Preparation method of molecular sieve encapsulated metal catalyst and application thereof

Abstract

The present application belongs to the technical field of biomass resource utilization, and particularly relates to a preparation method of a molecular sieve encapsulated metal catalyst and application thereof. x M y @The preparation method is to in-situ encapsulate active metal AM alloy nanoclusters in the pore of a MFI structure zeolite by a hydrothermal synthesis method, to synthesize a catalyst with metal-acid "limited adjacent" characteristics, wherein x:y = 1:(0-4). Under the action of the catalyst, cellulose can be efficiently hydrogenolysis converted into alcohol compounds such as ethanol, the ethanol selectivity is 69.2%, and the total alcohol yield can reach more than 90%. The present application uses non-food cellulose as raw material to produce ethanol, which provides a new idea for direct utilization of biomass resources, can not only solve the problem of energy shortage caused by rapid consumption of fossil fuels, but also can reduce greenhouse gas emissions, alleviate the increasingly serious global environmental and climate problems, and realize green and sustainable development.

Description

Technical Field

[0001] This invention belongs to the field of biomass resource utilization technology, specifically relating to a method for preparing a molecular sieve-encapsulated metal catalyst and its application. Background Technology

[0002] Bioethanol, as an important sustainable and renewable low-carbon fuel, plays a significant role in meeting energy demands and reducing greenhouse gas emissions. Currently, ethanol production is mainly achieved through bio-fermentation, but since the raw materials involve food crops, it inevitably faces the drawback of competing with humans for food and land. In the long run, technological innovation is essential to expand the sources of raw materials. Cellulose, as the main component of lignocellulose, is the most widely distributed and abundant carbohydrate on Earth, making it another ideal source for producing fuel ethanol. Utilizing non-edible cellulose as a raw material to produce ethanol can not only solve the energy shortage problem caused by the rapid depletion of fossil fuels but also reduce greenhouse gas emissions and alleviate the increasingly serious global environmental and climate problems.

[0003] In recent years, research on the chemical hydrogenolysis of cellulose to ethanol has been reported in authoritative international journals. Since Academician Zhang Tao's team first reported the direct one-pot conversion of cellulose to ethanol in 2019, the process of cellulose to ethanol conversion has remained a hot and challenging one, attracting increasing attention from researchers. Compared with biological methods, the chemical catalytic hydrogenolysis of cellulose to ethanol breaks through the theoretical limit of carbon atom economy efficiency in biological methods. Furthermore, chemical methods can improve reaction efficiency, reduce or even avoid aldose side reactions, and achieve high product selectivity by controlling catalysts and reaction conditions. However, due to the involvement of dense cascade reactions, the direct one-pot conversion of cellulose to ethanol is quite difficult. This process mainly includes hydrolysis to produce sugars, anti-aldol condensation to produce C2 fragments, hydrogenation dehydration, and side reactions caused by unstable intermediates. Therefore, developing highly efficient and multifunctional catalysts that can effectively control complex reactions is crucial.

[0004] There are already some reports on the catalytic hydrogenolysis of cellulose to prepare high-value-added products. Firstly, catalytic materials prepared by encapsulating transition bimetallic or magnetic metals (Co, Fe, Ni, Mo, Ru, Sn, Cu, Pt, etc.) in a graphene-like carbon shell can efficiently convert cellulose into hydroxyacetone or dominant diols such as ethylene glycol and propylene glycol (CN 116726937A, CN115259995A). There are also reports on the conversion of cellulose into isopropanol using copper-chromium catalysts (CuCr2O4 / CuO) (CN102757310B). In addition, the catalytic conversion of cellulose into ethylene glycol using Ni-W catalysts has also been reported (CN101723802, CN101735014A). The application of solid acidic zeolites in the hydrogenolysis conversion of cellulose has also been reported (CN 106905109A).

