Self-synthesis all-silicon Beta molecular sieve catalyst for preparing butadiene from ethanol as well as preparation method and application of self-synthesis all-silicon Beta molecular sieve catalyst

Abstract

The invention discloses a self-synthesis all-silicon Beta molecular sieve catalyst for preparing butadiene from ethanol as well as a preparation method and application of the self-synthesis all-silicon Beta molecular sieve catalyst. According to the catalyst, an all-silicon Beta molecular sieve which is directly synthesized through a hydrothermal method and does not contain framework aluminum serves as a carrier, Cu and Pr are loaded on the all-silicon Beta molecular sieve to serve as bimetallic active components, Cu provides excellent ethanol dehydrogenation activity, Pr and a silicon hydroxyl nest interact to form a Lewis acid site, an active center for aldol condensation and MPV hydrogen transfer is provided for the catalyst, and the activity of the catalyst is improved. The synergistic effect of Cu and Pr jointly promotes efficient and oriented proceeding of the reaction path to butadiene. The catalyst disclosed by the invention has the advantages of no strong acid pollution in the preparation process, low active component cost, controllable structure, excellent catalytic performance and the like, and has a good prospect in industrial application of preparing butadiene from bioethanol.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a self-synthesized all-silica Beta molecular sieve catalyst for the production of butadiene from ethanol, its preparation method, and its application. Background Technology

[0002] Butadiene is the third largest olefin chemical raw material after ethylene and propylene, widely used in the manufacture of synthetic rubber, synthetic resins, and nylon products. Synthetic rubbers made from butadiene mainly include polybutadiene rubber, nitrile rubber, chloroprene rubber, and styrene-butadiene rubber. Previously, global butadiene production largely used the C4 fraction extraction method, making its raw material highly dependent on petroleum resources. With the gradual maturation of coal-based ethanol and bioethanol production technologies, production costs are continuously decreasing. Against this backdrop, to promote the development of coal chemical industry and reduce dependence on petroleum routes, using renewable ethanol as a raw material to synthesize butadiene is a green and feasible technological route that aligns with the "dual-carbon" strategy.

[0003] In the reaction mechanism of ethanol to butadiene, the aldol condensation route is widely accepted in academia. Its core lies in the condensation and dehydration of acetaldehyde to generate butadiene. The steps include: 1. Ethanol dehydrogenation to acetaldehyde; 2. Aldol condensation of two acetaldehyde molecules to 3-hydroxybutyraldehyde; 3. Crotonaldehyde and ethanol react via the Meerwein-Pondorf-Verley process to generate crotonol; 4. Crotonol dehydration to butadiene. The ethanol-to-butadiene process is a highly complex series reaction, therefore the catalyst needs to possess both dehydrogenation active sites and Lewis acid sites. The synergistic effect of these active sites is key to improving the catalyst's reaction performance. Beta molecular sieves, due to their regular microporous structure, tunable acidity, and good hydrothermal stability, are considered an ideal catalyst support or active component.

[0004] Ivanova et al. [Sushkevich VL, Ivanova, II, Ordomsky VV, et al. Design of a Metal-Promoted Oxide Catalyst for the Selective Synthesis of Butadiene from Ethanol[J]. Chemsuschem, 2014, 7(9): 2527-2536.] proposed the concept of the coexistence of "closed" and "open" sites in Zr-BEA, and also found that the "open" sites of Zr are more active for the aldol condensation of acetaldehyde. However, their preparation method has inherent defects: the authors used concentrated nitric acid to subject commercial Beta zeolite to a drastic dealumination treatment to create silanol nest defect sites to anchor the metal active center. This process not only generates a large amount of strong acid waste liquid, which is environmentally unfriendly, but the drastic acid treatment may also damage the integrity of the molecular sieve structure. In addition, the performance of this catalyst is not ideal, with an ethanol conversion rate of only 48% and a butadiene selectivity of 56%, indicating that there is huge room for improvement in both ethanol conversion rate and butadiene selectivity of its catalytic system.

