An Fe-based catalyst for preparing mixed alcohols by CO2 hydrogenation and a preparation method and application thereof

Abstract

The application belongs to the technical field of CO2 resource utilization and catalyst preparation, and provides an Fe-based catalyst for preparing mixed alcohols by CO2 hydrogenation, a preparation method and application thereof. x M-yA; wherein M is a metal additive; A is an alkali metal additive; in the formula, x is the molar ratio of Fe to M, and the value range is 0.5-7; y is the mass fraction of A in the Fe-based catalyst, and the value is 0.5-5%. The Fe catalyst for preparing mixed alcohols by CO2 hydrogenation has excellent CO2 conversion rate and C 2+ The mixed alcohols have high selectivity, extremely low C1 product selectivity (CO, CH4, methanol), the preparation method is simple, easy to operate, easy to repeat and scale up production, and has potential industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of CO2 resource utilization and catalyst preparation technology, and relates to an Fe-based catalyst for the preparation of mixed alcohols by CO2 hydrogenation, its preparation method and application. Background Technology

[0002] Under the dual pressures of environmental degradation and the goal of "carbon peaking and carbon neutrality," converting CO2 into chemicals and liquid fuels through hydrogenation not only reduces CO2 emissions but also serves as an effective way to utilize CO2 resources. For the catalytic conversion of CO2 hydrogenation, C1 small molecules such as carbon monoxide (CO), methane (CH4), and methanol have low reaction energy barriers, making them easy to generate and become the dominant products.

[0003] Due to the chemical inertness of CO2 and the high energy barrier of C-C coupling, CO2 can be converted into a carbon-containing compound (C2 ... 2+ High-value-added chemicals or liquid fuels still face significant challenges, among which mixed alcohols (straight-chain alcohols with two or more carbon atoms, C60-C60) are particularly problematic. 2+ Alcohols can be used as clean fuels, oil additives, solvents, and chemical intermediates, with high added value and wide applications. The hydrogenation conversion of CO2 usually consists of a two-step series reaction: first, the reverse water-gas shift reaction (RWGS: CO2 + H2 → CO + H2O) occurs to obtain abundant CO intermediates, and then CO undergoes Fischer-Tropsch synthesis to achieve C-C coupling carbon chain growth. However, this series reaction and subsequent coupling process are difficult to control precisely, and the chemical inertness of CO2 often requires high temperature (>300℃) for activation, which leads to an increase in C1 byproducts (CO, CH4, methanol) and limited improvement in the selectivity of mixed alcohols.

[0004] For industrial applications, catalysts for the hydrogenation of CO2 to produce mixed alcohols (mainly ethanol) are primarily noble metal-based Rh-, Au-, and Ru-based catalysts, such as those in Chinese invention patent applications CN111434382A, CN110292937A, CN106582627A, and CN105001048A. While these catalysts offer advantages in conversion rate and selectivity, their high cost makes them unsuitable for industrial production. Chinese invention patent applications CN103191747A and CN104549299A disclose CuZn-based catalysts, which, although inexpensive, exhibit low conversion rates, with methanol as the main product. Chinese invention patent applications CN110465302A and CN110947384A disclose CuFe-based catalysts... 2+ Alcohol selectivity improved somewhat, but remained below 45%, while CO selectivity was above 20%, failing to meet industry requirements. Chinese invention patent applications CN111659432A and CN114887625A disclose Fe-based catalysts, which maintain C... 2+It exhibits both alcohol selectivity and high catalytic activity.

[0005] In summary, the high reactivity and low cost of the non-precious metal Fe give it great potential for industrial development. Chinese invention patent application CN111659432A discloses the activation treatment of auxiliary modified iron oxide with syngas or CO to obtain iron carbides of different types and proportions, which constitute active sites for CO2 hydrogenation to ethanol, with ethanol selectivity ≥20%, CO selectivity ≤10%, but CH4 selectivity >10%.

