A gallium-modified dealuminated h-zsm-5 catalyst, a preparation method and application thereof

Abstract

The application belongs to the technical field of biomass catalytic conversion, and specifically discloses a gallium-modified dealuminized H-ZSM-5 catalyst, a preparation method and application thereof, and the method comprises the following steps: ion exchange is performed on Na-ZSM-5 molecular sieve and an ammonium salt solution; selective dealuminization is performed on NH4-ZSM-5 molecular sieve and an ammonium hexafluorosilicate solution; and the impregnation method is used to load a gallium salt solution to the dealuminized molecular sieve carrier DeAl-H-ZSM-5, so as to obtain the gallium-modified dealuminized H-ZSM-5 catalyst. The application adopts the above-mentioned gallium-modified dealuminized H-ZSM-5 catalyst, the preparation method and application thereof, and the method is characterized in that the composite strategy of purifying the base by selectively dealuminizing first and then precisely loading Ga to regulate the acidity is adopted, the prepared catalyst can efficiently catalyze the preparation of furfural from pentose in a γ-valerolactone / water system, and high conversion rate and high selectivity are realized.

Description

Technical Field

[0001] This invention belongs to the field of biomass catalytic conversion technology, specifically relating to a gallium-modified dealuminated H-ZSM-5 catalyst, its preparation method, and its application. Background Technology

[0002] Furfural is a key bio-based platform compound and an important precursor for the preparation of biofuels, solvents, and polymer materials. Traditional preparation methods rely on homogeneous mineral acid catalysts such as sulfuric acid, which suffer from inherent drawbacks such as equipment corrosion, environmental pollution, and difficulty in catalyst separation and recovery. Solid acid catalysts, particularly H-ZSM-5 molecular sieves, have been widely studied as alternatives to liquid acid catalysts for the dehydration of xylose to furfural due to their regular pore structure and tunable acidity. The xylose-to-furfural conversion is a typical tandem reaction, requiring Lewis acids and... Synergistic effect of acid sites.

[0003] However, conventional commercial H-ZSM-5 molecular sieves have the following specific structural defects when used in this reaction:

[0004] (1) Imbalance in the proportion of acidic sites: The acid sites primarily originate from framework aluminum-linked Si-OH-Al species, while the Lewis acid sites mainly originate from randomly distributed non-framework aluminum species. This intrinsic acidic structure leads to... The ratio of acid to Lewis acid ( The imbalance between acid and Lewis acid makes it difficult to meet the precise requirements of the number and spatial proximity of the two types of acid sites in tandem reactions.

[0005] (2) Competition for side reactions: The excessively strong side reaction in conventional H-ZSM-5 While acid sites ensure a high initial xylose conversion rate, they also significantly promote side reactions such as polymerization and condensation of furfural products and reaction intermediates. This not only reduces the selectivity of furfural but also makes it easier for carbon deposits to form on the catalyst surface and within the pores, covering the active sites and leading to a rapid decline in catalyst stability.

[0006] The dehydration of xylose to furfural is known to be a series reaction, and its efficient execution requires Lewis acid and... The synergistic effect of acid sites. In existing technologies, dealumination is often achieved through hydrothermal treatment or acid treatment, or the acidity of H-ZSM-5 is adjusted by loading metals (such as Sn, Zr, Ga, etc.) through impregnation. However, regarding "NH4+",... 4+ The molecular sieve modification method of "exchange → selective dealuminization of ammonium hexafluorosilicate → metal loading" has not yet been shown by any research or technical insights to be applicable to the xylose dehydration to furfural reaction.

[0007] Therefore, there is a need in this field to develop a gallium-modified dealaluminized H-ZSM-5 catalyst, its preparation method, and its application, which can effectively solve the above problems. Summary of the Invention

[0008] The purpose of this invention is to provide a gallium-modified dealaluminized H-ZSM-5 catalyst, its preparation method, and its application. The method employs a strategy of "selectively dealaluminizing the substrate first, and then precisely loading Ga to regulate acidity." The resulting catalyst can be applied to the reaction of catalyzing the dehydration of biomass-derived pentoses to prepare furfural.