[0005] Patent application CN118454730A discloses a bifunctional Nb-second metal (M=Zn, Cu, etc.) catalyst supported on a dealuminized Beta molecular sieve. While this technology integrates the isolated Nb(V) Lewis acid centers in its design with a dehydrogenating metal (such as Zn) and achieves a high ethanol conversion rate of 94.8%, the reported best catalyst, under optimal conditions, exhibits a butadiene selectivity of only 64.9%. This indicates that the combination of Nb with conventional transition metals (Zn, Cu, Co, etc.) has inherent limitations in regulating complex reaction pathways and suppressing byproduct formation. Furthermore, this process generates a large amount of aluminum-containing strong acid wastewater, polluting the environment, and the harsh acid treatment may irreversibly damage the integrity of the molecular sieve framework, affecting the long-term stability of the catalyst.

[0006] Davis et al. [K. Mamedov, RJ Davis, Cascade Reaction of Ethanol to Butadiene over Ag-Promoted, Silica- or Zeolite-Supported Ta, Y, Pr, or LaOxide Catalysts, ACS Catalysis, 13 (2023) 3333-3344.] systematically studied the effects of different Lewis acid cations (Ta, Y, Pr, La) on the ethanol-to-butadiene reaction on dealullated Beta zeolite and amorphous SiO2 supports. This study confirmed that Beta zeolite as a support significantly enhances the C-C coupling rate, highlighting its advantage of microporous confinement. However, in terms of catalyst configuration design, this study adopted a strategy of physically mixing Ag / SiO2 and M / Beta components. While convenient for research, this non-integrated structure may lead to low mass transfer efficiency between active sites. Intermediates need to diffuse between different particles, failing to fully utilize the synergistic effect of multiple active sites within the molecular sieve channels, potentially limiting the overall reaction rate and affecting selectivity.

[0007] Patent application CN120838462A discloses a method and application for synthesizing fly ash-based hierarchical porous ZnY / Si-Beta catalysts using a solvent-free method. This method provides a solution for synthesizing hierarchical porous pure silicon Beta molecular sieves using industrial solid waste fly ash as a silicon source. While this technology achieves solid waste resource utilization and can achieve 100% ethanol conversion with a butadiene selectivity of 66.4%, its preparation process is extremely complex and carries the risk of secondary pollution. Furthermore, the complex and unstable composition of fly ash leads to fluctuations in the purity of the extracted silicon source, making it difficult to guarantee the quality of the synthesized molecular sieve support and the reproducibility of the catalyst's performance, which is detrimental to large-scale industrial production.

[0008] Dai et al. [WL Dai, SS Zhang, ZY Yu, TT Yan, GJ Wu, NJ Guan, LD Li, Zeolite Structural Confinement Effects Enhance One-Pot Catalytic Conversion of Ethanol to Butadiene, Acs Catalysis, 7 (2017) 3703-3706.] reported a two-component Zn-Y / Beta catalyst with zeolite structural confinement effect. They synthesized a Zn-Y / Beta molecular sieve using dealulated Beta molecular sieves for the production of butadiene from ethanol, achieving an ethanol conversion of 82% and a butadiene selectivity of 63%. However, this catalytic system exhibits serious long-term operational stability issues. Under optimal conditions, the ethanol conversion of the 2%Zn-8%Y / Beta catalyst decreased sharply from an initial 90% to approximately 50% after about 20 hours of operation, and the butadiene selectivity also decreased significantly. The catalyst support is a Beta molecular sieve that has undergone dealuminization with concentrated nitric acid. The residual strong acid sites or defect sites are uncontrollable, which can easily lead to deep dehydration and carbon deposition during the reaction, thus reducing the stability of the catalyst.

