Photo-thermal catalyst for outputting propylene through propane dehydrogenation as well as preparation method and application of photo-thermal catalyst

Abstract

The invention discloses a photo-thermal catalyst for propane dehydrogenation to output propylene and a preparation method and application of the photo-thermal catalyst. The catalyst comprises a transition metal M oxide semiconductor MxOy, and the transition metal M oxide semiconductor MxOy is further loaded with first transition metal; and the MxOy is selected from at least one of TiO2, Fe2O3 and ZnO2. The photo-thermal catalyst provided by the invention can provide energy required by reaction by locally heating catalyst sites through light energy in a gas-solid reaction device, efficiently catalyzes propane dehydrogenation under relatively mild conditions, and shows excellent catalytic stability in a flowing system.

Description

Technical Field

[0001] The present invention belongs to the technical field of photothermal catalytic reaction, and particularly relates to a photothermal catalyst for propane dehydrogenation to produce propylene, a preparation method thereof, and an application thereof. Background Art

[0002] As a basic raw material for producing polyolefins, the global supply-demand gap of propylene is very large. For a long time, the production of propylene has mainly relied on petroleum cracking, but the low yield and complex separation process have increased the supply pressure and environmental pressure of fossil resources. This traditional method is facing many challenges. Propane dehydrogenation, especially the reduction dehydrogenation without an external hydrogen acceptor, is expected to become an effective way to address these challenges. It not only benefits from the rich propane supply brought by the booming development of shale gas but also from the high selectivity of propane conversion to propylene and H2 fuel. Producing propylene from propane is much more economical than petroleum cracking.

[0003] Currently, the research on propane dehydrogenation (PDH) mainly focuses on thermal catalysis, mainly relying on two major categories of commercial catalysts, namely chromium-based catalysts and platinum-based catalysts supported with heterogeneous oxides. Both of these two types of catalysts have high production costs due to poisoning by high-valent carbon deposition. In recent years, non-noble metal catalysts with high activity have been developed, which can convert propane into propylene with high selectivity and have received great attention. However, the direct dehydrogenation of propane is a strongly endothermic process controlled by the thermodynamic equilibrium, and these developed catalysts still require a high temperature of 500-600 °C. It has been found that under mild conditions, photocatalysts can release hydrogen from alkanes in the form of H2. Especially visible light photocatalysis based on the utilization of solar energy, which can convert solar energy into chemical energy and does not require the heat energy provided by fossil energy to promote the reaction, is a very green and potentially huge application market. In a classical gas-solid phase batch reactor, a platinum-based photocatalyst generates hydrogen at a rate of about 350 mmol·g 2 under visible light irradiation of 1.6 W / cm Pt -1 ·h -1 at a temperature of 43 °C. Inspired by C-H bond functionalization, researchers have developed a synergistic photocatalysis strategy that uses sodium decatungstate (Na4[W 10 O 32 ) to extract a proton from propane to form an alkyl radical, and then uses cobalt pyridine chloride oxime (COPC) to extract another proton from this radical to obtain propylene products. All these reported examples indicate that photocatalysis technology has broad application prospects in PDH. However, despite the progress made in photocatalysis technology in the laboratory, it still faces many challenges in industrial applications. How to improve the efficiency of the photocatalytic reaction to meet the scale requirements of industrial production remains an urgent problem to be solved.

[0004] Traditional photocatalytic reactions mainly rely on electron-hole pairs generated by photoexcitation to complete the conversion, and their efficiency is limited by the lifetime of electron-hole pairs. When the temperature increases, although the thermal effect can accelerate mass transfer and provide the energy to overcome the activation energy, the lifetime of electron-hole pairs will be significantly shortened due to the increase in temperature, and even negative effects will occur. This makes it infeasible to increase the quantum efficiency by using the photothermal effect to increase the reaction temperature. In addition, the efficiency of photocatalytic reactions is not linearly related to the incident light intensity. The efficiency is higher under low-intensity light illumination, while under high-intensity light illumination, the efficiency will decrease significantly due to the self-quenching effect. Therefore, photocatalytic reactions usually can only be carried out in large-area two-dimensional reactors and need to be carried out under mild light illumination and room temperature conditions to ensure the best quantum efficiency. However, such reaction conditions are seriously incompatible with the high-intensity and high-frequency reactors required for industrial scale applications.

