A molecular sieve-based catalyst, its preparation method and application

Abstract

The present invention discloses a molecular sieve-based catalyst, its preparation method and application, belonging to the technical field of catalysts. The catalyst includes a sandwich core-shell structure, and the inner shell layer is composed of ultrafine Pt nanoclusters anchored by porous carbon; the middle shell layer is composed of a silicon-aluminum molecular sieve Zeolite (Ov) composed; the surface shell layer is composed of HfO2 oxide. The "sandwich" core-shell structure molecular sieve-based catalyst prepared by the present invention, the inner shell layer overcomes the structural limitations of poor dispersion, easy aggregation and poor cyclic stability of Pt nanoclusters; the middle shell layer improves the transport resistance of the microporous channels of the silicon-aluminum molecular sieve, and the introduced oxygen vacancies (Ov) not only bring new Lewis acid sites to the catalyst, but also promote the rapid isomerization of oxygen-containing intermediates; the surface shell layer HfO2 enhances the selective adsorption of the catalyst support to the substrate, ensuring the rapid activation of reactant molecules.

Description

Technical Field

[0001] The present invention relates to a molecular sieve-based catalyst, a preparation method thereof and an application thereof, and belongs to the technical field of catalysts. Background Art

[0002] Inducing strong metal-support interaction (SMSI) has always been a useful method to improve the dispersion and stability of active sites and to improve the intrinsic activity of active sites. Constructing a unique interface preferred for the target reaction can further optimize the conversion rate and selectivity of the reaction. As a practical approach, it is of great significance to produce biofuels and platform chemicals using sustainable biomass resources. The hydrogenation conversion of levulinic acid (LA) to γ-valerolactone (GVL) is a key reaction for realizing the conversion of biomass resources. The hydrogenation of LA to GVL involves a series of tandem reaction processes such as adsorption of reactants, cleavage of hydrogen molecules, activation of carbonyl groups, dehydration hydrogenation, and lactonization, and usually requires a relatively high temperature (>160 °C) to occur. Therefore, it is necessary to prepare a metal-acid bifunctional catalyst to effectively improve the catalytic activity of the tandem reaction. Pt-based molecular sieve catalysts have great potential in the hydrogenation conversion of biomass-derived platform molecules.

[0003] In recent years, there have been many patent reports on the preparation of catalysts for the hydrogenation conversion of levulinic acid to γ-valerolactone. Chinese Patent CN110227473 discloses a short rod-shaped solid acid Ni@ZrO2-CeO2 catalyst, which obtained a 98% γ-valerolactone yield when catalyzing the conversion of levulinic acid to γ-valerolactone at a reaction temperature of 180 °C and a reaction time of 6 h. Nevertheless, the catalyst requires a relatively high reaction temperature and a relatively long reaction time. Chinese Patent CN110665505B reports a Cu@mZrO2 core-shell catalyst for the hydrogenation of levulinic acid to γ-valerolactone. The prepared Cu@mZrO2 core-shell catalyst shows high activity, good stability, and a γ-valerolactone yield of up to 100% at the reaction temperature during the hydrogenation of levulinic acid to γ-valerolactone, but there are few reports on the controllable highly dispersed Cu nanoparticles. Chinese Patent CN109569589B discloses an M-B@Al2O3 catalyst for the hydrogenation of levulinic acid to γ-valerolactone, which is composed of an active component M-B and an auxiliary agent Al2O3. The catalyst shows high activity and high γ-valerolactone selectivity, but there is little research on the synergistic promotion effect between each component and the catalyst interface. To further soften the reaction conditions and improve the hydrogenation activity of levulinic acid, it is of great significance to develop a metal-acid bifunctional catalyst with both structural stability and synergistic catalysis of each component. Summary of the Invention

[0004] The object of the present invention is to provide a molecular sieve-based hydrogenation catalyst with a "sandwich" core-shell structure that can soften the reaction conditions, reduce the agglomeration of active components, lower the molecular transport resistance of reactants, and have the synergistic effect of each component, and simultaneously have high conversion rate and high selectivity in the hydrogenation reaction of levulinic acid.

[0005] The second object of the present invention is to provide a preparation method of the above catalyst.

[0006] The third object of the present invention is to provide the application of the above catalyst.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A molecular sieve-based catalyst includes a sandwich core-shell structure, and the inner shell layer is composed of ultrafine Pt nanoclusters anchored by porous carbon; the middle shell layer is composed of a silicon-aluminum molecular sieve Zeolite (Ov) rich in oxygen vacancies; the surface shell layer is composed of HfO2 oxide.

[0009] The silicon-aluminum molecular sieve Zeolite (Ov) rich in oxygen vacancies includes Beta (Ov) molecular sieve or SSZ-39 (Ov) molecular sieve.

[0010] The crystal size of the catalyst is 240-970 nm, the average particle size of the Pt nanoclusters is 0.8-2.8 nm, and the thickness of the HfO2 surface shell layer is 15-30 nm.

[0011] After the catalyst reacts at 100 °C for 3 h: the conversion rate of LA is 92.5-99.1%, and the selectivity of GVL is 100%; after the catalyst catalyzes the selective hydrogenation cyclic reaction of levulinic acid 10 times, the conversion rate of LA remains at 89.5-97.3%, and the selectivity of GVL is 100%.