[0009] In summary, the existing catalysts for the production of butadiene from ethanol have the following main problems: (1) The synthesis process of the support is subject to strong acid pollution, complex process or raw material problems, resulting in poor environmental performance, high cost and low reproducibility; (2) The distribution of defect sites on the Beta molecular sieve support after dealumination is unknown and cannot be controlled, and there is still a lot of room for improvement in the selectivity of the target product; (3) The long-term stability of the catalyst needs to be enhanced. Summary of the Invention

[0010] To address the problems of existing catalysts, the present invention aims to provide a self-synthesized all-silica Beta molecular sieve catalyst for the ethanol-to-butadiene reaction, its preparation method, and its application. By using a Si-Beta molecular sieve directly synthesized via a hydrothermal method as a support, the dealumination step using concentrated nitric acid is avoided. The self-synthesized all-silica Beta molecular sieve can generate abundant, uniform, and reproducible silanol nest defect sites for metal site anchoring through controlled synthesis conditions. The resulting catalyst exhibits high ethanol conversion and high butadiene selectivity in the ethanol-to-butadiene reaction, and the synthesis steps are simple, showing promising prospects for industrial application.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A self-synthesized all-silica Beta molecular sieve catalyst for the production of butadiene from ethanol, wherein the catalyst uses a self-synthesized Si-Beta molecular sieve as a support, the surface of which has abundant and uniform silanol nest defect sites; active metal components Cu and Pr are anchored on the defect sites.

[0013] The method for preparing a self-synthesized all-silica Beta molecular sieve catalyst for ethanol-to-butadiene production includes the preparation of a catalyst support and the loading of an active metal, with the following steps:

[0014] 1) Mix the template agent, alkali source and water, stir at room temperature for 10-15 min to form a clear solution, then add the silicon source to form the initial gel mixture;

[0015] The silicon source is divided into three parts and added in three batches. Adding the silicon source in batches can promote dispersion and ensure uniform mixing.

[0016] 2) The gel mixture was aged at room temperature for 10-20 h, then seed crystals were added, and the mixture was aged at room temperature for another 10-20 h. The gel mixture was then transferred to a polytetrafluoroethylene (PTFE) liner, and the PTFE liner was placed in a stainless steel hydrothermal synthesis reactor. The mixture was crystallized at 120-160 °C for 24-42 h. The crystallized product was filtered, washed until neutral, and dried in a 100 °C oven for 12-16 h to obtain a dried sample.

[0017] 3) After grinding the dried sample, mix it with 1 mol / L NH4Cl solution at a solid-liquid ratio of 1:3-12. Then, perform ion exchange in a water bath at 50-100 ℃ for 2-8 h. Centrifuge to recover the solid, repeat once. Calcine the centrifuged and dried sample at 300-600 ℃ for 3-8 h to obtain the catalyst support, i.e., Si-Beta molecular sieve.

[0018] 4) Dissolve Cu metal precursor and Pr metal precursor in water to form a precursor solution. Add the precursor solution to Si-Beta molecular sieve, stir evenly, let stand at room temperature for 3-6 h, dry at 90-110 ℃ for 6-12 h, and then place in a muffle furnace and calcine at 300-600 ℃ for 3-8 h to obtain Cu-Pr / Beta catalyst.

[0019] Furthermore, the template agent is one of tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and tetrapropylammonium hydroxide; the silicon source is one of silica, tetraethyl orthosilicate, silica sol, and solid silica gel; and the alkali source is one or two of sodium hydroxide, tetraethylammonium chloride, sodium chloride, and ammonia water.

[0020] Furthermore, the molar ratio of the template agent to the silicon source is 0.15-0.35, and the molar ratio of water to the silicon source is 3-8.

[0021] Furthermore, the alkali source is a mixture of tetraethylammonium chloride and sodium chloride, wherein the molar ratio of tetraethylammonium chloride to the silicon source is 0.05-0.15, and the molar ratio of sodium chloride to the silicon source is 0.06-0.13.

[0022] Preferably, the crystallization time is 30-36 h.

[0023] Furthermore, the Cu metal precursor is one of copper nitrate, copper chloride, and copper acetate; the Pr metal precursor is one of praseodymium nitrate, praseodymium chloride, and praseodymium acetate.

