CuZn-based composite catalyst for preparing low-carbon alcohol from synthesis gas and preparation method of CuZn-based composite catalyst

Abstract

The invention relates to the technical field of preparation of composite catalysts, in particular to a CuZn-based composite catalyst for preparing low-carbon alcohol from synthesis gas and a preparation method of the CuZn-based composite catalyst. S2, preparation of precursor gel; s3, modifying the precursor gel; and S4, forming the catalyst. The Ga element is introduced into the oxygen vacancy modifying solvent, so that the oxygen vacancy content in the CuZn catalyst can be effectively regulated and controlled. The existence of oxygen vacancies can promote the transfer of electrons from ZnO to Cu, enhance the interaction between Cu and ZnO, generate more Zn delta < + > defects, and adjust the proportion of Cu0 / (Cu0 + Cu < + >), and the electron-rich Cu is beneficial to the dissociation and adsorption of CO, thereby promoting the formation of a key surface intermediate CHx *. Meanwhile, the oxygen vacancies can promote activation and adsorption of CO to generate more key intermediates (such as CO * and CHxO *), so that the selectivity of the low-carbon alcohol is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of composite catalysts, and specifically to a CuZn-based composite catalyst for synthesizing lower alcohols from syngas and a preparation method thereof. Background Art

[0002] The reduction in the supply of fossil fuel resources and environmental problems have promoted in-depth research on alternative energy sources. Lower alcohols, as clean energy, are considered intermediates for many chemical products, green and clean gasoline additives, and potential fuel additives. So far, existing methods for synthesizing lower alcohols have been reported, such as the hydration of petroleum-derived olefins and biological fermentation. Unfortunately, the above technologies have problems such as low efficiency, high raw material costs, and complex product separation. For these reasons, the catalytic synthesis of lower alcohols from syngas derived from non-petroleum carbon resources such as coal, natural gas, biomass, or CO2 has become the most effective and cleanest way to utilize energy resources and is also the most promising research focus. Currently, the catalytic conversion of syngas into lower alcohols through CuZnAl catalysts has broad prospects due to its low raw material cost and low energy consumption, but still faces daunting challenges due to the high methanol content.

[0003] Alkali metal and transition metal modified CuZnAl methanol catalysts focus on strengthening C-O dissociation and C-C coupling, improving the selectivity of lower alcohols. Recently, significant progress has been made in the synthesis of lower alcohols from syngas over CuZnAl catalysts, where the CLP method (complete liquid phase technology) is used to manufacture CuZnAl catalysts in the form of slurries. High selectivity of lower alcohols can be achieved on these slurry catalysts without introducing alkali or Fischer-Tropsch elements, breaking through the general understanding of CuZnAl as a methanol catalyst and providing a new understanding of the active sites in carbon chain growth. However, in existing research, the influence of reaction conditions (such as temperature, pressure, gas composition, etc.) on the catalyst performance has not been fully clarified and further optimization is needed. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a CuZn-based composite catalyst for synthesizing lower alcohols from syngas and a preparation method thereof.

[0005] To achieve the above purpose, the present invention provides the following technical solutions: A preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas, comprising the following preparation steps: S1. Preparation of the modified solution: Dissolve 0.8 - 2.2 parts of Al(NO3)3·9H2O, 1.5 - 2 parts of 10% chloroplatinic acid solution, and 6 - 7 parts of citric acid in 45 - 55 parts of absolute ethanol, ultrasonically disperse at 60 - 70 °C for 25 - 30 min, then add 0.1 - 0.3 parts of cetyltrimethylammonium bromide and 0.5 - 0.8 parts of sodium dodecyl sulfate, stir at 48 - 53 °C for 2 - 3 h, then raise the temperature to 92 - 98 °C and maintain for 25 - 35 min to obtain the modified solution; S2. Preparation of the precursor gel: Dissolve 0.6 - 0.82 parts of Cu(NO3)2·3H2O and 0.18 - 0.4 parts of Zn(NO3)2·6H2O in 50 - 70 parts of the oxygen vacancy modified solvent, stir for 25 - 30 min to obtain the precursor gel; S3. Modification of the precursor gel: Add 8 - 12 parts of the modified solution obtained in step S1 to the precursor gel obtained in step S2, continuously stir until a green sol is formed, and age for 10 days to obtain the modified precursor gel; S4. Formation of the catalyst: Add liquid paraffin to the modified precursor gel obtained in step S3, and under a nitrogen atmosphere of 50 mL / min, heat-treat the mixture for 7 - 8 h to obtain a CuZn-based composite catalyst for the synthesis of lower alcohols from syngas.