[0005] Therefore, to solve the current problem of photocatalytic propane dehydrogenation moving towards practical applications, it is necessary to prepare photocatalysts with high efficiency and high light-receiving ability that can be used in industrial applications. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the present invention provides a photothermal catalyst for propane dehydrogenation to produce propylene, its preparation method and application. Under the condition of light irradiation, the photothermal catalyst can utilize its own photothermal conversion effect to heat itself with the excited and relaxed light energy, realizing an efficient catalytic propane dehydrogenation reaction under the synergistic effect of light and heat.

[0007] Based on this, the technical solution of the present invention is as follows:

[0008] A photothermal catalyst, the catalyst includes a transition metal M oxide semiconductor M x O y , and a first transition metal is loaded on the transition metal M oxide semiconductor M x O y ;

[0009] The M x O y is selected from at least one of TiO2, Fe2O3, ZnO2.

[0010] In the transition metal M oxide semiconductor M x O y of the present invention, x and y are integers that balance the charge.

[0011] According to the embodiment of the present invention, the transition metal M oxide semiconductor M x O y does not contain oxygen vacancies.

[0012] According to the embodiment of the present invention, the first transition metal is selected from at least one of Cu, Ni, Co, Fe.

[0013] According to an embodiment of the present invention, the loading amount of the first transition metal on M x O y is 0.1 to 10 wt%, preferably 0.2 to 8 wt%, more preferably 0.3 to 5 wt%, and for example 0.5 to 2 wt%.

[0014] According to an embodiment of the present invention, under illumination (the light intensity of the light is 0.1 to 5 w / cm 2 ; the wavelength of the light is 100 - 1200 nm), the photothermal catalyst can be heated to above 155 °C, for example 156 - 185 °C, and for example 170 - 185 °C, and further 175 - 180 °C.

[0015] According to an embodiment of the present invention, under illumination (the light intensity of the light is 0.1 to 5 w / cm 2 ; the wavelength of the light is 100 - 1200 nm), the photothermal catalyst can catalyze propane dehydrogenation, and the production rate of propylene is not less than 3 mmol / g / h, for example 3 - 5 mmol / g / h, and for example 3.6 - 4.5 mmol / g / h.

[0016] According to an embodiment of the present invention, the selectivity of the photothermal catalyst for propane dehydrogenation to carbon products is greater than 70%, preferably greater than 80%, and for example 85%.

[0017] The present invention also provides a preparation method of the above photothermal catalyst, which includes the following steps:

[0018] (1) React a reducing agent with M x O y to prepare V O -M x O y containing oxygen vacancies;

[0019] (2) Mix the V O -M x O y in step (1) with a precursor containing a first transition metal, and carry out a heating reaction to obtain a photothermal catalyst, denoted as Q / V O -M x O y ; Q is the first transition metal, selected from at least one of Cu, Ni, Co, and Fe.

[0020] According to an embodiment of the present invention, in step (1), the mass ratio of M x O y to the reducing agent is 1 - 12:1, preferably 3 - 8:1.

[0021] According to an embodiment of the present invention, in step (1), the reducing agent is selected from sodium borohydride or hydrogen. When the reducing agent is hydrogen, an inert gas may be mixed in the reducing agent. The inert gas is, for example, argon. Preferably, the reducing agent is, for example, a mixture of hydrogen and argon, and the volume ratio of hydrogen to argon is 1-10:49-90, exemplarily 1:19.

[0022] According to an embodiment of the present invention, in step (1), the temperature of the reaction is 200-400 °C, preferably 300-350 °C; the time of the reaction is 20-60 min, preferably 30-40 min. The heating rate during the reaction is 1-8 °C / min (when there is heating, the reaction time is calculated from the start of heating to the predetermined reaction temperature).

[0023] According to an embodiment of the present invention, step (1) further includes post-treatment steps such as washing and drying, specifically including the following steps: The reaction product obtained in step (1) is stirred in water overnight, filtered, and dried at a temperature of 60-120 °C, and the drying time can be 2-48 h.

[0024] According to an embodiment of the present invention, in step (1), the oxygen vacancy-containing V O -M x O y includes at least one of V O -TiO2, V O -Fe2O3 or V O -ZnO2.

[0025] According to an embodiment of the present invention, in step (2), the V O -M x O y is added in the form of a V O -M x O y dispersion. The V O -M x O y dispersion is obtained by dispersing V O -M x O y in an organic solvent; preferably, the organic solvent is selected from weakly polar solvents, such as acetonitrile. Preferably, the concentration of the V O -M x O y dispersion is 2-10 mg / mL.

[0026] According to an embodiment of the present invention, in step (2), V O -M x O yThe mass ratio with the precursor containing the first transition metal is 2 - 12:1, preferably 3 - 8:1.

