Preparation of a Molecular Sieve-Supported Metal Catalyst and Its Application in the Catalytic Hydrogenation of Carbon Dioxide to Lower Alcohols

Abstract

The present invention relates to the technical field of catalysts, and particularly relates to the preparation of a molecular sieve-supported metal catalyst and its application in the catalytic hydrogenation of carbon dioxide to lower alcohols. The preparation method of the molecular sieve-supported metal catalyst includes: step (1), preparing A-ZSM-48 molecular sieve: A includes at least one of potassium or sodium; step (2), preparing a modification solution: adding water to a water-soluble salt containing B to obtain a modification solution; B is at least one of Cu, Zn, Fe, Co, Pt, Ru; step (3), mixing the A-ZSM-48 molecular sieve with the modification solution, concentrating, drying, and calcining to obtain a molecular sieve-supported metal catalyst. The catalyst has a high carbon dioxide conversion rate, a high selectivity for the obtained lower alcohols, reduces the use requirement of precious metals, and realizes a more cost-effective resource utilization of carbon dioxide.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly to the preparation of a molecular sieve supported metal catalyst and its application in the catalytic hydrogenation of carbon dioxide to lower alcohols. Background Art

[0002] Catalysts for the hydrogenation of CO2 to lower alcohols can be roughly divided into four categories: metal catalysts, tandem catalysts, metal carbide catalysts, and supported catalysts. Metal catalysts can be further subdivided into noble metal catalysts and transition metal catalysts.

[0003] Noble metals (such as platinum, palladium, rhodium, etc.) exhibit high activity and selectivity during the catalytic process, and have good reaction stability and catalytic efficiency. However, due to the limited resources and high price of noble metals, this restricts their widespread use in industrial applications.

[0004] In contrast, transition metal catalysts (such as iron, cobalt, copper, etc.) show obvious advantages in terms of economy and have high catalytic activity in the CO2 hydrogenation reaction. However, these catalysts are prone to metal particle sintering or carbon deposition under high-temperature reaction conditions, resulting in catalyst deactivation, and the selectivity of the products is poor, usually accompanied by the generation of by-products.

[0005] Tandem catalysts can more efficiently promote the conversion of CO2 to lower alcohols by combining different types of catalysts, significantly improving the reaction efficiency and selectivity. However, the design of the tandem catalyst system is complex, requiring precise adjustment of the combination ratio of different catalysts, and different catalysts may require different reaction conditions, which greatly increases the operation difficulty and complexity.

[0006] Metal carbide catalysts, due to their excellent electronic properties, can regulate the electron density of metal active sites, thereby enhancing the catalytic activity and effectively reducing the generation of by-products, improving the selectivity of target products. However, the structure of metal carbide catalysts is relatively sensitive and prone to decomposition or transformation, leading to the decline of catalyst performance and the decrease of catalytic stability.

[0007] Supported catalysts can effectively disperse metal active sites by selecting suitable carriers (such as metal-organic frameworks, oxides, nitrides, etc.), thereby improving the stability of the catalyst. However, the rapid growth and aggregation of metal particles on the carrier will cause catalyst deactivation. Therefore, the selection of the carrier has an important impact on the dispersion of metal particles and the catalytic performance. In addition, the synthesis methods of some carriers are relatively complex, which may not be conducive to the industrial application of the catalyst.

[0008] Ding L et al. (see specifically: Ding L, Shi T, Gu J, et al. CO2 hydrogenation to ethanol over Cu@Na-Beta[J]. Chem, 2020, 6(10): 2673-2689) prepared a high-performance Cu@Na-Beta catalyst by a two-step method. During the synthesis of the Cu@Na-Beta catalyst, 6.00 g of Na-Beta zeolite (Si / Al about 25), with a particle size of about 0.1 mm, was used. Intra-crystalline mesopores were introduced by alkaline treatment. 200 mL of 0.200 mol / L NaOH solution was used and treated at 65 °C for 30 minutes, followed by filtration, washing, and drying (labeled as alk-Beta). Then, CuO was introduced into the pores of alk-Beta by impregnating with a Cu(NO3)2 ethanol solution, and then calcined at 450 °C for 3 hours (labeled as CuO / alk-Beta). In the next step, 1.00 g of CuO / alk-Beta was thoroughly mixed with a Na-Beta zeolite synthesis gel, which was composed of 0.125 g of Al2(SO4)3·18H2O, 3.16 g of 20% tetraethylammonium hydroxide (TEAOH), 0.540 g of SiO2, and 0.0275 g of NaOH. The synthesis gel was crystallized at 180 °C for 2 days by the dry gel conversion method, followed by thorough washing with water and calcined in air at 550 °C for 4 hours to remove the template agent. The sample was labeled as CuO@Na-Beta. Before the catalytic test, CuO@Na-Beta was reduced with 5% H2 / N2 gas at 350 °C for 1.5 hours (labeled as the Cu@Na-Beta catalyst). At 300 °C, a pressure of 1.3 MPa, and a space velocity of 12000 mL / gcat / h, the CO2 conversion rate of the Cu@Na-Beta catalyst could reach 12.2%.