[0005] While some progress has been made, many problems remain to be solved, such as the synergistic construction of multifunctional active site catalytic systems, precise regulation of hydrogenation activity, and effective suppression of related side reactions. Developing a functional catalyst with efficient and suitable acid and hydrogenation sites, and the ability to orderly regulate each catalytic site to reduce side reactions, is a key task for the efficient hydrogenolysis conversion of cellulose. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a method for preparing a molecular sieve-encapsulated metal catalyst and its application. This invention uses a hydrothermal synthesis method to in-situ encapsulate AM alloy nanoclusters within the pores of a zeolite with an MFI structure, synthesizing an AM alloy catalyst with a metal-acid "confined adjacency" characteristic. x M y The MFI catalyst can efficiently hydrogenate cellulose into ethanol. The technical solution employed is as follows:

[0007] A method for preparing a molecular sieve-encapsulated metal catalyst involves in-situ encapsulating active metal AM alloy nanoclusters within the pores of an MFI-structured zeolite to synthesize A. x M y The catalyst with an MFI molecular sieve structure, the preparation method of which includes the following steps:

[0008] (1) Weigh out the active metal precursors A and M respectively, add the same volume of ethylenediamine solution to each, and then make up to the same volume with deionized water to prepare metal ethylenediamine solution of A and metal ethylenediamine solution of M.

[0009] (2) Place the organic base reagent in a wide-mouth bottle, add deionized water, stir for 0.5 to 1 hour, then add tetraethyl orthosilicate to the system and stir until the solution becomes clear and transparent;

[0010] (3) First, add the metal ethylenediamine solution of M to the clear and transparent solution of step (2), stir for 0.5 to 1 hour, then add the metal ethylenediamine solution of A, stir for 0.5 to 1 hour;

[0011] (4) The system from step (3) is transferred to a hydrothermal reactor and placed in a forced-air drying oven for crystallization to prepare a molecular sieve-based material with an MFI structure;

[0012] (5) After the crystallization process is completed and the temperature drops to room temperature, the upper alkaline solution is poured into a recovery tank, and the lower solid is washed with deionized water by centrifugation and freeze-dried to obtain A. x M y @MFI structured molecular sieve-based catalysts;

[0013] The ratio of x to y is 1:(0~4).

[0014] Preferably, the active metal A includes Pd, Pt, Ru, and Ir; the active metal M includes Zn, Co, Ni, and Zr; the molecular sieve with MFI structure includes all-silica Silicalite-1 and ZSM-5 with different Si / Al ratios (30-100), etc.; wherein the molar ratio of A to M is 1:(0-4).

[0015] Preferably, A is Pd, and the active metal precursor of A is palladium chloride (PdCl2); M is Zn, and the active metal precursor of M is Zn(CH3COO)2·2H2O (zinc acetate dihydrate). As a further preferred embodiment, the molar ratio of A to M is 1:0.5.

[0016] Preferably, the organic base reagent includes any one or a mixture of more than one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide. More preferably, the organic base reagent is tetrapropylammonium hydroxide.

[0017] Preferably, in step (2), the molar ratio of the organic base reagent, tetraethyl orthosilicate, and deionized water is (0.2-1):1:36. As a further preferred embodiment, the molar ratio is 0.4:1:36.

[0018] Preferably, in step (4), the crystallization temperature is 150–190°C and the crystallization time is 24–120 h. More preferably, the crystallization temperature is 170°C, the crystallization time is 96 h, and the molecular sieve is all-silica Silicalite-1.

[0019] Preferably, in step (5), the product is washed by centrifugation with deionized water 3 to 5 times.

[0020] The application of a molecular sieve-encapsulated metal catalyst prepared using the above method in the conversion of cellulose to ethanol includes the following steps:

[0021] a. Before using the catalyst, it is reduced for a certain period of time in a vertical tube furnace under a pure hydrogen atmosphere;

[0022] b. Disperse the cellulose and the catalyst in deionized water, place them in a reaction vessel, and seal it.

[0023] c. After sealing, repeatedly inject H2 into the reactor to purify the internal gas;

[0024] d. Introduce H2 at a certain pressure, and allow for a continuous reaction;

[0025] f. After the reaction is complete, remove the liquid mixture and centrifuge to separate the solid catalyst and liquid product.