[0012] A preparation method of a molecular sieve-based catalyst includes the following steps:

[0013] S01, at room temperature, mix the platinum source: zinc nitrate hexahydrate: 2-methylimidazole: organic solvent according to a mass ratio of 1:(12.5-20):(15-23):(200-300), stir evenly, place it in a reaction kettle, and let it stand for reaction for 7-24 h. Then filter, wash with an organic solvent, and dry the filter cake to obtain an ultrafine Pt nanocluster precursor Pt 2+ / ZIF-8 anchored by porous carbon;

[0014] S02, the silicon source: aluminum source: structure-directing agent: multi-block polymer surfactant: ultrafine Pt nanocluster precursor Pt 2+ / ZIF-8: Hafnium source: Deionized water is added to a microwave hydrothermal synthesizer with an output power of 1200 - 1600 W at a mass ratio of 1:(0.56 - 3.8):(1.6 - 8.3):(0.6 - 3.9):(0.2 - 0.56):(0.08 - 0.6):(10 - 16). Heat up to 150 - 200 °C for microwave hydrothermal treatment for 0.7 - 1.5 h, cool to room temperature, filter, wash the filter cake with deionized water until the washing liquid is neutral, and dry the filter cake at 60 - 100 °C for 10 - 18 h. Then, heat it in air at a rate of 2 °C / min to 200 - 300 °C and hold for 2 - 4 h, and then heat it at a rate of 10 °C / min to 800 - 1000 °C and calcine for 3 - 6 h, and then cool to room temperature to obtain the molecular sieve-based catalyst Pt@Zeolite (Ov) @HfO2.

[0015] In S01, the platinum source is tetraammineplatinum(II) acetate or potassium amminetrichloroplatinate(II).

[0016] In S01, the organic solvent is methanol or deuterated dimethyl sulfoxide.

[0017] In S02, the silicon source is one of silica sol, sodium silicate or tetramethyl orthosilicate; the aluminum source is one of pseudoboehmite, sodium metaaluminate or aluminum isopropoxide; the structure-directing agent is one of tetrapropylammonium hydroxide, tetraethylammonium bromide, N,N-dimethyl-3,5-dimethylpiperidinium hydroxide, N-methyl-N-ethyl-2,6-dimethylpiperidinium hydroxide; the multi-block polymeric surfactant is one of poly(n-butyl acrylate)-poly(2-hydroxyethyl methacrylate), poly(tributyl acrylate)-polymethyl methacrylate or poly(ethyl acrylate)-polymethyl methacrylate multi-block polymers.

[0018] In S02, the hafnium source is one of hafnium chloride or dichlorodicyclopentadienyl hafnium.

[0019] Application of a molecular sieve-based catalyst in the selective hydrogenation reaction of levulinic acid.

[0020] The present invention has the following beneficial effects:

[0021] In the present invention, the transition metal oxide HfO2 is used as the surface shell of the catalyst. The HfO2 shell as an amphoteric oxide not only helps to adjust the surface acidity of the catalyst, but also alleviates the competitive adsorption of reactant molecules LA and H2 on the surface; using the silicon-aluminum molecular sieve Zeolite (Ov) rich in oxygen vacancies as the intermediate shell can not only play a physical barrier role to prevent the aggregation of Pt nanoclusters, but also the oxygen vacancies enhance the interaction force between the oxygen-containing intermediates and the catalyst, effectively promoting the intermediate molecules between the Pt nanoclusters and Zeolite (Ov)In addition, the removal of multi-block polymer surfactants formed hierarchical pores that reduced the transport resistance of reactant molecules and alleviated the Zeolite (Ov) The molecular diffusion barrier caused by the microporous structure of the molecular sieve itself. Pt@Zeolite (Ov) The synergistic effect of the components among @HfO2 catalysts effectively inhibited the production of by-products in the cascade reaction and significantly improved the yield and selectivity of the target product.

[0022] The present invention mainly solves the problems of poor dispersion of Pt nanoclusters, easy loss and agglomeration, and low atomic utilization. To this end, by means of the highly ordered periodic metal nodes of ZIF-8, the high dispersion and stable anchoring of Pt nanoclusters in ZIF-8 derivatives are achieved through "metal substitution". 2+ During the calcination of the ZIF-8 precursor, the Zn element evaporates and leaves a large number of metal vacancies and surface defects. Under the synergistic promotion of the highly unsaturated coordination environment and the uniform anchoring center, Pt replaces Zn and is uniformly anchored in the ZIF-8 derivative in the form of Pt-N. 2+ The metal ions are effectively adsorbed and anchored, which improves the dispersion and stability of Pt nanoclusters.

[0023] The present invention prepares Pt by in-situ growth method and microwave hydrothermal method. 2+ / ZIF-8 precursor and "sandwich" core-shell metal-acid bifunctional Pt@Zeolite (Ov) @HfO2 catalyst, the present invention uses Pt 2+ The structural advantages of the ZIF-8 precursor as the inner shell are mainly manifested in two aspects: on the one hand, Pt 2+ / ZIF-8 precursor provides a "space occupation" effect, and after calcination, a "sandwich" shell structure with a hollow interior is formed. The hollow structure promotes the concentration and enrichment of reactant molecules, prolongs the residence time of reactant molecules at the active site, and thus improves the conversion rate of the reactants. On the other hand, Pt 2 + The ZIF-8 precursor ensures the high dispersion of ultrafine Pt nanoclusters. The metal vacancies generated by Zn evaporation and the periodic metal nodes of ZIF-8 are Pt 2+ The metal ions provide sufficient anchoring sites, which not only enhances the thermal stability of Pt nanoclusters in tandem reactions but also maximizes the atomic utilization of Pt.

[0024] The technical problems that cannot be solved by the existing technology are: achieving high dispersion and effective encapsulation of Pt nanoclusters at the same time, overcoming the reactant transport limitations of microporous molecular sieves, and controllably regulating Lewis acid and The number and proportion of acidic sites, improve the adsorption stability of reactants and achieve selective adsorption of LA and H2. Pt 2+ The "metal substitution" that occurs during the calcination of the Pt / ZIF-8 precursor significantly improves the dispersion of Pt nanoclusters; the effective encapsulation of the Pt nanoclusters by the intermediate shell inhibits the aggregation and sintering of metal species, ensuring that the catalyst has sufficient hydrogenation sites and enhancing the thermal stability of the hydrogenation sites; Zeolite (Ov) The carbonization of the multi-block polymeric surfactant in the zeolite molecular sieve introduces a hierarchical pore structure (the hierarchical pore structure includes three types: micropores <2 nm, mesopores 2 nm - 50 nm, and macropores >50 nm, and hierarchical pores refer to the presence of two or more multi-level pore structures in the same host material) and oxygen vacancies. The hierarchical pore structure reduces the molecular transport resistance; the oxygen vacancies bring rich acid sites and Lewis acid sites (the four-coordinated Al in the framework provides acid sites, and the three-coordinated Al provides Lewis acid sites), which promotes the rapid isomerization of oxygen-containing intermediates, the acid sites promote the lactonization of intermediates to the target product GVL, and the Lewis acid sites improve the selectivity of GVL; the HfO2 surface shell improves the selective adsorption between the substrate molecules and the catalyst. The unique metal-oxygen vacancy-oxide interface composed of the "sandwich" core-shell structure enables the target reaction to proceed efficiently at low temperature (100 °C). The catalyst exhibits excellent LA conversion rate (92.5 - 99.1%) and GVL selectivity (100%). After 10 cycles of reaction, the LA conversion rate still remains at 89.5 - 97.3%, maintaining a high selectivity of 100% for GVL.

