Preparation method and application of a platinum single-atom coupled zinc oxide cluster catalyst

Abstract

The present invention relates to the technical field of petrochemical catalysts, and specifically relates to a preparation method and application of a platinum single-atom coupled zinc oxide cluster catalyst. The catalyst preparation method is as follows: A solution containing tetraethyl orthosilicate and tetrapropylammonium hydroxide undergoes a hydrothermal reaction to obtain a first precipitate, which is calcined and dispersed in a tetrapropylammonium hydroxide solution to obtain a second precipitate, and then calcined to obtain DPS-1; A solution containing ethylenediamine and zinc ions and a solution containing ethylenediamine and platinum ions are prepared, and are successively added dropwise to a dispersion containing a carrier, and after drying, a solid powder is obtained; The solid powder is added to a solution containing tetraethyl orthosilicate, tetrapropylammonium hydroxide and absolute ethanol, undergoes a hydrothermal reaction to obtain a third precipitate, and then is pyrolytically reduced to obtain the catalyst. This solution solves problems such as unclear platinum-based active sites and rapid deactivation at high temperatures. This catalyst is a single-atom platinum-based catalyst with clear active sites and can be applied to the catalytic propane dehydrogenation reaction, having potential application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical catalysts, and particularly relates to a preparation method and application of a platinum single-atom coupled zinc oxide cluster catalyst. Background Art

[0002] Propylene is an important raw material for producing chemical products such as propylene oxide, acetone, and acrylonitrile. Traditional processes for producing propylene by petroleum catalytic cracking and refinery gas steam cracking have problems such as high energy consumption, low yield, and low energy utilization rate. There is an urgent need to use economically sustainable energy to increase the production of propylene to meet the growing demand for propylene in human society. The exploitation of shale gas provides a large amount of available propane. Preparing high-value-added propylene from low-value-added propane through dehydrogenation reaction (PDH) is an effective way to alleviate the demand for propylene. Currently, industrial PDH catalysts include Pt-based and CrO x -based catalysts. However, Pt-based catalysts have problems such as limited resource reserves and high costs, and are quickly deactivated due to carbon deposition during catalytic dehydrogenation reactions. Chromium-based catalysts have biological toxicity, and improper use will cause serious environmental pollution. CrO3 generated during catalytic propane dehydrogenation will cause irreversible loss of activity. Therefore, it is of great significance to develop a catalyst with low cost, environmental friendliness, and excellent stability for catalytic propane dehydrogenation to propylene.

[0003] Reducing the Pt loading and regulating the electronic structure and geometric configuration of Pt sites through the promoter Zn can effectively reduce the rapid deactivation behavior of Pt-based catalysts caused by carbon deposition during dehydrogenation reactions. However, there are still the following problems in the development of Pt catalysts: 1) low utilization rate of Pt; 2) poor dispersion of metal sites; 3) poor stability of Pt. The possible reasons are as follows:

[0004] 1) The selection of catalyst carriers. The Al coordination unsaturated sites in carriers (such as γ-Al2O3, Beta zeolite, high-silica or low-silica ZSM-5 zeolites with different Si / Al ratios, etc.) have strong Lewis acidity, and catalyze the dehydrogenation of propylene to form coke during the catalytic PDH reaction, resulting in low propylene selectivity.

[0005] 2) In the synthesis of catalysts, the dispersion of metal substances on the carriers is poor, resulting in aggregation to form large particles during high-temperature reactions. This not only reduces the utilization rate of metal sites in catalytic reactions, but also larger-sized metals have a stronger adsorption effect on the product propylene, leading to serious side reactions and rapid deactivation of the catalyst;

[0006] 3) Metal Pt is loaded on the catalyst surface in the form of nanoparticles, and is extremely easy to migrate and aggregate to form large nanoparticles during high-temperature reactions, resulting in the loss of catalytic active sites and the decline of performance.

[0007] In summary, there is an urgent need to develop a new type of catalyst with a low Pt loading for the dehydrogenation of propane to propylene to solve problems such as unclear Pt-based active sites and rapid deactivation during high-temperature reactions, improve the performance of the catalyst, and reduce costs simultaneously. Summary of the Invention

[0008] The present invention aims to provide a preparation method of a platinum single-atom coupled zinc oxide cluster catalyst to solve technical problems such as unclear existing Pt-based active sites and rapid deactivation during high-temperature reactions. This technical solution regulates the synthesis strategy to prepare a single-atom Pt-based PDH catalyst (S-1@PtZn@DPS-1) stabilized by ZnO clusters, which is a new type of single-atom Pt-based catalyst with clear active sites, and applies this catalyst to the practical operation of catalytic propane dehydrogenation reaction.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A preparation method of a platinum single-atom coupled zinc oxide cluster catalyst, comprising the following steps carried out in sequence:

[0011] S1: A solution containing tetraethyl orthosilicate and tetrapropylammonium hydroxide undergoes a hydrothermal reaction to obtain a first precipitate; the first precipitate is then subjected to a calcination treatment to obtain an S-1 support;

[0012] S2: The S-1 support is dispersed in a tetrapropylammonium hydroxide solution, and a second precipitate is collected after the reaction; the second precipitate is subjected to a calcination treatment to obtain a DPS-1 support;

[0013] S3: Prepare solution A containing ethylenediamine and zinc ions and solution B containing ethylenediamine and platinum ions; prepare a dispersion of the DPS-1 support, and sequentially dropwise add solution A and solution B into the dispersion, and obtain a solid powder after mixing, stirring, and drying;

[0014] S4: Add the solid powder into solution C containing tetraethyl orthosilicate, tetrapropylammonium hydroxide, and absolute ethanol, and obtain a third precipitate after a hydrothermal reaction; the third precipitate is obtained as a catalyst after a pyrolysis reduction treatment.

[0015] This technical solution also provides a catalyst prepared by the preparation method of a platinum single-atom coupled zinc oxide cluster catalyst.

[0016] This technical solution also provides the application of the platinum single-atom coupled zinc oxide cluster catalyst in the catalytic propane dehydrogenation reaction.

[0017] Further, in S1, the solution containing tetraethyl orthosilicate and tetrapropylammonium hydroxide is prepared by the following method: Dissolve 1 - 9 g of tetrapropylammonium hydroxide in 1 - 50 mL of water, then add 1 - 20 mL of tetraethyl orthosilicate, and stir at 100 - 400 rpm for 1 - 20 h to obtain.

[0018] Further, in S1, the temperature of the hydrothermal reaction is 80 - 190 °C and the duration is 1 - 96 h; the temperature of the calcination treatment of the first precipitate is 500 - 600 °C and the duration is 1 - 8 h; before calcination, the first precipitate is successively subjected to centrifugation, washing with water, washing with absolute ethanol, and drying treatment.

[0019] Further, in S2, the solute concentration of the tetrapropylammonium hydroxide solution is 0.1 - 1 M and the volume is 1 - 100 mL; the reaction temperature is 25 - 100 °C and the duration is 1 - 48 h.

[0020] Further, in S2, after the second precipitate is dried, it is then subjected to calcination treatment, and the temperature of the calcination treatment is 500 - 600 °C.

[0021] Further, in S3, solution A is prepared by the following method: dissolve 0.1 - 0.5 mL of ethylenediamine in 1 - 3 mL of water, then add 0.1 - 0.4 g of zinc acetate dihydrate, and ultrasonically disperse for 0.1 - 1 h;

[0022] Solution B is prepared by the following method: dissolve 0.1 - 0.5 mL of ethylenediamine in 1 - 3 mL of water, then add 0.001 - 0.005 g of tetraammineplatinum nitrate, and ultrasonically disperse for 0.1 - 1 h;

[0023] Disperse 0.1 - 1.5 g of the DPS-1 support in 0.1 - 10 mL of water, stir for 0.1 - 1 h to obtain a dispersion of the DPS-1 support; successively add solution A and solution B dropwise to the dispersion, mix and stir for 0.1 - 0.5 h; then dry at 25 - 100 °C for 1 - 12 h to obtain a solid powder.

[0024] Further, in S4, add 0.1 - 1.5 g of the ground solid powder to solution C; solution C is composed of a tetrapropylammonium hydroxide solution, absolute ethanol, and tetraethyl orthosilicate with a volume ratio of 40:0.1 - 5:0.1 - 5, and the concentration of the tetrapropylammonium hydroxide solution is 0.1 - 1 M; the temperature of the hydrothermal reaction is 170 °C and the duration is 1 - 6 h; the conditions for pyrolysis reduction treatment are: 20% H2 / 80% N2 mixed gas atmosphere, 500 - 600 °C, 1 - 3 h.

[0025] Further, the molar ratio of Pt to Zn in the catalyst is 1:360 - 1:50.

[0026] The principle of this technical solution is as follows:

[0027] Synthesis of ZnO cluster-stabilized single-atom Pt-based PDH catalysts includes the following method: Using DPS-1 as the carrier for dispersing metal substances, highly dispersed active metal sites are synthesized inside the molecular sieve through in-situ crystallization, and a catalyst with ZnO nanoclusters regulating Pt active sites is prepared by direct thermal decomposition reduction with H2. The ZnO cluster-stabilized single-atom Pt-based catalyst can be applied to propane dehydrogenation reaction to produce high-value-added product propylene.