[0026] Liquid products were detected and analyzed on an Agilent 1260 Infinity II high-performance liquid chromatograph equipped with a differential detector (RID) using the external standard method.

[0027] Preferably, in step a, the reduction temperature is 300–700°C under a pure hydrogen atmosphere, the heating rate is 2–5°C / min, and the reduction time is 1–5 h. As a further preferred embodiment, the reduction temperature, heating rate, and reduction time are 600°C, 3°C / min, and 2 h, respectively.

[0028] Preferably, in step b, the mass ratio of cellulose to the catalyst is (1-4):1;

[0029] In step d, the reaction temperature is 215–260°C, the H2 pressure is 2.5–5.5 MPa, and the reaction time is 2–5 h.

[0030] Different material ratios, reaction temperatures, H2 pressures, and reaction times all have varying degrees of influence on the cellulose conversion process. As a further preferred option, the mass ratio of cellulose to the catalyst, the reaction temperature, pressure, and time are 2:1, 245℃, 4.5MPa, and 4h, respectively.

[0031] Studies have shown that A δ+ The Lewis acid sites formed by the -O(H)-Si coordination primarily promote the breaking of C-C bonds, resulting in small molecule products. Simultaneously, the adjacent AM alloy sites act as hydrogenation sites for the CO bonds, playing a crucial role in the subsequent hydrogenation and dehydration of ethylene glycol to ethanol. This unique encapsulation structure ultimately yields the highest selectivity for ethanol, highlighting the ability of this specific structure to maximize the synergistic effect between acid and metal sites. This invention not only provides a new approach for the direct utilization of biomass resources but also holds promise for addressing the energy shortages and environmental pollution caused by the rapid depletion of fossil fuels, thus achieving green and sustainable development.

[0032] Compared with the prior art, the advantages of the present invention are:

[0033] Currently, ethanol production mainly relies on bio-fermentation, which has drawbacks such as competing with humans for food and land. This invention uses non-food cellulose as a raw material to produce ethanol, which not only solves the energy shortage problem caused by the rapid depletion of fossil fuels but also reduces greenhouse gas emissions, alleviating the increasingly serious global environmental and climate problems. This invention uses a hydrothermal synthesis method to in-situ encapsulate AM alloy nanoclusters within the pores of zeolite with an MFI structure, synthesizing A alloys with metal-acid "confined adjacency" characteristics. x M y @MFI catalyst. Under the action of this catalyst, cellulose can be efficiently hydrogenated into alcohols such as ethanol, achieving an ethanol selectivity of 69.2% and a total alcohol yield of over 90%.

[0034] This invention not only provides a new approach to the direct utilization of biomass resources, but also holds promise for solving the energy shortage and environmental pollution problems caused by the rapid consumption of fossil fuels, thus achieving green and sustainable development. Attached Figure Description

[0035] Figure 1 This is a flowchart of a method for preparing a molecular sieve-encapsulated metal catalyst according to the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention in any way. Unless otherwise specified, the methods, reagents, and equipment used in this invention are conventional methods, reagents, and equipment in this technical field, and all such reagents and equipment are commercially available.

[0037] Example 1

[0038] like Figure 1 As shown, a method for preparing a molecular sieve-encapsulated metal catalyst includes the following steps:

[0039] Weigh out a certain amount of palladium chloride and zinc acetate dihydrate, add 2 mL of ethylenediamine solution to each, and then dilute to a certain volume with deionized water to prepare 0.18 M palladium chloride ethylenediamine solution and 0.36 M zinc acetate ethylenediamine solution.

[0040] Weigh a certain amount of tetrapropylammonium hydroxide (25wt% aqueous solution, TPAOH) and place it in a wide-mouth bottle. Add a certain amount of deionized water and stir for 0.5 h. Then add tetraethyl orthosilicate (TEOS) to the system and stir until the solution becomes clear and transparent. The molar ratio of tetrapropylammonium hydroxide, tetraethyl orthosilicate, and deionized water is 0.4:1:36.

