A molecular sieve catalyst and its application in the photo-thermal synergistic catalysis of alkane dehydrogenation

Abstract

The present invention discloses a molecular sieve catalyst and its application in the photocatalytic and thermal synergistic dehydrogenation of alkanes. The molecular sieve catalyst is a PtM multi-metal-based catalyst confined in a microporous molecular sieve, comprising a microporous molecular sieve support and a PtM component, wherein the PtM component is confined in the microporous molecular sieve support, and M can be selected from at least one of Zn, Cu, Co, Ni, Sn, Ce, and In. The molecular sieve catalyst of the present invention can realize the photocatalytic and thermal synergistic dehydrogenation of light alkanes to prepare olefins at low temperatures, and has the characteristics of high conversion rate and high selectivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of petrochemical industry, and particularly relates to a molecular sieve catalyst and its application in the photo-thermal synergistic catalysis of alkane dehydrogenation. More specifically, it relates to a method for the photo-thermal synergistic catalysis of C2-C3 alkane dehydrogenation to prepare olefins using a molecular sieve-based catalyst. Background Art

[0002] Light olefins are of great significance in the petrochemical field. The anaerobic dehydrogenation technology in ethane or propane dehydrogenation has received extensive attention and research in recent years due to its few by-products. However, this reaction is a strongly endothermic reaction. The general reaction temperature for propane dehydrogenation is 550-650°C, and the reaction temperature for ethane dehydrogenation is 600-800°C. Moreover, the separation of products also consumes a large amount of energy. Therefore, maintaining a high single-pass conversion while reducing the reaction temperature is the key to reducing energy consumption. Developing low-cost metals with green and environmentally friendly low-temperature and highly efficient propane dehydrogenation catalysts is of great significance.

[0003] Light can drive the progress of a reaction through both thermal effects and non-thermal effects. The specific principle is that when photons are incident on the catalyst surface, due to the Landau damping phenomenon, energy exchange occurs between the photons and the atomic surface due to interference. However, since the system is in an excited state, the energy is not stable. After reducing the energy of the system through non-radiative relaxation, electron-hole pairs are generated. These generated hot electrons and holes can transfer to the catalyst surface to participate in redox reactions. This process is called the non-thermal effect, and most photocatalysis also follows this mechanism. Due to the electron-phonon interaction, light energy can also be converted into heat energy on the picosecond scale. Due to the temperature difference between the local sites of the catalyst and the environment, heat can transfer from the catalyst to the environment to participate in the catalytic reaction, accelerating the transformation of reactants into modified states. This process is called the thermal effect. This process of coupling the photo-induced non-thermal effect and thermal effect for co-catalysis is called photo-thermal synergistic catalysis, which means that this process does not follow the traditional laws of thermodynamics. Developing green and highly efficient photo-thermal synergistic low-carbon alkane dehydrogenation catalysts is of great significance for solving the problem of insufficient olefin demand in China and the energy transformation strategy. Summary of the Invention

[0004] The purpose of the present invention is to provide a microporous molecular sieve-confined PtM (M = Zn, Cu, Co, Ni, Sn) multi-metal-based catalyst, its preparation method, and its application in the photo-thermal synergistic catalysis of alkane dehydrogenation. This catalyst can realize the dehydrogenation of ethane or propane to prepare ethylene or propylene in the low-temperature region under photo-thermal synergistic conditions, with both high conversion and high selectivity.

[0005] The microporous molecular sieve-confined PtM multi-metal-based catalyst provided by the present invention includes a microporous molecular sieve support and a PtM component, and the PtM component is confined in the microporous molecular sieve support.

[0006] The microporous molecular sieve support can be selected from one or more of: Silicalite-1, ZSM-5, and dealuminated beta zeolite by nitric acid; specifically, it can be Silicalite-1 molecular sieve;

[0007] In the PtM component, Pt is the main catalyst and M is a modifier metal as a promoter. M can be selected from at least one of Zn, Cu, Co, Ni, Sn, Ce, and In;

[0008] In the PtM multi-metal-based catalyst confined by the microporous molecular sieve, Pt accounts for 0.01-5 wt% of the total weight of the catalyst, preferably 0.1-0.5 wt%; the molar ratio of the amount of M used to the amount of Pt atoms used is 1:1.