[0028] More specifically, this application provides a synthesis method of a ZnO nanocluster-regulated coordination structure-optimized single-atom Pt catalyst: The S-1 carrier is subjected to defect and pore structure regulation, and the DPS-1 carrier for dispersing metal substances is synthesized. Subsequently, the DPS-1 carrier is impregnated with a metal salt (Pt-EDA+Zn-EDA) solution and uniformly dispersed in the precursor solution for preparing S-1, and hydrothermal crystallization treatment is carried out. In the in-situ hydrothermal crystallization synthesis, EDA as a protective ligand can effectively avoid the agglomeration of metal substances and regulate the coordination environment of metals. Subsequently, the obtained grayish-white precipitate is pyrolytically reduced in a tubular furnace under a mixed gas of 20% H2 / 80% N2 (100 mL min -1 ) to prepare the catalyst. The direct pyrolytic reduction synthesis of the catalyst with the H2 / N2 mixed gas can effectively avoid the oxidation of Pt metal substances and the formation of agglomerated large particle Pt substances during high-temperature synthesis.

[0029] Among them, the application of the protective ligand EDA and the defective porous carrier DPS-1 in the catalyst synthesis can provide a favorable environment for the dispersion and coordination of ZnO substances, play a positive role in regulating the formation of single-site Pt substances by Pt, and ultimately improve the activity performance of the catalyst in catalytic propane dehydrogenation. The preferred S-1@0.1Pt9Zn@DPS-1 catalyst synthesis in this scheme applies the in-situ hydrothermal crystallization strategy, showing the superiority of in-situ crystallization. The common wet impregnation strategy can also be applied to prepare a 0.1Pt9Zn catalyst with the same theoretical content of Pt / Zn. However, its performance is relatively poor compared with the preferred catalyst in catalytic propane dehydrogenation. This technical solution regulates the dispersion degree and coordination environment of ZnO, has a positive impact on the synthesis of optimized catalysts modified with single-atom Pt active sites, and improves the catalyst efficiency in catalytic propane dehydrogenation.

[0030] The beneficial effects of this technical solution are summarized as follows:

[0031] (1) The DPS-1 prepared by regulating the defects and pore structure of S-1 is beneficial to the dispersion of metal salt substances and improves the efficiency of the synthesized catalyst.

[0032] (2) The application of the protective ligand of ethylenediamine (EDA) can inhibit the agglomeration of metal salts into large particle bulk metal substances during synthesis, and ligand regulation helps to synthesize catalysts with good atomic coordination environment and metal dispersion.

[0033] (3) In-situ hydrothermal crystallization combined with direct thermal pyrolysis reduction of H2 is beneficial to the formation of single-atom Pt active sites regulated by ZnO nanoclusters with optimized atomic structure and coordination environment.

[0034] (4) The Pt loading used in this scheme is 0.1 wt%, which has the advantage of cost economy.

[0035] (5) The S-1@0.1Pt9Zn@DPS-1 catalyst prepared by this scheme has good catalytic activity, a high propylene yield, and recyclable stability with recoverable activity. The method provided by the present invention is simple, relatively low in cost, and has good reproducibility. Description of the Drawings

[0036] Figure 1 It is the TEM spectrum of the S-1@0.1Pt9Zn@DPS-1 catalyst of Example 1 of the present invention.

[0037] Figure 2 It is the AC HAADF-TEM image of the S-1@0.1Pt9Zn@DPS-1 catalyst of Example 1 of the present invention.

[0038] Figure 3 It is the in-situ diffuse reflectance Fourier transform infrared (in situ CO-FTIR) spectrum of the S-1@0.1Pt9Zn@DPS-1 catalyst of Example 1 of the present invention.

[0039] Figure 4 It is the ultraviolet-visible (UV-vis) spectrum of the catalysts of Example 1 and Comparative Examples 1-3 of the present invention.

[0040] Figure 5 It is the catalytic performance diagram of the catalysts of Example 1 and Comparative Examples 1-3 of the present invention.

[0041] Figure 6 It is the catalytic performance diagram of the catalysts of Examples 1-4 of the present invention.

[0042] Figure 7 It is the recycling diagram of the S-1@0.1Pt9Zn@DPS-1 catalyst of Example 1 of the present invention. Detailed Embodiments

[0043] The present invention will be further described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments and experimental examples are conventional means well known to those skilled in the art, and the materials, reagents, etc. used can be obtained from commercial sources.

[0044] The main reagents and equipment used in this scheme are as follows:

[0045] Tetraethyl orthosilicate (TEOS), tetrapropylammonium hydroxide (TPAOH), deionized water (DI), zinc acetate dihydrate (Zn(OAC)2 . 2H2O), Pt(NH3)4(NO3)2 (tetraammineplatinum nitrate), absolute ethanol (EtOH), hydrothermal reaction kettle (100 mL PTFE liner + stainless steel reaction kettle), CO-FTIR (Thermo iS10), TEM (FEI TF20), AC HAADF-STEM (FEI TitanG2 60-300), diffuse reflectance UV-Vis (Shimadzu UV-3600plus), fixed bed micro-reactor, gas chromatograph (Shimadzu GC-2014).