[0025] In the prior art, general catalysts need to exhibit good catalytic activity at a relatively high temperature (160 °C). However, through a series of structural designs and compositional regulations, the present invention achieves excellent low-temperature (100 °C) catalytic activity.

[0026] The present invention adopts a simple in-situ growth and microwave hydrothermal method to construct a Pt@Zeolite (Ov) @HfO2 catalyst with a unique metal-oxygen vacancy-oxide interface. The "sandwich" core-shell type metal-acid bifunctional catalyst exhibits enhanced low-temperature (100 °C) catalytic activity and structural stability in the tandem reaction of LA hydrogenation to GVL.

[0027] The "sandwich" core-shell structured zeolite-based catalyst prepared by the present invention has an inner shell layer that overcomes the structural limitations of poor Pt nanocluster dispersion, easy aggregation, and poor cycling stability; the middle shell layer improves the transport resistance of the microporous channels of the silica-alumina zeolite, and the introduced oxygen vacancies (Ov) not only bring new Lewis acid sites to the catalyst but also promote the rapid isomerization of oxygen-containing intermediates; the surface shell layer HfO2 enhances the selective adsorption of the catalyst support for the substrate and ensures the rapid activation of reactant molecules. The synergistic effect at the metal-oxygen vacancy-oxide shell interface improves the efficiency of the tandem reaction, and the catalyst exhibits high low-temperature activity (high conversion rate, high selectivity) and good high-temperature durability.

[0028] A zeolite-based catalyst and its preparation method and application. The catalyst has a "sandwich" core-shell structure, with porous carbon anchored ultrafine Pt nanoclusters derived from ZIF-8 as the inner shell layer, silica-alumina zeolite (Zeolite (Ov) ) rich in oxygen vacancies as the middle shell layer, and HfO2 as the surface shell layer. It is prepared by microwave hydrothermal method using a silicon source, an aluminum source, a structure-directing agent, a multi-block polymeric surfactant, a precursor of porous carbon anchored ultrafine Pt nanoclusters (Pt 2+ / ZIF-8), and a hafnium source as raw materials. The "sandwich" core-shell structure of the zeolite-based catalyst prepared by the present invention effectively inhibits the sintering of Pt nanoclusters; the silica-alumina zeolite Zeolite (Ov) rich in oxygen vacancies promotes the rapid isomerization of oxygen-containing intermediates and restricts the occurrence of side reactions; the transition metal oxide HfO2 improves the interaction between the substrate and the catalyst through chemisorption, enhances the adsorption stability of reactants, and promotes the selective adsorption of reactant molecules. Using the Pt@Zeolite (Ov) @HfO2 catalyst for the selective hydrogenation of levulinic acid to γ-valerolactone, the unique metal-oxygen vacancy-oxide interface formed improves the intrinsic activity and catalytic hydrogenation efficiency of the tandem reaction, and the synergistic effect between the acidic sites and the hydrogenation sites improves the conversion rate and selectivity of the target reaction. This research provides a strategy for the design and practical application of zeolite catalysts for the hydrogenation conversion of biomass derivative levulinic acid to γ-valerolactone. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is the TEM image of the catalyst in Example 1 of the present invention;

[0030] Figure 2 It is the SEM image of the catalyst in Example 1 of the present invention;

[0031] Figure 3 It is the XRD diffraction pattern of the catalyst in Example 3 of the present invention;

[0032] Figure 4TEM image of the catalyst in Example 5 of the present invention;

[0033] Figure 5 TEM image of the catalyst in Comparative Example 1 of the present invention;

[0034] Figure 6 TEM image of the catalyst in Comparative Example 2 of the present invention;

[0035] Figure 7 SEM image of the catalyst in Comparative Example 3 of the present invention;

[0036] Figure 8 TEM image of the catalyst in Comparative Example 4 of the present invention;

[0037] Figure 9 Tricoordinate 27 Structure schematic diagram of Al of Example 4 of the present invention;

[0038] Figure 10 Structure schematic diagram of the hierarchical pores of Example 2 of the present invention. Detailed implementation manners

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0040] Example 1

[0041] A preparation method of a molecular sieve-based catalyst, comprising the following steps:

[0042] (1) At room temperature, 0.02 g of Pt(NH3)4(CH3COO)2, 0.25 g of Zn(NO3)2·6H2O, and 0.3 g of 2-methylimidazole are dissolved in 4 g of a methanol solution, mixed evenly, placed in a reaction kettle, and allowed to stand for reaction for 7 h. Subsequently, it is filtered, washed with methanol, and the filter cake is dried to obtain Pt 2+ / ZIF-8;

[0043] (2) 0.5 g of silica sol, 0.28 g of pseudo-boehmite, 0.8 g of tetrapropylammonium hydroxide, 0.3 g of poly(n-butyl acrylate)-poly(2-hydroxyethyl methacrylate), 0.15 g of Pt 2+ / ZIF-8, 0.04 g of hafnium chloride, and 5 g of deionized water are added to a microwave hydrothermal synthesizer with an output power of 1200 W, and the temperature is raised to 150 °C for microwave hydrothermal treatment for 0.7 h. Cool to room temperature, filter, wash the filter cake with deionized water until the washing liquid is neutral, and dry the filter cake at 60 °C for 10 h. Heat it in air at a rate of 2 °C / min to 200 °C and hold for 2 h, then heat it to 800 °C at a rate of 10 °C / min and calcine for 6 h, and cool to room temperature to obtain the molecular sieve-based Pt@Beta (Ov)@HfO2 catalyst.