[0009] Chinese invention patent CN115283008A discloses a catalyst for converting carbon dioxide to lower alcohols, its preparation method and application. The preparation method is as follows: A uniformly mixed cobalt precursor one, cobalt precursor two, and molecular sieve are mechanically ball-milled and then heat-treated to obtain the catalyst product. The preparation method of a catalyst for converting carbon dioxide to lower alcohols provided by this invention uses cobalt precursor one, cobalt precursor two, and molecular sieve as raw materials. Under the action of mechanical ball-milling, Co single-atom sites (Co x+ ) and Co nanocluster sites (Co 0 ) are introduced into the molecular sieve to create Co 0 -Co x+ double sites. These double sites can catalyze the formation of alcohols and the growth of carbon chains, greatly promoting the selectivity of lower alcohols. The selectivity of lower alcohols is higher than 85%, where C 3+The alcohol selectivity is higher than 40%.

[0010] Existing catalysts for the hydrogenation of CO2 to lower alcohols still face several problems, mainly manifested as high cost, complex synthesis methods or high design difficulty, and poor catalyst stability (such as deactivation caused by the loss, sintering or aggregation of active components), which significantly restrict the further development and practical application of catalysts for the hydrogenation of CO2 to lower alcohols.

[0011] Therefore, the technical problem to be solved by the present invention is to overcome the problems of high cost of catalysts for the hydrogenation of CO2 to lower alcohols in the prior art, easy aggregation of metal active sites during the catalyst preparation process, easy sintering or carbon deposition of metal particles during use, resulting in poor stability and easy deactivation of the catalyst. Summary of the Invention

[0012] Based on the purpose of solving the above technical problems, the technology of the present invention is proposed, specifically relating to the preparation of a molecular sieve supported metal catalyst and its application in the catalytic hydrogenation of carbon dioxide to lower alcohols.

[0013] The present invention provides a method for preparing a molecular sieve supported metal catalyst, comprising the following steps:

[0014] Step (1), preparing A-ZSM-48 molecular sieve: mixing an A-containing alkali source with water, adding a template agent and mixing, then adding an aluminum source and mixing, then adding a silicon source and mixing, adding ZSM-48 as a seed crystal and mixing, and then placing it in an autoclave for crystallization at 140-180 °C for 40-80 hours, filtering, washing, drying, and calcining at 500-600 °C for 3-7 hours to obtain A-ZSM-48 molecular sieve;

[0015] Wherein, A includes at least one of potassium or sodium; the A-containing alkali source includes at least one of an A-containing hydroxide, carbonate, or bicarbonate;

[0016] Step (2), preparing a modification solution: mixing water with a water-soluble salt containing B to obtain a modification solution;

[0017] Wherein, B is at least one of Cu, Zn, Fe, Co, Pt, Ru; the water-soluble salt containing B includes at least one of a sulfate or chloride containing B;

[0018] Step (3), preparing a molecular sieve supported metal catalyst: mixing the A-ZSM-48 molecular sieve prepared in step (1) with the modification solution prepared in step (2), concentrating, drying, and then transferring it to a muffle furnace for calcination at 500-600 °C for 3-7 hours to obtain a molecular sieve supported metal catalyst.

[0019] Further, the template agent includes at least one of hexamethylenediamine, 1,6-pentanediamine, 1,8-octanediamine, hexamethonium bromide, and dimethylbicyclohexylammonium hydroxide.

[0020] Further, the aluminum source includes at least one of boehmite, sodium aluminate, pseudoboehmite, and aluminum sulfate.

[0021] Further, the silicon source includes at least one of silica sol, fumed silica, macroporous silica gel, tetraethyl orthosilicate, and sodium silicate.

[0022] Further, the alkali source containing A includes at least one of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, and sodium bicarbonate.

[0023] Further, the alkali source containing A includes sodium hydroxide and potassium hydroxide.

[0024] Further, the alkali source containing A includes sodium hydroxide and potassium hydroxide with a molar ratio of 1:(0.9 - 1.3).

[0025] Further, step (1) is as follows: Mix 1 - 3 g of the alkali source containing A with 80 - 120 mL of water, add 3 - 6 g of the template agent and mix, then add 0.1 - 0.5 g of the aluminum source and mix, then add 30 - 50 g of the silicon source and mix, and finally add 0.5 - 1 g of ZSM-48 as a seed crystal and mix. Then place it in an autoclave and crystallize at 140 - 180 °C for 40 - 80 hours, filter, wash, dry, and calcine at 500 - 600 °C for 3 - 7 hours to obtain the A-ZSM-48 molecular sieve.