[0027] According to an embodiment of the present invention, in step (2), triethylamine is further added in the method.

[0028] According to an embodiment of the present invention, in step (2), the precursor containing the first transition metal is selected from at least one of soluble salts containing the first transition metal (such as chlorides), for example, at least one of copper chloride, nickel chloride, cobalt chloride or ferrous chloride.

[0029] According to an embodiment of the present invention, step (2) includes the following steps: Dispersing V O -M x O y in an organic solvent, adding the precursor containing the first transition metal and triethylamine and mixing them to obtain a dispersion, and heating and reacting the dispersion to obtain a photothermal catalyst.

[0030] According to an embodiment of the present invention, in the dispersion, the mass fraction of the precursor containing the first transition metal is 10 - 40 wt%, preferably 20 - 30 wt%.

[0031] According to an embodiment of the present invention, in the dispersion, the mass fraction of triethylamine is 0.3 - 2 wt%, preferably 0.6 - 1 wt%.

[0032] According to an embodiment of the present invention, in step (2), the temperature of the mixing is 15 - 35 °C, such as room temperature; the mixing time is 0.5 - 2 h, preferably 1 - 1.5 h.

[0033] According to an embodiment of the present invention, in step (2), the heating temperature is 50 - 80 °C, preferably 60 - 80 °C; the heating time is 1 - 10 h, such as 3 - 8 h. Preferably, the heating is microwave heating; the microwave heating temperature is 50 - 80 °C, preferably 60 - 80 °C; the microwave heating time is 1 - 5 h.

[0034] As an example, step (2) includes the following steps: Dispersing V O -M x O y in acetonitrile, adding copper chloride and triethylamine, stirring at room temperature for 1 h, then placing it in a microwave for 2 h, and obtaining the photothermal catalyst, namely Cu / V O -M x O y .

[0035] The present invention also provides an application of the above photothermal catalyst in the catalytic dehydrogenation of propane to prepare propylene.

[0036] The present invention also provides a method for preparing propylene by propane dehydrogenation, which comprises the following steps:

[0037] In the presence of the above-mentioned photothermal catalyst, propane is irradiated with light for reaction to prepare propylene.

[0038] According to an embodiment of the present invention, the reaction is carried out in a photoreactor. The photoreactor is a light-transmitting reactor, such as Pyrex glass.

[0039] According to an embodiment of the present invention, an inert gas can also be introduced into the method, and the inert gas is, for example, argon.

[0040] According to an embodiment of the present invention, the wavelength of the light is 100 - 1200 nm. Preferably, a xenon lamp is used to apply light irradiation.

[0041] According to an embodiment of the present invention, the light intensity of the light is 0.1 - 5 w / cm 2 ; the irradiation time of the light is more than 0.5 h, for example, 0.5 - 6 h.

[0042] According to an embodiment of the present invention, the flow rate of propane introduced into the reactor is 0.1 - 100 mL / min, preferably 20 - 100 mL / min, and also, for example, 50 - 100 mL / min.

[0043] According to an embodiment of the present invention, the method is specifically as follows:

[0044] Place the above-mentioned photothermal catalyst in the photoreactor, introduce propane into the photoreactor, and irradiate the photothermal catalyst with light.

[0045] According to an embodiment of the present invention, the mass of the photocatalyst / the flow rate of propane is 1 - 1000 mg catalyst / propane flow rate (1 - 100) mL·min -1 .

[0046] According to an embodiment of the present invention, the mass of the photocatalyst can be 1 - 1000 mg.

[0047] According to an embodiment of the present invention, after the photothermal catalyst is first coated on the surface of the carrier, the carrier is then placed in the photoreactor, and the carrier is, for example, a quartz sheet.

[0048] Advantages of the present invention:

[0049] (1) The photothermal catalyst of the present invention is sensitive to temperature and can convert the traditionally ineffective excited relaxation heat into the driving force for dehydrogenation reaction, thus greatly improving the light quantum efficiency.

[0050] (2) The present invention expands the application scope of the solar spectrum; in addition, the present invention does not use an external heat source, and only uses focused high-intensity solar energy to make the surface temperature of the catalyst reach 200 °C to drive propane dehydrogenation.

[0051] (3) The present invention studies the valuable propylene obtained by photothermal catalytic dehydrogenation of propane, and at the same time does not produce coking to cause catalyst poisoning, and can achieve low-cost, long-term operation and clean production.