[0044] See Figure 1 , the crystal size of the above catalyst is 240 nm, the average particle size of the Pt nanoclusters is 1.5 nm, and the surface shell thickness of HfO2 is 15 nm. Figure 2 SEM image of the catalyst obtained in this example.

[0045] The above "sandwich" core-shell structured Pt@Beta (Ov) @HfO2 catalyst for the catalytic performance of the hydrogenation conversion of levulinic acid to γ-valerolactone. After reacting at 100 °C for 3 h: the conversion rate of LA is 95.1%, and the selectivity of GVL is 100%.

[0046] After using the above catalyst to catalyze the selective hydrogenation of levulinic acid for 10 cycles, the conversion rate of LA remains at 93.2%, and the selectivity of GVL is 100%.

[0047] Example 2

[0048] A preparation method of a molecular sieve-based catalyst, comprising the following steps:

[0049] (1) At room temperature, 0.05 g of potassium amminetrichloroplatinate(II), 0.75 g of Zn(NO3)2·6H2O, and 1 g of 2-methylimidazole are dissolved in 11 g of deuterated dimethyl sulfoxide solution and mixed evenly. The mixture is placed in a reaction kettle and allowed to stand for 10 h. Subsequently, it is filtered, washed with deuterated dimethyl sulfoxide, and the filter cake is dried to obtain Pt 2+ / ZIF-8;

[0050] (2) 0.5 g of sodium silicate, 0.5 g of aluminum isopropoxide, 1.5 g of tetraethylammonium bromide, 1.2 g of poly(n-butyl acrylate)-poly(2-hydroxyethyl methacrylate), 0.28 g of Pt 2+ / ZIF-8, 0.15 g of hafnium chloride, and 7.5 g of deionized water are added to a microwave hydrothermal synthesizer with an output power of 1350 W. The temperature is raised to 170 °C and microwave hydrothermal treatment is carried out for 1 h. It is cooled to room temperature, filtered, and the filter cake is washed with deionized water until the washing liquid is neutral. Then the filter cake is dried at 60 °C for 18 h. After heating in air at a rate of 2 °C / min to 220 °C and maintaining for 2.5 h, it is heated to 850 °C at a rate of 10 °C / min and calcined for 5 h, and then cooled to room temperature to obtain a molecular sieve-based Pt@Beta (Ov) @HfO2 catalyst.

[0051] The crystal size of the above catalyst is 270 nm, the average particle size of the Pt nanoclusters is 1.8 nm, and the surface shell thickness of HfO2 is 22 nm.

[0052] The above "sandwich" core-shell structured Pt@Beta (Ov)The catalytic performance of the @HfO2 catalyst for the hydrogenation conversion of levulinic acid to γ-valerolactone. After reacting at 100 °C for 3 h: the conversion rate of LA is 96.5%, and the selectivity of GVL is 100%.

[0053] After using the above catalyst to catalyze the selective hydrogenation cycle reaction of levulinic acid 10 times, the conversion rate of LA remains at 94.2%, and the selectivity of GVL is 100%.

[0054] Example 3

[0055] A preparation method of a molecular sieve-based catalyst, comprising the following steps:

[0056] (1) At room temperature, 0.03 g of Pt(NH3)4(CH3COO)2, 0.39 g of Zn(NO3)2·6H2O, and 0.45 g of 2-methylimidazole are dissolved in 7 g of methanol solution and mixed evenly, placed in a reaction kettle and left to react for 12 h, then filtered, washed with methanol, and the filter cake is dried to obtain Pt 2+ / ZIF-8;

[0057] (2) 0.8 g of tetramethyl orthosilicate, 1.5 g of sodium metaaluminate, 3 g of N,N-dimethyl-3,5-dimethylpiperidine hydroxide, 1.6 g of polyethylacrylic acid-poly(methyl methacrylate), 0.17 g of Pt 2+ / ZIF-8, 0.35 g of hafnium chloride, and 8.3 g of deionized water are added to a microwave hydrothermal synthesizer with an output power of 1600 W, heated to 180 °C for microwave hydrothermal treatment for 1.2 h. Cool to room temperature, filter, wash the filter cake with deionized water until the washing liquid is neutral, and dry the filter cake at 80 °C for 18 h. Heat it in air at a rate of 2 °C / min to 280 °C and keep it for 3.5 h, then heat it to 900 °C at a rate of 10 °C / min and calcine for 5 h, and cool to room temperature to obtain the molecular sieve-based Pt@SSZ-39 (Ov) @HfO2 catalyst.

[0058] The crystal size of the above catalyst is 970 nm, the average particle size of the Pt nanoclusters is 2.5 nm, and the surface shell thickness of HfO2 is 30 nm.

[0059] The above "sandwich" core-shell structured Pt@SSZ-39 (Ov) The catalytic performance of the @HfO2 catalyst for the hydrogenation conversion of levulinic acid to γ-valerolactone. After reacting at 100 °C for 3 h: the conversion rate of LA is 92.5%, and the selectivity of GVL is 100%.

[0060] After using the above catalyst to catalyze the selective hydrogenation cycle reaction of levulinic acid 10 times, the conversion rate of LA remains at 90.0%, and the selectivity of GVL is 100%.