[0006] Therefore, for Fe-based catalysts, while higher reaction temperatures in the CO2 hydrogenation reaction are beneficial for CO2 activation and promote the endothermic RWGS reaction, high temperatures are detrimental to the exothermic C reaction. 2+ The synthesis of alcohols also leads to the generation of excessive C1 byproducts. Therefore, the development of highly active and selective catalysts for the hydrogenation of CO2 to produce mixed alcohols is particularly urgent. Summary of the Invention

[0007] This invention addresses the problems existing in the prior art by providing an Fe-based catalyst for the preparation of mixed alcohols by CO2 hydrogenation, its preparation method, and its application. This Fe-based catalyst is a low-temperature, high-activity catalyst that enhances the reverse water-gas shift-Fischer-Tropsch synthesis process, thereby promoting CC coupling and CO insertion, significantly improving the reaction activity and selectivity of mixed alcohols. It can effectively suppress C1 byproducts in the CO2 hydrogenation reaction to prepare mixed alcohols.

[0008] The technical solution of the present invention is as follows:

[0009] A Fe-based catalyst for the hydrogenation of CO2 to produce mixed alcohols, wherein the general molecular formula of the Fe-based catalyst is Fe. x M-yA; where M is a metal additive and A is an alkali metal additive;

[0010] In the formula, x is the molar ratio of Fe to M, ranging from 0.5 to 7; y is the mass fraction of A in the Fe-based catalyst, ranging from 0.5 to 5%.

[0011] Furthermore, the Fe x In M-yA, the value of x ranges from 2 to 5; the value of y ranges from 3 to 5%.

[0012] Preferably, x is 3 and y is 3%.

[0013] Preferably, the metal additive is selected from transition metal elements Zn or Zr.

[0014] More preferably, the metal additive is selected from the transition metal element Zn.

[0015] Preferably, the alkali metal auxiliary agent is selected from Na or K.

[0016] More preferably, the alkali metal auxiliary is K.

[0017] This invention also provides a method for preparing any of the Fe-based catalysts described above, comprising the following steps:

[0018] (1) Dissolve Fe salt and M salt in water to obtain solution L1;

[0019] (2) Dissolve the precipitant containing A in water to obtain solution L2;

[0020] (3) Simultaneously add solutions L1 and L2 to obtain a suspension, which is then aged, separated, washed, dried, and calcined to obtain the Fe-based catalyst Fe. x M-yA.

[0021] Furthermore, the Fe salt and M salt are selected from any one of their respective nitrates, chlorides, sulfates and acetates;

[0022] Preferably, the Fe salt and M salt are selected from their respective nitrates.

[0023] Furthermore, the Fe salt is specifically selected from any one of ferric nitrate nonahydrate, ferric chloride hexahydrate, ferric sulfate, and ferric acetate tetrahydrate; preferably ferric nitrate nonahydrate.

[0024] Furthermore, the M salt is specifically selected from any one of zinc nitrate hexahydrate, zinc chloride, zinc sulfate heptahydrate, zinc acetate dihydrate, zirconium nitrate pentahydrate, zirconium chloride octahydrate, zirconium sulfate tetrahydrate, and zirconium acetate tetrahydrate; preferably zinc nitrate hexahydrate or zirconium nitrate pentahydrate.

[0025] Furthermore, the Fe x The A in M-yA comes from the precipitant, which is selected from any combination of its carbonate and hydroxide.

[0026] The preferred formulation is Na2CO3+NaOH or K2CO3+KOH.

[0027] A further preferred option is K2CO3+KOH.

[0028] Furthermore, the total molar concentration of metal ions in solution L1 is 0.5-2 mol / L; preferably 1 mol / L.

[0029] Furthermore, the molar concentration of the precipitant in solution L2 is 0.5-2 mol / L; preferably 2 mol / L.

[0030] Furthermore, the pH value of the suspension is 6-12, preferably 8-10.