[0046] Example 1: Preparation of catalyst S-1@0.1Pt9Zn@DPS-1

[0047] (1) Preparation of DPS-1 support:

[0048] Dissolve 1 - 9 g (specifically 8.1 g in this example) of TPAOH in 1 - 50 mL (specifically 25.2 mL in this example) of deionized water, then add 1 - 20 mL (specifically 9 mL in this example) of TEOS, and stir for 1 - 20 h (specifically 6 h in this example) at a rotation speed of 100 - 400 rpm (specifically 200 rpm in this example). Transfer the uniformly mixed solution into a hydrothermal reaction kettle equipped with a 100 mL PTFE (polytetrafluoroethylene) inner liner, and react in an oven at 80 - 190 °C (specifically 170 °C in this example) for 1 - 96 h (specifically 96 h in this example). Centrifuge the white precipitate prepared by hydrothermal reaction, wash it with deionized water until neutral, and rinse it 3 times with absolute ethanol. Then transfer it to a forced-air drying oven and treat it at 25 - 100 °C (specifically 80 °C in this example) for 1 - 12 h (specifically 12 h in this example). Grind the dried solid and calcine it in a muffle furnace at 500 - 600 °C (specifically 550 °C in this example) for 1 - 8 h (specifically 8 h in this example). The powder prepared by calcination is named S-1 (silicalite-1). Disperse S-1 into 1 - 100 mL (specifically 40 mL in this example) of a 0.1 - 1 M (specifically 0.3 M in this example) TPAOH solution, and stir it in an oil bath at 25 - 100 °C (specifically 80 °C in this example) for 1 - 48 h (specifically 6 h in this example). Subsequently, collect the precipitate by centrifuging the above liquid and treat it in an oven at 25 - 100 °C (specifically 100 °C in this example) for 2 - 48 h (specifically 12 h in this example). Grind the dried white solid and calcine it in a muffle furnace at 500 - 600 °C (specifically 550 °C in this example) for 1 - 10 h (specifically 8 h in this example). The sample prepared after calcination is denoted as DPS-1.

[0049] (2) Preparation of S-1@0.1Pt9Zn@DPS-1:

[0050] Dissolve 0.1 - 0.5 mL (specifically 0.5 mL in this example) of ethylenediamine (EDA) in 1 - 3 mL (specifically 2 mL in this example) of deionized water (DI), and then add 0.1 - 0.4 g (specifically 0.307 g in this example) of Zn(OAC)2 .2H2O was ultrasonically dispersed for 0.1 - 1 h (specifically 0.5 h in this example), and the solution after uniform ultrasonic dispersion was denoted as A. 0.1 - 0.5 mL (specifically 0.5 mL in this example) of ethylenediamine (EDA) was dissolved in 1 - 3 mL (specifically 2 mL in this example) of deionized water (DI), and then 0.001 - 0.005 g (specifically 0.004 g in this example) of Pt(NH3)4(NO3)2 was added. It was ultrasonically dispersed for 0.1 - 1 h (specifically 0.5 h in this example), and the solution after uniform ultrasonic dispersion was denoted as B. 0.1 - 1.5 g (specifically 1 g in this example) of the DPS-1 support was added to 0.1 - 10 mL (specifically 10 mL in this example) of deionized water, and stirred for 0.1 - 1 h (specifically 1 h in this example). Solutions A and B were added dropwise in sequence, and mixed and stirred for 0.1 - 0.5 h (specifically 0.5 h in this example). The above solution was placed in a forced-air drying oven and treated at 25 - 100 °C (specifically 80 °C in this example) for 1 - 12 h (specifically 12 h in this example). The dried solid above was ground and 0.1 - 1.5 g (specifically 1 g in this example) was added to the mixed solution C (the composition of solution C was: 40 mL of 0.1 - 1 M TPAOH + 0.1 - 5 mL of EtOH solution + 0.1 - 5 mL of TEOS, specifically 40 mL of 0.3 M TPAOH + 4.5 mL of EtOH solution + 4.3 mL of TEOS solution). The solution was transferred to a hydrothermal reaction kettle and reacted at 170 °C for 1 - 6 h (specifically 6 h in this example). The precipitate after the reaction was centrifuged, washed, dried, ground, and pyrolyzed in a 20% H2 / 80% N2 mixed gas at 500 - 600 °C (specifically 550 °C in this example) for 1 - 3 h (specifically 2 h in this example). The prepared catalyst was named S-1@0.1Pt9Zn@DPS-1.