[0026] Further, in step (2), the dosage ratio of the water-soluble salt containing B to water is 1 - 3 g:8 - 15 mL.

[0027] Further, in step (2), the water-soluble salt containing B includes at least one of copper sulfate, zinc sulfate, iron sulfate, ferrous sulfate, cobalt sulfate, copper chloride, zinc chloride, iron chloride, ferrous chloride, cobalt chloride or hydrates thereof.

[0028] Further, in step (2), the water-soluble salt containing B includes copper sulfate pentahydrate and zinc sulfate.

[0029] Further, in step (2), the water-soluble salt containing B includes copper sulfate pentahydrate and zinc sulfate with a mass ratio of 9 - 15:1.

[0030] Further, in step (3), the mass ratio of the A-ZSM-48 molecular sieve to the modification liquid is 4 - 6 g:10 - 20 g.

[0031] Further, in step (3), the calcination heating rate is 1.5 - 2.5 °C / min.

[0032] The present invention also provides a molecular sieve supported metal catalyst prepared according to the above preparation method.

[0033] The present invention also provides the use of the above molecular sieve supported metal catalyst in the catalytic hydrogenation of carbon dioxide to lower alcohols.

[0034] Further, the steps of the use include: forming the molecular sieve supported metal catalyst into particles, loading the particles in a catalytic reactor, and reducing the particles in a hydrogen atmosphere; then feeding a mixed gas composed of hydrogen, carbon dioxide and nitrogen into the reactor for catalytic reaction, and controlling the catalytic reaction pressure, temperature and mixed gas flow rate to prepare lower alcohols.

[0035] Compared with the prior art, the progressiveness of the present invention lies in:

[0036] Using a ZSM-48 molecular sieve supported metal catalyst for the hydrogenation conversion of carbon dioxide to lower alcohols has significant advantages. First, the unique pore structure of the ZSM-48 molecular sieve effectively promotes the uniform dispersion of the metal, avoids the sintering or carbon deposition of metal particles, and significantly improves the stability and reaction efficiency of the catalyst. Second, the synergistic effect of the metal active sites optimizes the selectivity for ethanol and inhibits the formation of by-products. In addition, the ZSM-48 molecular sieve support can maintain the stability of the catalyst at high temperatures and extend its service life. While improving the catalytic activity and optimizing the selectivity, the high stability and high temperature resistance of the ZSM-48 molecular sieve supported metal catalyst endow it with good potential for industrial application, further reducing the demand for precious metals, thereby realizing a more cost-effective resource utilization of carbon dioxide.

[0037] The molecular sieve supported metal catalyst prepared by the present invention has good selectivity for lower alcohols such as methanol, ethanol, and C3 + alcohols, has a high catalytic CO2 conversion rate, and has good catalytic effects in the synthesis of lower alcohols.

[0038] In the present invention, an alkali source containing potassium and sodium is combined with a ZSM-48 molecular sieve to prepare a sodium-type or potassium-type molecular sieve supported metal catalyst, both of which have good selectivity for lower alcohols. The catalyst prepared with the alkali source containing potassium has better total alcohol selectivity, while the catalyst prepared with the alkali source containing sodium has better selectivity for methanol.

[0039] In the present invention, the catalyst prepared by simultaneously containing sodium and potassium in the alkali source has higher total alcohol selectivity, and the two promote each other and synergistically enhance the total alcohol selectivity and CO2 conversion rate.

[0040] In the present invention, the water-soluble salt containing zinc has a worse effect than the catalyst prepared from the water-soluble salt containing copper; when the total amount of the water-soluble salt remains unchanged, the catalyst prepared from the water-soluble salt containing both copper and zinc (for example, the ratio of the two water-soluble salts is 9-15:1) has a higher CO2 conversion rate, and higher selectivities for methanol, C3 + alcohols, and total alcohols.

[0041] The catalyst of the present invention has excellent performance and good application prospects. Description of the Drawings

[0042] Figure 1 It is the XRD pattern of Cu / Na-ZSM-48 in Example 1.

[0043] Figure 2 It is the SEM pattern of Cu / Na-ZSM-48 in Example 1.

[0044] Figure 3 It is the TEM pattern of Cu / Na-ZSM-48 in Example 1. Detailed Embodiments

[0045] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0046] Silica sol: HS-40, Guangdong Huierte Nano Technology Co., Ltd.

[0047] ZSM-48: Molecular sieve, product number NKF-17-100, Tianjin Nanhua Catalyst Co., Ltd.