[0031] Furthermore, in step (3), the aging temperature is 25°C and the aging time is 2-12 hours;

[0032] The drying temperature is 80-120℃, and the drying time is 6-48h;

[0033] The roasting temperature is 350-450℃; the roasting time is 2-10h;

[0034] The drying and roasting atmosphere is selected from any one of air, nitrogen, or argon.

[0035] Preferably, the calcination temperature is 400℃ and the calcination time is 3 hours.

[0036] This invention also provides the application of any of the Fe-based catalysts described above or the Fe-based catalysts prepared by any of the preparation methods described above in the preparation of mixed alcohols by CO2 hydrogenation.

[0037] Furthermore, the application employs a fixed-bed CO2 hydrogenation process to prepare mixed alcohols.

[0038] Furthermore, the process parameters for the fixed-bed CO2 hydrogenation to prepare mixed alcohols are as follows:

[0039] The reduction pressure is 0.1-0.3 MPa;

[0040] The reducing gas is selected from any one of pure H2, pure CO, 10% H2 / Ar, and 10% CO / Ar;

[0041] The reduction temperature is 350-400℃, and the reduction time is 2-8 hours.

[0042] The feed gas composition ratio is H2 / CO2 / N2 = 72 / 24 / 4, and the space velocity is 3000-6000 mLg. cat -1 h -1 ;

[0043] The reaction temperature is 240-300℃, and the reaction pressure is 3-5MPa.

[0044] The mixed alcohol is C 2+ alcohol.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The Fe-based catalyst Fe prepared in this invention x M-yA mainly promotes CC coupling and CO insertion by enhancing the reverse water gas shift-Fischer-Tropsch synthesis process. It can maintain a high CO2 conversion rate at relatively low temperatures and is a low-temperature, high-activity catalyst.

[0047] (2) Compared with Cu-based, CuZn-based, CuCo-based, and noble metal catalysts, the Fe-based catalyst of the present invention can provide favorable conditions for C due to the special valence state (divalent / trivalent) of Fe and the phase change. 2+ The bifunctional active site for alcohol formation, through combined modification with transition and alkali metals, can effectively inhibit the formation of C1 products (CO, CH4, methanol), promote the carbon chain growth of intermediate species, and increase the C... 2+ Selectivity of alcohols;

[0048] (3) Furthermore, this invention further improves catalytic activity by selecting and limiting the amount of each component in the catalyst; it also features low C1 byproducts (CO, CH4, methanol) and low C2 content. 2+ The high selectivity of alcohols, its C 2+ The alcohol selectivity is higher than 40%, and the product has high added value.

[0049] (4) Based on the high CO2 conversion rate and C 2+ Alcohol selectivity: Overall, this catalyst offers higher final yields for the hydrogenation of CO2 to produce mixed alcohols.

[0050] (5) The Fe provided by the present invention x M-yA catalysts are simple to prepare, easy to operate, and easy to reproduce and scale up, and have great potential for industrial development. Detailed Implementation

[0051] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection of the present invention, and those skilled in the art can make various changes and modifications to the invention based on the disclosed content, which should also fall within the scope of protection of the present invention.

[0052] I. Investigation of the types of metal auxiliaries M: Fe-based catalyst Fe3M-3K

[0053] Example 1:

[0054] Based on a metal molar ratio of Fe / Zn = 3, 30.5 g of ferric nitrate nonahydrate and 7.5 g of zinc nitrate hexahydrate were weighed and dissolved in deionized water to prepare a 1 mol / L solution L1. Similarly, 19.2 g of anhydrous potassium carbonate and 7.8 g of potassium hydroxide were weighed and dissolved in deionized water to prepare a 2 mol / L solution L2. Under stirring at 500 rpm and 25 °C, solutions L1 and L2 were simultaneously added dropwise to a 500 mL beaker, maintaining the pH at 9. After the addition was complete, the mixture was aged at 25 °C for 2 h, then centrifuged and washed four times. It was then dried in a 120 °C oven for 12 h and calcined in a muffle furnace at 400 °C for 3 h to obtain the catalyst. The K content was determined to be 3.0% using inductively coupled plasma atomic emission spectrometry (ICP-OES, Optima 8000, PerkinElmer). The obtained catalyst was named Fe3Zn-3K.