[0061] Example 4

[0062] A preparation method of a molecular sieve-based catalyst, comprising the following steps:

[0063] (1) At room temperature, 0.03 g of potassium amminetrichloroplatinate(II), 0.6 g of Zn(NO3)2·6H2O, and 0.7 g of 2-methylimidazole are dissolved in 9 g of deuterated dimethyl sulfoxide solution, mixed evenly, placed in a reaction kettle, and allowed to stand for reaction for 20 h. Subsequently, it is filtered, washed with deuterated dimethyl sulfoxide, and the filter cake is dried to obtain Pt 2+ / ZIF-8;

[0064] (2) 1 g of sodium silicate, 3.5 g of pseudo-boehmite, 8 g of N-methyl-N-ethyl-2,6-dimethylpiperidine hydroxide, 3.9 g of polyethylacrylic acid-poly(methyl methacrylate), 0.3 g of Pt 2+ / ZIF-8, 0.6 g of hafnium dichloride bis(cyclopentadienyl), and 12 g of deionized water are added to a microwave hydrothermal synthesizer with an output power of 1500 W, heated to 160 °C, and subjected to microwave hydrothermal treatment for 1.5 h. It is cooled to room temperature, filtered, and the filter cake is washed with deionized water until the washing liquid is neutral, and the filter cake is dried at 100 °C for 12 h. It is heated to 250 °C at a rate of 2 °C / min in air and maintained for 4 h, then heated to 1000 °C at a rate of 10 °C / min and calcined for 3 h, and then cooled to room temperature to obtain the molecular sieve-based Pt@SSZ-39 (Ov) @HfO2 catalyst.

[0065] The crystal size of the above catalyst is 830 nm, the average particle size of the Pt nanoclusters is 2.8 nm, and the surface shell thickness of HfO2 is 20 nm.

[0066] The above Pt@SSZ-39 (Ov) @HfO2 catalyst is used for the catalytic performance of the hydrogenation conversion of levulinic acid to γ-valerolactone. After reacting at 100 °C for 3 h: the conversion rate of LA is 93.3%, and the selectivity of GVL is 100%.

[0067] After using the above catalyst to catalyze the selective hydrogenation cycle reaction of levulinic acid 10 times, the conversion rate of LA remains at 89.5%, and the selectivity of GVL is 100%.

[0068] Example 5

[0069] A preparation method of a molecular sieve-based catalyst, comprising the following steps:

[0070] (1) At room temperature, 0.09 g of potassium amminetrichloroplatinate(II), 1.8 g of Zn(NO3)2·6H2O, and 1.8 g of 2-methylimidazole were dissolved in 20 g of deuterated dimethyl sulfoxide solution, mixed evenly, placed in a reaction kettle, and allowed to stand and react for 24 h. Subsequently, filtration was carried out, the filter cake was washed with deuterated dimethyl sulfoxide, and then dried to obtain Pt 2+ / ZIF-8;

[0071] (2) 1 g of sodium silicate, 3.8 g of sodium aluminate, 8.3 g of tetraethylammonium bromide, 2.3 g of tributyl acrylate-polymethyl methacrylate, 0.2 g of Pt 2+ / ZIF-8, 0.5 g of hafnium dichloride bis(cyclopentadienyl), and 16 g of deionized water were added to a microwave hydrothermal synthesizer with an output power of 1600 W, and the temperature was raised to 200 °C for microwave hydrothermal treatment for 0.8 h. After cooling to room temperature, filtration was carried out, and the filter cake was washed with deionized water until the washing liquid was neutral, and then dried at 90 °C for 16 h. After heating in air at a rate of 2 °C / min to 300 °C and maintaining for 2.3 h, it was heated to 950 °C at a rate of 10 °C / min and then calcined for 5 h, and then cooled to room temperature to obtain the molecular sieve-based Pt@Beta (Ov) @HfO2 catalyst.

[0072] The crystal size of the above catalyst is 320 nm, the average particle size of the Pt nanoclusters is 0.8 nm, and the surface shell thickness of HfO2 is 16 nm.

[0073] The above Pt@Beta (Ov) @HfO2 catalyst with a "sandwich" core-shell structure was used for the catalytic performance of the hydrogenation conversion of levulinic acid to γ-valerolactone. After reacting at 100 °C for 3 h: the conversion rate of LA was 99.1%, and the selectivity of GVL was 100%.

[0074] After using the above catalyst to catalyze the selective hydrogenation cycle reaction of levulinic acid 10 times, the conversion rate of LA remained at 97.3%, and the selectivity of GVL was 100%.

[0075] Comparative Example 1 (In this comparative example, Pt 2+ / ZIF-8 precursor was not used to prepare Pt / Beta (Ov) @HfO2)

[0076] Pt / Beta (Ov)Preparation of @HfO2: 1.2 g of tetramethyl orthosilicate, 2.4 g of aluminum isopropoxide, 6 g of tetrapropylammonium hydroxide, 3.6 g of poly(n-butyl acrylate)-poly(2-hydroxyethyl methacrylate), 0.15 g of potassium amminetrichloroplatinate(II), 0.36 g of hafnium dichloride bis(cyclopentadienyl), and 13 g of deionized water were added to a microwave hydrothermal synthesizer with an output power of 1500 W. The temperature was raised to 160 °C and microwave hydrothermal treatment was carried out for 1.5 h. After cooling to room temperature, filtration was performed, and the filter cake was washed with deionized water until the washing liquid was neutral. Then the filter cake was dried at 100 °C for 10 h. After heating in air at a rate of 2 °C / min to 270 °C and holding for 2.5 h, it was heated to 980 °C at a rate of 10 °C / min and calcined for 4.5 h, and then cooled to room temperature to obtain the molecular sieve-based Pt / Beta (Ov) @HfO2 catalyst.

[0077] The crystal size of the above catalyst is 565 nm, the average particle size of the Pt nanoclusters is 3.5 nm, and the surface shell thickness of HfO2 is 55 nm.

[0078] The above Pt / Beta (Ov) The catalytic performance of the @HfO2 catalyst for the hydrogenation conversion of levulinic acid to γ-valerolactone: After reacting at 100 °C for 3 h, the conversion rate of LA is 72.3%, and the selectivity of GVL is 85.1%.

[0079] After using the above catalyst to catalyze the selective hydrogenation cycle reaction of levulinic acid 10 times, the conversion rate of LA remains at 65.5%, and the selectivity of GVL is 81.8%.

[0080] Comparative Example 2 (In this comparative example, Pt / SSZ-39 2+ @HfO2 was prepared without the ZIF-8 precursor (Ov) @HfO2).