[0048] ZSM-5: Molecular sieve, product number NKF-5-18H, Tianjin Nanhua Catalyst Co., Ltd.

[0049] ZSM-22: Molecular sieve, product number NKF-22-40, Tianjin Nanhua Catalyst Co., Ltd.

[0050] Example 1

[0051] (1)Preparation of Na-ZSM-48 zeolite: Under stirring conditions, 1.2 g (0.03 mol) of NaOH was added to 90 mL of deionized water and stirred until completely dissolved, then 4.34 g of H2N(CH2)6NH2 (HAD, hexamethylenediamine) was added. After sufficient stirring, 0.2 g of pseudo-boehmite was added. After stirring until the mixture was clear and transparent, 37.5 g of silica sol was slowly added. The mixture was stirred at room temperature for 2 hours, and then 0.75 g of ZSM-48 was added as a seed and stirred evenly to obtain a synthesis gel;

[0052] The synthesis gel was transferred to a stainless-steel autoclave with a polytetrafluoroethylene liner and crystallized at 160 °C for 2 days. The product was filtered, washed with ethanol and ultrapure water, dried in an oven at 110 °C for 8 hours, and then calcined at 550 °C for 5 hours to remove the template HAD, obtaining the product Na-ZSM-48 zeolite.

[0053] (2)Synthesis of Cu / Na-ZSM-48 catalyst: 1.96 g of CuSO4·5H2O was dissolved in 10 mL of ultrapure water and stirred until completely dissolved. 5 g of the product obtained in step (1) was added to the above impregnation solution, stirred at 80 °C for 4 hours, then left standing for 12 hours, rotary evaporated to dryness, placed in an oven and dried at 110 °C for 6 hours, and then transferred to a muffle furnace and calcined at 550 °C for 5 hours, with a calcination heating rate of 2 °C / min, obtaining the Cu / Na-ZSM-48 catalyst. XRD, SEM and TEM tests were carried out on this product, and the results are shown in Figures 1 - 3 .

[0054] According to Figures 1 - 3 the tests, the catalyst prepared in Example 1 has the characteristic peaks of ZSM-48 and good crystallinity; the morphology is spindle-shaped, the radial size is 0.3 - 1 µm, and the length is about 1 - 3 µm; the copper nanoparticles are evenly distributed on the ZSM-48 zeolite support, and the particle size is 1 - 6 nm.

[0055] (3)Catalytic performance evaluation: The Cu / Na-ZSM-48 catalyst obtained in step (2) was pressed into tablets and then made into particles between 60 - 100 mesh. 300 mg was weighed and loaded into a catalytic reactor. Under a H2 atmosphere, the gas velocity was 2000 mL / (g cat ·h -1 ), reduced at 300 °C for 2 hours, and then H2, CO2 and N2 with a volume ratio of 3:1:1 were fully mixed in a gas mixing device and then fed into the reactor. The catalytic reaction was controlled at a pressure of 4.0 MPa, a temperature of 240 °C, and a gas velocity of 4000 mL / (g cat ·h -1)It is carried out under the following conditions. Then, the reaction products are analyzed by gas chromatography, and the conversion rate of CO2 and the selectivity of lower alcohols are calculated. The test results are shown in Table 1.

[0056] The carbon dioxide conversion rate and product selectivity are calculated according to the following formulas:

[0057] Carbon dioxide conversion rate = (moles of carbon dioxide at inlet - moles of carbon dioxide at outlet) / moles of carbon dioxide at inlet × 100%; Product selectivity = moles of product at outlet × number of carbon atoms in the product / (moles of carbon dioxide at inlet - moles of carbon dioxide at outlet) × 100%.

[0058] Example 2

[0059] (1) Preparation of Na-ZSM-48 molecular sieve: Under stirring conditions, 1.10 g of NaOH is added to 95 mL of deionized water and stirred until completely dissolved, then 4.5 g of H2N(CH2)6NH2 (HAD, hexamethylenediamine) is added. After stirring well, 0.25 g of pseudoboehmite is added. After stirring until the mixture is clear and transparent, 35.5 g of silica sol is slowly added. After the mixture is stirred at room temperature for 3 hours, 0.8 g of ZSM-48 is added as a seed and stirred evenly to obtain a synthesis gel;

[0060] The synthesis gel is transferred to a stainless-steel autoclave with a polytetrafluoroethylene liner and crystallized at 170 °C for 2.5 days. The product is filtered, washed with ethanol and ultrapure water, dried in an oven at 110 °C for 8.5 hours, and then calcined at 570 °C for 6 hours to remove the template agent HAD, obtaining the product Na-ZSM-48 molecular sieve.