[0024] Preferably, the loading of Cu element in Cu-Pr / Beta catalyst is 0.1wt%-0.5wt%, and the loading of Pr element in Cu-Pr / Beta catalyst is 4wt%-6wt%.

[0025] Furthermore, the self-synthesized all-silica Beta molecular sieve (Cu-Pr / Beta catalyst) can be used in the ethanol-to-butadiene reaction, as follows: The catalyst is compressed into tablets and granulated, and 40-60 mesh particles are fixed in a quartz tube with quartz wool. The quartz tube is then installed in a fixed-bed reactor. Before the reaction, the catalyst is pretreated at 300-500 °C for 0.5-2 h under a nitrogen atmosphere at a flow rate of 30-50 ml / min. After pretreatment, the system is cooled to the target reaction temperature, and then ethanol feedstock is introduced to begin the reaction. The ethanol mass hourly space velocity (WHSV) is 0.1-2 h⁻¹. -1 The reaction temperature was 300-400 °C. The reaction products were analyzed online by gas chromatography (GC) equipped with a flame ionization detector (FID).

[0026] The present invention has the following advantages:

[0027] 1. This invention employs a direct synthesis method to prepare aluminum-free, all-silica Beta molecular sieves, thus eliminating the need for environmentally unfriendly subsequent steps such as dealuminization with concentrated nitric acid, washing, and re-calcination. This not only reduces equipment corrosion and environmental stress but also avoids damage to the molecular sieve framework caused by concentrated nitric acid, resulting in a synthesized support with superior stability.

[0028] 2. This invention can create abundant, uniform, and tunable silanol nesting defect sites in molecular sieves by controlling synthesis conditions, such as crystallization time, crystallization temperature, and water-to-silica ratio. These abundant silanol nesting defect sites can effectively anchor and highly disperse active metal species, preventing their aggregation during the reaction. The strong interaction between the metal and the support significantly enhances the stability of the catalyst.

[0029] 3. By simultaneously loading both Cu and Pr onto an all-silica Beta molecular sieve support, a unique Cu-Pr bimetallic active center was constructed. Cu provides excellent ethanol dehydrogenation activity, while Pr interacts with silanol nests to form Lewis acid sites, providing active centers for aldol condensation and MPV hydrogen transfer of the catalyst, while reducing the selectivity of ethylene and promoting the reaction towards the formation of butadiene.

[0030] 4. The catalyst of the present invention does not use precious metals, has high ethanol conversion rate and high butadiene selectivity in the reaction of ethanol to butadiene, mild reaction conditions, and simple preparation method, which is conducive to industrial production. Attached Figure Description

[0031] Figure 1 The graph shows the catalytic performance of the catalysts prepared in Comparative Example 1 and Example 10.

[0032] Figure 2 This is a TEM image of the catalyst prepared in Example 8. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments, but the implementation methods and protection scope of the present invention are not limited thereto.

[0034] Example 1

[0035] In this example, solid silica gel is selected as the silicon source, tetraethylammonium hydroxide (TEAOH) as the template agent, a combination of tetraethylammonium chloride (TEACl) and sodium chloride (NaCl) as the base source, and copper nitrate hexahydrate and praseodymium nitrate hexahydrate as metal precursors to prepare the CuPr / Beta catalyst. The specific steps are as follows:

[0036] 1) Mix 23g TEAOH, 3g TEACl, 1g NaCl and 10g H2O, stir at room temperature for 10 min to form a clear solution, and then add 12g solid silica gel in three batches to form the initial gel mixture;

[0037] 2) The initial gel mixture was aged at room temperature for 12 h, and 0.6 g of commercial dealuated Beta molecular sieve was added as a seed crystal. The mixture was then aged at room temperature for another 12 h. The mixture was then transferred to a polytetrafluoroethylene (PTFE) liner and placed in a stainless steel hydrothermal synthesis reactor. The mixture was crystallized at 140 °C for 24 h. The crystallized product was filtered, washed until neutral, and then dried in a 100 °C oven for 12 h to obtain a dried sample.