[0009] The microporous molecular sieve support is Silicalite-1 or ZSM-5. The PtM multi-metal-based catalyst confined by the microporous molecular sieve is prepared by a method including the following steps:

[0010] Add a precursor of the M modifier metal and a precursor of the Pt metal to the raw materials for hydrothermal crystallization to prepare the microporous molecular sieve Silicalite-1 or ZSM-5, conduct hydrothermal crystallization, drying, and hydrogen calcination to obtain the PtM multi-metal-based catalyst confined by the microporous molecular sieve;

[0011] The raw materials for hydrothermal crystallization to prepare the microporous molecular sieve include a silicon source (or a silicon source and an aluminum source), a template agent, and water;

[0012] Among them, the template agent is tetrapropylammonium hydroxide (TPAOH);

[0013] The silicon source is tetraethyl orthosilicate;

[0014] The aluminum source is aluminum isopropoxide;

[0015] The modifier metal M can be selected from at least one of Zn, Cu, Co, Ni, Sn, Ce, and In;

[0016] The precursor of the M modifier metal is a ligand-protected modifier metal precursor, which is prepared by dissolving a nitrate of the metal M in an aqueous solution and then adding ethylenediamine to form an ethylenediamine complex;

[0017] The precursor of the Pt metal is one or more of chloroplatinic acid, ammonium platinum nitrate, a complex of chloroplatinic acid and ethylenediamine, and a complex of ammonium platinum nitrate and ethylenediamine;

[0018] The molar ratio of the template agent to silicon in the silicon source is 0.4:1; the molar ratio of silicon contained in the silicon source, Pt in the precursor of the Pt metal, and the modified metal element in the precursor of the M modified metal is 10-80:0.01-0.5:0.01-0.5;

[0019] Or the molar ratio of silicon contained in the silicon source, aluminum contained in the aluminum source, Pt in the precursor of the Pt metal, and the modified metal element in the precursor of the M modified metal is 10-80:0.01-0.5:0.01-0.5:0.01-0.5.

[0020] The temperature of the hydrothermal crystallization can be 90°C to 200°C;

[0021] The hydrothermal crystallization time can be 1 to 4 days;

[0022] The drying conditions can be drying at 60-120°C for 6-12 hours;

[0023] The conditions for hydrogen calcination can be: heating from room temperature to 400-500°C at a rate of 10-20°C / min and holding for 2-8 hours.

[0024] Specifically, the microporous molecular sieve-confined PtM multi-metal-based catalyst is prepared by a method including the following steps:

[0025] First, weigh 300-600 μL of a Pt precursor with a concentration of 1 g / 20 mL, ultrasonicate for 5-15 min to obtain solution A; weigh the modified metal precursor and dissolve it in 300-600 μL of deionized water to obtain solution B; weigh 10-15 g of TPAOH (25%) and mix it with 10-18 g of deionized water, then successively add solution A and B, stir for 5-15 min and then add 6-10 g of TEOS, and stir in a beaker for 6-12 h; then transfer the mixed solution to a 100 mL polytetrafluoroethylene container and crystallize at 150-200°C for 1-3 days; after the crystallization is complete and the oven cools down, wash the obtained solid product three times with deionized water and ethanol, then place the solid in the oven and dry overnight at 60-120°C, and heat the obtained product from room temperature to 450°C at a rate of 10-20°C / min, hold for 2-8 hours, and undergo a reduction process for 2-8 h under the condition of pure hydrogen (10-40 mL / min), and finally obtain the PtM@S-1 catalyst.