[0006] Preferably, the preparation of the oxygen vacancy modified solvent in step S2 includes the following steps: S21. Dissolve 3 - 5 parts of modified hydrated gallium nitrate in 50 - 70 parts of a 60% ethylene glycol solution by mass to obtain a preliminary mixture; S22. Ultrasonically disperse the preliminary mixture at 30 - 40 °C for 15 - 20 min, and the ultrasonic dispersion frequency is 40 - 60 kHz to finally obtain the oxygen vacancy modified solvent.

[0007] Preferably, the preparation of the modified hydrated gallium nitrate in step S21 includes the following steps: S31. Dissolve 2 - 5 parts of Ga(NO3)3·5H2O in 60 - 80 parts of a mixed solvent, add 0.5 - 1.5 parts of disodium ethylenediaminetetraacetate, and magnetically stir at 30 - 40 °C for 0.5 - 1 h to form a preliminary mixture; S32. Slowly dropwise add ammonia water until the solution pH is 3 - 4, maintain stirring for 20 - 30 min, then transfer the solution to a high-pressure reaction kettle with a polytetrafluoroethylene inner lining, and react at 110 - 120 °C for 3 - 4 h to obtain a secondary mixture; S33. Cool the secondary mixture obtained in step S32, centrifuge and separate, wash the obtained precipitate with absolute ethanol 3 times, and vacuum dry at 55 - 60 °C for 10 - 12 h to finally obtain the modified hydrated gallium nitrate.

[0008] Preferably, in step S31, the mixed solvent is a mixture of ethylene glycol solution with a mass fraction of 60% and deionized water, wherein the mass ratio of the 60% ethylene glycol solution to deionized water is 3:1.

[0009] Preferably, the stirring speed in steps S1, S2, and S3 is 350 - 450 r / min.

[0010] Preferably, the aging condition in step S3 is at normal temperature and in the dark.

[0011] Preferably, the mass ratio of liquid paraffin to the modified precursor gel in step S4 is 2 - 3:1.

[0012] Preferably, the frequency of ultrasonic dispersion in step S1 is 40 - 60 kHz.

[0013] Preferably, the heat treatment temperature in step S4 is 275 - 285 °C.

[0014] A CuZn-based composite catalyst for synthesizing lower alcohols from syngas is prepared by the above preparation method.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The aluminum (Al) element in the modification liquid is uniformly loaded on the surface of the CuZn matrix in the form of nano-aluminum oxide. By enhancing the metal-support interaction, the sintering of Cu / Zn particles is inhibited, and the thermal stability of the catalyst is significantly improved. At the same time, the synergistic effect of citric acid and cetyltrimethylammonium bromide forms a mesoporous structure, increasing the specific surface area; the introduction of aluminum element regulates the surface acid-base balance of the catalyst, promotes CO adsorption and C-C coupling, thereby improving the catalytic effect of the present invention.