[0009] To achieve the above objectives, the present invention provides a method for preparing gallium-modified dealuminated H-ZSM-5 catalyst, comprising the following steps:

[0010] Step S1: Ion exchange is performed between Na-ZSM-5 molecular sieve and ammonium salt solution to obtain NH4-ZSM-5 molecular sieve, which is prepared for the subsequent aluminum removal step.

[0011] Step S2: React NH4-ZSM-5 molecular sieve with ammonium hexafluorosilicate solution to selectively remove aluminum, and then filter, wash, dry and calcine to obtain the dealuminized molecular sieve support DeAl-H-ZSM-5;

[0012] Prioritize the removal of randomly distributed non-framework aluminum species, eliminating the vast majority of excessively strong and uncontrollable strong Lewis acid centers. Simultaneously, gently and controllably remove some framework aluminum, achieving preliminary optimization. The quantity and strength of acids. By repairing the resulting framework vacancies through silicon insertion, a molecular sieve support with more uniform acid sites and a more complete framework structure is obtained, which provides an ideal "pure" substrate for subsequent precise modification.

[0013] Therefore, the ammonium hexafluorosilicate dealumination process can preferentially remove strong Lewis acid sites associated with non-framework aluminum, and also remove some framework aluminum (i.e., The acidic site precursor is gently removed, thereby achieving preliminary optimization of the number and distribution of acidic sites in the molecular sieve.

[0014] Step S3: The gallium salt solution is loaded onto the dealuminated molecular sieve support DeAl-H-ZSM-5 by impregnation. After drying and calcination, the gallium-modified dealuminated H-ZSM-5 catalyst is obtained, denoted as Ga / DeAl-H-ZSM-5.

[0015] Step S3 is the key to achieving a performance breakthrough in this scheme. By precisely introducing gallium species into the optimized pure carrier, a new and controllable Lewis acid center is constructed.

[0016] Preferably, step S1 specifically involves:

[0017] Step S11: Add Na-ZSM-5 molecular sieve to ammonium salt solution, stir at 80℃ for 2 hours, filter, wash 8 times with deionized water at 80℃ to obtain solid; repeat this step once.

[0018] Step S12: Dry the solid at 80℃ for 24h to obtain NH4-ZSM-5 molecular sieve.

[0019] Preferably, in step S11, the solid-liquid ratio of Na-ZSM-5 molecular sieve to ammonium salt solution is 1g:20mL;

[0020] The Na-ZSM-5 molecular sieve has a silica-alumina molar ratio of 20; the ammonium salt solution has a concentration of 1 mol / L, and the ammonium salt solution includes NH4Cl solution.

[0021] Preferably, step S2 specifically involves:

[0022] Step S21: Add NH4-ZSM-5 molecular sieve to ammonium hexafluorosilicate solution and stir at 80°C for 4 hours to carry out the reaction;

[0023] Step S22: After the reaction is complete, filter the solution, wash it 8 times with deionized water at 80℃, repeat this step once, dry it at 80℃ for 24 hours and calcine it to obtain the dealuminized molecular sieve DeAl-H-ZSM-5.

[0024] Preferably, in step S21, the solid-liquid ratio of NH4-ZSM-5 molecular sieve to ammonium hexafluorosilicate solution is 1g:20mL; the concentration of ammonium hexafluorosilicate solution is 0.05-0.2mol / L.

[0025] The reaction temperature is 70-90℃, and the reaction time is 2-6 hours.

[0026] In step S22, the calcination temperature is 500-600℃, the calcination time is 4-8h, and the calcination is carried out in an air atmosphere.

[0027] Preferably, step S3 specifically involves:

[0028] Step S31: Add the dealuminolite molecular sieve DeAl-H-ZSM-5 to the gallium salt solution and stir at room temperature for 8 hours;

[0029] Step S32: Dry at 100℃ for 12 hours, and finally calcine to obtain gallium-modified dealuminated H-ZSM-5 catalyst, denoted as Ga / DeAl-H-ZSM-5.