[0081] Pt / SSZ-39 (Ov) Preparation of @HfO2: 1.5 g of silica sol, 1 g of pseudo-boehmite, 5.5 g of N-methyl-N-ethyl-2,6-dimethylpiperidinium hydroxide, 2.2 g of poly(tributyl acrylate)-polymethyl methacrylate, 0.12 g of Pt(NH3)4(CH3COO)2, 0.76 g of hafnium chloride, and 25 g of deionized water were added to a microwave hydrothermal synthesizer with an output power of 1600 W. The temperature was raised to 180 °C and microwave hydrothermal treatment was carried out for 1.2 h. After cooling to room temperature, filtration was performed, and the filter cake was washed with deionized water until the washing liquid was neutral. Then the filter cake was dried at 85 °C for 15 h. After heating in air at a rate of 2 °C / min to 220 °C and holding for 4.5 h, it was heated to 880 °C at a rate of 10 °C / min and calcined for 6 h, and then cooled to room temperature to obtain the molecular sieve-based Pt / SSZ-39 (Ov) @HfO2 catalyst.

[0082] The crystal size of the above catalyst is 782 nm, the average particle size of the Pt nanoclusters is 3.3 nm, and the surface shell thickness of HfO2 is 42 nm.

[0083] The above Pt / SSZ-39 (Ov) @HfO2 catalyst was used for the catalytic performance of the hydrogenation conversion of levulinic acid to γ-valerolactone. After reacting at 100 °C for 3 h: the LA conversion rate was 76.6%, and the GVL selectivity was 87.4%.

[0084] After using the above catalyst to catalyze the selective hydrogenation cycle reaction of levulinic acid 10 times, the LA conversion rate remained at 73.5%, and the GVL selectivity was 83.8%.

[0085] Comparative Example 3 (In this comparative example, Pt@SSZ-39@HfO2 was prepared without a multi-block polymeric surfactant)

[0086] (1) At room temperature, 0.08 g of potassium amminetrichloroplatinate(II), 1 g of Zn(NO3)2·6H2O, and 1.6 g of 2-methylimidazole were dissolved in 13 g of deuterated dimethyl sulfoxide solution and mixed evenly. The mixture was placed in a reaction kettle and allowed to stand for reaction for 10 h. Subsequently, it was filtered, washed with deuterated dimethyl sulfoxide, and the filter cake was dried to obtain Pt 2+ / ZIF-8;

[0087] (2) 0.8 g of sodium silicate, 2.7 g of sodium aluminate, 5.6 g of N-methyl-N-ethyl-2,6-dimethylpiperidinium hydroxide, 0.18 g of Pt 2+ / ZIF-8, 0.25 g of hafnium chloride, and 10 g of deionized water were added to a microwave hydrothermal synthesizer with an output power of 1300 W, and the temperature was raised to 180 °C for microwave hydrothermal treatment for 1 h. It was cooled to room temperature, filtered, and the filter cake was washed with deionized water until the washing liquid was neutral, and the filter cake was dried at 70 °C for 16 h. It was heated in air at a rate of 2 °C / min to 230 °C and maintained for 4 h, and then heated to 1000 °C at a rate of 10 °C / min and calcined for 3.5 h, and then cooled to room temperature to obtain a molecular sieve-based Pt@SSZ-39@HfO2 catalyst.

[0088] The crystal size of the above catalyst is 989 nm, the average particle size of the Pt nanoclusters is 3.9 nm, and the surface shell thickness of HfO2 is 30 nm.

[0089] The catalytic performance of the above "sandwich" core-shell structured Pt@SSZ-39@HfO2 catalyst for the hydrogenation conversion of levulinic acid to γ-valerolactone. After reacting at 100 °C for 3 h: the LA conversion rate was 80.0%, and the GVL selectivity was 85.3%.

[0090] After 10 cycles of selective hydrogenation of levulinic acid catalyzed by the above catalyst, the conversion rate of LA remained at 76.2%, and the selectivity of GVL was 81.8%.

[0091] Comparative Example 4 (In this comparative example, Pt@Beta was prepared without the surface shell HfO2 (Ov) )

[0092] (1) At room temperature, 0.1 g of Pt(NH3)4(CH3COO)2, 1.5 g of Zn(NO3)2·6H2O, and 1.5 g of 2-methylimidazole were dissolved in 23 g of methanol solution and mixed evenly. The mixture was placed in a reaction kettle and allowed to stand for 12 h. Then, it was filtered, washed with methanol, and the filter cake was dried to obtain Pt 2+ / ZIF-8;

[0093] (2) 1.3 g of tetraethyl orthosilicate, 2.7 g of aluminum isopropoxide, 8.6 g of tetraethylammonium bromide, 1.7 g of polyethylacrylic acid-polymethyl methacrylate, 0.26 g of Pt 2+ / ZIF-8, and 14 g of deionized water were added to a microwave hydrothermal synthesizer with an output power of 1500 W. The temperature was raised to 170 °C and microwave hydrothermal treatment was carried out for 0.6 h. After cooling to room temperature, it was filtered, and the filter cake was washed with deionized water until the washing liquid was neutral. Then, the filter cake was dried at 95 °C for 12 h. After heating to 270 °C at a rate of 2 °C / min in air and maintaining for 3.3 h, it was heated to 900 °C at a rate of 10 °C / min and calcined for 5.5 h, and then cooled to room temperature to obtain the molecular sieve-based Pt@Beta (Ov) catalyst.

[0094] The crystal size of the above catalyst is 271 nm, and the average particle size of the Pt nanoclusters is 1.1 nm.

[0095] The above Pt@Beta (Ov) The catalytic performance of the catalyst for the hydrogenation conversion of levulinic acid to γ-valerolactone was as follows: after reacting at 100 °C for 3 h, the conversion rate of LA was 70.5%, and the selectivity of GVL was 89.8%.

[0096] After 10 cycles of selective hydrogenation of levulinic acid catalyzed by the above catalyst, the conversion rate of LA remained at 65.7%, and the selectivity of GVL was 86.1%.