[0051] Example 2: Preparation of catalyst S-1@0.1Pt5Zn@DPS-1

[0052] This example was basically the same as Example 1, the difference being: adjusting the input amounts of Zn(OAC)2 . 2H2O and Pt(NH3)4(NO3)2, and the molar ratio of Pt to Zn was 0.1:5 (different from 0.1:9 in Example 1), and the obtained catalyst was named S-1@0.1Pt5Zn@DPS-1. During the preparation process, the difference from Example 1 was: the Zn(OAC)2 . 2H2O added to solution A was 0.171 g, and the Pt(NH3)4(NO3)2 added to solution B was 0.004 g, and the rest of the operations were the same as in Example 1.

[0053] Example 3: Preparation of Catalyst S-1@0.05Pt9Zn@DPS-1

[0054] This example is basically the same as Example 1, except that: the input amounts of Zn(OAC)2 . 2H2O and Pt(NH3)4(NO3)2 are adjusted, and the molar ratio of Pt to Zn is 0.05:9 (different from 0.1:9 in Example 1), and the obtained catalyst is named S-1@0.05Pt9Zn@DPS-1. During the preparation process, the difference from Example 1 is that: 0.307 g of Zn(OAC)2·2H2O is added to solution A, and 0.002 g of Pt(NH3)4(NO3)2 is added to solution B, and the remaining operations are the same as those in Example 1.

[0055] Example 4: Preparation of Catalyst S-1@0.025Pt9Zn@DPS-1

[0056] This comparative example is basically the same as Example 1, except that: the input amounts of Zn(OAC)2 . 2H2O and Pt(NH3)4(NO3)2 are adjusted, and the molar ratio of Pt to Zn is 0.025:9 (different from 0.1:9 in Example 1), and the obtained catalyst is named S-1@0.025Pt9Zn@DPS-1. During the preparation process, the difference from Example 1 is that: 0.307 g of Zn(OAC)2·2H2O is added to solution A, and 0.001 g of Pt(NH3)4(NO3)2 is added to solution B, and the remaining operations are the same as those in Example 1.

[0057] Comparative Example 1: Preparation of Catalyst S-1@0.1Pt9Zn_ WLP @DPS-1

[0058] The preparation of the DPS-1 support in this comparative example is the same as that in Example 1. When preparing the catalyst, ethylenediamine (EDA) is not added. The preparation method of the catalyst S-1@0.1Pt9Zn_ WLP @DPS-1 is as follows: Referring to the raw material ratio and preparation process of Example 1, the DPS-1 support is dispersed in deionized water, and then Zn(OAC)2 . 2H2O and Pt(NH3)4(NO3)2 are added sequentially. After mixing, stirring, and air drying, the dried solid powder is obtained. The above dried solid is ground and weighed and added to the mixed solution C, and then through hydrothermal reaction and pyrolytic reduction and other steps, the catalyst is obtained, denoted as S-1@0.1Pt9Zn_ WLP @DPS-1. The main difference between the catalyst in this comparative example and that in Example 1 is that the process of preparing solutions A and B is omitted, and Zn(OAC)2 .2H2O and Pt(NH3)4(NO3)2 were added to the deionized water dispersion of the DPS-1 support, and other parameter settings were exactly the same as those in Example 1.

[0059] Comparative Example 2: Preparation of catalyst S-1@0.1Pt9Zn@S-1

[0060] The preparation of the S-1 support in this comparative example was the same as that in Example 1. The catalyst S-1@0.1Pt9Zn@DPS-1 was obtained in Example 1. In this comparative example, the DPS-1 support in Example 1 was replaced with the S-1 support to obtain the catalyst S-1@0.1Pt9Zn@S-1. The specific preparation method was as follows:

[0061] 0.5 mL of ethylenediamine (EDA) was dissolved in 2 mL of deionized water (DI), and then 0.307 g of Zn(OAC)2 . 2H2O was added, and ultrasonic dispersion was carried out for 0.5 h. The solution after uniform ultrasonic dispersion was denoted as A. 0.5 mL of ethylenediamine (EDA) was dissolved in 2 mL of deionized water (DI), and then 0.004 g of Pt(NH3)4(NO3)2 was added, and ultrasonic dispersion was carried out for 0.5 h. The solution after uniform ultrasonic dispersion was denoted as B. 1 g of the S-1 support was added to 10 mL of deionized water, and stirred for 1 h. Solutions A and B were added dropwise in sequence, and mixed and stirred for 0.5 h. The above solution was placed in a forced-air drying oven and treated at 80 °C for 12 h. The dried solid above was ground and 1 g was weighed and added to the mixed solution C. The solution was transferred to a hydrothermal reaction kettle and reacted at 170 °C for 6 h. The precipitate after the reaction was centrifuged, washed, dried, ground, and pyrolyzed in a 20% H2 / 80% N2 mixed gas for 2 h. The prepared catalyst was denoted as S-1@0.1Pt9Zn@S-1.