[0016] 2. In the present invention, the oxygen vacancy-modified solvent can effectively regulate the oxygen vacancy content in the CuZn catalyst by introducing the Ga element. The existence of oxygen vacancies can promote the transfer of electrons from ZnO to Cu, enhance the interaction between Cu / ZnO, generate more Zn δ+ defects, and regulate the ratio of Cu 0 / (Cu 0 + Cu + ). The electron-rich Cu is beneficial to the dissociation and adsorption of CO, thereby promoting the formation of the key surface intermediate CH x *. At the same time, oxygen vacancies can also promote the activation and adsorption of CO, generating more key intermediates (such as CO* and CH x O*), thereby improving the selectivity of lower alcohols. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1Process flow chart for the preparation of the CuZn-based composite catalyst for synthesizing lower alcohols from syngas according to the present invention; Figure 2 X-ray diffraction analysis diagram of the CuZn-based composite catalyst for synthesizing lower alcohols from syngas obtained in Examples 1-5 of the present invention; Figure 3 Transmission electron microscope (TEM), high-resolution transmission electron microscope (HRTEM) and particle size analysis diagrams of the CuZn-based composite catalyst for synthesizing lower alcohols from syngas obtained in Examples 1-5 of the present invention (where a1-e1 are the TEM images of Examples 1-5 respectively, a2-e2 are the HRTEM images of Examples 1-5 respectively, and a3-e3 are the columnar diagrams of the particle size distribution of Cu particles in Examples 1-5). Detailed implementation manners

[0018] 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. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work fall within the scope of protection of the present invention.

[0019] Please refer to Figures 1 - 3 , the present invention provides a technical solution: Example 1 A preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas (in this example, each mass part is based on 10 g): S1. Preparation of the modification liquid: Dissolve 0.8 parts of Al(NO3)3·9H2O, 1.5 parts of 10% chloroplatinic acid solution and 6 parts of citric acid in 45 parts of absolute ethanol, ultrasonically disperse at 60 °C for 25 min, the ultrasonic dispersion frequency is 40 kHz, then add 0.1 part of cetyltrimethylammonium bromide and 0.5 part of sodium dodecyl sulfate, stir at 350 r / min for 2 h at 48 °C and then raise the temperature to 92 °C and keep it for 25 min to obtain the modification liquid; S2. Preparation of the precursor gel: Dissolve 0.6 parts of Cu(NO3)2·3H2O and 0.4 parts of Zn(NO3)2·6H2O in 50 parts of ethylene glycol solution with a mass fraction of 60%, stir at 350 r / min for 25 min to obtain the precursor gel; S3. Modification of the precursor gel: Add 8 mL of the modification liquid obtained in step S1 to the precursor gel obtained in step S2, continuously stir at 350 r / min until a green sol is formed, and age for 10 days under normal temperature and light-shielded conditions to obtain the modified precursor gel; S4. Formation of catalyst: Liquid paraffin was added to the modified precursor gel obtained in step S3. The mass ratio of liquid paraffin to the modified precursor gel was 2:1. Under a nitrogen atmosphere of 50 mL / min, the mixture was heat-treated at 275 °C for 7 h to obtain a CuZn-based composite catalyst for the synthesis of lower alcohols from syngas.

[0020] Example 2 A preparation method of a CuZn-based composite catalyst for the synthesis of lower alcohols from syngas (in this example, each mass part is based on 1 g, ensuring that the molar ratio of Al and Ga is 2:1): S1. Preparation of the modified solution: 2.2 parts of Al(NO3)3·9H2O, 2 parts of 10% chloroplatinic acid solution and 7 parts of citric acid were dissolved in 55 parts of absolute ethanol. Ultrasonic dispersion was carried out at 70 °C for 30 min, and the ultrasonic dispersion frequency was 60 kHz. Subsequently, 0.3 part of cetyltrimethylammonium bromide and 0.8 part of sodium dodecyl sulfate were added. After stirring at a speed of 450 r / min at 53 °C for 3 h, the temperature was raised to 98 °C and maintained for 35 min to obtain the modified solution; S2. Preparation of the precursor gel: 0.655 part of Cu(NO3)2·3H2O and 0.345 part of Zn(NO3)2·6H2O were dissolved in 70 parts of the oxygen vacancy modified solvent. Stirring was carried out at a speed of 450 r / min for 30 min to obtain the precursor gel; S3. Modification of the precursor gel: 12 mL of the modified solution obtained in step S1 was added to the precursor gel obtained in step S2. Stirring was continuously carried out at a speed of 450 r / min until a green sol was formed. Aging was carried out for 10 days under normal temperature and light-shielded conditions to obtain the modified precursor gel; S4. Formation of catalyst: Liquid paraffin was added to the modified precursor gel obtained in step S3. The mass ratio of liquid paraffin to the modified precursor gel was 3:1. Under a nitrogen atmosphere of 50 mL / min, the mixture was heat-treated at 285 °C for 8 h to obtain a CuZn-based composite catalyst for the synthesis of lower alcohols from syngas.