[0030] Preferably, in step S31, the solid-liquid ratio of the dealuminolite molecular sieve DeAl-H-ZSM-5 to the gallium salt solution is 1g:10mL; the gallium salt solution includes gallium nitrate, wherein the mass of gallium nitrate hydrate is 0.036g, corresponding to a loading of 1.0wt% Ga;

[0031] The gallium loading, by mass, is 0.5wt%-2.0wt% of the mass of the dealuminized molecular sieve carrier DeAl-H-ZSM-5.

[0032] In step S32, the calcination temperature is 500-600℃, the calcination time is 4-8h, and the calcination is carried out in an air atmosphere.

[0033] Preferably, in step S31, the loading amount of gallium is 0.8wt%-1.2wt% of the mass of the dealuminized molecular sieve carrier DeAl-H-ZSM-5, based on the mass of gallium.

[0034] By precisely controlling the gallium loading in step S31, the final number of Lewis acid sites on the catalyst can be finely adjusted, thus enabling the control of... "Dual independent regulation" of the acid / Lewis acid ratio to achieve The optimal ratio of acids to Lewis acids. -Lewis acid synergistic pair, thus side reactions are effectively suppressed, and the prepared catalyst exhibits better anti-carbon deposition ability and longer service life.

[0035] In the cascade reaction of xylose to furfural, Acids are primarily responsible for the initial cyclization and dehydration steps of xylose, while Lewis acids can polarize C=O and C-OH bonds through coordination, promoting crucial enolization and subsequent dehydration steps. Therefore, a moderately strong, spatially proximate... Acid-Lewis acid pairs are key to achieving efficient and highly selective conversion.

[0036] The present invention also provides a method for preparing gallium-modified dealaluminized H-ZSM-5 catalyst.

[0037] This invention also provides a method for preparing gallium-modified dealaluminized H-ZSM-5 catalyst and its application in the highly selective preparation of furfural from pentose, specifically in the catalytic dehydration reaction of biomass-derived pentose to furfural.

[0038] Among them, the pentose is xylose; furfural is prepared by reacting in a system with γ-valerolactone / water as solvent; the reaction temperature is 170-190℃, which can obtain furfural efficiently and selectively.

[0039] This invention employs the above-mentioned gallium-modified dealaluminized H-ZSM-5 catalyst, its preparation method, and its application, with the following beneficial effects:

[0040] (1) This invention first applied the method of “selective aluminum removal of ammonium hexafluorosilicate-gallium loading” to the reaction of pentose to furfural, and found that the catalyst prepared by this method can synergistically achieve high conversion rate and high selectivity, breaking through the long-standing performance bottleneck in the reaction of pentose to furfural.

[0041] (2) By synergistically controlling specific parameters in the method of the present invention, a catalyst that can break the "inverse relationship" between pentose conversion and furfural selectivity can be prepared, thereby achieving a synergistic breakthrough in performance. Specifically, performance optimization is achieved by controlling the specific parameter combination of the selective dealumination step of ammonium hexafluorosilicate and the precise gallium loading of 0.8wt%-1.2wt%, which is crucial for obtaining the best performance in the efficient and highly selective catalytic dehydration of pentose to furfural reaction, thereby solving the technical problem that existing catalysts cannot achieve both high conversion and high selectivity in this specific reaction.

[0042] (3) Data from the embodiments of the present invention show that the 1.0 Ga / DeAl-H-ZSM-5 catalyst prepared with the specific parameters of the present invention has excellent catalytic performance. After reacting at 170℃ for 4 hours, it can achieve a xylose conversion rate of 88.2%, a furfural yield of 77.8%, and a selectivity of 88.2%. Its comprehensive performance (especially the balance between conversion rate and selectivity) is significantly better than all the comparative samples with single modification.

[0043] (4) The preparation method in this invention is controllable, has good repeatability, and the entire preparation process is mild with clear parameters, making it easy to control and scale up, and has prospects for industrial application.

[0044] The technical solution of the present invention will be further described in detail below through embodiments. Detailed Implementation

[0045] The technical solution of the present invention will be further described below through embodiments.