[0041] Add a certain amount of zinc acetate ethylenediamine solution to the above clear and transparent solution and stir for 0.5 h; then add a certain amount of palladium chloride ethylenediamine solution and stir for 0.5 h. The molar ratio of palladium to zinc added is 1:0.5.

[0042] The above system was transferred to a hydrothermal reactor and crystallized in a forced-air oven at 170°C for 96 hours to prepare Silicalite-1 molecular sieve-based materials.

[0043] After the crystallization process is complete and the temperature drops to room temperature, the upper alkaline solution is poured into a recovery tank; the lower solid layer is washed 3-5 times with deionized water by centrifugation, freeze-dried, and the sample is collected to obtain PdZn. 0.5 @Silicalite-1 structured molecular sieve-based catalyst.

[0044] Before use, the sample was heated to 600℃ in a pure H2 atmosphere at a heating rate of 3℃ / min and reduced at 600℃ for 2 hours.

[0045] The performance of the catalyst was determined in a 100 mL stainless steel autoclave. A certain amount of cellulose and catalyst (mass ratio 2:1) were dispersed in 30 mL of deionized water and placed in the autoclave. After sealing, H2 was repeatedly injected into the reactor 5 times to purify the internal gas. Then, H2 at 4.5 MPa was introduced, and the reaction was carried out continuously at 245 °C for 4 h.

[0046] After the reaction was complete, the liquid mixture was removed and the solid catalyst and liquid product were separated by centrifugation. The liquid product was detected and analyzed by an Agilent 1260 Infinity II high-performance liquid chromatograph equipped with a differential detector (RID) using the external standard method.

[0047] Based on the above operations, the final yield of ethanol obtained during the hydrogenolysis of cellulose was 69.2%.

[0048] Example 2

[0049] In a clear, transparent solution of tetrapropylammonium hydroxide, tetraethyl orthosilicate, and deionized water, palladium and zinc were added in a molar ratio of 1:2.

[0050] After crystallization, the lower solid layer was washed by centrifugation with deionized water, freeze-dried, and the sample was collected to obtain the PdZn2@ZSM-5 molecular sieve-based catalyst (Si / Al ratio of 50).

[0051] Other areas not mentioned are the same as in Example 1.

[0052] Before use, the sample was reduced for 2 hours at 600℃ in a pure H2 atmosphere. The performance of the catalyst was determined in a 100mL stainless steel autoclave. A certain amount of cellulose and catalyst (mass ratio 2:1) were dispersed in 30mL of deionized water and placed in the reactor. After sealing, H2 was repeatedly injected into the reactor 5 times to purify the internal gas. Then, 5.5MPa of H2 was introduced, and the reaction was carried out continuously at 260℃ for 4 hours.

[0053] After the reaction was complete, the liquid mixture was removed and the solid catalyst and liquid product were separated by centrifugation. The liquid product was detected and analyzed by an Agilent 1260 Infinity II high-performance liquid chromatograph equipped with a differential detector (RID) using the external standard method.

[0054] Based on the above operations, the final yield of ethanol obtained during the hydrogenolysis of cellulose was 18.1%.

[0055] Example 3

[0056] In a clear, transparent solution of tetrapropylammonium hydroxide, tetraethyl orthosilicate, and deionized water, palladium and zinc were added in a molar ratio of 1:1.

[0057] After crystallization, the lower solid layer was washed with deionized water by centrifugation, freeze-dried, and the sample was collected to obtain the PdZn@Silicalite-1 molecular sieve-based catalyst.

[0058] Other areas not mentioned are the same as in Example 1.

[0059] Before use, the sample was reduced for 2 hours at 600℃ in a pure H2 atmosphere. The performance of the catalyst was determined in a 100mL stainless steel autoclave. A certain amount of cellulose and catalyst (mass ratio 2:1) were dispersed in 30mL of deionized water and placed in the reactor. After sealing, H2 was repeatedly injected into the reactor 5 times to purify the internal gas. Then, 5.5MPa of H2 was introduced, and the reaction was carried out continuously at 260℃ for 4 hours.

