A catalyst for the hydrogenation of carbon dioxide to synthesize lower alcohols, a preparation method thereof, and applications thereof

Abstract

The present invention relates to the technical field of hydrogenation of carbon dioxide to synthesize lower alcohols, and specifically relates to a catalyst for catalytic hydrogenation of carbon dioxide to prepare lower alcohols, a preparation method thereof, and an application thereof. It can broaden the application field of noble metals in the hydrogenation of carbon dioxide to lower alcohols. In the present invention, an iron salt solution is used as a precursor, and Fe oxides are prepared by a sol-gel method or a precipitation method, and then noble metal Pd is loaded, and the PdFe / Fe3O4 catalyst can be obtained through high-temperature reduction. The catalyst provided by the present invention can achieve a maximum conversion rate of 40.9% for catalytic hydrogenation of CO2 to synthesize lower alcohols, a maximum selectivity of 19.1% for lower alcohols, and a maximum space-time yield of lower alcohols that can reach 87.8 mg g cat ‑1 h ‑1 。

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dioxide hydrogenation to synthesize lower alcohols, and particularly relates to a catalyst for catalytic carbon dioxide hydrogenation to synthesize lower alcohols, a preparation method thereof, and an application thereof, so as to effectively improve the selectivity of lower alcohols in the product and the space-time yield of lower alcohols. Background Art

[0002] The conversion of CO2 into high-value chemical energy has important application prospects. At present, the preparation of alcohol compounds by CO2 hydrogenation has been widely studied, and most of them are mainly methanol. Compared with methanol, lower alcohols (C2-C5 alcohols) can be directly used as high-quality power fuels, and due to the presence of oxygen in the alcohols, they burn more fully and are environmentally friendly fuels. Secondly, the blending of lower alcohols with gasoline can expand the gasoline supply and improve the octane number level, and has excellent anti-explosion and anti-knock performance. In addition to the above uses as fuels and additives, these lower alcohols are also good solvents and industrial raw materials in chemical production. The conversion of CO2 hydrogenation into lower alcohol liquid fuels is an extremely attractive research direction, but due to the complex reactions involved, the high-selectivity preparation of lower alcohols is still a severe challenge.

[0003] In the reaction of CO2 hydrogenation to prepare lower alcohols, there are many parallel and consecutive reactions. And due to the chemical inertness of CO2 molecules and the high C-C coupling energy barrier, the activation and controllable conversion of CO2 are extremely challenging. Therefore, lower alcohol synthesis catalysts generally require the synergistic cooperation of multiple components. For example, lower alcohol synthesis catalysts such as K-CuMgZnFe, K-CuZnAl / Na-Fe@C, KCuFeZn-CuZnAlZr, NaCo-Si3N4, RhNa-TiO2, etc. developed by scientific researchers. These catalysts generally require alkali metal modification, and phase separation problems will occur during the reaction, resulting in a decrease in catalyst activity. The catalyst components are complex and it is difficult to clearly explain the role of active sites. In particular, the role of alkali metals has not been fully determined at present. Therefore, it is necessary to further develop a catalytic system with relatively simple components and high activity.

[0004] Therefore, the present invention has developed a novel PdFe-based catalytic system. Through reduction and in-situ carbonization, a catalyst with two active phases of iron carbide species and PdFe alloy species is obtained, which has high lower alcohol synthesis activity. Compared with other types of catalysts, this type of catalyst has simple structure and components and high activity, and has very important academic research and application value. Summary of the Invention

[0005] The object of the present invention is to provide a catalyst for catalytic carbon dioxide hydrogenation to synthesize lower alcohols, a preparation method thereof, and an application thereof in view of the deficiencies of the prior art.

[0006] To achieve the above-mentioned invention object, the technical solution provided by the present invention is as follows:

[0007] A preparation method of a catalyst for catalytic hydrogenation of carbon dioxide to synthesize lower alcohols, comprising the following steps:

[0008] (1) Take a certain mass, according to the Pd mass fraction of 0.1 wt% to 20 wt%, take a certain amount of Pd salt solution, and add it to FeO x powder of iron oxide (FeO x );

[0009] (2) Stir, evaporate the water, and dry to obtain a powder sample;

[0010] (3) Put the obtained powder sample into a muffle furnace and calcine it for 0.5 - 9 h at a calcination temperature of 300 - 700 °C, and collect the sample after cooling.