[0046] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0047] Example

[0048] A method for preparing a gallium-modified dealuminated H-ZSM-5 catalyst includes the following steps:

[0049] Step S1: Add 4g of Na-ZSM-5 molecular sieve (Si / Al=20) to 80mL of 1mol / L NH4Cl solution, stir at 80℃ for 2 hours, filter, and wash 8 times with deionized water at 80℃ to obtain a solid. Repeat this process once. Dry the solid at 80℃ for 24 hours to obtain NH4-ZSM-5 molecular sieve.

[0050] Step S2: Add 4g of NH4-ZSM-5 molecular sieve to 80mL of 0.1mol / L ammonium hexafluorosilicate solution and stir at 80℃ for 4 hours. After the reaction is complete, filter, wash with deionized water at 80℃ 8 times, repeat the process once, dry at 80℃ for 24 hours, and then calcine in air at 540℃ for 6 hours to obtain dealuminized molecular sieve DeAl-H-ZSM-5.

[0051] Step S3: Weigh 1g of dealuminized molecular sieve DeAl-H-ZSM-5 and add it to 10mL of gallium nitrate aqueous solution (where the mass of gallium nitrate hydrate is 0.036g, corresponding to a loading of 1.0wt% Ga). Stir at room temperature for 8 hours, then dry at 100℃ for 12 hours, and finally calcine at 540℃ for 6 hours to obtain gallium-modified dealuminized H-ZSM-5 catalyst, denoted as 1.0 Ga / DeAl-H-ZSM-5.

[0052] Comparative Example 1

[0053] A method for preparing an unmodified H-ZSM-5 catalyst is as follows: commercial NH4-ZSM-5 molecular sieve is directly calcined at 540℃ for 6 hours to obtain an unmodified H-ZSM-5 catalyst, denoted as H-ZSM-5.

[0054] Comparative Example 2

[0055] A method for preparing a dealumination-only DeAl-H-ZSM-5 catalyst includes the following steps:

[0056] Step S1: Add 4g of Na-ZSM-5 molecular sieve (Si / Al=20) to 80mL of 1mol / L NH4Cl solution, stir at 80℃ for 2 hours, filter, and wash 8 times with deionized water at 80℃ to obtain a solid. Repeat this process once. Dry the solid at 80℃ for 24 hours to obtain NH4-ZSM-5 molecular sieve.

[0057] Step S2: Add 4g of NH4-ZSM-5 molecular sieve to 80mL of 0.1mol / L ammonium hexafluorosilicate solution and stir at 80℃ for 4 hours. After the reaction is complete, filter and wash with deionized water at 80℃ 8 times. Repeat the above steps once, dry at 80℃ for 24 hours, and then calcine in air at 540℃ for 6 hours to obtain a dealumination-only DeAl-H-ZSM-5 catalyst, denoted as DeAl-H-ZSM-5.

[0058] Comparative Example 3

[0059] A method for preparing a low-load Ga / un-dealuminized H-ZSM-5 catalyst, specifically comprising:

[0060] Weigh 1 g of the unmodified H-ZSM-5 catalyst obtained in Comparative Example 1 and add it to 10 mL of gallium nitrate aqueous solution (where the mass of gallium nitrate hydrate is 0.018 g, corresponding to a loading of 0.5 wt% Ga). Stir at room temperature for 8 hours, then dry at 100 °C for 12 hours, and finally calcine at 540 °C for 6 hours to obtain the low-loading Ga / undealuminized H-ZSM-5 catalyst, denoted as 0.5 Ga / H-ZSM-5.

[0061] Experimental Example

[0062] (1) In a high-pressure reactor, add 10 mL of a mixed solvent of γ-valerol / water (volume ratio 1:1), the raw material is 0.05 g xylose, and the catalyst is 0.05 g of the catalyst prepared in Examples 1 and 3.

[0063] The reaction mixture was stirred at 170℃ for 4 hours. After centrifugation and dilution, the product composition was analyzed by high performance liquid chromatography. The xylose conversion rate, furfural selectivity, and yield were calculated, and the results are shown in Table 1.

[0064] Table 1. Calculation results of xylose conversion rate, furfural selectivity, and yield.