[0026] The microporous molecular sieve support is a nitrate dealuminated beta molecular sieve, and the microporous molecular sieve-confined PtM multi-metal-based catalyst is prepared by a method including the following steps:

[0027] The precursor solution of Pt metal and the precursor solution of M-modified metal are impregnated on the beta zeolite after dealumination with nitric acid, and then calcined to obtain a microporous zeolite-confined PtM multi-metal-based catalyst.

[0028] Among them, the molar ratio of the number of moles of silicon atoms contained in the beta zeolite after dealumination with nitric acid to Pt in the precursor of Pt metal and the modified metal element in the precursor of M-modified metal can be: 10-80:0.01-0.5:0.01-0.5;

[0029] The calcination is carried out in an air atmosphere, and the temperature of the calcination is 450-650 °C and the time is 2-8 h.

[0030] The application of the above-mentioned microporous zeolite-confined PtM multi-metal-based catalyst in the photocatalytic and thermal catalytic dehydrogenation of alkanes to olefins also belongs to the protection scope of the present invention.

[0031] In the above application, the alkane can specifically be a light alkane, and more specifically can be a C2-C3 alkane (ethane or propane);

[0032] The dehydrogenation is dehydrogenation without oxygen;

[0033] The dehydrogenation of the alkane is carried out at a low temperature, and the low temperature can specifically be 250-450 °C.

[0034] The present invention also provides a method for dehydrogenating light alkanes to prepare olefins at low temperature.

[0035] The method for dehydrogenating light alkanes to prepare olefins at low temperature provided by the present invention includes the following steps:

[0036] Using light alkanes as raw materials, in the presence of the microporous zeolite-confined PtM multi-metal-based catalyst, reacting through a photocatalytic and thermal catalytic manner to generate the corresponding olefins and hydrogen;

[0037] Among them, the reaction temperature can be 250-450 °C;

[0038] The light wavelength is 320-2500 nm (preferably 320-800 nm, more preferably 400-600 nm);

[0039] The light intensity is 0.1-100 W / cm 2 (preferably 0.1-50 W / cm 2 , more preferably 0.1-5 W / cm 2 ).

[0040] The volume concentration of light alkanes in the raw material gas is 1%-10% (preferably 2%-8%, more preferably 4%-5%), and the rest is an inert gas;

[0041] The space velocity of the feed gas is 0.1 - 10 h -1 (preferably 0.1 - 5 h -1 , more preferably 0.1 - 1 h -1 );

[0042] The inert gas is one or more of He, Ar, and N2.

[0043] The PtM (M = metal promoter, such as Zn, Cu, Sn, etc.) catalyst used in the present invention can produce ethylene or propylene from ethane or propane in a low - temperature region under photothermal conditions. As the reaction center of photothermal catalysis, PtM can not only convert light energy into heat energy to promote the adsorption and activation of C2 - C3 alkanes, but also generate high - energy carriers and inject them into the antibonding orbitals of the alkane C - H bond to promote the activation of the alkane C - H bond. The catalyst in the present invention has obvious advantages in the low - temperature production of ethylene and propylene. This method has a simple operation mode and improves the energy utilization efficiency. Description of the Drawings

[0044] Figure 1 It is the HAADF - STEM image of 0.5Pt0.5Zn@S - 1 prepared in Example 1 of the present invention.

[0045] Figure 2a It is the propylene production rate diagram measured for Comparative Example 4 (Zn@S - 1), 5 (Pt@S - 1), 6 (PtZn@S - 1 - C) and Example 4 (PtZn@S - 1), 5 (PtZn / DeAl - beta) at 400 °C and 5% dilution gas respectively, Figure 2b It is the propylene production rate diagram measured for Example 4 (PtZn@S - 1), 6 (PtZn@ZSM - 5 - 600) under pure propane conditions at 450 °C.

[0046] Figure 3 It is the ethylene production rate diagram before and after turning on the light of PtZn@S - 1.

[0047] Figure 4 It is the ethylene production rate diagram before and after turning on the light of PtIn@S - 1, PtSn@S - 1, PtCo@S - 1, PtCe@S - 1.