[0011] Preferably, the Pd salt compound used is one or a mixture of palladium nitrate, palladium chlorate, and palladium acetate, and the solvent used for preparing the solution is one or a mixed solvent of water, methanol, and ethanol, and the concentration of the prepared Pd salt solution is 0.001 - 0.05 g·mL -1 .

[0012] Preferably, Pd is taken according to the Pd mass fraction of 5 wt% - 15 wt% of the iron oxide (FeO x ) powder to take Pd salt. It has better activity for synthesizing lower alcohols.

[0013] According to the above scheme, the step (2) is: after stirring for 0.5 - 5 h, evaporate the water, the evaporation temperature is 30 - 100 °C, and send it into a vacuum drying oven for drying, and the drying temperature is 30 - 120 °C.

[0014] According to the above scheme, the calcination heating rate in the step (3) is 1 - 15 °C·min -1 .

[0015] According to the above scheme, the above preparation method further includes step (4): reducing the sample obtained in step (3) in an atmosphere containing H2 to obtain a PdFe alloy catalyst supported on FeO x Preferably, the reduction conditions are: at a gas hourly space velocity of 2000 - 15000 mL g -1 h -1 , a reduction temperature of 300 - 400 °C, and a reduction heating rate of 1 - 8 °C min -1 , and perform atmospheric pressure reduction for 1 - 3 h under these conditions.

[0016] According to the above scheme, the above preparation method further includes step (5): the FeO reduced in step (4) xThe supported PdFe alloy catalyst is carbonized to completely transform it into PdFe alloy and Fe5C2 active components, obtaining a catalyst with iron carbide species and PdFe alloy species as the main active phases.

[0017] According to the above scheme, in step (5), preferably, the carbonization pressure is 1 - 5 MPa, the carbonization temperature is 300 - 400 °C, the carbonization time is 1 - 3 h, and the gas hourly space velocity is 3000 - 12000 mL g -1 h -1 。

[0018] Preferably, the particle size of the iron oxide (FeO x , including one or more iron oxides among Fe3O4, Fe2O3 or FeO) is 10 - 150 nm, and it is prepared by the propylene oxide sol - gel method, PVP sol - gel method or precipitation method.

[0019] Preferably, the main process of the propylene oxide sol - gel method is as follows: A certain amount of iron salt is added to the corresponding solvent, and stirring and ultrasonic treatment are repeated multiple times to dissolve and mix it evenly; According to the molar ratio of iron to 1,2 - propylene oxide being 1:(0.1 - 10), a certain molar amount of 1,2 - propylene oxide is taken; Under stirring conditions, 1,2 - propylene oxide is added to the beaker and stirred for 1 - 40 min; Then the solution is poured into the polytetrafluoroethylene inner liner of the hydrothermal autoclave for reaction, the temperature is 100 - 250 °C, and it is maintained for 1 - 50 h; After cooling, the polytetrafluoroethylene inner liner is taken out and dried in an oven at 40 - 100 °C for 8 - 48 h; After the liquid inside the inner liner has evaporated, the oven temperature is raised to 150 - 250 °C and dried for 0.5 - 6 h; After cooling, the obtained solid powder is ground and collected, and then put into a muffle furnace for calcination: The temperature is raised to 300 - 700 °C and maintained for 0.5 - 7 h, and then naturally cooled to room temperature for collection and standby. Preferably, the calcination heating rate is 1 - 10 °C·min -1 。

[0020] Preferably, the iron salt is one or a mixture of ferric nitrate nonahydrate, ferric sulfate, ferric chloride and ferric acetate.

[0021] Preferably, the Fe salt dispersion solvent is one or a mixture of solvents such as water, methanol, ethanol, butanol, isopropanol and ethylene glycol;

[0022] Preferably, the addition rate of 1,2 - propylene oxide is 1 - 10 d·s -1 ;

[0023] The main process of the PVP sol-gel method is as follows: Add ferric salt and polyvinylpyrrolidone (PVP) to a solvent according to a molar ratio of Fe3+ to PVP monomers of 1:(0.1 - 10), and dissolve under heating and stirring; Evaporate the solvent at 30 - 100 °C until a gel is formed; Transfer the obtained gel to an oven for drying to obtain a dried product, grind it into powder and collect it; Heat up to 300 - 700 °C and hold for 0.5 - 7 h, then naturally cool to room temperature and collect for standby. Preferably, the heating rate is 1 - 10 °C·min -1 。

[0024] The solvent used in the PVP sol-gel method is one or a mixture of more than one of water, methanol, ethanol, butanol, isopropanol and ethylene glycol;

[0025] The ferric salt used in the PVP sol-gel method is one or a mixture of more than one of ferric nitrate, ferric sulfate, ferric chloride and ferric acetate.

