add solution B to solution A while stirring continuously for 0.5 hours.

[0102] Step 4: After the mixed emulsion obtained in Step 3 has cooled, add 10 mL of 0.84 mol / L sodium citrate aqueous solution and stir until homogeneous.

[0103] Step 5: Transfer the mixture obtained in Step 4 to a 200 mL hydrothermal reactor and hydrothermally heat it at 175 °C for 48 h.

[0104] Step six: Wash the mixture obtained in step five by centrifugation three times with distilled water, then by centrifugation once with ethanol, and dry it at 70°C.

[0105] Step 7: The solid obtained in Step 6 is heated from room temperature to 250°C at a heating rate of 5°C / min and calcined in air for 2 hours. After it is cooled to room temperature, it is then heated from room temperature to 600°C at a heating rate of 5°C / min and calcined in argon for 2 hours to obtain a black powder.

[0106] Step 8: The black powder obtained in Step 7 is added to a 7.5% (w / w) aqueous solution of hydrogen peroxide, stirred at 60°C for 3 hours, filtered, washed, and dried to obtain the final catalyst MoVTeNbO. x .

[0107] Test Example 4: Physicochemical Properties of the Catalyst Prepared in Example 4

[0108] 1. Characterization Test

[0109] The catalyst prepared in Example 4 was found to have a specific surface area of ​​20.2 m². 2 / g (The specific surface area of ​​the catalyst is tested using the BET method. The principle is to determine the absolute amount of nitrogen adsorbed by the sample under different partial pressures, and then calculate the monolayer adsorption amount through BET theory to obtain the specific surface area).

[0110] The morphology of the catalyst was characterized by scanning electron microscopy, such as... Figure 10 As shown;

[0111] The prepared catalyst was analyzed by XRD, and the results are as follows: Figure 11As shown. It can be seen that MoVTeNbO x No TeO load on the surface y At that time, its surface regularity was better, and its structure was still mainly M1 phase.

[0112] 2. Catalytic performance test

[0113] The obtained catalyst was pressed into 40-60 mesh particles, and 0.3 g was placed in a quartz glass U-tube. The catalytic reaction was carried out in the range of 300-450℃, at atmospheric pressure, and under continuous air and toluene vapor conditions. The liquid toluene injection rate was 1 μL / min, and the air flow rate was 25 mL / min.

[0114] Qualitative and quantitative analysis of the product was performed using gas chromatography, and its specific catalytic activity was as follows: Figure 12 As shown, the selectivity of benzaldehyde gradually decreases as the reaction temperature increases. When the reaction temperature is 400℃, although the toluene conversion rate reaches 93.73%, no benzaldehyde is generated in the product; all products are over-oxidized products.

Claims

1. A supported composite oxide catalyst, characterized in that, the general formula of the catalyst is TeOy / MoVTeNbOx; wherein the molar ratio of Mo, V, Te, Nb is 1:(0.1-0.4):(0.2-0.4):(0.1-0.25), and MoVTeNbOx is the carrier, and the mass ratio of TeOy to (TeOy+MoVTeNbOx) is (1-3):25; the supported composite oxide catalyst is prepared by the following method: an aqueous solution of molybdenum salt, vanadium salt and telluric acid is prepared to obtain solution A; an aqueous solution of niobium salt is prepared to obtain solution B; solution B is mixed with solution A; sodium citrate is added to the mixed solution; the mixture is placed in a reaction container for reaction; then water washing, alcohol washing and drying treatment are performed; the obtained solid is subjected to air calcination and argon atmosphere calcination in sequence; the obtained solid is then treated in hydrogen peroxide aqueous solution, and then separated, washed and dried to obtain the carrier MoVTeNbOx; telluric acid is loaded on the MoVTeNbOx carrier by the over-volume impregnation method; the obtained solid is subjected to argon atmosphere calcination to obtain the supported composite oxide catalyst.

2. A preparation method of the supported composite oxide catalyst according to claim 1, characterized in that, the preparation steps are as follows: step one, an aqueous solution of molybdenum salt, vanadium salt and telluric acid is prepared, and the solution temperature is controlled at 60-90℃ to obtain solution A; step two, an aqueous solution of niobium salt is prepared, and the solution temperature is controlled at 60-90℃ to obtain solution B; step three, solution B is mixed with solution A at 30-50℃; step four, sodium citrate is added to the mixed solution obtained in step three; step five, the mixture obtained in step four is placed in a reaction container for reaction at 170-190℃; step six, the mixture obtained in step five is subjected to water washing, alcohol washing and drying treatment; step seven, the solid obtained in step six is subjected to air calcination and argon atmosphere calcination in sequence; step eight, the solid obtained in step seven is treated in hydrogen peroxide aqueous solution, and then separated, washed and dried to obtain the carrier MoVTeNbOx; step nine, telluric acid is loaded on the carrier obtained in step eight by the over-volume impregnation method; step ten, the solid obtained in step nine is subjected to argon atmosphere calcination to obtain the catalyst.

3. The preparation method according to claim 2, characterized in that, The molybdenum salt, vanadium salt, telluric acid, niobium salt are (NH4)6Mo7O 24 4H2O, VOSO4xH2O, H6TeO6and C4H4NNbO9xH2O respectively.

4. The preparation method according to claim 2, characterized in that, molybdenum salt, vanadium salt, telluric acid, niobium salt and sodium citrate are added according to the molar ratio of Mo, V, Te, Nb and sodium citrate as 1:(0.1-0.4):(0.2-0.4):(0.1-0.25):(0.1-0.25).

5. The preparation method according to claim 2, characterized in that, the volume impregnation method in step nine is that an aqueous solution of telluric acid is prepared, and the raw material to be treated is added to the aqueous solution of telluric acid for heating and dryness treatment.

6. The preparation method according to claim 2, characterized in that, The argon atmosphere treatment in step ten is to calcine the solid obtained in step nine at a temperature rising rate of 4-8 ℃ / min from room temperature to 350-500 ℃ for 2-4 h.

7. Use of the catalyst according to claim 1 or the catalyst obtained by the preparation method according to claims 2-6 in the selective oxidation of toluene in gas phase or in liquid phase to benzaldehyde.

8. The use according to claim 7, wherein the selective oxidation in gas phase is carried out by feeding toluene, air and the catalyst according to the ratio of toluene (μL) : air (mL) : catalyst (g) = 1 : (2-50) : (0.1-0.6) under the conditions of a reaction temperature of 200-400 ℃ and a reaction pressure of 0.05-0.15 MPa, and benzaldehyde is obtained after the reaction.

9. The use according to claim 7 or 8, wherein the mass ratio of TeOy to (TeOy+MoVTeNbOx) in the catalyst is 1:25 or 2:25 or 3:25; and the molar ratio of Mo, V, Te and Nb in MoVTeNbOx is 1:0.25:0.23:0.

12. ​ ​

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