[0048] Figure 5 It is the propane reaction order before and after turning on the light in the propane dehydrogenation of PtZn.

[0049] Figure 6 It is the hydrogen reaction order before and after turning on the light in the propane dehydrogenation of PtZn.

[0050] Figure 7 It is the KIE value test for propane co - hydrogen. Detailed Embodiments

[0051] The present invention will be further described in detail below in conjunction with specific embodiments. The provided embodiments are only for clarifying the present invention and not for limiting the scope of the present invention. The following embodiments can be used as a guide for those of ordinary skill in the art to make further improvements and do not constitute any limitation to the present invention in any way.

[0052] The experimental methods in the following embodiments are all conventional methods unless otherwise specified, and are carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. The materials, reagents, etc. used in the following embodiments can be obtained from commercial sources unless otherwise specified.

[0053] Comparative Example 1: Preparation of Zn@S-1 catalyst

[0054] Weigh 0.018 g of zinc nitrate, add 63 μL of ethylenediamine and 637 μL of deionized water to obtain Solution A. Weigh 13 g of TPAOH (25%) and mix it with 15 g of deionized water, then add Solution A successively. After stirring for 15 min, add 8.32 g of TEOS and stir in a beaker for 12 h. Then transfer the mixed solution to a 100 mL polytetrafluoroethylene container and crystallize at 170 °C for 3 days. After the crystallization is complete and the oven has cooled, wash the obtained solid product three times with deionized water and ethanol, then place the solid in the oven and dry it overnight at 80 °C. The obtained product undergoes a reduction process at a rate of 15 °C / min from room temperature to 450 °C, holding for 2 hours under the condition of pure hydrogen (40 mL / min), and finally 0.5Zn@S-1 catalyst is prepared.

[0055] Comparative Example 2: Preparation of Pt@S-1 catalyst

[0056] Weigh 603 μL of an aqueous solution of chloroplatinic acid with a concentration of 1 g / 20 mL, add 63 μL of ethylenediamine and 637 μL of deionized water, and ultrasonicate for 15 min to obtain Solution A. Weigh 13 g of TPAOH (25%) and mix it with 15 g of deionized water, then add Solution A successively. After stirring for 15 min, add 8.32 g of TEOS and stir in a beaker for 12 h. Then transfer the mixed solution to a 100 mL polytetrafluoroethylene container and crystallize at 170 °C for 3 days. After the crystallization is complete and the oven has cooled, wash the obtained solid product three times with deionized water and ethanol, then place the solid in the oven and dry it overnight at 80 °C. The obtained product undergoes a reduction process at a rate of 15 °C / min from room temperature to 450 °C, holding for 2 hours under the condition of pure hydrogen (40 mL / min), and finally 0.5Pt@S-1 catalyst is prepared.

[0057] Example 1: Preparation of PtZn@S-1 catalyst

[0058] Weigh 603 μL of an aqueous solution of chloroplatinic acid with a concentration of 1 g / 20 mL, add 63 μL of ethylenediamine and 637 μL of deionized water, and ultrasonicate for 15 min to obtain solution A. Weigh 0.018 g of zinc nitrate metal, ensuring that the molar ratio of metal atoms to Pt atoms is 1:1, add 63 μL of ethylenediamine and 637 μL of deionized water to obtain solution B. Weigh 13 g of TPAOH (25%) and mix it with 15 g of deionized water, then successively add solution A and B, stir for 15 min, and then add 8.32 g of TEOS, and stir in a beaker for 12 h. Then transfer the mixed solution to a 100 mL polytetrafluoroethylene container, and crystallize at 170 °C for 3 days. After the crystallization is complete and the oven has cooled, wash the obtained solid product three times with deionized water and ethanol, then place the solid in the oven and dry it overnight at 80 °C. The obtained product undergoes a reduction process of heating from room temperature to 450 °C at a rate of 15 °C / min, holding for 2 hours under the condition of pure hydrogen (40 mL / min), and finally prepare a 0.5Pt0.5Zn@S-1 catalyst.