[0021] Among them, the preparation of the oxygen vacancy modified solvent in step S2 includes the following steps: S21. 5 parts of modified hydrated gallium nitrate were dissolved in 70 parts of a 60% ethylene glycol solution by mass to obtain a preliminary mixture; S22. The preliminary mixture was ultrasonicated at 40 °C for 20 min, and the ultrasonic dispersion frequency was 60 kHz to finally obtain the oxygen vacancy modified solvent.

[0022] The preparation of the modified hydrated gallium nitrate in step S21 includes the following steps: S31. Dissolve 1 part of Ga(NO3)3·5H2O in 80 parts of a mixed solvent (a mixture of a 60% ethylene glycol solution and deionized water with a mass ratio of 3:1), add 1.5 parts of disodium ethylenediaminetetraacetate, and magnetically stir at 40 °C for 1 h to form a preliminary mixture; S32. Slowly add ammonia water until the pH of the solution is 4. After maintaining stirring for 30 min, transfer the solution to a high-pressure reaction kettle with a polytetrafluoroethylene inner lining and react at 120 °C for 4 h to obtain a secondary mixture; S33. Cool the secondary mixture obtained in step S32, centrifuge and separate it. Wash the obtained precipitate with absolute ethanol 3 times and vacuum dry it at 60 °C for 12 h to finally obtain modified hydrated gallium nitrate.

[0023] Example 3 A preparation method of a CuZn-based composite catalyst for synthesizing low-carbon alcohols from syngas (in this example, each mass part is based on 10 g, ensuring a molar ratio of Al to Ga of 1:1): S1. Preparation of the modification solution: Dissolve 1.1 parts of Al(NO3)3·9H2O, 1.6 parts of a 10% chloroplatinic acid solution, and 6.5 parts of citric acid in 50 parts of absolute ethanol, ultrasonically disperse at 65 °C for 27 min, the ultrasonic dispersion frequency is 50 kHz, then add 0.2 parts of cetyltrimethylammonium bromide and 0.6 parts of sodium dodecyl sulfate, stir at a speed of 400 r / min at 50 °C for 2.5 h, and then raise the temperature to 95 °C and maintain for 30 min to obtain the modification solution; S2. Preparation of the precursor gel: Dissolve 0.71 parts of Cu(NO3)2·3H2O and 0.29 parts of Zn(NO3)2·6H2O in 60 parts of the oxygen vacancy modification solvent, and stir at a speed of 400 r / min for 27 min to obtain the precursor gel; S3. Modification of the precursor gel: Add 10 mL of the modification solution obtained in step S1 to the precursor gel obtained in step S2, continuously stir at a speed of 400 r / min until a green sol is formed, and age for 10 days under normal temperature and dark conditions to obtain a modified precursor gel; S4. Formation of the catalyst: Add liquid paraffin to the modified precursor gel obtained in step S3, the mass ratio of liquid paraffin to the modified precursor gel is 2.5:1. Under a nitrogen atmosphere of 50 mL / min, heat-treat the mixture at 280 °C for 7.5 h to obtain a CuZn-based composite catalyst for synthesizing low-carbon alcohols from syngas.

[0024] Among them, the preparation of the oxygen vacancy modification solvent in step S2 includes the following steps: S21. Dissolve 3 parts of the modified hydrated gallium nitrate in 60 parts of a 60% ethylene glycol solution by mass to obtain a preliminary mixture; S22. Ultrasonically disperse the preliminary mixture at 35 °C for 17 min at an ultrasonic dispersion frequency of 50 kHz to finally obtain an oxygen vacancy-modified solvent.