[0061] (2) Synthesis of Cu / Na-ZSM-48 catalyst: 2.05 g of CuSO4·5H2O is dissolved in 12.5 mL of ultrapure water and stirred until completely dissolved. 5.2 g of the product obtained in step (1) is added to the above impregnation solution, stirred at 85 °C for 3.2 hours, then left standing for 10 hours, rotary evaporated to dryness, placed in an oven and dried at 105 °C for 4.5 hours, and then transferred to a muffle furnace and calcined at 560 °C for 5.5 hours. The heating rate of calcination is 2.2 °C / min to obtain the Cu / Na-ZSM-48 catalyst.

[0062] (3) The prepared Cu / Na-ZSM-48 catalyst is loaded into a catalytic reactor, and the catalytic performance of the catalyst is evaluated according to the method of step (3) in Example 1. The results are shown in Table 1.

[0063] Example 3

[0064] (1)Preparation of K-ZSM-48 zeolite: Under stirring conditions, 1.683 g (0.03 mol) of KOH was added to 90 mL of deionized water, stirred until completely dissolved, 4.34 g of HAD was added and stirred thoroughly, 0.2 g of pseudo-boehmite was added and stirred until the mixture was clear and transparent, then 37.5 g of silica sol was slowly added. After stirring at room temperature for 2 hours, 0.75 g of ZSM-48 was added as a seed crystal and stirred evenly to obtain a synthesis gel;

[0065] The synthesis gel was transferred to a stainless-steel autoclave lined with polytetrafluoroethylene and crystallized at 160 °C for 2 days. The product was filtered, washed, dried in an oven at 110 °C for 8 hours, and then calcined at 550 °C for 5 hours to remove the template agent HAD, obtaining the product K-ZSM-48 zeolite.

[0066] (2)Synthesis of Cu / K-ZSM-48 catalyst: 1.96 g of CuSO4·5H2O was dissolved in 10 mL of ultrapure water and stirred until completely dissolved. 5 g of the product obtained in step (1) was added to the impregnation solution, stirred at 80 °C for 4 hours, then left standing for 12 hours. After rotary evaporation to dryness, it was placed in an oven and dried at 110 °C for 6 hours, and then transferred to a muffle furnace and calcined at 550 °C for 5 hours to remove the template agent HAD, obtaining the product Cu / K-ZSM-48 catalyst.

[0067] (3)The prepared Cu / K-ZSM-48 catalyst was loaded into a catalytic reactor, and the catalytic performance of the catalyst was evaluated according to the method in step (3) of Example 1. The results are shown in Table 1.

[0068] Example 4

[0069] (1)Preparation of K / Na-ZSM-48 zeolite: Under stirring conditions, 0.6 g (0.015 mol) of NaOH and 0.8415 g (0.015 mol) of KOH were added to 90 mL of deionized water, stirred until completely dissolved, 4.34 g of HAD was added and stirred thoroughly, 0.2 g of pseudo-boehmite was added and stirred until the mixture was clear and transparent, then 37.5 g of silica sol was slowly added. After stirring at room temperature for 2 hours, 0.75 g of ZSM-48 was added as a seed crystal and stirred evenly to obtain a synthesis gel;

[0070] The synthesis gel was transferred to a stainless-steel autoclave lined with polytetrafluoroethylene and crystallized at 160 °C for 2 days. The product was filtered, washed, dried in an oven at 110 °C for 8 hours, and then calcined at 550 °C for 5 hours to remove the template agent HAD, obtaining the product K / Na-ZSM-48 zeolite.

[0071] (2)Synthesis of Cu / K / Na-ZSM-48 catalyst: Dissolve 1.96 g of CuSO4·5H2O in 10 mL of ultrapure water and stir until completely dissolved. Add 5 g of the product obtained in step (1) to the impregnation solution, stir at 80 °C for 4 hours, then let it stand for 12 hours. After rotary evaporation to dryness, place it in an oven and dry at 110 °C for 6 hours, and then transfer it to a muffle furnace and calcine at 550 °C for 5 hours to remove the template agent HAD, obtaining the product Cu / K / Na-ZSM-48 catalyst.

[0072] (3)Load the prepared Cu / K / Na-ZSM-48 catalyst into a catalytic reactor and evaluate the catalytic performance of the catalyst according to the method in step (3) of Example 1. The results are shown in Table 1.