[0055] The performance of the above catalyst in the preparation of mixed alcohols by CO2 hydrogenation in a fixed bed was evaluated. 1 g of the catalyst was weighed and mixed with 2 g of quartz sand particles (40-60 mesh). Reduction was carried out at 350 °C for 3 h in a 0.1 MPa H2 atmosphere. After reduction, the temperature was lowered to 280 °C, and a feed gas with an H2 / CO2 / N2 ratio of 72 / 24 / 4 was introduced at a space velocity of 3000 mLg. cat -1 h -1 The reaction temperature was 280℃ and the reaction pressure was 3MPa. The performance results are shown in Table 1.

[0056] Example 2:

[0057] The catalyst preparation method and evaluation process were the same as in Example 1, except that Zn was replaced with Zr, the metal molar ratio Fe / Zr = 3, the mass of ferric nitrate nonahydrate was 32.5 g, and the mass of zirconium nitrate pentahydrate was 11.5 g. The K content was measured to be 3.1%, and the obtained catalyst was named Fe3Zr-3K. Its performance results are shown in Table 1.

[0058] Example 3:

[0059] The catalyst preparation method and evaluation process were the same as in Example 1, except that Zn was replaced with Mn, the metal molar ratio Fe / Mn = 3, the mass of ferric nitrate nonahydrate was 31.6 g, and the mass of manganese nitrate tetrahydrate was 6.6 g. The K content was measured to be 3.0%, and the obtained catalyst was named Fe3Mn-3K. Its performance results are shown in Table 1.

[0060] Example 4:

[0061] The catalyst preparation method and evaluation process were the same as in Example 1, except that Zn was replaced with Al, the metal molar ratio Fe / Al = 3, the mass of ferric nitrate nonahydrate was 28.7 g, and the mass of aluminum nitrate nonahydrate was 8.9 g. The K content was measured to be 2.9%, and the obtained catalyst was named Fe3Al-3K. Its performance results are shown in Table 1.

[0062] Table 1 Catalytic performance results of each embodiment

[0063]

[0064] II. Investigation of Alkali Metal Additive Type A: Fe-based Catalyst Fe3Zn-3A

[0065] Example 5

[0066] The catalyst preparation method and evaluation process were the same as in Example 1, except that the precipitant was changed to 14.7 g of anhydrous sodium carbonate and 5.5 g of sodium hydroxide, which were dissolved in deionized water to prepare a 2 mol / L solution L2. The K content was measured to be 3.1%, and the obtained catalyst was named Fe3Zn-3Na. Its performance results are shown in Table 2.

[0067] Example 6

[0068] The catalyst preparation method and evaluation process were the same as in Example 1, except that the precipitant was replaced with 38.3 g of anhydrous potassium carbonate, which was dissolved in deionized water to prepare a 2 mol / L solution L2. The K content was measured to be 3.0%, and the obtained catalyst was named Fe3Al-3K1. Its performance results are shown in Table 2.

[0069] Example 7

[0070] The catalyst preparation method and evaluation process were the same as in Example 1, except that the precipitant was replaced with 15.6 g of potassium hydroxide, which was dissolved in deionized water to prepare a 2 mol / L solution L2. The K content was measured to be 3.0%, and the obtained catalyst was named Fe3Al-3K2. Its performance results are shown in Table 2.