[0059] The results of surface scanning show that the Pt loading is 0.5 wt%, and the atomic ratio between Zn and Pt is approximately 1:1. The high-angle annular dark-field image of scanning transmission electron microscopy shows that the particle size of the PtZn atomic cluster is approximately 1.7 nm (see Figure 1 ).

[0060] Comparative Example 3. Preparation of PtZn@S-1-C catalyst

[0061] The preparation process and conditions are the same as in Example 1, except that the final reduction and calcination process is modified as follows: calcine in air, heat to 450 °C at a rate of 15 °C / min, and hold for 2 h to finally obtain the PtZn@S-1-C catalyst.

[0062] Example 2. PtZn / DeAl-beta

[0063] Weigh 603 μL of an aqueous solution of chloroplatinic acid with a concentration of 1 g / 20 mL, add 63 μL of ethylenediamine and 637 μL of deionized water, and ultrasonicate for 15 min to obtain solution A. Weigh 0.018 g of zinc nitrate metal, ensuring that the molar ratio of metal atoms to Pt atoms is 1:1, add 63 μL of ethylenediamine and 637 μL of deionized water to obtain solution B. Treat 2 g of a commercially purchased beta catalyst with a Si / Al of 50 overnight with concentrated nitric acid (70%), then dry it overnight at 80 °C and calcine it at 550 °C for 6 h. Immerse the above solutions A and B successively on the beta catalyst, and then calcine in a muffle furnace in air at 450 °C for 2 h to finally obtain a 0.5Pt0.5Zn / DeAl-beta catalyst.

[0064] Example 3. PtZn@ZSM-5-600

[0065] Weigh 603 μL of an aqueous solution of chloroplatinic acid with a concentration of 1 g / 20 mL, add 63 μL of ethylenediamine and 637 μL of deionized water, and ultrasonicate for 15 min to obtain Solution A. Weigh 0.018 g of zinc nitrate, ensuring that the molar ratio of metal atoms to Pt atoms is 1:1, add 63 μL of ethylenediamine and 637 μL of deionized water to obtain Solution B. Weigh 13 g of TPAOH (25%) and mix it with 15 g of deionized water. Then, successively add Solution A and B. After stirring for 15 min, add 0.027 g of aluminum isopropoxide and 8.32 g of TEOS, and stir in a beaker for 12 h. Then, transfer the mixed solution to a 100 mL polytetrafluoroethylene container and crystallize at 170 °C for 3 days. After the crystallization is complete and the oven has cooled, wash the obtained solid product three times with deionized water and ethanol. Then, place the solid in the oven and dry it overnight at 80 °C. The obtained product is heated from room temperature to 450 °C at a rate of 15 °C / min, held at this temperature for 2 h, and reduced under the condition of pure hydrogen (40 mL / min) to finally prepare the 0.5Pt0.5Zn@ZSM-5-600 catalyst.

[0066] Example 4: Photothermal catalytic propane dehydrogenation activity test of PtZn@S-1

[0067] Using the catalyst obtained in Example 1 as the test sample, the photothermal co-catalytic propane dehydrogenation to produce propylene and hydrogen was studied. The results are as Figure 2a shown. The test conditions were as follows: a photothermal co-fixed bed reactor (patent number CN202010132319.5) was used, a Perfectlight xenon lamp (PLS-SXE300) was used, the light intensity was 0.5 W / cm 2 , the wavelength was 320 - 2500 nm, the temperature of the heating furnace was maintained at 400 °C, the raw material gas composition was 5% propane gas and 95% nitrogen diluent gas, the mass of the catalyst used was 0.15 g, the space velocity was 0.36 h -1 , and the reaction products were analyzed by gas chromatography. The yields of propylene before and after illumination analyzed online were 25.2·10 8 mol·g -1 ·s -1 and 37.3·10 8 mol·g -1 ·s -1 .

[0068] To compare with PtZn@ZSM-5-600, the reaction conditions were changed to 450 °C, 0.15 g of catalyst, and pure propane at 5 ml / min for the reaction. The results are as Figure 2b shown.