[0052] (4) The photothermal catalyst of the present invention can locally heat the catalyst sites through light energy in a gas-solid reaction device to provide the energy required for the reaction, efficiently catalyze propane dehydrogenation under relatively mild conditions, and exhibit excellent catalytic stability in a flowing system.

[0053] (5) The preparation method of the photothermal catalyst of the present invention is simple and efficient, and can be mass-produced; moreover, its recovery cost is extremely low, and its recycling performance is excellent, which is conducive to large-scale production and has great potential for industrial production of photocatalytic propane dehydrogenation. Description of the Drawings

[0054] Figure 1 It is the surface thermal imaging diagram of different samples in Example 1 under simulated sunlight conditions;

[0055] Figure 2 It is the absorption spectrum diagram of different samples in Example 1;

[0056] Figure 3 It is the gas-solid flow phase reaction device diagram in the flow system test example;

[0057] Figure 4 It is the reaction rate change diagram of the photocatalyst in Example 1 catalyzing propane dehydrogenation in the flow system test example.

[0058] Figure 5 It is the result diagram of the photocatalytic propylene production rate in the cyclic test performance in Test Example 2. Detailed Description of the Invention

[0059] The technical solution of the present invention will be further described in detail below in combination with specific embodiments. It should be understood that the following embodiments are only used to illustrate and explain the present invention exemplarily, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection of the present invention.

[0060] Unless otherwise specified, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by known methods.

[0061] Example 1

[0062] A preparation method of a photothermal catalyst for driving propane dehydrogenation in a gas-solid system, comprising the following steps:

[0063] S1. Grind 1 g of P25TiO2 and 200 mg of sodium borohydride and mix them evenly, then calcine them at 350 °C for 30 minutes in an argon atmosphere at a heating rate of 5 °C / min to obtain black powder.

[0064] S2. Disperse these powders in ultrapure water and stir overnight. Then filter the dispersion, wash the filtered solid and dry it under vacuum to obtain V O -TiO2.

[0065] S3. Disperse 100 mg of V O -TiO2 powder and 30 mg of CuCl2 in 30 mL of acetonitrile, add 0.6 mL of triethylamine and stir for 1 h, then heat it to 80 °C by microwave and keep it for 2 h. Filter the reconstituted dispersion, wash and dry the filtered solid to obtain Cu / V O -TiO2. Among them, the loading amount of Cu on V O -TiO2 is 0.8 wt%.

[0066] Figure 1 is the surface thermal imaging diagram of different samples in Example 1 under simulated sunlight conditions; the V O -TiO2 and Cu / V O -TiO2 prepared in Example 1 can be heated to 172 °C and 179 °C respectively.

[0067] Figure 2 is the absorption spectrum diagram of different samples in Example 1. It can be seen from Figure 2 that from the absorption spectrum diagrams of TiO2, V O -TiO2 and Cu / V O -TiO2, the visible light absorption ability is enhanced.

[0068] Example 2

[0069] S1. Grind 1 g of Fe2O3 and 300 mg of sodium borohydride and mix them evenly, then calcine them at 350 °C for 30 minutes in an argon atmosphere at a heating rate of 5 °C / min to obtain black powder.

[0070] S2. Disperse these powders in ultrapure water and stir overnight. Then filter the dispersion, wash it and dry it under vacuum to obtain V O -Fe2O3.

[0071] S3. Take 100 mg of V O-Fe2O3 powder and 30 mg of CuCl2 were dispersed in 30 mL of acetonitrile. After adding 0.6 mL of triethylamine, the mixture was stirred for 1 hour, then microwave-heated to 80 °C and maintained for 2 h. The reconstituted dispersion was filtered, washed, and dried to obtain Cu / V O -Fe2O3. Among them, the loading amount of Cu on V O -Fe2O3 was 0.9 wt%.

[0072] Example 3

[0073] S1. 1 g of ZnO2 and 300 mg of sodium borohydride were ground and mixed evenly, and then calcined at 350 °C for 30 minutes in an argon atmosphere at a heating rate of 5 °C / min to obtain black powder.

[0074] S2. These powders were dispersed in ultrapure water and stirred overnight. The dispersion was filtered, washed, and dried in vacuo to obtain V O -TiO2.

[0075] S3. 100 mg of V O -ZnO2 powder and 30 mg of CuCl2 were dispersed in 30 mL of acetonitrile. After adding 0.6 mL of triethylamine, the mixture was stirred for 1 hour, then microwave-heated to 80 °C and maintained for 2 hours. The reconstituted dispersion was filtered, washed, and dried to obtain Cu / V O -ZnO2. Among them, the loading amount of Cu on V O -ZnO2 was 1.2 wt%.