[0025] The preparation of the modified gallium nitrate hydrate in step S21 includes the following steps: S31. Dissolve 1 part of Ga(NO3)3·5H2O in 65 parts of a mixed solvent (a mixture of a 60% ethylene glycol solution and deionized water with a mass ratio of 3:1), add 0.7 part of disodium ethylenediaminetetraacetate, and magnetically stir at 33 °C for 0.8 h to form a preliminary mixture; S32. Slowly add ammonia water until the solution pH is 3.5, maintain stirring for 22 min, then transfer the solution to a high-pressure reactor lined with polytetrafluoroethylene, and react at 112 °C for 3.5 h to obtain a secondary mixture; S33. Cool the secondary mixture obtained in step S32, centrifuge and separate it, wash the obtained precipitate with anhydrous ethanol 3 times, and vacuum dry at 56 °C for 10.5 h to finally obtain the modified gallium nitrate hydrate.

[0026] Example 4 A preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas (in this example, each mass part is based on 5 g, ensuring that the molar ratio of Al and Ga is 1:2): S1. Preparation of the modification solution: Dissolve 1.2 parts of Al(NO3)3·9H2O, 1.7 parts of 10% chloroplatinic acid solution and 6.6 parts of citric acid in 52 parts of absolute ethanol, ultrasonically disperse at 67 °C for 29 min at an ultrasonic dispersion frequency of 55 kHz, then add 0.2 part of cetyltrimethylammonium bromide and 0.7 part of sodium dodecyl sulfate, stir at a speed of 400 r / min at 52 °C for 2.5 h, and then raise the temperature to 96 °C and keep it for 33 min to obtain the modification solution; S2. Preparation of the precursor gel: Dissolve 0.764 part of Cu(NO3)2·3H2O and 0.236 part of Zn(NO3)2·6H2O in 65 parts of the oxygen vacancy-modified solvent, and stir at a speed of 400 r / min for 28 min to obtain the precursor gel; S3. Modification of the precursor gel: Add 11 mL of the modification solution obtained in step S1 to the precursor gel obtained in step S2, continuously stir at a speed of 400 r / min until a green sol is formed, and age for 10 days under normal temperature and light-shielded conditions to obtain the modified precursor gel; S4. Formation of the catalyst: Liquid paraffin was added to the modified precursor gel obtained in step S3, and the mass ratio of liquid paraffin to the modified precursor gel was 2.6:1. Under a nitrogen atmosphere of 50 mL / min, the mixture was heat-treated at 283 °C for 7.5 h to obtain a CuZn-based composite catalyst for the synthesis of lower alcohols from syngas.

[0027] Among them, the preparation of the oxygen vacancy-modified solvent in step S2 includes the following steps: S21. 4 parts of modified hydrated gallium nitrate were dissolved in 65 parts of a 60% ethylene glycol solution by mass to obtain a preliminary mixture; S22. The preliminary mixture was ultrasonically dispersed at 37 °C for 19 min, and the ultrasonic dispersion frequency was 55 kHz to finally obtain the oxygen vacancy-modified solvent.

[0028] The preparation of the modified hydrated gallium nitrate in step S21 includes the following steps: S31. 1.9 parts of Ga(NO3)3·5H2O were dissolved in 70 parts of a mixed solvent (a mixture of a 60% ethylene glycol solution and deionized water with a mass ratio of 3:1), 1 part of disodium ethylenediaminetetraacetate was added, and the mixture was magnetically stirred at 35 °C for 0.7 h to form a preliminary mixture; S32. Ammonia water was slowly added dropwise until the solution pH reached 3.4. After maintaining stirring for 25 min, the solution was transferred to a high-pressure reaction kettle lined with polytetrafluoroethylene and reacted at 115 °C for 3.5 h to obtain a secondary mixture; S33. The secondary mixture obtained in step S32 was cooled, centrifuged, and separated. The obtained precipitate was washed 3 times with absolute ethanol and vacuum dried at 58 °C for 11 h to finally obtain the modified hydrated gallium nitrate.