[0069] Comparative Example 4: Photothermal propane dehydrogenation activity test of Zn@S-1

[0070] The difference from Example 4 is that the catalyst used is the Zn@S-1 catalyst described in Comparative Example 1, and the test conditions are the same as those in Example 4 (using a photothermal synergistic fixed-bed reactor (patent number: CN202010132319.5), using a PerfectLight xenon lamp (PLS-SXE300), with a light intensity of 0.5 W / cm 2 , a wavelength of 320 - 2500 nm, the heating furnace is maintained at a temperature of 400 °C, the raw material gas composition is 5% propane gas and 95% nitrogen dilution gas, the mass of the catalyst used is 0.15 g, and the space velocity is 0.36 h -1 ). The results are as Figure 2a shown, the conversion rate of the catalyst is low, and at the same time the relative improvement ratio is low.

[0071] Comparative Example 5, Activity Test of Pt@S-1

[0072] The difference from Example 4 is that the catalyst used is the Pt@S-1 catalyst described in Comparative Example 2, and the test conditions are the same as those in Example 4 (using a photothermal synergistic fixed-bed reactor (patent number: CN202010132319.5), using a PerfectLight xenon lamp (PLS-SXE300), with a light intensity of 0.5 W / cm 2 , a wavelength of 320 - 2500 nm, the heating furnace is maintained at a temperature of 400 °C, the raw material gas composition is 5% propane gas and 95% nitrogen dilution gas, the mass of the catalyst used is 0.15 g, and the space velocity is 0.36 h -1 ). The results are as Figure 2a shown, the conversion rate of the catalyst is low, but higher than that of the Zn@S-1 catalyst described in Comparative Example 4. At the same time, the relative improvement ratio is also higher than that of Zn@S-1.

[0073] Comparative Example 6, Activity Test of PtZn@S-1-C

[0074] The difference from Example 4 is that the catalyst used is the PtZn@S-1-C catalyst described in Comparative Example 3, and the test conditions are the same as those in Example 4 (using a photothermal synergistic fixed-bed reactor (patent number: CN202010132319.5), using a PerfectLight xenon lamp (PLS-SXE300), with a light intensity of 0.5 W / cm 2 , a wavelength of 320 - 2500 nm, the heating furnace is maintained at a temperature of 400 °C, the raw material gas composition is 5% propane gas and 95% nitrogen dilution gas, the mass of the catalyst used is 0.15 g, and the space velocity is 0.36 h -1 ). The results are as Figure 2a shown, the conversion rate of the catalyst is low. The relative improvement ratio is also lower than that of the PtZn@S-1 catalyst. Comparing with the sample calcined in air, it is found that only the catalyst calcined with hydrogen has high thermal catalytic activity and high photo-thermal catalytic activity.

[0075] Example 5, Activity Test of PtZn / DeAl-beta

[0076] The difference from Example 4 is that the catalyst used is the PtZn / DeAl-beta catalyst described in Example 2, and the test conditions are the same as those in Example 4 (using a photo-thermal synergistic fixed-bed reactor (patent number: CN202010132319.5), using a Perfect Light xenon lamp (PLS-SXE300), with a light intensity of 0.5 W / cm 2 , a wavelength of 320 - 2500 nm, the heating furnace is maintained at a temperature of 400 °C, the raw material gas composition is 5% propane gas and 95% nitrogen dilution gas, the mass of the catalyst used is 0.15 g, and the space velocity is 0.36 h -1 ). The results are as Figure 2a shown. The conversion rate of the catalyst is relatively high, but slightly lower than that of the PtZn@S-1 catalyst described in Example 4. At the same time, the relative improvement ratio is almost the same as that of PtZn@S-1, proving that the active component is PtZn nanoclusters and has little relationship with the carrier because pure silica molecular sieve does not absorb light.