[0026] The K value of the PVP used in the PVP sol-gel method is 10 - 100, and the molecular weight is between 3000 - 1500000;

[0027] The main process of the precipitation method is as follows: Add a certain amount of ferric salt to a solvent, stir and repeat ultrasonic treatment several times to dissolve and mix evenly, stir at a certain temperature (30 - 100 °C), add a basic precipitating agent with a concentration of 0.01 - 5 mol·L -1 for precipitation until the system pH reaches 3 - 8, continue aging for 0.5 - 5 h, adjust to pH 5 - 7.5 with deionized water, centrifuge and filter to obtain a solid, place it in an oven and dry at 40 - 90 °C for 6 - 12 h; Take out, grind into powder, and calcine in a muffle furnace: Heat up to 300 - 700 °C and hold for 0.5 - 7 h, then naturally cool to room temperature and collect for standby. Preferably, the calcination heating rate is 1 - 10 °C·min -1 。

[0028] The ferric salt used in the precipitation method is one or a mixture of more than one of ferric nitrate, ferric sulfate, ferric chloride and ferric acetate;

[0029] The solvent used in the precipitation method is one or a mixture of more than one of water, methanol and ethanol;

[0030] The basic precipitating agent in the precipitation method is an aqueous solution of one or a mixture of more than one of potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, potassium bicarbonate, sodium bicarbonate, ammonium bicarbonate, ammonium carbonate and ammonia water;

[0031] The addition rate of the precipitating agent in the precipitation method is 0.1 - 6 mL·min -1 。

[0032] A method for catalytically synthesizing lower alcohols from CO2, using the above catalyst to catalytically synthesize lower alcohols from CO2.

[0033] According to the above scheme, the above method includes carbonizing the catalyst prepared by reduction with an atmosphere containing CO2 / H2 and then catalytically synthesizing lower alcohols from CO2. Preferably, the carbonization pressure is 1-5 MPa, the carbonization temperature is 300-400 °C, the carbonization time is 1-3 h, and the gas hourly space velocity is 3000-12000 mL g -1 h -1 。

[0034] According to the above scheme, the reaction gas is a CO2 / H2 / inert gas mixture, and lower alcohols are catalytically synthesized under the conditions of a reaction pressure of 3-7 MPa and a reaction temperature of 280-330 °C.

[0035] Furthermore, the inert gas in the CO2 / H2 / inert gas mixture includes but is not limited to N2; the ratio of CO2 to H2 is 1:3, the proportion of the inert gas is 2%-6%, and the gas hourly space velocity is 3000-6000 mL g -1 cat h -1 。

[0036] A catalyst for catalytically synthesizing lower alcohols by hydrogenating carbon dioxide, which contains active phases of iron carbide Fe5C2 species and PdFe alloy species.

[0037] Advantages of the present invention:

[0038] (1) In the present invention, PdO / FeO is first prepared and obtained, x , and then PdFe / Fe3O4 is in-situ reduced, and then carbonized to be completely transformed into active components of PdFe alloy and Fe5C2. In the process of catalytically hydrogenating CO2 to prepare lower alcohols with this PdFe-Fe5C2 catalyst, PdFe plays a similar role to Cu and can produce CO through the RWGS reaction and non-dissociatively activate CO, while Fe5C2 can dissociatively activate CO and further complete carbon chain growth. Thus, efficient conversion of CO2 hydrogenation to lower alcohols is achieved through the synergistic cooperation of the two components.

[0039] (2) The CO2 conversion rate of the catalytic synthesis method provided by the present invention can reach up to 40.9%, the selectivity of lower alcohols can reach up to 19.1%, and the space-time yield of lower alcohols can reach up to 87.8 mg g cat -1 h -1 。 Description of the drawings

[0040] Figure 1 For 10.4Pd-FeO prepared in Example 6x In-situ XRD pattern of the catalyst during hydrogen reduction at 350 °C

[0041] Figure 2 For the 10.4Pd-FeO prepared in Example 6 x In-situ XRD pattern of the catalyst during the CO2 / H2 reaction at 320 °C Specific implementation manners

[0042] The following describes the specific implementation manners in detail in conjunction with the following examples and the attached drawings and tables, but it should be understood that the protection scope of the present invention is not limited by the specific implementation manners. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. All raw materials used in the examples are obtained commercially.