[0076] Example 4

[0077] Under the same other conditions as in Example 1, the difference was that in S3, CuCl2 was replaced by CoCl2 to prepare Co / V O -TiO2. Among them, the loading amount of Co on V O -TiO2 was 0.9 wt%.

[0078] Example 5

[0079] Under the same other conditions as in Example 1, the difference was that in S3, CuCl2 was replaced by NiCl2 to prepare Ni / V O -TiO2. Among them, the loading amount of Ni on V O -TiO2 was 0.5 wt%.

[0080] Example 6

[0081] Under the same other conditions as in Example 1, the difference was that in S3, CuCl2 was replaced by FeCl2 to prepare Fe / V O -TiO2. Among them, the loading amount of Fe on V OThe loading amount on -TiO2 is 1.3 wt%.

[0082] Example 7

[0083] A preparation method of a photothermal catalyst for driving propane dehydrogenation in a gas - solid system, comprising the following steps:

[0084] S1. Calcinate 1 g of P25TiO2 in a hydrogen / argon environment with a volume ratio of 1:19 at a heating rate of 5 °C / min at 350 °C for 30 minutes to obtain black powder.

[0085] S2. Disperse these powders in ultrapure water and stir overnight. Then filter, wash and vacuum - dry the dispersion to obtain V O -TiO2.

[0086] S3. Disperse 100 mg of V O -TiO2 powder and 30 mg of CuCl2 in 30 mL of acetonitrile, add 0.6 mL of triethylamine and stir for 1 h, then microwave - heat to 80 °C and keep for 2 h. Filter, wash and dry the reconstituted dispersion to obtain Cu / V O -TiO2. Among them, the loading amount of Cu on V O -TiO2 is 0.7 wt%.

[0087] Comparative Example 1

[0088] S1. Grind and mix 1 g of P25TiO2 and 200 mg of sodium borohydride evenly, then calcinate in an argon environment at a heating rate of 5 °C / min at 350 °C for 30 minutes to obtain black powder.

[0089] S2. Disperse these powders in ultrapure water and stir overnight. Then filter, wash and vacuum - dry the dispersion to obtain V O -TiO2.

[0090] Performance test

[0091] Test Example 1

[0092] Flow - system test example: Disperse 1 mg of the photothermal catalyst prepared in Example 1 in 2 mL of absolute ethanol, ultrasonically oscillate for 20 min to achieve uniform dispersion, and then evenly drop the dispersion on a 2×2 cm 2On a quartz sheet, wait for anhydrous ethanol to naturally volatilize to obtain a quartz sheet loaded with the catalyst. Then seal the quartz sheet loaded with the catalyst in a gas-solid reactor. Inject 3 vol.% C3H8 / Ar into the reactor in a vacuum-inflation-vacuum manner for 3 cycles to clean the inside of the reactor and expel as much oxygen in the device as possible. After the outlet of the reactor (the reactor has no external heat source) is connected to a gas chromatograph, continuously purge the reactor with 3 vol.% C3H8 / Ar at a maximum flow rate of 100 mL / min to ensure that the air in the gas path is completely removed, and then reduce the flow rate to 10 mL / min and continuously purge the reactor. After irradiation with a xenon lamp of 300 W (1 W / cm 2 ), set automatic sampling every 30 minutes in the gas chromatograph. The peak production rate of propylene reaches 3 mmol / g / h. Figure 4 It is the reaction rate change diagram of photocatalyst-catalyzed propane dehydrogenation, Figure 4 It can be seen that the reaction rate first increases and then decreases to a stable state over time.

[0093] Test Example 2

[0094] Batch system test example: Disperse 1 mg of the photothermal catalyst prepared in Example 1 and the catalyst of Comparative Example 1 in 2 mL of anhydrous ethanol respectively, and ultrasonically oscillate for 20 min to achieve uniform dispersion. Then evenly drop the dispersion on a 2×2 cm 2 quartz sheet, wait for anhydrous ethanol to naturally volatilize to obtain a quartz sheet loaded with the catalyst. Then seal the quartz sheet loaded with the catalyst in a gas-solid reactor. Inject 3 vol.% C3H8 / Ar into the reactor (the reactor has no external heat source) in a vacuum-inflation-vacuum manner for 3 cycles. Use a xenon lamp of 300 W (1 W / cm 2 ) to simulate sunlight to irradiate the reactor. After 30 minutes, take 1 mL of gas sample for gas chromatographic test and record it as one cycle. The production rate of propylene can reach 4 mmol / g / h, and the selectivity reaches 83.3%. The photothermal catalytic propylene production rate of Comparative Example 1 is 0.084 mmol / g / h, and the selectivity is 93.2%.