[0071] Table 2 Catalytic performance results of each example

[0072]

[0073] III. Investigation of the Fe / metal additive M molar ratio: Fe-based catalyst Fe x Zn-3K

[0074] Example 8

[0075] The catalyst preparation method and evaluation process were the same as in Example 1, except that the metal molar ratio Fe / Zn was changed to 0.5, the mass of ferric nitrate nonahydrate was 16.0 g, and the mass of zinc nitrate hexahydrate was 23.6 g. The K content was measured to be 2.9%, and the resulting catalyst was named Fe... 0.5 Zn-3K. Its performance results are shown in Table 3.

[0076] Example 9

[0077] The catalyst preparation method and evaluation process were the same as in Example 1, except that the metal molar ratio Fe / Zn was changed to 1, the mass of ferric nitrate nonahydrate was 22.5 g, and the mass of zinc nitrate hexahydrate was 16.6 g. The K content was measured to be 3.0%, and the obtained catalyst was named Fe1Zn-3K. Its performance results are shown in Table 3.

[0078] Example 10

[0079] The catalyst preparation method and evaluation process were the same as in Example 1, except that the metal molar ratio Fe / Zn was changed to 2, the mass of ferric nitrate nonahydrate was 28.1 g, and the mass of zinc nitrate hexahydrate was 10.4 g. The K content was measured to be 3.1%, and the obtained catalyst was named Fe2Zn-3K. Its performance results are shown in Table 3.

[0080] Example 11

[0081] The catalyst preparation method and evaluation process were the same as in Example 1, except that the metal molar ratio Fe / Zn was changed to 5, the mass of ferric nitrate nonahydrate was 33.0 g, and the mass of zinc nitrate hexahydrate was 4.9 g. The K content was measured to be 3.1%, and the obtained catalyst was named Fe5Zn-3K. Its performance results are shown in Table 3.

[0082] Example 12

[0083] The catalyst preparation method and evaluation process were the same as in Example 1, except that the metal molar ratio Fe / Zn was changed to 7, the mass of ferric nitrate nonahydrate was 34.2 g, and the mass of zinc nitrate hexahydrate was 3.6 g. The K content was measured to be 3.0%, and the obtained catalyst was named Fe7Zn-3K. Its performance results are shown in Table 3.

[0084] Table 3 Catalytic performance results of each example

[0085]

[0086] IV. Investigation into the content of alkali metal promoter A in the catalyst: Fe-based catalyst Fe3Zn-yK

[0087] Example 13

[0088] The catalyst preparation method and evaluation process were the same as in Example 1, except that the number of centrifugation and washing cycles was changed to 6. The K content was measured to be 0.5%, and the obtained catalyst was named Fe3Zn-0.5K. Its performance results are shown in Table 4.

[0089] Example 14

[0090] The catalyst preparation method and evaluation process were the same as in Example 1, except that the number of centrifugation and washing cycles was changed to 5. The K content was measured to be 2.5%, and the obtained catalyst was named Fe3Zn-2.5K. Its performance results are shown in Table 4.

[0091] Example 15

[0092] The catalyst preparation method and evaluation process were the same as in Example 1, except that the number of centrifugation and washing cycles were changed to 3. The K content was measured to be 3.5%, and the obtained catalyst was named Fe3Zn-3.5K. Its performance results are shown in Table 4.

[0093] Example 16

[0094] The catalyst preparation method and evaluation process were the same as in Example 1, except that the number of centrifugation and washing cycles were changed to 2. The K content was measured to be 5.0%, and the obtained catalyst was named Fe3Zn-5K. Its performance results are shown in Table 4.

[0095] Table 4 Catalytic performance results of each example

[0096]

[0097] V. Investigation of Reduction Temperature

[0098] Example 17

[0099] The catalyst preparation method and evaluation process were the same as in Example 4. The catalyst was Fe3Zn-3K, except that the reduction temperature was changed to 300℃. The performance results are shown in Table 5.

[0100] Example 18

[0101] The catalyst preparation method and evaluation process were the same as in Example 4. The catalyst was Fe3Zn-3K, only the reduction temperature was changed to 400℃. The performance results are shown in Table 5.