[0043] Example 1

[0044] Weigh 5.656 g of iron(III) nitrate nonahydrate and dissolve it in 50 mL of ethanol. Ultrasonically stir to dissolve and mix evenly. At the same time, use a pipette to transfer 2 mL of 1,2-epoxypropane and add it to the beaker under stirring at a rate of 3 d·s -1 After stirring for 10 min, pour the solution into the polytetrafluoroethylene inner liner of a 100 mL hydrothermal autoclave, tighten it, and place it in an oven at 150 °C for 20 h. After cooling, take out the polytetrafluoroethylene inner liner and place it in an oven at 60 °C for drying for 24 h. After the liquid inside the inner liner has evaporated, raise the oven temperature to 200 °C and dry for 3 h. Wait for natural cooling, grind and collect the obtained solid powder, put it into a muffle furnace for calcination. The calcination conditions are to heat from room temperature to 600 °C at a rate of 5 °C / min, hold for 4 h, and then naturally cool to room temperature to collect FeO x powder. Then perform the CO2 hydrogenation catalytic performance test. Catalytic test conditions: Take 0.2 g of the catalyst, reduce it at 350 °C for 1 h in a H2 / Ar atmosphere, then cool it down to 320 °C, use a CO2 / H2 mixed gas at 5 MPa, and carbonize it for 3 h at a gas flow rate of 20 mL / min. Subsequently, carry out the reaction of CO2 hydrogenation to produce lower alcohols at 300 °C, 5 MPa, and 6000 mL g cat -1 h -1 The reaction is carried out under the conditions of, and the gas used is CO2 / H2 / N2 (24 / 72 / 4). The specific test performance is shown in Table 1.

[0045] Example 2

[0046] Weigh a certain amount of the FeO x powder in Example 1. According to a Pd loading of 0.1 wt%, take a certain volume of a solution with a concentration of 10 mg·mL -1Palladium nitrate solution was added to FeO x powder, stirred for 5 h, the water was evaporated to dryness at 110 °C, and then dried at 100 °C for 12 h. It was calcined at 300 °C in a muffle furnace at a heating rate of 1 °C·min -1 for 2 h, and the sample was collected after cooling. 0.1Pd / FeO x catalyst was prepared. Then the catalytic performance test of CO2 hydrogenation was carried out. The catalytic test conditions were the same as those in Example 1, and the specific test performance is shown in Table 1.

[0047] Example 3

[0048] A certain amount of FeO powder in Example 1 was weighed. According to the Pd loading of 0.9 wt%, a certain volume of palladium nitrate solution with a concentration of 10 mg·mL x was taken and added to the FeO -1 powder, stirred for 5 h, the water was evaporated to dryness at 110 °C, and then dried at 100 °C for 12 h. It was calcined at 300 °C in a muffle furnace at a heating rate of 1 °C·min x for 2 h, and the sample was collected after cooling. 0.9Pd / FeO -1 catalyst was prepared. Then the catalytic performance test of CO2 hydrogenation was carried out. The catalytic test conditions were the same as those in Example 1, and the specific test performance is shown in Table 1. x catalyst was prepared. Then the catalytic performance test of CO2 hydrogenation was carried out. The catalytic test conditions were the same as those in Example 1, and the specific test performance is shown in Table 1.

[0049] Example 4

[0050] A certain amount of FeO powder in Example 1 was weighed. According to the Pd loading of 4.3 wt%, a certain volume of palladium nitrate solution with a concentration of 10 mg·mL x was taken and added to the FeO -1 powder, stirred for 5 h, the water was evaporated to dryness at 110 °C, and then dried at 100 °C for 12 h. It was calcined at 300 °C in a muffle furnace at a heating rate of 1 °C·min x for 2 h, and the sample was collected after cooling. 4.3Pd / FeO -1 catalyst was prepared. Then the catalytic performance test of CO2 hydrogenation was carried out. The catalytic test conditions were the same as those in Example 1, and the specific test performance is shown in Table 1. x catalyst was prepared. Then the catalytic performance test of CO2 hydrogenation was carried out. The catalytic test conditions were the same as those in Example 1, and the specific test performance is shown in Table 1.