[0038] 3) After grinding the dried sample, it was mixed with 1 mol / L NH4Cl solution at a solid-liquid ratio of 1:10. Then, the mixture was ion-exchanged in a water bath at 80 °C for 4 h. The solid was recovered by centrifugation and the process was repeated once. The centrifuged and dried sample was calcined at 550 °C for 6 h to obtain the catalyst support, namely Si-Beta / 24h molecular sieve.

[0039] 4) Weigh 0.02 g of copper nitrate hexahydrate and 0.3 g of praseodymium nitrate hexahydrate and dissolve them in 1.5 g of water to form a precursor solution. Add the precursor solution to the Si-Beta / 24h molecular sieve, stir evenly, let stand at room temperature for 4 h, dry at 100 ℃ for 4 h, and then calcine in a muffle furnace at 550 ℃ for 4 h to obtain the Cu-Pr / Beta / 24h catalyst.

[0040] The Cu-Pr / Beta / 24h catalyst was tableted, granulated to 40-60 mesh, and then placed in a quartz tube, with both ends secured with quartz wool. The quartz tube was then placed in a fixed-bed reactor for the ethanol-to-butadiene production process for reaction evaluation. First, the catalyst bed was pretreated at 400 °C for 30 min under a nitrogen flow of 40 ml / min. After catalyst activation, the temperature was lowered to the set reaction temperature of 360 °C. Ethanol, the reactant, was introduced into the reaction system via bubbling using nitrogen at a flow rate of 40 ml / min, with the WHSV of ethanol controlled at 0.3 h⁻¹. -1 The reaction products were analyzed online using a gas chromatograph equipped with an FID detector, and the obtained catalytic performance data are recorded in Table 1.

[0041] Example 2

[0042] The crystallization time in step 3) of Example 1 was changed to 30 h while other steps remained unchanged. The resulting catalyst was denoted as Cu-Pr / Beta / 30h. The specific reaction evaluation results are shown in Table 1.

[0043] Example 3

[0044] The crystallization time in step 3) of Example 1 was changed to 36 h while other steps remained unchanged. The resulting catalyst was denoted as Cu-Pr / Beta / 36h. The specific reaction evaluation results are shown in Table 1.

[0045] Example 4

[0046] The crystallization time in step 3) of Example 1 was changed to 42 h while other steps remained unchanged. The resulting catalyst was denoted as Cu-Pr / Beta / 42h. The specific reaction evaluation results are shown in Table 1.

[0047] Table 1. Reaction evaluation results at different crystallization times

[0048]

[0049] The catalyst evaluation results showed that the butadiene selectivity generally increased with increasing crystallization time, reaching a peak at 36 h. A crystallization time of 24 h resulted in insufficient silanol defects, leading to uneven dispersion of anchored Cu and Pr active sites, thus resulting in the lowest butadiene selectivity (25.1%). At a crystallization time of 36 h, Cu and Pr species were more uniformly and stably anchored at these defect sites, forming highly selective active centers, resulting in the highest butadiene selectivity (46.7%). At a crystallization time of 42 h, the molecular sieve underwent transition crystallization, resulting in impurity peaks and potential changes in the defect site structure, leading to a decrease in the number of active sites and a slight decrease in butadiene selectivity (40.5%).

[0050] Example 5

[0051] The crystallization time in step 3) of Example 1 was changed to 36 h, and the crystallization temperature was changed to 120 °C. The resulting catalyst was designated Cu-Pr-120Beta. Other reaction conditions were the same as in Example 1. The specific reaction evaluation results are shown in Table 2.

[0052] Example 6

[0053] The crystallization time in step 3) of Example 1 was changed to 36 h, and the crystallization temperature was changed to 130 °C. The resulting catalyst was designated Cu-Pr-130Beta. Other reaction conditions were the same as in Example 1. The specific reaction evaluation results are shown in Table 2.