[0097] See Figure 3 , it can be observed from the figure that the XRD pattern shows the characteristic peaks corresponding to the SSZ-39 molecular sieve. The introduction of oxygen vacancies has an impact on Pt@SSZ-39 (Ov)The XRD pattern of the Pt@HfO2 catalyst has no significant effect. Due to the low content of Pt nanoclusters, the characteristic peaks of elemental Pt are not observed in the figure. Since the XRD diffraction peak positions of HfO2 overlap with the characteristic peaks of the SSZ-39 zeolite, no obvious diffraction peaks corresponding to HfO2 are observed.

[0098] Figure 4 、 Figure 5 and Figure 8 Comparing with (Ov) the Pt@Beta Figure 4 @HfO2 catalyst obtained in Example 5 ( (Ov) ) has an obvious "sandwich" shell structure. The Pt nanoclusters are highly dispersed in the hierarchical inner shell, and the Beta (Ov) encapsulated in the middle shell. Mesopores also appear due to the removal of the multi-block polymeric surfactant. This structure is beneficial for the low-resistance transport of reactant molecules. HfO2 is uniformly encapsulated on the catalyst surface, and a clear metal-oxygen vacancy-oxide interface is formed between different shells. The Pt / Beta Figure 5 @HfO2 catalyst obtained in Comparative Example 1 ( 2+ ) does not have a "sandwich" shell structure because the Pt (Ov) / ZIF-8 precursor is missing in the preparation process, and the TEM image shows that the size of the Pt nanoclusters is relatively large. The Pt@Beta Figure 8 catalyst obtained in Comparative Example 4 ( (Ov) ) has an inner shell composed of ultrafine Pt nanoclusters anchored by porous carbon and a Beta 2+ zeolite encapsulated on the surface, and the Pt nanoclusters are uniformly dispersed inside the catalyst. The above information shows that the Pt

[0099] Figure 6 / ZIF-8 precursor plays an indispensable role in the formation of highly stable and ultrafine Pt nanoclusters and the construction of the "sandwich" shell structure. (Ov) The TEM image of the Pt / SSZ-39 Figure 7 @HfO2 catalyst (Comparative Example 2) shown in

[0100] Figure 9 further corroborates the above statement. (Ov) The SEM image of the Pt@SSZ-39 27 @HfO2 catalyst (Comparative Example 3) shown in 27The peak of Al MAS NMR corresponds to the three - coordinated Al in the framework. The peak of Al MAS NMR at 55.0 ppm in the Pt@SSZ - 39@HfO2 catalyst (Comparative Example 3) corresponds to the four - coordinated Al in the framework. The appearance of three - coordinated Al is attributed to the introduction of oxygen vacancies promoted by the multi - block polymeric surfactant. The oxygen vacancies bring new Lewis acid sites to the molecular sieve (the four - coordinated Al in the framework provides 27 acid sites, and the three - coordinated Al provides Lewis acid sites). acid sites, and the three - coordinated Al provides Lewis acid sites).

[0101] Figure 10 The nitrogen isothermal adsorption - desorption curve of the Pt / Beta (Ov) @HfO2 catalyst (Comparative Example 1) shown in is a typical type - I adsorption isotherm, revealing its microporous characteristics. The nitrogen isothermal adsorption - desorption curve of the Pt@Beta (Ov) @HfO2 catalyst (Example 2) is a type - IV adsorption isotherm, indicating the formation of hierarchical pores in the presence of Pt 2+ / ZIF - 8. The corresponding changes in specific surface area (S BET ), total pore volume (V total ), micropore volume (V micro ), and mesopore volume (V meso ) further reveal the promoting effect of the formation of hierarchical pores on the transport of reactants.

[0102] The catalytic performances of the above - mentioned examples and comparative examples are shown in Table 1 below.

[0103] Table 1 Analysis of the catalytic performance of the catalyst for the selective hydrogenation of levulinic acid

[0104] Catalytic material Conversion rate of levulinic acid Selectivity of γ-valerolactone Example 1 95.1 100 Example 2 96.5 100 Example 3 92.5 100 Example 4 93.3 100 Example 5 99.1 100 Comparative example 1 72.3 85.1 Comparative example 2 76.6 87.4 Comparative example 3 80.0 85.3 Comparative example 4 70.5 89.8

[0105] As can be seen from the data in Table 1, compared with the Pt@Beta (Ov) @HfO2 catalyst (Example 1) prepared in the present invention, the hydrogenation activity of the Pt / Beta 2+ @HfO2 catalyst (Comparative Example 1) obtained without the Pt (Ov) / ZIF - 8 precursor as the inner shell layer decreases significantly. This is because the lack of the "metal substitution" and "space occupation" effects provided by Pt 2+ / ZIF - 8 in terms of structure leads to the ineffective dispersion of Pt nanoclusters, and the microporous porosity of the Pt / Beta (Ov) @HfO2 catalyst is not conducive to the rapid transport of reactants, and the absence of the inner shell layer is not conducive to the concentration and enrichment of reactants. The Pt@Beta (Ov) @HfO2 catalyst prepared in the present invention benefits from Pt 2+The nitrogen-rich coordination environment and "space occupation" effect of the ZIF-8 precursor enabled the highly dispersed and anchored Pt nanoclusters during high-temperature calcination, avoiding the sintering and agglomeration of Pt nanoclusters during the catalytic reaction, thereby improving the catalytic reaction activity and stability. The highly dispersed active sites and the advantages of the hierarchical pore structure promoted the rapid improvement of the hydrogenation activity.

[0106] As can be seen from the data in Table 1, compared with the Pt@SSZ-39@HfO2 catalyst (Comparative Example 3) without the addition of the multi-block polymeric surfactant, the Pt@SSZ-39 (Ov) @HfO2 (Example 4) catalyst prepared in the present invention contains abundant acid sites (tetracoordinated Al in the framework) and Lewis acid sites (tricoordinated Al), which is attributed to the abundant oxygen vacancies brought by the removal of the multi-block polymeric surfactant for the catalyst (generating tricoordinated Al). The acid sites promoted the lactonization of the intermediate to the target product γ-valerolactone, and the Lewis acid sites improved the selectivity of γ-valerolactone. Compared with the Pt@SSZ-39@HfO2 catalyst, the Pt@SSZ-39 (Ov) @HfO2 catalyst showed complete catalytic selectivity (100%) for γ-valerolactone.