[0051] Example 5

[0052] A certain amount of FeO powder in Example 1 was weighed. According to the Pd loading of 6.9 wt%, a certain volume of palladium nitrate solution with a concentration of 10 mg·mL x was taken and added to the FeO -1 powder, stirred for 5 h, the water was evaporated to dryness at 110 °C, and then dried at 100 °C for 12 h. It was calcined at 300 °C in a muffle furnace at a heating rate of 1 °C·min x for 2 h, and the sample was collected after cooling. 6.9Pd / FeO -1The temperature was raised to 300℃ and calcined for 2 h. The sample was collected after cooling. x Catalyst. Then, the catalytic performance test of CO2 hydrogenation was carried out. The catalytic test conditions were the same as those in Example 1, and the specific test performance is shown in Table 1.

[0053] Example 6

[0054] Weigh a certain amount of FeO in Example 1 x Powder, according to the Pd loading of 10.4wt%, a certain volume concentration of 10mg·mL -1 Palladium nitrate solution, added to FeO x The powder was stirred for 5 h, the water was evaporated at 110 °C, and the drying was continued at 100 °C for 12 h. -1 The temperature was raised to 300℃ and calcined for 2h. The sample was collected after cooling. x Catalyst. Then, the catalytic performance test of CO2 hydrogenation was carried out. The catalytic test conditions were the same as those in Example 1, and the specific test performance is shown in Table 1.

[0055] 10.4Pd-FeO prepared in Example 6 x The in-situ XRD pattern of the catalyst during hydrogen reduction at 350°C is shown in Figure 1 .like Figure 1 As shown, 10.4Pd-FeO x During the reduction process of the catalyst at 350℃, Fe2O3 can be completely transformed into Fe3O4 within 20 minutes. Since the further reduction of Fe3O4 requires a higher reduction temperature, no metallic Fe species are formed. It is noted that the diffraction peak of the Pd species at around 40° shifts to a higher angle, indicating that the Pd species is slowly alloyed during reduction.

[0056] 10.4Pd-FeO prepared in Example 6 x The in-situ XRD spectrum of the catalyst during the CO2 / H2 reaction at 320°C is shown in Figure 2 . Figure 2 It shows that when the catalyst is reduced for 3 hours and the gas is switched to CO2 / H2, the intensity of the Fe3O4 diffraction peak decreases significantly after 10 minutes, accompanied by the formation of a large number of Fe5C2 species. Fe3O4 completes the complete carbonization process within 20 minutes, and at this time the catalyst contains only two components, PdFe-Fe5C2. In the CO2 hydrogenation process, PdFe plays a similar role to Cu in that it can produce CO through the RWGS reaction and non-dissociative activation of CO, while Fe5C2 can dissociatively activate CO and further complete the carbon chain growth. The PdFe-Fe5C2 catalyst thus achieves efficient conversion of CO2 hydrogenation to low-carbon alcohols through the synergistic cooperation of the two components.

[0057] Example 7

[0058] Take the 6.9Pd / FeO catalyst in Example 5 x and raise the reaction temperature to 320 °C, with other reaction conditions the same as in Example 1.

[0059] Table 1 Catalytic performance test data of Examples 1 - 7

[0060]

[0061] As can be seen from the data in Table 1, compared with the FeO catalyst prepared in Example 1, better still, the high - loading Pd catalysts prepared in Examples 4 - 6 can significantly improve the selectivity and yield of lower - carbon alcohols. The Pd / FeO catalyst prepared in Example 5 has the best catalytic effect on lower - carbon alcohols, and when the reaction temperature is increased, the reaction performance is further improved. x catalyst, the high - loading Pd catalysts prepared in Examples 4 - 6 can significantly improve the selectivity and yield of lower - carbon alcohols, and the Pd / FeO x catalyst prepared in Example 5 has the best catalytic effect on lower - carbon alcohols, and when the reaction temperature is increased, the reaction performance is further improved.