[0073] Example 5

[0074] (1)Preparation of K / Na-ZSM-48 molecular sieve: Under stirring conditions, add 0.6 g (0.015 mol) of NaOH and 0.8415 g (0.015 mol) of KOH to 90 mL of deionized water, stir until completely dissolved, add 4.34 g of HAD and stir well, add 0.2 g of pseudo-boehmite and stir until the mixed solution is clear and transparent, then slowly add 37.5 g of silica sol. After stirring at room temperature for 2 hours, add 0.75 g of ZSM-48 as a seed crystal and stir evenly to obtain a synthesis gel;

[0075] Transfer the synthesis gel to a stainless steel autoclave with a polytetrafluoroethylene lining and carry out crystallization at 160 °C for 2 days. After the product is filtered and washed, dry it in an oven at 110 °C for 8 hours, and then calcine it at 550 °C for 5 hours to remove the template agent HAD, obtaining the product K / Na-ZSM-48 molecular sieve.

[0076] (2)Synthesis of Zn / K / Na-ZSM-48 catalyst: Dissolve 1.96 g of ZnSO4 in 10 mL of ultrapure water and stir until completely dissolved. Add 5 g of the product obtained in step (1) to the impregnation solution, stir at 80 °C for 4 hours, then let it stand for 12 hours. After rotary evaporation to dryness, place it in an oven and dry at 110 °C for 6 hours, and then transfer it to a muffle furnace and calcine at 550 °C for 5 hours to remove the template agent HAD, obtaining the product Zn / K / Na-ZSM-48 catalyst.

[0077] (3)Load the prepared Zn / K / Na-ZSM-48 catalyst into a catalytic reactor and evaluate the catalytic performance of the catalyst according to the method in step (3) of Example 1. The results are shown in Table 1.

[0078] Example 6

[0079] (1)Preparation of K / Na-ZSM-48 zeolite: Under stirring conditions, 0.6 g (0.015 mol) of NaOH and 0.8415 g (0.015 mol) of KOH were added to 90 mL of deionized water, stirred until completely dissolved, 4.34 g of HAD was added and stirred well, 0.2 g of pseudo-boehmite was added and stirred until the mixture was clear and transparent, then 37.5 g of silica sol was slowly added. After stirring at room temperature for 2 hours, 0.75 g of ZSM-48 was added as a seed and stirred evenly to obtain a synthesis gel;

[0080] The synthesis gel was transferred to a stainless-steel autoclave with a polytetrafluoroethylene liner and crystallized at 160 °C for 2 days. The product was filtered, washed, dried in an oven at 110 °C for 8 hours, and then calcined at 550 °C for 5 hours to remove the template agent HAD, obtaining the product K / Na-ZSM-48 zeolite.

[0081] (2)Synthesis of Cu-Zn / K / Na-ZSM-48 catalyst: 1.82 g of CuSO4·5H2O and 0.14 g of ZnSO4 (the sum of their masses was 1.96 g and the mass ratio was 13:1) were dissolved in 10 mL of ultrapure water and stirred until completely dissolved. 5 g of the product obtained in step (1) was added to the impregnation solution, stirred at 80 °C for 4 hours, then left standing for 12 hours. After rotary evaporation to dryness, it was placed in an oven and dried at 110 °C for 6 hours, and then transferred to a muffle furnace and calcined at 550 °C for 5 hours to remove the template agent HAD, obtaining the product Cu-Zn / K / Na-ZSM-48 catalyst.

[0082] (3)The prepared Cu-Zn / K / Na-ZSM-48 catalyst was loaded into a catalytic reactor, and the catalytic performance of the catalyst was evaluated according to the method in step (3) of Example 1. The results are shown in Table 1.

[0083] Comparative Example 1

[0084] (1)Preparation of Na-ZSM-48 zeolite: Under stirring conditions, 1.2 g (0.03 mol) of NaOH was added to 90 mL of deionized water, stirred until completely dissolved, then 4.34 g of H2N(CH2)6NH2 (HAD, hexamethylenediamine) was added, stirred well, 0.2 g of pseudo-boehmite was added, and after stirring until the mixture was clear and transparent, 37.5 g of silica sol was slowly added. The mixture was stirred at room temperature for 2 hours to obtain a synthesis gel;

[0085] Transfer the synthesized gel to a stainless-steel autoclave lined with polytetrafluoroethylene and crystallize it at 160 °C for 10 days (since no seed was used, the crystallization time was extended). After the crystallization product was filtered, washed with ethanol and ultrapure water, it was dried in an oven at 110 °C for 8 hours, and then calcined at 550 °C for 5 hours to remove the templating agent HAD, obtaining the product Na-ZSM-48 molecular sieve.

[0086] (2) Synthesis of the Cu / Na-ZSM-48 catalyst: Dissolve 1.96 g of CuSO4·5H2O in 10 mL of ultrapure water and stir to dissolve it completely. Add 5 g of the product obtained in step (1) to the above impregnation solution, stir at 80 °C for 4 hours, then let it stand for 12 hours. After rotary evaporation to dryness, place it in an oven and dry at 110 °C for 6 hours, and then transfer it to a muffle furnace and calcine at 550 °C for 5 hours. The heating rate of the calcination is 2 °C / min to obtain the Cu / Na-ZSM-48 catalyst.