[0062] Comparative Example 3: Preparation of catalyst 0.1Pt9Zn / DPS-1 support

[0063] The preparation of the DPS-1 support in this comparative example was the same as that in Example 1, but S-1 was not covered on the outer layer of the catalyst (i.e., not treated with the mixed solution C). The preparation of the catalyst 0.1Pt9Zn / DPS-1 was as follows:

[0064] Solutions A and B were prepared by referring to Example 1. 1 g of the DPS-1 support was added to 10 mL of deionized water, and stirred for 1 h. Solutions A and B were added dropwise in sequence, and mixed and stirred for 0.5 h. The above solution was placed in a forced-air drying oven and treated at 80 °C for 12 h. The dried solid above was not ground and added to the mixed solution C. Instead, it was directly pyrolyzed in a 20% H2 / 80% N2 mixed gas at 550 °C for 2 h. The prepared catalyst was denoted as 0.1Pt9Zn / DPS-1.

[0065] Experimental Example: PDH Reaction Test

[0066] The catalytic activity of propane dehydrogenation was evaluated in a fixed-bed micro-reactor. Among them, the inner diameter of the stainless-steel reaction tube was 12 mm. A certain amount of catalyst was mixed with quartz sand and placed in the isothermal zone of the stainless-steel reaction tube. Subsequently, the reaction device was heated to 550 °C under N2 blowing. After the temperature was stabilized at 550 °C, the total flow rate of the reaction gas (5% C3H8 / 95% N2, volume ratio) was switched for propane dehydrogenation reaction. The gas reaction products were analyzed by a gas chromatograph (Shimadzu GC-2014) through a flame ionization detector (FID). The regeneration operation of the catalyst was carried out at 550 °C for 1 h of charring reaction under a flowing air of 50 mL min -1 The calculation methods of propane conversion (Conversion), propylene selectivity (Selectivity), and propylene yield (Yield) are as follows:

[0067]

[0068]

[0069] Yield=Conversion×Selectivity

[0070] Where nC x H y is the composition of the reaction gas outlet (μmol min -1 ) quantified by the external standard curve in the GC.

[0071] As shown in the appendix Figure 1 The TEM image of S-1@0.1Pt9Zn@DPS-1 in Example 1 shows that a hollow porous structure was formed in the S-1 zeolite. A small amount of metal particles were distributed in the hollow structure. The average metal particle size distribution was 3.9 nm.

[0072] As shown in the appendix Figure 2 The AC HAADF-STEM image of S-1@0.1Pt9Zn@DPS-1 in Example 1 shows the presence of ZnO nanoclusters and Pt sites with single-atom distribution. Its elemental distribution image (Mapping) further reveals the uniform distribution of metal substances on the zeolite support, where Pt atoms are mainly distributed in the vicinity of ZnO clusters.

[0073] As shown in the appendix Figure 3 The CO diffuse reflectance Fourier transform infrared spectrum (CO-FTIR) of S-1@0.1Pt9Zn@DPS-1 in Example 1 was at 2168 and 2118 cm -1The two characteristic peaks at are attributed to the linearly adsorbed CO peaks on the Pt sites. In addition, the peak at 2046 cm -1 corresponds to the CO adsorption peak on the single-site Pt. No CO adsorption characteristic peaks were observed below 2000 cm -1 , indicating that there are no large particle Pt substances in the catalyst.

[0074] As shown in the Figure 4 attachment, the ultraviolet-visible spectrum (UV-vis) shows that a single Zn site and ZnO nanoclusters are formed in S-1@0.1Pt9Zn@DPS-1 of Example 1. In addition, the ultraviolet-visible spectra of S-1@0.1Pt9Zn_ WLP @DPS-1 of Comparative Example 1 and S-1@0.1Pt9Zn@S-1 of Comparative Example 2 show the formation of a single Zn site and ZnO nanoclusters. Compared with S-1@0.1Pt9Zn@DPS-1, the different adsorption intensities can be attributed to the coordination environments and dispersions of different Zn species. For 0.1Pt9Zn / DPS-1 of Comparative Example 3, there are single Zn sites and bulk ZnO nanoparticles on the catalyst.

[0075] As shown in the Figure 5 attachment, the PDH performance test (550 °C, C3H8 / N2 = 2 / 38, 40 mL min -1 , WHSV = 0.47 h -1 ) gives the performance of the catalyst in a 6-h reaction. Among them, S-1@0.1Pt9Zn@DPS-1 exhibits the best dehydrogenation activity (initial propane conversion: 40.7, initial propylene selectivity: 97.5, initial propylene yield: 39.6).