[0062] Example 8

[0063] Weigh 5 g of polyvinylpyrrolidone (PVP) with a molecular mass of 360,000 and add it to 100 mL of deionized water. Heat and dissolve it, then add 3.03 g of ferric nitrate nonahydrate, stir for 2 h, evaporate the water at 110 °C to form a gel, place it in a drying oven at 100 °C for 12 h, grind it, and put it into a muffle furnace for calcination. The calcination conditions are heating at 2 °C·min -1 to 150 °C and holding for 2 h, then continue heating to 350 °C and calcining for 4 h. Then weigh 0.3 g of the above - prepared FeO x powder. According to a Pd loading of 8 wt%, take a certain volume of palladium nitrate solution with a concentration of 10 mg·mL -1 and add it to the FeO x powder, stir for 3 h, evaporate the water at 60 °C until dry, and continue vacuum - drying at 80 °C for 12 h. Heat in a muffle furnace at 1 °C·min -1 to 300 °C and calcine for 2 h, and collect the sample after cooling. Prepare a 6.9Pd / FeO x -6P catalyst for synthesizing lower - carbon alcohols from carbon dioxide. The catalytic test conditions are the same as in Example 1, and the specific test performance is shown in Table 2.

[0064] Example 9

[0065] Weigh 5 g of polyvinylpyrrolidone (PVP) with a molecular mass of 360,000 and add it to 100 mL of deionized water. Heat and dissolve it, then add 6.06 g of ferric nitrate nonahydrate, stir for 2 h, evaporate the water at 110 °C to form a gel, place it in a drying oven at 100 °C for 12 h, grind it, and put it into a muffle furnace for calcination. The calcination conditions are heating at 2 °C·min -1Heat to 150 °C and hold for 2 h, then continue to heat to 350 °C and calcine for 4 h. Then weigh 0.3 g of the prepared FeO obtained above x powder. According to the Pd loading of 8 wt%, take a certain volume of palladium nitrate solution with a concentration of 10 mg·mL -1 , add it to the FeO x powder, stir for 3 h, evaporate the water at 60 °C until dry, and continue vacuum drying at 80 °C for 12 h. In a muffle furnace, heat at 1 °C·min -1 to 300 °C and calcine for 2 h, and collect the sample after cooling. Prepare a carbon dioxide synthesis of lower alcohols catalyst of 6.9Pd / FeO x -3P. The catalytic test conditions are the same as those in Example 1, and the specific test performance is shown in Table 2.

[0066] Example 10

[0067] Weigh 5 g of polyvinylpyrrolidone (PVP) with a molecular mass of 360,000 and add it to 100 mL of deionized water, heat to dissolve, add 6.06 g of ferric nitrate nonahydrate, stir for 2 h, evaporate the water at 110 °C to form a gel, place it in a drying oven at 100 °C and dry for 12 h, grind it, and place it in a muffle furnace for calcination. The calcination conditions are heating at 2 °C·min -1 to 150 °C and hold for 2 h, then continue to heat to 600 °C and calcine for 4 h. Then weigh 0.3 g of the prepared FeO obtained above x powder. According to the Pd loading of 8 wt%, take a certain volume of palladium nitrate solution with a concentration of 10 mg·mL -1 , add it to the FeO x powder, stir for 3 h, evaporate the water at 60 °C until dry, and continue vacuum drying at 80 °C for 12 h. In a muffle furnace, heat at 1 °C·min -1 to 300 °C and calcine for 2 h, and collect the sample after cooling. Prepare a carbon dioxide synthesis of lower alcohols catalyst of 6.9Pd / FeO x -3P(600). The catalytic test conditions are the same as those in Example 1, and the specific test performance is shown in Table 2.

[0068] Example 11

[0069] Weigh 5.656 g of ferric nitrate nonahydrate and dissolve it in 50 mL of water, stir ultrasonically to dissolve and mix evenly, add ammonia water at a rate of 3 mL·min -1 at 80 °C until the pH of the system is 8 - 9, age for 3 h, wash the precipitate with deionized water to 7.0, centrifuge and filter to obtain a solid, dry at 80 °C for 12 h, grind it; place it in a muffle furnace for calcination, heat at 2 °C·min -1 to 350 °C and hold for 4 h, then naturally cool to room temperature, collect and reserve. Then weigh 0.3 g of the prepared FeO obtained above xPowder. According to a Pd loading of 8 wt%, a certain volume of palladium nitrate solution with a concentration of 10 mg·mL -1 was added to the FeO x powder, stirred for 3 h, the water was evaporated to dryness at 60 °C, and then further vacuum dried at 80 °C for 12 h. It was calcined in a muffle furnace at a heating rate of 1 °C·min -1 to 300 °C for 2 h, and the sample was collected after cooling. The 6.9Pd / FeO x -(ammonia) carbon dioxide synthesis of lower alcohols catalyst was prepared. The catalytic test conditions were the same as those in Example 1, and the specific test performance is shown in Table 2.