[0107] As can be seen from the data in Table 1, compared with the Pt@Beta (Ov) catalyst lacking the surface shell HfO2 (Comparative Example 4), the "sandwich" core-shell structured Pt@Beta (Ov) @HfO2 catalyst (Example 5) prepared in the present invention showed excellent selective hydrogenation activity because the amphoteric HfO2 improved the surface acidity of the catalyst, enhanced the adsorption stability of the reactants, and achieved the selective adsorption of levulinic acid and H2. The synergistic effect of the catalytic sites (hydrogenation sites and acid sites) and the promoting effect of the metal-oxygen vacancy-oxide interface made the Pt@Beta (Ov) @HfO2 catalyst show a high levulinic acid conversion rate (99.1%) and complete selectivity for γ-valerolactone (100%).

[0108] It should be understood that, in order to streamline the present disclosure and assist in understanding one or more of the various inventive aspects, in the foregoing description of the exemplary embodiments of the present invention, the various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, the disclosed method should not be construed as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected by the claims, the inventive aspects lie in less than all of the features of the previously disclosed embodiments. Thus, the claims following the detailed description hereby expressly incorporate the detailed description, where each claim itself serves as a separate embodiment of the present invention.

[0109] Although the present invention has been described in terms of a limited number of embodiments, those skilled in the art, having the benefit of the foregoing description, will appreciate that other embodiments can be contemplated within the scope of the invention as thus described. Additionally, it should be noted that the language used in this specification has been principally selected for readability and instructional purposes and not for the purpose of explaining or limiting the subject matter of the invention. Accordingly, many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the appended claims. For the scope of the present invention, the disclosure of the present invention is illustrative and not restrictive, and the scope of the present invention is defined by the appended claims.

[0110] The foregoing are only the preferred embodiments of the present invention, and it should be pointed out that: for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A molecular sieve-based catalyst, characterized in that, It includes a sandwich core-shell structure. The inner shell layer consists of ultrafine Pt nanoclusters anchored by ZIF-8-derived porous carbon; the middle shell layer is composed of zeolite (Ov) which is a silica-alumina molecular sieve rich in oxygen vacancies; the surface shell layer is composed of HfO2 oxide.

2. The molecular sieve-based catalyst according to claim 1, characterized in that, Silicoaluminophosphate zeolite rich in oxygen vacancies (Ov) including Beta (Ov) molecular sieve or SSZ-39 (Ov) molecular sieve.

3. The molecular sieve-based catalyst according to claim 1, characterized in that, The catalyst crystal size is 240 - 970 nm, the average particle size of the Pt nanoclusters is 0.8 - 2.8 nm, and the surface shell thickness of HfO2 is 15 - 30 nm.

4. A preparation method of the molecular sieve-based catalyst according to any one of claims 1 to 3, characterized in that, It includes the following steps: S01, at room temperature, mix the platinum source: zinc nitrate hexahydrate: 2-methylimidazole: organic solvent in a mass ratio of 1: (12.5 - 20): (15 - 23): (200 - 300), stir evenly, then place it in a reaction kettle and let it stand for reaction for 7 - 24 h. Subsequently, filter, wash with an organic solvent, and dry the filter cake to obtain a porous carbon-anchored ultrafine Pt nanocluster precursor Pt 2+ / ZIF-8; S02, add silicon source:aluminum source:structure-directing agent:multi-block polymeric surfactant:ultrafine Pt nanocluster precursor Pt anchored on porous carbon 2+ / ZIF-8:hafnium source:deionized water into a microwave hydrothermal synthesizer with an output power of 1200-1600 W according to a mass ratio of 1:(0.56-3.8):(1.6-8.3):(0.6-3.9):(0.2-0.56):(0.08-0.6):(10-16), raise the temperature to 150-200 °C for microwave hydrothermal treatment for 0.7-1.5 h, cool to room temperature, filter, wash the filter cake with deionized water until the washing liquid is neutral, and dry the filter cake at 60-100 °C for 10-18 h. After heating to 200-300 °C at a rate of 2 °C / min in air and holding for 2-4 h, then heat to 800-1000 °C at a rate of 10 °C / min and calcine for 3-6 h, and cool to room temperature to obtain the molecular sieve-based catalyst Pt@Zeolite (Ov) @HfO2.

5. The preparation method of the molecular sieve-based catalyst according to claim 4, characterized in that, In S01, the platinum source is tetraammineplatinum(II) acetate or potassium amminetrichloroplatinate(II).

6. The preparation method of the molecular sieve-based catalyst according to claim 4, characterized in that, In S01, the organic solvent is methanol or deuterated dimethyl sulfoxide.

7. The preparation method of the molecular sieve-based catalyst according to claim 4, characterized in that, In S02, the silicon source is one of silica sol, sodium silicate or tetramethyl orthosilicate; the aluminum source is one of pseudoboehmite, sodium metaaluminate or aluminum isopropoxide; the structure-directing agent is one of tetrapropylammonium hydroxide, tetraethylammonium bromide, N,N-dimethyl-3,5-dimethylpiperidinium hydroxide, N-methyl-N-ethyl-2,6-dimethylpiperidinium hydroxide; the multi-block polymeric surfactant is one of poly(n-butyl acrylate)-poly(2-hydroxyethyl methacrylate), poly(tributyl acrylate)-polymethyl methacrylate or poly(ethylacrylic acid)-polymethyl methacrylate multi-block polymers.

8. The preparation method of the molecular sieve-based catalyst according to claim 4, characterized in that, In S02, the hafnium source is one of hafnium chloride or dichlorodicyclopentadienylhafnium.

9. Application of the molecular sieve-based catalyst according to any one of claims 1 to 3 in the catalytic selective hydrogenation reaction of levulinic acid.

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