[0060] After the reaction was complete, the liquid mixture was removed and the solid catalyst and liquid product were separated by centrifugation. The liquid product was detected and analyzed by an Agilent 1260 Infinity II high-performance liquid chromatograph equipped with a differential detector (RID) using the external standard method.

[0061] Based on the above operations, the final yield of ethanol obtained during the hydrogenolysis of cellulose was 49.1%.

[0062] Example 4

[0063] In a clear, transparent solution of tetrapropylammonium hydroxide, tetraethyl orthosilicate, and deionized water, palladium and zinc were added in a molar ratio of 1:2.

[0064] After crystallization, the lower solid layer was washed with deionized water by centrifugation, freeze-dried, and the sample was collected to obtain the PdZn2@Silicalite-1 molecular sieve-based catalyst.

[0065] Other areas not mentioned are the same as in Example 1.

[0066] Before use, the sample was reduced for 2 hours at 600℃ in a pure H2 atmosphere. The performance of the catalyst was determined in a 100mL stainless steel autoclave. A certain amount of cellulose and catalyst (mass ratio 2:1) were dispersed in 30mL of deionized water and placed in the reactor. After sealing, H2 was repeatedly injected into the reactor 5-6 times to purify the internal gas. Then, 5.5MPa of H2 was introduced, and the reaction was carried out continuously at 260℃ for 4 hours.

[0067] After the reaction was complete, the liquid mixture was removed and the solid catalyst and liquid product were separated by centrifugation. The liquid product was detected and analyzed by an Agilent 1260 Infinity II high-performance liquid chromatograph equipped with a differential detector (RID) using the external standard method.

[0068] Based on the above operations, the final yield of ethanol obtained during the hydrogenolysis of cellulose was 23.3%.

[0069] Example 5

[0070] In a clear, transparent solution of tetrapropylammonium hydroxide, tetraethyl orthosilicate, and deionized water, palladium and zinc were added in a molar ratio of 1:0.5.

[0071] After crystallization, the lower solid layer was washed with deionized water by centrifugation, freeze-dried, and the sample was collected to obtain PdZn. 0.5 @Silicalite-1 molecular sieve-based catalyst.

[0072] Other areas not mentioned are the same as in Example 1.

[0073] Before use, the sample was reduced for 2 hours at 600℃ in a pure H2 atmosphere. The performance of the catalyst was determined in a 100mL stainless steel autoclave. A certain amount of cellulose and catalyst (mass ratio 2:1) was dispersed in 30mL of deionized water and placed in the reactor. After sealing, H2 was repeatedly injected into the reactor 5 times to purify the internal gas. Then, 5.5MPa of H2 was introduced, and the reaction was carried out continuously at 230℃ for 4 hours.

[0074] After the reaction was complete, the liquid mixture was removed and the solid catalyst and liquid product were separated by centrifugation. The liquid product was detected and analyzed by an Agilent 1260 Infinity II high-performance liquid chromatograph equipped with a differential detector (RID) using the external standard method.

[0075] Based on the above operations, the final yield of ethanol obtained during the hydrogenolysis of cellulose was 57.1%.

[0076] The yields of cellulose to ethanol prepared by the catalysts in Examples 1-5 under different reaction conditions were analyzed, and the results are shown in Table 1.

[0077] Table 1. Yields of the prepared catalysts catalyzing the conversion of cellulose to ethanol under different reaction conditions

[0078]

[0079]

[0080] Table 1 shows that different Pd / Zn molar ratios of catalysts have a significant impact on the cellulose conversion process and the ethanol yield. With increasing Zn content, the ethanol yield gradually decreases, with the optimal molar ratio being 1:0.5. The addition of trace amounts of Zn enhances the electronic structure of Pd, while excessive Zn adversely affects the electronic structure of the Pd core, hindering H2 adsorption and dissociation into active H species. Furthermore, increased Zn content leads to the formation of Pd-Zn on the Pd core surface. x The multi-coordinate system reduces the formation of Pd-O(H) coordination, resulting in a decrease in Lewis acid. Different reaction conditions also have a significant impact on the yield of ethanol. The optimal reaction conditions are 245℃, 4h, 4.5MPa H2, under which the ethanol selectivity is the highest.