[0029] Example 5 A preparation method of a CuZn-based composite catalyst for the synthesis of lower alcohols from syngas (in this example, each mass part is based on 10 g): S1. Preparation of the modified liquid: 1.9 parts of a 10% chloroplatinic acid solution and 6.5 parts of citric acid were dissolved in 50 parts of absolute ethanol, ultrasonically dispersed at 65 °C for 27 min, and the ultrasonic dispersion frequency was 50 kHz. Subsequently, 0.2 part of cetyltrimethylammonium bromide and 0.6 part of sodium dodecyl sulfate were added, and the mixture was stirred at 50 °C at a rotation speed of 420 r / min for 2.5 h, then the temperature was raised to 95 °C and maintained for 30 min to obtain the modified liquid; S2. Preparation of the precursor gel: 0.82 part of Cu(NO3)2·3H2O and 0.18 part of Zn(NO3)2·6H2O were dissolved in 60 parts of the oxygen vacancy-modified solvent and stirred at a rotation speed of 420 r / min for 27 min to obtain the precursor gel; S3. Modification of the precursor gel: Add 10 mL of the modification solution obtained in step S1 to the precursor gel obtained in step S2, and continuously stir at a speed of 420 r / min until a green sol is formed. Age for 10 days under normal temperature and dark conditions to obtain a modified precursor gel; S4. Formation of the catalyst: Add liquid paraffin to the modified precursor gel obtained in step S3. The mass ratio of liquid paraffin to the modified precursor gel is 2.5:1. Under a nitrogen atmosphere of 50 mL / min, heat-treat the mixture at 280 °C for 7.5 h to obtain a CuZn-based composite catalyst for the synthesis of lower alcohols from syngas.

[0030] Among them, the preparation of the oxygen vacancy modification solvent in step S2 includes the following steps: S21. Dissolve 3 parts of modified hydrated gallium nitrate in 60 parts of a 60% ethylene glycol solution by mass to obtain a preliminary mixture; S22. Ultrasonically disperse the preliminary mixture at 35 °C for 17 min. The ultrasonic dispersion frequency is 50 kHz to finally obtain the oxygen vacancy modification solvent.

[0031] The preparation of the modified hydrated gallium nitrate in step S21 includes the following steps: S31. Dissolve 4 parts of Ga(NO3)3·5H2O in 75 parts of a mixed solvent (a mixture of a 60% ethylene glycol solution and deionized water with a mass ratio of 3:1), add 1.3 parts of disodium ethylenediaminetetraacetate, and magnetically stir at 38 °C for 0.9 h to form a preliminary mixture; S32. Slowly add ammonia water until the solution pH is 3.6. After maintaining stirring for 28 min, transfer the solution to a high-pressure reaction kettle with a polytetrafluoroethylene inner liner and react at 118 °C for 3.6 h to obtain a secondary mixture; S33. Cool the secondary mixture obtained in step S32, centrifuge and separate it. Wash the obtained precipitate with absolute ethanol 3 times and vacuum dry it at 59 °C for 11.5 h to finally obtain the modified hydrated gallium nitrate.

[0032] In the performance test and characterization test, the CuZn-based composite catalyst for the synthesis of lower alcohols from syngas is named CZA x G y , where x and y represent the molar ratios of Al and Ga respectively. In the following performance test and characterization test, the CuZn-based composite catalysts for the synthesis of lower alcohols from syngas obtained in Examples 1-5 are named CZA, CZA2G1, CZA1G1, CZA1G2, and CZG respectively.