[0077] Example 6, Activity Test of PtZn@ZSM-5-600

[0078] The difference from Example 4 is that the catalyst used is the PtZn@ZSM-5-600 catalyst described in Example 3, and the test conditions are 450 °C, 0.15 g of catalyst, and reaction with pure propane at 5 ml / min. The results are as Figure 2b shown. The conversion rate of the catalyst is relatively high, but also slightly lower than that of the PtZn@S-1 catalyst. At the same time, the relative improvement ratio is not much different from that of PtZn@S-1, proving that the active component is PtZn nanoclusters, and introducing a small amount of Al atoms into the catalyst will not seriously affect the photo-thermal catalytic performance.

[0079] Example 7, Activity Test of Photo-Thermal Synergistic Catalytic Ethane Dehydrogenation

[0080] The difference from Example 4 is that the diluted propane reaction gas is changed to a diluted ethane reaction gas. Using the catalyst obtained in Example 1 as the test sample, the photo-thermal synergistic catalytic dehydrogenation of ethane to produce ethylene and hydrogen was studied. The results are as Figure 3 shown. The test temperature is 450 °C, and the rest of the test conditions are the same as those in Example 4. The experimental results are as Figure 3 shown. The ethylene yield before and after illumination increased from 26.2·10 8 mol·g -1 ·s -1 to 30.1·10 8 mol·g -1 ·s-1 。

[0081] Example 8: Activity Test of Ethane Dehydrogenation with Different Promoters

[0082] The promoters were replaced in the same method as in Example 1 to prepare PtIn@S-1, PtSn@S-1, PtCo@S-1, and PtCe@S-1 (where the dosage of Pt was 0.5 wt%, and the atomic molar ratio of M to Pt was 1:1). Under the same reaction conditions as in Example 7, the activity test of diluted ethane was carried out, and the results are as Figure 4 shown. Each catalyst exhibited good photothermal catalytic ethane dehydrogenation performance, proving that Pt is the main active component and the promoter plays a role in modifying Pt atoms.

[0083] Example 9: Reaction Order Test of Propane

[0084] Using the catalyst obtained in Example 1 as the test sample, the reaction order test of propane dehydrogenation under photothermal conditions was carried out. In the test of the reaction order of propane, the test conditions were 0.15 g of catalyst, a total flow rate of 60 ml / min, and 5% diluted gas of propane gas. The flow rate of propane was changed to change the partial pressure of propane. A graph was plotted with the logarithm of the reaction rate and the logarithm of the pressure to obtain the reaction order of propane, as Figure 5 shown. In the test of the reaction order of hydrogen, the total flow rate and the flow rate of propane were kept constant, the flow rates of hydrogen and nitrogen were changed, and 10% diluted gas of hydrogen was used to obtain the reaction order of hydrogen, as Figure 6 shown. The results show that the increase in temperature is beneficial to the coupled desorption of hydrogen atoms. After illumination, this process becomes difficult, proving the existence of non-thermal effects and the participation of high-energy carriers.

[0085] Example 10: KIE Value Test

[0086] Using the catalyst obtained in Example 1 as the test sample, the KIE value test of propane dehydrogenation under photothermal conditions was carried out. The conditions used were 0.15 g of catalyst. The test conditions were a total flow rate of 60 ml / min, including 50 ml / min of nitrogen, 5 ml / min of pure propane, and 5 ml / min of H2 or D2. The KIE value was the ratio of the propylene formation rate of common hydrogen to the propylene formation rate of common deuterium. The results are as Figure 7 shown. When the light is not turned on, this ratio does not change with the change in temperature. After turning on the light, it decreases with the increase in temperature, proving the existence of non-thermal effects, and with the increase in temperature, this KIE isotope effect is slowly offset.

[0087] The present invention has been described in detail above. For those skilled in the art, without departing from the spirit and scope of the present invention and without the need for unnecessary experiments, the present invention can be implemented within a relatively wide range under equivalent parameters, concentrations, and conditions. Although specific embodiments of the present invention are given, it should be understood that the present invention can be further improved. In short, according to the principle of the present invention, this application intends to cover any modifications, uses, or improvements to the present invention, including those that depart from the scope disclosed in this application but are made using conventional techniques known in the art.