[0054] Example 7

[0055] The crystallization time in step 3) of Example 1 was changed to 36 h, and the crystallization temperature was changed to 150 °C. The resulting catalyst was designated Cu-Pr-150Beta. Other reaction conditions were the same as in Example 1. The specific reaction evaluation results are shown in Table 2.

[0056] Example 8

[0057] The crystallization time in step 3) of Example 1 was changed to 36 h, and the crystallization temperature was changed to 160 °C. The resulting catalyst was designated Cu-Pr-160Beta. Other reaction conditions were the same as in Example 1. The specific reaction evaluation results are shown in Table 2.

[0058] Table 2. Reaction evaluation results at different crystallization temperatures

[0059]

[0060] The evaluation results of the catalyst show that by adjusting the crystallization temperature of the support to regulate the silanol nest defects on the support, the butadiene selectivity shows an increasing trend with the increase of crystallization temperature. The catalytic performance is best at a crystallization temperature of 160 °C, with an ethanol conversion rate of 83.6% and a butadiene selectivity of 69.5%.

[0061] Example 9

[0062] The water-to-silica molar ratio in step 1) of Example 1 was adjusted to 6 (i.e., 6.44 g H2O, 12 g solid silica gel), and the resulting catalyst was denoted as Cu-Pr / Beta / 6H2O. Other reaction conditions were the same as in Example 1. The specific reaction evaluation results are shown in Table 3.

[0063] Example 10

[0064] The water-to-silicon molar ratio in step 1) of Example 1 was adjusted to 5 (i.e., 2.84 g H2O, 12 g solid silicon), and the resulting catalyst was Cu-Pr / Beta / 5H2O. Other reaction conditions were the same as in Example 1. Specific reaction evaluation results are shown in Table 3.

[0065] Example 11

[0066] The water-to-silicon molar ratio in step 1) of Example 1 was adjusted to 4 (i.e., 0.032 g H2O, 12 g solid silicon), and the resulting catalyst was Cu-Pr / Beta / 4H2O. Other reaction conditions were the same as in Example 1. The specific reaction evaluation results are shown in Table 3.

[0067] Table 3. Reaction evaluation results for different water-to-silicon molar ratios

[0068]

[0069] Catalyst evaluation results showed that as the water-silicon molar ratio decreased from 7 to 4, the ethanol conversion rate gradually increased, while the butadiene selectivity exhibited a trend of first increasing and then decreasing. The highest butadiene selectivity (73.4%) was achieved at a water-silicon molar ratio of 5. Decreasing the water-silicon molar ratio increased the gel concentration, promoted nucleation, and generated molecular sieves with smaller crystallites and larger specific surface areas. It also generated more silanol nest defects that are beneficial for anchoring highly selective active centers. However, when the water-silicon molar ratio decreased to 4, the ethylene content increased, and excessive system concentration may introduce non-selective acidic sites, promoting side reactions.

[0070] Comparative Example 1

[0071] Weigh 0.02 g of copper nitrate hexahydrate and 0.3 g of praseodymium nitrate hexahydrate and dissolve them in 1.5 g of water to form a solution. Add the solution to 2 g of commercial DeAlBEA molecular sieve, stir well, let stand at room temperature for 4 h, and then dry in a constant temperature oven at 100 ℃ for 4 h. Place the resulting solid in a muffle furnace and calcine at 550 ℃ for 4 h to obtain Cu-Pr / DeAlBEA catalyst.

[0072] The reaction evaluation conditions for the Cu-Pr / DeAlBEA catalyst were the same as in Example 1, and the evaluation results are shown in Table 4.

[0073] Table 4 Reaction Evaluation Results

[0074]

[0075] The evaluation results of the catalyst show that the self-synthesized all-silica Beta molecular sieve support used in this invention, compared with the traditional dealumination modified support, avoids the destruction of the framework by the acid treatment step, and can provide more uniform and controllable silanol nest defect sites, thereby achieving higher butadiene selectivity and stability.