[0070] Example 12

[0071] Take the 6.9Pd / FeO x -6P catalyst prepared in Example 8, and raise the reaction temperature to 320 °C, and other reaction conditions are the same as those in Example 1.

[0072] Table 2 Catalytic performance test data of Examples 8 - 12

[0073]

[0074] The above results show that: The Pd catalysts supported on FeO x obtained by different preparation methods all have good catalytic performance for the hydrogenation of carbon dioxide to synthesize lower alcohols.

[0075] The present invention can broaden the application field of noble metals in the hydrogenation of carbon dioxide to produce lower alcohols. Specifically, the present invention uses an iron salt solution as a precursor, prepares Fe oxides by methods such as sol-gel method or precipitation method, then loads the noble metal Pd, and can obtain a PdFe / Fe3O4 catalyst through high-temperature reduction, and further reduction and post-reduction carbonization steps can be implemented as needed. The PdFe-based catalyst provided thereby can directly and efficiently synthesize high-value-added alcohol fuels such as lower alcohols (including ethanol, propanol, butanol) for the catalytic hydrogenation of carbon dioxide. Among them, the regulation of Pd loading and the synthesis method and particle size of Fe oxides can adjust the synthesis performance of lower alcohols.

[0076] The foregoing description of specific exemplary embodiments of the present invention is for the purposes of illustration and exemplification. These descriptions are not intended to limit the invention to the precise forms disclosed, and obviously, many changes and variations are possible in light of the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical applications, so that those skilled in the art can implement and utilize various different exemplary embodiments of the present invention, as well as various different selections and changes. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A preparation method of a catalyst for catalytic hydrogenation of carbon dioxide to synthesize lower alcohols, characterized in that: It includes the following steps: (1) Take a certain mass of iron oxide powder. According to the Pd mass fraction of 0.1 wt% to 20 wt%, take a certain amount of Pd salt solution and add it to the iron oxide powder; (2) Stir, evaporate the water to dryness, and dry to obtain a powder sample; (3) Put the obtained powder sample into a muffle furnace and calcine it for 0.5 - 9 h at a calcination temperature of 300 - 700 °C. After cooling, collect the sample; (4): The sample obtained in step (3) is reduced in an atmosphere containing H2 to obtain FeO x Supported PdFe alloy catalyst; (5): The FeO obtained by restoring step (4) x The supported PdFe alloy catalyst is carbonized. Specifically, the catalyst prepared by reduction is carbonized using an atmosphere containing CO2 / H2, so that it is completely transformed into PdFe alloy and Fe5C2 active components, and a catalyst with iron carbide species and PdFe alloy species as the main active phases is obtained.

2. The preparation method according to claim 1, wherein: The Pd salt compound used is one or a mixture of palladium nitrate, palladium chlorate, and palladium acetate, and the solvent used to prepare the solution is one or a mixed solvent of water, methanol, and ethanol. The concentration of the prepared Pd salt solution is 0.001-0.05 g·mL -1 ; The step (2) is: after stirring for 0.5 - 5 h, evaporate the water to dryness at an evaporation temperature of 30 - 100 °C, and send it into a vacuum drying oven for drying at a drying temperature of 30 - 120 °C; In the step (3), the calcination heating rate is 1-15 °C·min -1 .

3. The preparation method according to claim 1, characterized in that: Pd is taken as a Pd salt at 5 wt% - 15 wt% of the iron oxide (FeO x ) powder by mass fraction of Pd.

4. The preparation method according to claim 1, characterized in that: The reduction conditions are as follows: at a gas hourly space velocity of 2000 - 15000 mL g -1 h -1 , a reduction temperature of 300 - 400 °C, and a reduction heating rate of 1 - 8 °C min -1 , under normal pressure, reduce for 1 - 3 h; The carbonization conditions are as follows: the carbonization pressure is 1 - 5 MPa, the carbonization temperature is 300 - 400 °C, the carbonization time is 1 - 3 h, and the gas hourly space velocity is 3000 - 12000 mL g -1 h -1 .

5. The preparation method according to claim 1, characterized in that: The iron oxides used include one or more of Fe3O4, Fe2O3, or FeO, with a particle size of 10 - 150 nm; they can be prepared by the propylene oxide sol - gel method, PVP sol - gel method, or precipitation method.