[0095] Seal the quartz sheet loaded with the catalyst of Example 1 in the gas-solid reactor again. Inject 3 vol.% C3H8 / Ar into the reactor in a vacuum-inflation-vacuum manner for 3 cycles. Use a xenon lamp of 300 W (1 W / cm 2 ) to simulate sunlight to irradiate the reactor. After 30 minutes, take 1 mL of gas sample for gas chromatographic test and record it as the second cycle, and so on for 7 cycles. Figure 5 It is the result diagram of the photothermal catalytic propylene production rate in the cyclic test performance, Figure 5 It can be seen that after 7 cycles, there is no obvious performance loss in the photothermal catalytic propylene production rate.

[0096] The above has given an exemplary description of the embodiments of the present invention. However, the protection scope of the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A photothermal catalyst, characterized in that, The catalyst includes a transition metal M oxide semiconductor M x O y , and a first transition metal is further loaded on the transition metal M oxide semiconductor M x O y ; The M x O y is selected from at least one of TiO2, Fe2O3, and ZnO2.

2. The catalyst according to claim 1, characterized in that, The first transition metal is selected from at least one of Cu, Ni, Co, and Fe. Preferably, the loading amount of the first transition metal on M x O y is 0.1 to 10 wt%.

3. The catalyst according to claim 1, wherein Under light irradiation, the photothermal catalyst can be heated to a temperature higher than 155 °C. Preferably, under light irradiation, the photothermal catalyst can catalyze propane dehydrogenation, and the production rate of propylene is not less than 3 mmol / g / h. Preferably, the selectivity of the photothermal catalyst for propane dehydrogenation to carbon products is greater than 70%.

4. The preparation method of the catalyst according to any one of claims 1-3, characterized in that, It includes the following steps: (1) React the reducing agent with M x O y to prepare V O -M x O y containing oxygen vacancies; (2) Mix V in step (1) O -M x O y with a precursor containing a first transition metal, and carry out a heating reaction to obtain a photothermal catalyst.

5. The method according to claim 4, wherein In step (1), the mass ratio of M x O y to the reducing agent is 1 - 12:

1. Preferably, in step (1), the reducing agent is selected from sodium borohydride or hydrogen. Preferably, in step (1), the reaction temperature is 200-400 °C; the reaction time is 20-60 min.

6. The method according to claim 5, characterized in that In step (2), the V O -M x O y is added in the form of a V O -M x O y dispersion; Preferably, in step (2), the concentration of the V O -M x O y dispersion liquid is 2-10 mg / mL. Preferably, in step (2), the mass ratio of V O -M x O y to the precursor containing the first transition metal is 2-12:

1. Preferably, in step (2), triethylamine is further added to the method. Preferably, in step (2), the precursor containing the first transition metal is selected from at least one of soluble salts containing the first transition metal (such as chlorides), for example, at least one of copper chloride, nickel chloride, cobalt chloride, or ferrous chloride.

7. The method according to claim 5, characterized in that Step (2) includes the following steps: Disperse V O -M x O y in an organic solvent, add a precursor containing a first transition metal and triethylamine and mix them to obtain a dispersion, and heat and react the dispersion to obtain a photothermal catalyst. Preferably, in the dispersion liquid, the mass fraction of the precursor containing the first transition metal is 10-40 wt%. Preferably, in the dispersion liquid, the mass fraction of triethylamine is 0.3-2 wt%, preferably 0.6-1 wt%. Preferably, in step (2), the heating temperature is 50-80 °C, and the heating time is 1-10 h.

8. Use of the catalyst according to any one of claims 1-3 in the preparation of propylene by catalyzing propane dehydrogenation.

9. A method for preparing propylene by propane dehydrogenation, characterized in that, It includes the following steps: In the presence of the catalyst according to any one of claims 1-3, propane is irradiated with light for reaction to prepare propylene.

10. The method according to claim 9, wherein The wavelength of the light is 100-1200 nm. Preferably, a xenon lamp is used to apply light irradiation. Preferably, the light intensity of the light is 0.1 to 5 W / cm 2 ; the irradiation time of the light is more than 0.5 h. Preferably, the flow rate of propane introduced is 0.1-100 mL / min.

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