Claims

1. A method for preparing a self-synthesized all-silica Beta molecular sieve catalyst for the production of butadiene from ethanol, characterized in that, Includes the following steps: 1) Mix the template agent, alkali source and water to obtain a solution, then add the silicon source to form an initial gel mixture; 2) The initial gel mixture was aged at room temperature for 10-20 h, and then commercial dealuded Beta molecular sieve was added as seed crystals. The mixture was aged at room temperature for another 10-20 h. The gel mixture was then transferred to a polytetrafluoroethylene (PTFE) liner and placed in a stainless steel hydrothermal synthesis reactor. The mixture was crystallized at 120-160 °C for 24-42 h. The crystallized product was filtered, washed until neutral, and dried to obtain a dry sample. 3) Grind the dried sample and mix it with NH4Cl solution. Then, perform ion exchange in a water bath at 50-100 ℃ for 2-8 h. Centrifuge to recover the solid. Repeat once. Calcine the centrifuged and dried sample to obtain the catalyst support, i.e., Si-Beta molecular sieve. 4) Dissolve Cu metal precursor and Pr metal precursor in water to form a precursor solution. Add the precursor solution to Si-Beta molecular sieve, stir evenly, let stand at room temperature, dry, and then calcine in a muffle furnace to obtain Cu-Pr / Beta catalyst.

2. The method for preparing a self-synthesized all-silica Beta molecular sieve catalyst for ethanol-to-butadiene production according to claim 1, characterized in that, The template agent is one of tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and tetrapropylammonium hydroxide; the silicon source is one of silica, tetraethyl orthosilicate, silica sol, and solid silica gel; the alkali source is one or two of sodium hydroxide, tetraethylammonium chloride, sodium chloride, and ammonia water.

3. The method for preparing a self-synthesized all-silica Beta molecular sieve catalyst for ethanol-to-butadiene production according to claim 1, characterized in that, The molar ratio of the template agent to the silicon source is 0.15-0.35, and the molar ratio of water to the silicon source is 3-8.

4. The method for preparing a self-synthesized all-silica Beta molecular sieve catalyst for ethanol-to-butadiene production according to claim 1, characterized in that, The alkaline source is a mixture of tetraethylammonium chloride and sodium chloride, wherein the molar ratio of tetraethylammonium chloride to the silicon source is 0.05-0.15, and the molar ratio of sodium chloride to the silicon source is 0.06-0.

13.

5. The method for preparing a self-synthesized all-silica Beta molecular sieve catalyst for ethanol-to-butadiene production according to claim 1, characterized in that, In step 2), the crystallization time is 30-36 h; in step 3), the concentration of the NH4Cl solution is 1 mol / L, the solid-liquid ratio of the dried sample to the NH4Cl solution is 1:3-12, and the calcination is carried out at 300-600 ℃ for 3-8 h.

6. The method for preparing a self-synthesized all-silica Beta molecular sieve catalyst for ethanol-to-butadiene production according to claim 1, characterized in that, In step 4), the Cu metal precursor is one of copper nitrate, copper chloride, and copper acetate; the Pr metal precursor is one of praseodymium nitrate, praseodymium chloride, and praseodymium acetate.

7. The method for preparing a self-synthesized all-silica Beta molecular sieve catalyst for ethanol-to-butadiene production according to claim 1, characterized in that, In step 4), the standing time is 3-6 h, the drying conditions are drying at 90-110 ℃ for 6-12 h, and the calcination conditions are calcination at 300-600 ℃ for 3-8 h.

8. The method for preparing a self-synthesized all-silica Beta molecular sieve catalyst for ethanol-to-butadiene production according to claim 1, characterized in that, The loading of Cu in Cu-Pr / Beta catalyst is 0.1wt%-0.5wt%, and the loading of Pr in Cu-Pr / Beta catalyst is 4wt%-6wt%.

9. The Cu-Pr / Beta catalyst obtained by the preparation method according to any one of claims 1-8.

10. The application of the Cu-Pr / Beta catalyst as described in claim 9 in the direct conversion of ethanol to 1,3-butadiene.

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