[0076] The performance parameters of the catalysts of Comparative Examples 1-3 are listed in Table 1 for intuitive comparison. Compared with S-1@0.1Pt9Zn@DPS-1, S-1@0.1Pt9Zn_ WLPThe @DPS-1 and S-1@ 0.1Pt9Zn@S-1 catalyst exhibits relatively poorer activity. This may be due to the absence of the protective ligand EDA and the defective porous support DPS-1 in the catalyst synthesis, resulting in different dispersion and coordination environments of ZnO substances, showing different influencing effects in regulating the formation of single-site Pt substances, and ultimately resulting in different activity performances in the catalytic dehydrogenation of propane. In addition, an in-situ hydrothermal crystallization strategy was applied in the synthesis of the preferred S-1@0.1Pt9Zn@DPS-1 catalyst. To prove the superiority of in-situ crystallization, the common wet impregnation strategy was also applied to prepare a 0.1Pt9Zn catalyst with the same theoretical content of Pt / Zn, which showed relatively poor performance compared with the preferred catalyst in the catalytic dehydrogenation of propane. This is because the bulk ZnO nanoparticles formed in the wet impregnation lead to the further dehydrogenation reaction of the product propylene in the catalytic dehydrogenation of propane, and the generated coke blocks the active sites and causes the rapid loss of catalyst activity. In summary, regulating the dispersion degree and coordination environment of ZnO has a positive influence on the synthesis of optimized single-atom Pt active site modified catalysts and regulates the activity performance in the catalytic dehydrogenation of propane.

[0077] Table 1: Propane dehydrogenation performance of catalysts

[0078]

[0079] As attached Figure 6 shows, the performance effects of different Pt / Zn ratios in the catalytic dehydrogenation of propane were investigated. As can be seen from Figure 6 and Table 2, when the Pt / Zn ratio is between 50 and 360, the performance of the catalyst shows an activity trend of a volcano plot, S-1@0.1Pt9Zn@DPS-1 > S-1@0.05Pt9Zn@DPS-1 > S-1@0.025Pt9Zn@DPS-1 > S-1@0.1Pt5Zn@DPS-1. Specifically, the catalyst prepared at a low Pt / Zn ratio (1 / 50) shows limited catalytic activity due to the lack of Zn substances to regulate the Pt metal active sites. Further, when the Pt / Zn is increased to 1 / 90, the S-1@0.1Pt9Zn@DPS-1 catalyst has the best composition of ZnO clusters to regulate the Pt single-atom site structure and shows good activity in the catalytic dehydrogenation of propane. When the Pt / Zn is increased to 1 / 180 and 1 / 360, too much Zn substance will sinter and agglomerate in the high-temperature reaction and cause carbon deposition, ultimately showing reduced activity. Therefore, an appropriate Zn loading has a positive influence on the formation of Pt single-site active substances.

[0080] Table 2: Propane dehydrogenation performance of catalysts

[0081]

[0082] As attachedFigure 7 As shown, the regeneration cycle performance of the preferred catalyst S-1@0.1Pt9Zn@DPS-1 was evaluated. The catalyst was charred in air and activated by H2 / N2, and there was a phenomenon of activity recovery in the subsequent dehydrogenation reaction. This indicates that the loss of its activity in the PDH reaction is mainly due to the deposition of carbonaceous deposits on the active sites, and the activity of the catalyst can be effectively restored by charring and the service life of the catalyst can be extended.

[0083] In summary, the technical key points of this technical solution are as follows: (1) The S-1 support is subjected to defect and pore structure regulation, and the DPS-1 support for dispersing metal substances is synthesized; (2) In the in-situ hydrothermal crystallization synthesis, EDA is used as a protective ligand to effectively avoid the agglomeration of metal substances and regulate the coordination environment of metals; (3) After obtaining 0.1Pt9Zn@DPS-1, it is treated with the precursor solution (TPAOH + TEOS + ethanol) for preparing S-1 to form the S-1 layer on the outer layer of the catalyst; (4) Control of the ratio of Pt element and Zn element. In Comparative Example 1, EDA was not used as a protective ligand, resulting in a decrease in the overall performance of the catalyst, and the propane conversion rate and propylene yield of the catalyst were not ideal, indicating the importance of the above technical key point (2). In Comparative Example 2, the DPS-1 support was not prepared, and the formed catalyst had the S-1 support as the core, resulting in a decrease in the overall performance of the catalyst, and the propane conversion rate and propylene yield of the catalyst were not ideal, indicating the importance of the above technical key point (1). In Comparative Example 3, the S-1 layer was not covered on the catalyst, resulting in a decrease in the overall performance of the catalyst, and the propane conversion rate and propylene yield of the catalyst were not ideal, indicating the importance of the above technical key point (3). In Examples 2-4, the dosage ratio of Pt:Zn = 1:90 was not adopted, resulting in a decrease in the overall performance of the catalyst, and the propane conversion rate and propylene yield of the catalyst were not ideal, indicating the importance of the above technical key point (4).

[0084] The above are only the embodiments of the present invention, and the specific technical solutions and / or common knowledge such as characteristics known to the public are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can still be made, and these should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicability of the patent. The protection scope required by this application should be subject to the content of its claims, and the specific implementation manners and the like described in the specification can be used to explain the content of the claims.