[0033] Performance test: The CuZn-based composite catalyst for synthesizing lower alcohols from syngas prepared in Examples 1-5 was supplemented with liquid paraffin to 300 mL, and then placed in a reactor. The temperature was 280 °C, the pressure was 4 MPa, and the syngas entered the reactor at a flow rate of 150 mL / min. The reaction was carried out while maintaining the ratio of n(H2) / n(CO) at 2. During the reaction process, a Hisense GC-950 chromatograph was used to analyze the composition of the products. In the gas-phase products, the organic components (C1-C5 hydrocarbons, dimethyl ether, methanol, ethanol) were analyzed online by a flame ionization detector (FID detector, HP-PLOT / Q column), and the inorganic components (H2, CO, CH4, CO2) were analyzed online by a thermal conductivity detector (TCD detector, TDX-01 column). The alcohols in the liquid-phase products were detected offline by an FID detector (HP-INNOWAX column). The external standard method was used for quantitative analysis of the content of each component in the products. The CO conversion rate and product selectivity were calculated as follows: , , where i represents all C-containing compounds except CO in the gas-phase and liquid-phase products, n(CO) out represents the amount of CO in the outlet gas (mol), and n i (g) and n i (I) represent the number of carbon atoms of component i in the outlet gas and liquid phase (mol), respectively; S(i) represents the selectivity of the catalyst for product i, S(lower alcohols) = S(ethanol) + S(propanol) + S(butanol) + S(pentanol) + S(hexanol), Space-time yield (STY, g·g -1 ·h -1 ) = (total alcohol mass / catalyst mass) / reaction time, S(total alcohols) = S(methanol) + S(ethanol) + S(propanol) + S(butanol) + S(pentanol) + S(hexanol), C 2+ alcohol / total alcohols = S(lower alcohols) / S(total alcohols), and the results are shown in Table 1 below: Table 1 Catalytic performance of the catalyst for synthesizing lower alcohols from syngas at 280 °C, 4 MPa, n(H2) / n(CO) = 2.0, and 150 mL / min

[0034] The CZG catalyst (Cu particles with a size of 27.3 nm) exhibits the highest CO conversion rate (56.4%) and lower alcohol selectivity (76.5%), verifying that smaller Cu particles are beneficial to improving the exposure of active sites and the oxygen vacancy effect. The lower alcohol selectivity of the Ga-containing catalysts (CZA1G2, CZG) is significantly improved, indicating that the oxygen vacancies introduced by Ga promote CO adsorption and C-C coupling and inhibit the formation of by-products such as methane. The comparison between CZA2G1 (molar ratio of Al to Ga is 2:1) and CZA1G2 (molar ratio of Al to Ga is 1:2) shows that a higher Ga content is more conducive to improving the lower alcohol selectivity.

[0035] Characterization tests: 1. X-ray diffraction analysis Attached Figure 2 is the X-ray diffraction (XRD) pattern of the CuZn-based composite catalysts prepared in Examples 1-5 for the synthesis of lower alcohols from syngas. Three distinct diffraction peaks appear at 43.4°, 50.5° and 74.2°, corresponding to the Cu (111), (200) and (220) crystal planes respectively. These diffraction peaks are caused by the reduction of CuO by carbon / hydrogen free radicals generated from the decomposition of liquid paraffin during the heat treatment of the catalyst precursor. No signal peak of ZnO is observed, indicating that ZnO exists in an amorphous form or is below the detection limit of XRD. There is a weak carbon peak at 23.6°, indicating the decomposition of liquid paraffin. No diffraction peaks corresponding to Al and Ga are observed in the catalyst, indicating that they exist in a highly dispersed form or are encapsulated in the ZnO matrix.

[0036] 2. Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and particle size analysis TEM and HRTEM were used to study the microstructure and affinity of Cu and ZnO in the products obtained in Examples 1-5. As attached Figure 3 (a3-e3) shows. We can observe that black spherical nanoparticles exist in all catalysts. These nanoparticles correspond to Cu, and the average particle sizes of Cu in the CZA, CZA2G1, CZA1G1, CZA1G2 and CZG catalysts are 33.2 nm, 32.9 nm, 48.2 nm, 30.3 nm and 27.3 nm respectively. Although the Cu particle sizes obtained by TEM analysis are larger than those obtained by XRD analysis, their changing trends are consistent, so there is no essential difference in the conclusions. In addition, the microstructure of Cu and ZnO was observed through HRTEM images (attached Figure 3 (a2-e2)). The lattice spacings of 0.21 nm and 0.25 nm correspond to the Cu (111) and ZnO (101) planes respectively, and these two substances are adjacent, which helps to induce a strong Cu / ZnO interaction, thus promoting the formation of catalytic active sites during the hydrogenation of CO to lower alcohols.