[0087] (3) Load the prepared Cu / Na-ZSM-48 catalyst into a catalytic reactor and evaluate the catalytic performance of the catalyst according to the method in step (3) of Example 1. The results are shown in Table 1.

[0088] Comparative Example 2

[0089] (1) Preparation of the Cu / Al2O3 catalyst: Calcinate Al2O3 in a muffle furnace at 550 °C for 2 hours to remove adsorbed water and impurities. Weigh 1.96 g of CuSO4·5H2O powder and dissolve it in 5 mL of ultrapure water to prepare a copper sulfate solution. Then, gradually add the above copper sulfate solution dropwise to 5 g of calcined Al2O3 and stir well. Then, place it in an oven and dry at 110 °C for 10 hours to remove water, and then transfer it to a muffle furnace and calcine at 550 °C for 5 hours to obtain the Cu / Al2O3 catalyst.

[0090] (2) Load the prepared Cu / Al2O3 catalyst into a catalytic reactor and evaluate the catalytic performance of the catalyst according to the method in step (3) of Example 1.

[0091] Comparative Example 3

[0092] (1) Preparation of the Cu / ZSM-5 catalyst: Dissolve 1.96 g of CuSO4·5H2O in 10 mL of ultrapure water and stir to dissolve it completely to prepare an impregnation solution. Add 5 g of ZSM-5 molecular sieve, stir at 80 °C for 4 hours, then let it stand for 12 hours. After rotary evaporation to dryness, place it in an oven and dry at 110 °C for 6 hours, and then transfer it to a muffle furnace and calcine at 550 °C for 5 hours to obtain the Cu / ZSM-5 catalyst.

[0093] (2) The prepared Cu / ZSM-5 catalyst was loaded into a catalytic reactor, and the catalytic performance of the catalyst was evaluated according to the method in step (3) of Example 1.

[0094] Comparative Example 4

[0095] (1) Preparation of Cu / ZSM-22 catalyst: Dissolve 1.96 g of CuSO4·5H2O in 10 mL of ultrapure water, stir to completely dissolve it to make an impregnation solution, add 5 g of ZSM-22 molecular sieve, stir at 80 °C for 4 hours, then let it stand for 12 hours, rotary evaporate to dryness, place it in an oven at 110 °C for 6 hours, and then transfer it to a muffle furnace and calcine at 550 °C for 5 hours.

[0096] (2) The prepared Cu / ZSM-22 catalyst was loaded into a catalytic reactor, and the catalytic performance of the catalyst was evaluated according to the method in step (3) of Example 1.

[0097] The catalytic performance test results of each example and comparative example are shown in Table 1.

[0098] Table 1: Catalytic performance test results of the catalyst

[0099] Test Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 CO2 Conversion Rate (%) 16.8 15.9 16.6 18.9 5.2 20.4 14.1 6.3 14.6 11.2 CO Selectivity (%) 8.7 8.1 8.6 7.8 38.7 5.7 10.3 58.7 14.5 19.9 CH4 Selectivity (%) 5.6 6.8 5.0 4.4 24.6 4.1 9.5 10.1 9.0 14.3 Methanol Selectivity (%) 54.3 53.7 40.2 43.7 30.3 46.8 44.7 22.8 38.2 39.0 Ethanol Selectivity (%) 20.8 20.0 30.9 28.6 5.5 27.6 23.9 5.0 24.9 20.6 C3+ Alcohol Selectivity (%) 10.6 11.4 15.3 15.5 0.9 15.8 11.6 3.4 13.4 6.2 Total Alcohol Selectivity (%) 85.7 85.1 86.4 87.8 36.7 90.2 80.2 31.2 76.5 65.8

[0100] Combined with the test results in Table 1, it can be seen that the molecular sieve supported metal catalyst prepared by the present invention has good selectivity for lower alcohols such as methanol, ethanol, and C3 + alcohols, has a high catalytic CO2 conversion rate, and has good catalytic effects in the synthesis of lower alcohols.

[0101] According to the test results of Examples 1 and 3 in Table 1, the sodium-type or potassium-type molecular sieve supported metal catalysts prepared by combining potassium and sodium alkali sources with ZSM-48 molecular sieve both have good lower alcohol selectivity. The total alcohol selectivity of the catalyst prepared with the potassium alkali source is better, while the catalyst prepared with the sodium alkali source has better selectivity for methanol.

[0102] According to the test results of Examples 1, 3, and 4 in Table 1, the catalyst prepared with sodium and potassium in the alkali source simultaneously has a higher total alcohol selectivity, and the two promote each other to improve the total alcohol selectivity and CO2 conversion rate.