6. The preparation method according to claim 5, characterized in that: The main process of the propylene oxide sol - gel method is: add a certain amount of iron salt to the corresponding solvent, stir and repeat ultrasonic treatment multiple times to dissolve and mix evenly; according to the molar ratio of iron to 1,2 - propylene oxide of 1:(0.1 - 10), take a certain molar amount of 1,2 - propylene oxide; add 1,2 - propylene oxide to the beaker under stirring conditions and stir for 1 - 40 min; then pour the solution into the polytetrafluoroethylene inner liner of a hydrothermal autoclave for reaction at a temperature of 100 - 250 °C for 1 - 50 h; after cooling, take out the polytetrafluoroethylene inner liner and place it in an oven for drying at 40 - 100 °C for 8 - 48 h; after the liquid inside the inner liner is evaporated to dryness, raise the oven temperature to 150 - 250 °C and dry for 0.5 - 6 h; after cooling, grind and collect the obtained solid powder, put it into a muffle furnace for calcination: heat up to 300 - 700 °C and keep it for 0.5 - 7 h, and then naturally cool to room temperature for collection and standby; The main process of the PVP sol - gel method is to add iron salt and polyvinylpyrrolidone according to the molar ratio of Fe3+ to PVP monomer of 1:(0.1 - 10) to the solvent, dissolve it under heating and stirring; evaporate the solvent at 30 - 100 °C until a gel is formed; transfer the obtained gel to an oven for drying to obtain the dried product, grind it into powder and collect it; heat up to 300 - 700 °C and keep it for 0.5 - 7 h, and then naturally cool to room temperature for collection and standby; The main process of the precipitation method is to add a certain amount of iron salt into the solvent, stir and ultrasonicate repeatedly to dissolve and mix it evenly, stir at 30 - 100 °C, and add a basic precipitant with a concentration of 0.01 - 5 mol·L -1 for precipitation until the pH of the system reaches 3 - 8, continue aging for 0.5 - 5 h, wash with deionized water until the pH is 5 - 7.5, centrifuge and filter to obtain a solid, and then dry it in an oven at 40 - 90 °C for 6 - 12 h; take it out, grind it into powder, and calcine it in a muffle furnace: heat it up to 300 - 700 °C and keep it for 0.5 - 7 h, and then naturally cool it to room temperature for collection and standby.

7. The preparation method according to claim 5, characterized in that: In the propylene oxide sol-gel method, the iron salt is one or a mixture of more than one of iron(III) nitrate nonahydrate, iron(III) sulfate, iron(III) chloride, and iron(III) acetate; the Fe salt dispersion solvent is one or a mixed solvent of more than one of water, methanol, ethanol, butanol, isopropyl alcohol, and ethylene glycol; the addition rate of 1,2-propylene oxide is 1-10 d·s -1 ; The solvent used in the PVP sol - gel method is one or a mixture of more of water, methanol, ethanol, butanol, isopropanol, and ethylene glycol; the iron salts used are one or a mixture of more of ferric nitrate, ferric sulfate, ferric chloride, and ferric acetate; the K value of the PVP used is 10 - 100, and the molecular weight is 3000 - 1500000; The iron salt used in the precipitation method is one or a mixture of more than one of iron nitrate, iron sulfate, iron chloride and iron acetate; the solvent used is one or a mixture of more than one of water, methanol and ethanol; the alkaline precipitant is an aqueous solution of one or a mixture of more than one of potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide, potassium bicarbonate, sodium bicarbonate, ammonium bicarbonate, ammonium carbonate and ammonia water; the addition rate of the precipitant is 0.1-6 mL·min -1 .

8. A method for catalytically synthesizing lower alcohols from CO2, characterized in that, Use the catalyst described in any one of claims 1 to 7 to catalyze the synthesis of lower alcohols from CO2.

9. The method according to claim 8, characterized in that: The reaction gas is a CO2 / H2 / inert gas mixture, and lower alcohols are catalytically synthesized under the conditions of a reaction pressure of 3 - 7 MPa and a reaction temperature of 280 - 330 °C.

10. The method according to claim 8, wherein: The inert gas in the CO2 / H2 / inert gas mixture includes, but is not limited to, N2; the ratio of CO2 to H2 is 1:3, the proportion of the inert gas is 2%-6%, and the gas hourly space velocity is 3000-6000 mL g -1 cat h -1 。 11. A catalyst for catalytic hydrogenation of carbon dioxide to synthesize lower alcohols, which contains active phases of Fe5C2 species and PdFe alloy species.

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