Claims

1. Application of Microporous Molecular Sieve-Confined PtM Multimetallic Catalyst in Photothermal Synergistic Catalytic Dehydrogenation of Alkanes to Olefins, The microporous molecular sieve-confined PtM multimetallic catalyst comprises a microporous molecular sieve support and a PtM component, and the PtM component is confined in the microporous molecular sieve support. In the PtM component, Pt is the main catalyst and M is a modified metal as a promoter. M is selected from at least one of Zn, Cu, Co, Ni, Sn, Ce, and In. The microporous molecular sieve support is selected from one or more of Silicalite-1 and ZSM-5. In the microporous molecular sieve-confined PtM multimetallic catalyst, Pt accounts for 0.01 - 5 wt% of the total weight of the catalyst; the atomic molar ratio of M to Pt is 1:

1. The microporous molecular sieve is Silicalite-1 or ZSM-5. The method for preparing the PtM multi-metal based catalyst confined in the microporous molecular sieve includes the following steps: adding a precursor of an M-modifying metal and a precursor of a Pt metal to the raw materials for hydrothermal crystallization to prepare the microporous molecular sieve Silicalite-1 or ZSM-5, followed by hydrothermal crystallization, drying, and hydrogen calcination to obtain the PtM multi-metal based catalyst confined in the microporous molecular sieve, wherein, The precursor of the M modified metal is a ligand-protected modified metal precursor, which is prepared by dissolving metal M nitrate in an aqueous solution and then adding ethylenediamine to form an ethylenediamine complex.

2. The application according to claim 1, wherein The raw materials for hydrothermal crystallization to prepare the microporous molecular sieve include a silicon source or a silicon source and an aluminum source, a template agent, and water. Among them, the template agent is tetrapropylammonium hydroxide. The silicon source is tetraethyl orthosilicate. The aluminum source is aluminum isopropoxide. The modified metal M is selected from at least one of Zn, Cu, Co, Ni, Sn, Ce, and In. The precursor of the Pt metal is one or more of chloroplatinic acid, ammonium platinum nitrate, a complex of chloroplatinic acid and ethylenediamine, and a complex of ammonium platinum nitrate and ethylenediamine. The molar ratio of the template agent to the silicon atoms in the silicon source is 0.4:1; the molar ratio of the silicon element contained in the silicon source, the Pt in the precursor of the Pt metal, and the modified metal element in the precursor of the M modified metal is 10 - 80:0.01 - 0.5:0.01 - 0.

5. Or the molar ratio of the silicon element contained in the silicon source, the aluminum element contained in the aluminum source, the Pt in the precursor of the Pt metal, and the modified metal element in the precursor of the M modified metal is 10 - 80:0.01 - 0.5:0.01 - 0.5:0.01 - 0.

5. The temperature of the hydrothermal crystallization is 90°C to 200°C. The hydrothermal crystallization time is 1 to 4 days. The drying conditions are drying at 60 - 120°C for 6 - 12 hours. The conditions for hydrogen calcination are: heating from room temperature to 400 - 500°C at a rate of 10 - 20°C / min and holding for 2 - 8 hours.

3. The application according to claim 1, wherein: In the said application, the alkane is a light alkane. The dehydrogenation is anaerobic dehydrogenation. The alkane dehydrogenation is carried out at low temperature, and the low temperature is 250 - 450°C.

4. A method for preparing olefins by dehydrogenation of light alkanes at low temperature, comprising the following steps: Using light alkanes as raw materials, in the presence of the microporous molecular sieve-confined PtM multimetallic catalyst described in the application of claim 1, reacting through a photothermal synergistic catalytic method to generate the corresponding olefins and hydrogen.

5. The method according to claim 4, characterized in that: The temperature of the reaction is 250 - 450 °C; the wavelength of the light is 320 - 2500 nm; the light intensity is 0.1 - 100 W / cm 2 .

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