[0065]

[0066] As shown in Table 1, the dealuminated DeAl-H-ZSM-5 (Comparative Example 2) exhibited the highest selectivity, but its conversion rate was limited, demonstrating that dealumination optimized the "quality" of the acid sites. Loading 0.5 wt% Ga onto the un-dealuminated support (Comparative Example 3) improved the conversion rate, but significantly reduced the selectivity, indicating that simply introducing Lewis acid under random acidic conditions exacerbates side reactions.

[0067] Only the 1.0 Ga / DeAl-H-ZSM-5 catalyst prepared in the examples successfully achieved both high conversion and high selectivity. This fully demonstrates the necessity and synergy of the technical route of "first selectively removing aluminum to optimize the acidic substrate, and then introducing a controllable Lewis acid by precisely controlling the loading (e.g., 1.0 wt% Ga)". The examples effectively solved the problems of acidic site imbalance and side reaction competition mentioned in the background art through a step-by-step, independent control strategy.

[0068] (2) The acid content of the catalysts prepared in Examples 1-3 and Comparative Examples 1-3 The acid / Lewis acid ratio was tested, and the results are shown in Table 2.

[0069] Table 2 Catalyst Acid Content and Acid / Lewis acid ratio

[0070]

[0071] Table 2 further shows that the dealuminized DeAl-H-ZSM-5 (Comparative Example 2) of the carrier... The total acid content decreased slightly, but The increased ratio of acid to Lewis acid to 2.2 indicates that the dealumination process preferentially removes disordered Lewis acid sites, reducing the promoting effect of excessively strong Lewis acid centers on side reactions, thus contributing to improved furfural selectivity. However, the significant reduction in the number of Lewis acids in DeAl-H-ZSM-5 after dealumination weakens the coordination activation of the C=O / C-OH bond in the intermediate, thereby limiting the crucial subsequent dehydration step and leading to a decrease in xylose conversion.

[0072] In contrast, although the number of Lewis acids increased in 0.5 Ga / H-ZSM-5 (Comparative Example 3), The ratio of acid to Lewis acid remained largely unchanged (1.9), indicating the continued presence of numerous strong acid sites and resulting in enhanced side reactions; this is consistent with the decreasing selectivity trend (as shown in Table 1). This suggests that introducing Ga alone in a random acidic environment without dealumination is insufficient to achieve high selectivity.

[0073] In the examples, the Lewis acid content of the 1.0 Ga / DeAl-H-ZSM-5 prepared was significantly increased to 23.4 μmol / g, while... The ratio of acid to Lewis acid was adjusted to 1.5, achieving... The appropriate matching of acids and Lewis acids allows for the effective synergistic action of the xylose cyclization-dehydration step and the subsequent dehydration-stabilization step of furfural formation, achieving both high conversion rate (88.2%) and high selectivity (77.8%) (as shown in Table 1). Therefore, the strategy of "selectively removing aluminum to purify the substrate first, then precisely controlling the acidity by loading" achieves coupled regulation of the number and spatial proximity of acidic sites, effectively suppressing competition from side reactions, which is key to performance improvement.

[0074] Therefore, this invention employs the aforementioned gallium-modified dealumination H-ZSM-5 catalyst, its preparation method, and its application. This method utilizes a composite strategy of "selectively dealuminating and purifying the substrate first, then precisely loading Ga to regulate acidity," achieving synergistic optimization of the acid site ratio and spatial distribution. This catalyst can efficiently catalyze the preparation of furfural from pentose in a γ-valerolactone / water system, achieving high conversion and high selectivity, and is suitable for the green and efficient production of furfural.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. The application of a gallium-modified dealuminated H-ZSM-5 catalyst in the highly selective preparation of furfural from pentoses, characterized in that, Specifically, its application is in the catalytic dehydration of biomass-derived pentoses to prepare furfural; Among them, the pentose is xylose; the preparation of furfural is carried out in a system with γ-valerolactone / water as solvent; the reaction temperature is 170-190℃; The preparation method of the gallium-modified dealaluminized H-ZSM-5 catalyst includes the following steps: Step S1: Ion exchange is performed between Na-ZSM-5 molecular sieve and ammonium salt solution to obtain NH4-ZSM-5 molecular sieve; Step S2: React NH4-ZSM-5 molecular sieve with ammonium hexafluorosilicate solution to selectively remove aluminum, and then filter, wash, dry and calcine to obtain the dealuminized molecular sieve support DeAl-H-ZSM-5; Step S3: The gallium salt solution is loaded onto the dealuminated molecular sieve support DeAl-H-ZSM-5 by impregnation, and then dried and calcined to obtain the gallium-modified dealuminated H-ZSM-5 catalyst, denoted as Ga / DeAl-H-ZSM-5. Based on the mass of gallium, its loading is 0.8-1.2 wt% of the mass of the dealuminolite molecular sieve carrier DeAl-H-ZSM-5.