[0103] According to the test results of Examples 4-5 in Table 1, the catalyst prepared with a zinc-containing water-soluble salt has a worse effect than that prepared with a copper-containing water-soluble salt; and according to the comparison of Examples 4-6, when the total amount of the water-soluble salt remains unchanged, the CO2 conversion rate of the catalyst prepared with the water-soluble salt containing both copper and zinc in Example 6 is higher, and the selectivities for methanol, C3 + alcohol, and total alcohol are higher.

[0104] It can be seen from the comparison between Example 1 and Comparative Examples 1-2 in Table 1 that without using ZSM-48 seeds to prepare the catalyst and without using ZSM-48 to prepare the catalyst, the catalytic CO2 conversion rate is low and the total alcohol selectivity efficiency is low.

[0105] It can be seen from the comparison between Example 1 and Comparative Examples 3-4 in Table 1 that the catalyst prepared by using other types of molecular sieves has a worse effect than the molecular sieve-supported metal catalyst obtained by using ZSM-48 of the present invention as a seed to obtain A-ZSM-48 molecular sieve and then preparing; using ZSM-48 as a seed to prepare the molecular sieve-supported metal catalyst is more suitable for the preparation system of the present invention and the obtained catalyst has excellent effects.

[0106] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, for those of ordinary skill in the art, it is still possible to modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and for these modifications or replacements, the essence of the corresponding technical solutions does not deviate from the spirit and scope of the technical solutions required to be protected by the present invention.

Claims

1. Application of a molecular sieve supported metal catalyst in catalytic hydrogenation of carbon dioxide to lower alcohols, characterized in that, The preparation method of the molecular sieve supported metal catalyst comprises the following steps: Step (1), preparing A-ZSM-48 molecular sieve: Mix an A-containing alkali source with water, add a template agent and mix, then add an aluminum source and mix, then add a silicon source and mix, add ZSM-48 as a seed crystal and mix, and then place it in an autoclave and crystallize at 140-180 °C for 40-80 hours, filter, wash, dry, and calcine at 500-600 °C for 3-7 hours to obtain the A-ZSM-48 molecular sieve; wherein, A includes potassium and sodium; the A-containing alkali source includes sodium hydroxide and potassium hydroxide with a molar ratio of 1:(0.9-1.3); Step (2), preparing a modification solution: Add water to a water-soluble salt containing B and mix to obtain a modification solution; wherein, B is Cu and Zn, and the water-soluble salt containing B includes copper sulfate pentahydrate and zinc sulfate with a mass ratio of (9-15):1; Step (3), preparing the molecular sieve supported metal catalyst: Mix the A-ZSM-48 molecular sieve prepared in step (1) with the modification solution prepared in step (2), concentrate, dry, and then transfer it to a muffle furnace and calcine at 500-600 °C for 3-7 hours to obtain the molecular sieve supported metal catalyst.

2. The application according to claim 1, wherein The template agent includes at least one of hexamethylenediamine, 1,8-octanediamine, hexamethonium bromide, and dimethylbicyclohexylammonium hydroxide; and / or, the aluminum source includes at least one of hydroxyaluminum oxide, sodium aluminate, pseudoboehmite, and aluminum sulfate; and / or, the silicon source includes at least one of silica sol, fumed silica, macroporous silica gel, tetraethyl orthosilicate, and sodium silicate.

3. The application according to claim 1, characterized in that, In step (2), the dosage ratio of the water-soluble salt containing B to water is 1-3 g:8-15 mL.

4. The application according to claim 1, wherein In step (3), the mass ratio of the A-ZSM-48 molecular sieve to the modification solution is 4-6 g:10-20 g.

5. The application according to claim 1, wherein Step (1) is: Mix 1-3 g of the A-containing alkali source with 80-120 mL of water, add 3-6 g of the template agent and mix, then add 0.1-0.5 g of the aluminum source and mix, then add 30-50 g of the silicon source and mix, and finally add 0.5-1 g of ZSM-48 as a seed crystal and mix, and then place it in an autoclave and crystallize at 140-180 °C for 40-80 hours, filter, wash, dry, and calcine at 500-600 °C for 3-7 hours to obtain the A-ZSM-48 molecular sieve.

6. The application according to claim 1, characterized in that, In step (3), the calcination heating rate is 1.5-2.5 °C / min.

7. The application according to claim 1, characterized in that, The steps of the application include: making the molecular sieve supported metal catalyst into particles, loading them in a catalytic reactor, and reducing the particles in a hydrogen atmosphere; then feeding a mixed gas composed of hydrogen, carbon dioxide, and nitrogen into the reactor for catalytic reaction, and controlling the catalytic reaction pressure, temperature, and mixed gas flow rate to prepare lower alcohols.

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