[0102] Example 19

[0103] The catalyst preparation method and evaluation process were the same as in Example 4. The catalyst was Fe3Zn-3K, except that the reduction temperature was changed to 500℃. The performance results are shown in Table 5.

[0104] Table 5 Catalytic performance results of each example

[0105]

[0106] VI. Investigation of Reaction Temperature

[0107] Example 20

[0108] The catalyst preparation method and evaluation process were the same as in Example 1. The catalyst was Fe3Zn-3K, only the reaction temperature was changed to 240℃. The performance results are shown in Table 6.

[0109] Example 21

[0110] The catalyst preparation method and evaluation process were the same as in Example 1. The catalyst was Fe3Zn-3K, only the reaction temperature was changed to 260℃. The performance results are shown in Table 6.

[0111] Example 22

[0112] The catalyst preparation method and evaluation process were the same as in Example 1. The catalyst was Fe3Zn-3K, only the reaction temperature was changed to 300℃. The performance results are shown in Table 6.

[0113] Table 6 Catalytic performance results of each example

[0114]

[0115] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. The application of an Fe-based catalyst in the preparation of mixed alcohols by CO2 hydrogenation, characterized in that, The general molecular formula of the Fe-based catalyst is Fe x M-yA; where M is a metal additive and A is an alkali metal additive; The metal additive is the transition metal element Zn; the alkali metal additive is K; In the formula, x is the molar ratio of Fe to M, ranging from 2 to 5; y is the mass fraction of A in the Fe-based catalyst, ranging from 2.5% to 3.0%. The preparation method of Fe-based catalysts includes the following steps: (1) Dissolve Fe salt and M salt in water to obtain solution L1; (2) Dissolve the precipitant containing A in water to obtain solution L2; (3) Simultaneously add solutions L1 and L2 to obtain a suspension, which is then aged, separated, washed, dried, and calcined to obtain the Fe-based catalyst Fe. x M-yA; The precipitant is K2CO3+KOH.

2. The application according to claim 1, characterized in that, Fe x In M-yA, x takes the value 3; y takes the value 3.0%.

3. The application according to claim 1, characterized in that, The Fe salt and M salt are selected from any one of their respective nitrate, chloride, sulfate and acetate salts.

4. The application according to claim 3, characterized in that, The Fe salt and M salt are selected from their respective nitrates.

5. The application according to claim 1, characterized in that, The total metal ion molar concentration in solution L1 is 0.5-2 mol / L; the precipitant molar concentration in solution L2 is 0.5-2 mol / L; and the pH value of the suspension is 6-12.

6. The application according to claim 5, characterized in that, The total metal ion molar concentration in solution L1 is 1 mol / L; the precipitant molar concentration in solution L2 is 2 mol / L; and the pH value of the suspension is 8-10.

7. The application according to claim 1, characterized in that, In step (3), The aging temperature is 25℃, and the aging time is 2-12 hours; The drying temperature is 80-120℃, and the drying time is 6-48h; The roasting temperature is 350-450℃; the roasting time is 2-10h; The drying and roasting atmosphere is selected from any one of air, nitrogen, or argon.

8. The application according to claim 1, characterized in that, The application employs a fixed-bed CO2 hydrogenation process to prepare mixed alcohols, with the specific process parameters as follows: The reduction pressure is 0.1-0.3 MPa; The reducing gas is selected from any one of pure H2, pure CO, 10% H2 / Ar, and 10% CO / Ar; The reduction temperature is 350-400℃, and the reduction time is 2-8 hours. The feed gas composition ratio is H2 / CO2 / N2 = 72 / 24 / 4, and the space velocity is 3000-6000 mLg. cat -1 h -1 ; The reaction temperature is 240-300℃, and the reaction pressure is 3-5MPa. The mixed alcohol is C 2+ alcohol.

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