[0081] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. The application of a molecular sieve-encapsulated metal catalyst in the conversion of cellulose to ethanol, characterized in that, The catalyst is prepared by in-situ encapsulating active metal Pd and Zn alloy nanoclusters within the pores of an MFI-structured zeolite, specifically including the following steps: (1) Weigh out the active metal precursors of Pd and Zn respectively, add the same volume of ethylenediamine solution to each, and then make up to the same volume with deionized water to prepare metal ethylenediamine solution of Pd and metal ethylenediamine solution of Zn. (2) Place the organic base reagent in a wide-mouth bottle, add deionized water, stir for 0.5-1 h, then add tetraethyl orthosilicate to the system and stir until the solution becomes clear and transparent; (3) First, add Zn metal ethylenediamine solution to the clear and transparent solution in step (2), stir for 0.5~1 h, then add Pd metal ethylenediamine solution, stir for 0.5~1 h; (4) Transfer the system from step (3) to a hydrothermal reactor and place it in a forced-air drying oven for crystallization; (5) After the crystallization process is completed and the temperature drops to room temperature, the upper alkaline solution is poured into a recovery tank, and the lower solid is washed with deionized water by centrifugation and then freeze-dried to obtain Pd. x Zn y @MFI structure molecular sieve-based catalyst; wherein, the ratio of x to y is 1:0.5, and the molecular sieve with the MFI structure is all-silica Silicalite-1; The application method includes the following steps: a. Before using the catalyst, it is reduced for a certain period of time in a vertical tube furnace under a pure hydrogen atmosphere; b. Disperse the cellulose and the catalyst in deionized water, place them in a reaction vessel and seal it; c. After sealing, repeatedly inject H2 into the reactor to purify the internal gas; d. Introduce H2 at a certain pressure, and allow for a continuous reaction; f. After the reaction is complete, remove the liquid mixture and centrifuge to separate the solid catalyst and liquid product.

2. The application of a molecular sieve-encapsulated metal catalyst according to claim 1 in the conversion of cellulose to ethanol, characterized in that, The active metal precursor for Pd is PdCl2; the active metal precursor for Zn is Zn(CH3COO)2·2H2O.

3. The application of a molecular sieve-encapsulated metal catalyst according to claim 1 in the conversion of cellulose to ethanol, characterized in that, The organic base reagent includes any one or a mixture of multiple of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

4. The application of a molecular sieve-encapsulated metal catalyst according to claim 1 in the conversion of cellulose to ethanol, characterized in that, In step (2), the molar ratio of the organic base reagent, tetraethyl orthosilicate, and deionized water is (0.2~1): 1:

36.

5. The application of a molecular sieve-encapsulated metal catalyst according to claim 1 in the conversion of cellulose to ethanol, characterized in that, In step (4), the crystallization temperature is 150~190°C. o C, crystallization time is 24~120 h.

6. The application of a molecular sieve-encapsulated metal catalyst according to claim 1 in the conversion of cellulose to ethanol, characterized in that, In step (5), the product is washed by centrifugation with deionized water 3 to 5 times.

7. The application of a molecular sieve-encapsulated metal catalyst according to claim 1 in the conversion of cellulose to ethanol, characterized in that, In step a, the reduction temperature is 300~700°C under a pure hydrogen atmosphere. o C, heating rate is 2 ~ 5 o C / min, reduction time is 1 ~ 5 h.

8. The application of a molecular sieve-encapsulated metal catalyst according to claim 1 in the conversion of cellulose to ethanol, characterized in that, In step b, the mass ratio of cellulose to the catalyst is (1 ~ 4): 1; in step d, the reaction temperature is 215 ~ 260°C. o C, the H2 pressure is 2.5 ~ 5.5 MPa, and the reaction time is 2 ~ 5 h.

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