2. The application of the gallium-modified dealuminated H-ZSM-5 catalyst according to claim 1 in the highly selective preparation of furfural from pentoses, characterized in that: Step S1 specifically involves: Step S11: Add Na-ZSM-5 molecular sieve to ammonium salt solution, stir at 80℃ for 2 hours, filter, wash 8 times with deionized water at 80℃ to obtain solid; repeat this step once. Step S12: Dry the solid at 80℃ for 24h to obtain NH4-ZSM-5 molecular sieve.

3. The application of the gallium-modified dealuminated H-ZSM-5 catalyst according to claim 2 in the highly selective preparation of furfural from pentoses, characterized in that: In step S11, the solid-liquid ratio of Na-ZSM-5 molecular sieve to ammonium salt solution is 1g:20mL; The Na-ZSM-5 molecular sieve has a silica-alumina molar ratio of 20; the ammonium salt solution has a concentration of 1 mol / L, and the ammonium salt solution includes NH4Cl solution.

4. The application of the gallium-modified dealuminated H-ZSM-5 catalyst according to claim 1 in the highly selective preparation of furfural from pentoses, characterized in that: Step S2 specifically involves: Step S21: Add NH4-ZSM-5 molecular sieve to ammonium hexafluorosilicate solution and stir at 80°C for 4 hours to carry out the reaction; Step S22: After the reaction is complete, filter the solution, wash it 8 times with deionized water at 80℃, repeat this step once, dry it at 80℃ for 24 hours and calcine it to obtain the dealuminized molecular sieve DeAl-H-ZSM-5.

5. The application of the gallium-modified dealuminated H-ZSM-5 catalyst according to claim 4 in the highly selective preparation of furfural from pentoses, characterized in that: In step S21, the solid-liquid ratio of NH4-ZSM-5 molecular sieve to ammonium hexafluorosilicate solution is 1g:20mL; the concentration of ammonium hexafluorosilicate solution is 0.05-0.2mol / L. In step S22, the calcination temperature is 500-600℃, the calcination time is 4-8h, and the calcination is carried out in an air atmosphere.

6. The application of the gallium-modified dealuminated H-ZSM-5 catalyst according to claim 1 in the highly selective preparation of furfural from pentoses, characterized in that: Step S3 specifically involves: Step S31: Add the dealuminolite molecular sieve DeAl-H-ZSM-5 to the gallium salt solution and stir at room temperature for 8 hours; Step S32: Dry at 100℃ for 12 hours, and finally calcine to obtain gallium-modified dealuminated H-ZSM-5 catalyst, denoted as Ga / DeAl-H-ZSM-5.

7. The application of the gallium-modified dealuminated H-ZSM-5 catalyst according to claim 6 in the highly selective preparation of furfural from pentoses, characterized in that: In step S31, the solid-liquid ratio of the dealuminolite molecular sieve DeAl-H-ZSM-5 to the gallium salt solution is 1g:10mL; the gallium salt solution includes gallium nitrate, wherein the mass of gallium nitrate hydrate is 0.036g, corresponding to a loading of 1.0wt% Ga; In step S32, the calcination temperature is 500-600℃, the calcination time is 4-8h, and the calcination is carried out in an air atmosphere.

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