[0037] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas, characterized in that, It includes the following preparation steps: S1. Preparation of the modification solution: Dissolve 0.8 - 2.2 parts of Al(NO3)3·9H2O, 1.5 - 2 parts of 10% chloroplatinic acid solution, and 6 - 7 parts of citric acid in 45 - 55 parts of absolute ethanol, ultrasonically disperse at 60 - 70 °C for 25 - 30 min, then add 0.1 - 0.3 parts of cetyltrimethylammonium bromide and 0.5 - 0.8 parts of sodium dodecyl sulfate, stir at 48 - 53 °C for 2 - 3 h, then raise the temperature to 92 - 98 °C and maintain for 25 - 35 min to obtain the modification solution; S2. Preparation of the precursor gel: Dissolve 0.6 - 0.82 parts of Cu(NO3)2·3H2O and 0.18 - 0.4 parts of Zn(NO3)2·6H2O in 50 - 70 parts of the oxygen vacancy modification solvent, stir for 25 - 30 min to obtain the precursor gel; S3. Modification of the precursor gel: Add 8 - 12 parts of the modification solution obtained in step S1 to the precursor gel obtained in step S2, continuously stir until a green sol is formed, and age for 10 days to obtain the modified precursor gel; S4. Formation of the catalyst: Add liquid paraffin to the modified precursor gel obtained in step S3, under a nitrogen atmosphere of 50 mL / min, heat-treat the mixture for 7 - 8 h to obtain a CuZn-based composite catalyst for the synthesis of lower alcohols from syngas.

2. The preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas according to claim 1, characterized in that, The preparation of the oxygen vacancy modification solvent in step S2 includes the following steps: S21. Dissolve 3 - 5 parts of modified gallium nitrate hydrate in 50 - 70 parts of a 60% ethylene glycol solution by mass to obtain a preliminary mixture; S22. Ultrasonically disperse the preliminary mixture at 30 - 40 °C for 15 - 20 min, and the ultrasonic dispersion frequency is 40 - 60 kHz to finally obtain the oxygen vacancy modification solvent.

3. The preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas according to claim 2, characterized in that, The preparation of the modified gallium nitrate hydrate in step S21 includes the following steps: S31. Dissolve 2 - 5 parts of Ga(NO3)3·5H2O in 60 - 80 parts of a mixed solvent, add 0.5 - 1.5 parts of disodium ethylenediaminetetraacetate, magnetically stir at 30 - 40 °C for 0.5 - 1 h to form a preliminary mixture; S32. Slowly add ammonia water until the solution pH is 3 - 4, maintain stirring for 20 - 30 min, then transfer the solution to a high-pressure reaction kettle with a polytetrafluoroethylene inner lining, react at 110 - 120 °C for 3 - 4 h to obtain a secondary mixture; S33. Cool the secondary mixture obtained in step S32, centrifuge and separate, wash the obtained precipitate with absolute ethanol 3 times, and vacuum dry at 55 - 60 °C for 10 - 12 h to finally obtain the modified gallium nitrate hydrate.

4. The preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas according to claim 3, characterized in that, In step S31, the mixed solvent is a mixed solution of a 60% ethylene glycol solution by mass and deionized water, and the mass ratio of the 60% ethylene glycol solution to deionized water is 3:

1.

5. The preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas according to claim 1, characterized in that, The stirring speed in steps S1, S2, and S3 is 350 - 450 r / min.

6. The preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas according to claim 1, characterized in that, The aging condition in step S3 is normal temperature and light avoidance.

7. The preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas according to claim 1, characterized in that, In step S4, the mass ratio of liquid paraffin to the modified precursor gel is 2 - 3:

1.

8. The preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas according to claim 1, characterized in that, The ultrasonic dispersion frequency in step S1 is 40 - 60 kHz.

9. The preparation method of a CuZn-based composite catalyst for synthesizing lower alcohols from syngas according to claim 1, characterized in that, The temperature of the heat treatment in step S4 is 275 - 285 °C.

10. A CuZn-based composite catalyst for synthesizing lower alcohols from syngas, characterized in that: The CuZn-based composite catalyst for synthesizing lower alcohols from syngas is prepared by the preparation method described in any one of claims 1-9 above.

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