Claims

1. A preparation method of a platinum single-atom coupled zinc oxide cluster catalyst, characterized in that: It includes the following steps carried out in sequence: S1: A solution containing tetraethyl orthosilicate and tetrapropylammonium hydroxide undergoes a hydrothermal reaction to obtain a first precipitate; the first precipitate is then subjected to a calcination treatment to obtain an S-1 support; S2: The S-1 support is dispersed in a tetrapropylammonium hydroxide solution, and a second precipitate is collected after the reaction; the second precipitate is subjected to a calcination treatment to obtain a DPS-1 support; S3: Prepare solution A containing ethylenediamine and zinc ions and solution B containing ethylenediamine and platinum ions; prepare a dispersion of the DPS-1 support, and sequentially add solution A and solution B dropwise to the dispersion, and obtain a solid powder after mixing, stirring, and drying; S4: Add the solid powder to solution C containing tetraethyl orthosilicate, tetrapropylammonium hydroxide, and absolute ethanol, and obtain a third precipitate through a hydrothermal reaction; the third precipitate is subjected to a thermal decomposition reduction treatment under a H2 / N2 mixed gas to obtain a catalyst.

2. The preparation method of a platinum single-atom coupled zinc oxide cluster catalyst according to claim 1, characterized in that: In S1, the solution containing tetraethyl orthosilicate and tetrapropylammonium hydroxide is prepared by the following method: Dissolve 1 - 9 g of tetrapropylammonium hydroxide in 1 - 50 mL of water, then add 1 - 20 mL of tetraethyl orthosilicate, and stir at 100 - 400 rpm for 1 - 20 h.

3. The preparation method of a platinum single-atom coupled zinc oxide cluster catalyst according to claim 2, wherein: In S1, the temperature of the hydrothermal reaction is 80 - 190 °C and the duration is 1 - 96 h; the temperature of the calcination treatment of the first precipitate is 500 - 600 °C and the duration is 1 - 8 h; before calcination, the first precipitate is sequentially subjected to centrifugation, water washing, absolute ethanol washing, and drying treatments.

4. The preparation method of a platinum single-atom coupled zinc oxide cluster catalyst according to claim 1, wherein: In S2, the solute concentration of the tetrapropylammonium hydroxide solution is 0.1 - 1 M and the volume is 1 - 100 mL; the reaction temperature is 25 - 100 °C and the duration is 1 - 48 h.

5. The preparation method of a platinum single-atom coupled zinc oxide cluster catalyst according to claim 4, characterized in that: In S2, after the second precipitate is dried, it is then subjected to a calcination treatment, and the temperature of the calcination treatment is 500 - 600 °C.

6. The preparation method of a platinum single-atom coupled zinc oxide cluster catalyst according to claim 1, characterized in that: In S3, solution A is prepared by the following method: Dissolve 0.1 - 0.5 mL of ethylenediamine in 1 - 3 mL of water, then add 0.1 - 0.4 g of zinc acetate dihydrate, and ultrasonically disperse for 0.1 - 1 h; Solution B is prepared by the following method: Dissolve 0.1 - 0.5 mL of ethylenediamine in 1 - 3 mL of water, then add 0.001 - 0.005 g of tetraammineplatinum nitrate, and ultrasonically disperse for 0.1 - 1 h; Disperse 0.1 - 1.5 g of the DPS-1 support in 0.1 - 10 mL of water, stir for 0.1 - 1 h to obtain a dispersion of the DPS-1 support; sequentially add solution A and solution B dropwise to the dispersion, mix and stir for 0.1 - 0.5 h; then dry at 25 - 100 °C for 1 - 12 h to obtain a solid powder.

7. The preparation method of a platinum single-atom coupled zinc oxide cluster catalyst according to claim 1, characterized in that: In S4, 0.1 - 1.5 g of the ground solid powder is added to solution C; solution C is composed of tetrapropylammonium hydroxide solution, absolute ethanol, and tetraethyl orthosilicate with a volume ratio of 40:0.1 - 5:0.1 - 5, and the concentration of the tetrapropylammonium hydroxide solution is 0.1 - 1 M; the temperature of the hydrothermal reaction is 170 °C and the duration is 1 - 6 h; the conditions for pyrolysis reduction treatment are: in an atmosphere of 20% H2 / 80% N2 mixture gas, at 500 - 600 °C, for 1 - 3 h.

8. A catalyst prepared by the preparation method of a platinum single-atom coupled zinc oxide cluster catalyst according to any one of claims 1 - 7.

9. The catalyst prepared by the preparation method of a platinum single-atom coupled zinc oxide cluster catalyst according to claim 8, characterized in that: The molar ratio of Pt to Zn in the catalyst is 1:360 - 1:

50.

10. Use of the catalyst according to claim 8 in the catalytic propane dehydrogenation reaction.

Images