Fe-based catalyst for preparing low-carbon alcohol through CO2 hydrogenation as well as preparation method and application of Fe-based catalyst

Abstract

The invention discloses a Fe-based catalyst for preparing low-carbon alcohol through CO2 hydrogenation as well as a preparation method and application of the Fe-based catalyst, and belongs to the field of catalysts. The Fe5C2 catalyst is synthesized through a hydrothermal synthesis method and in-situ carbonization, and alkali metal is added as an accelerant. According to the catalyst, preparation of the low-carbon alcohol is achieved on single metal Fe, the performance is excellent, the highest conversion rate of the catalyst for catalyzing CO2 hydrogenation to synthesize the low-carbon alcohol can reach 42.9%, the highest selectivity of the low-carbon alcohol can reach 24.3%, and the space time yield of the low-carbon alcohol can reach 143.9 mg g <-1 > cat <-1 >.

Description

Technical Field

[0001] The present invention belongs to the technical field of CO2 conversion, and specifically relates to an Fe-based catalyst for preparing low-carbon alcohols by hydrogenating CO2, and a preparation method and application thereof. Background Art

[0002] CO2 is the main component of greenhouse gases. In recent years, the global annual CO2 emissions have exceeded 30 billion tons. Its large-scale emissions have caused a serious greenhouse effect, which in turn has caused a series of environmental problems, including global climate change, glacier melting, and sea level rise. Converting CO2 into fuels and chemicals is an effective way to reduce the dependence of production and life on fossil fuels and reduce CO2 emissions. Using renewable clean energy H2 to react with CO2 can produce many valuable chemicals. Among these products, low-carbon alcohols have a wider range of applications due to their higher added value.

[0003] At present, the academic community generally believes that the synthesis of low-carbon alcohols requires the synergistic effect of two catalytic active sites: CO dissociation adsorption sites provide *CH x Species, CO non-dissociative adsorption sites provide molecular adsorbed CO insertion. Therefore, how to regulate the balance between the dissociative and non-dissociative activation abilities of CO is extremely challenging. In current research, there are few reports on the use of single Fe-based catalysts for CO2 hydrogenation to produce low-carbon alcohols. The main reason is that Fe-based catalysts have poor non-dissociative activation ability for CO, and generally need to be combined with other metals (such as Rh, Pd, Cu) to achieve the above process. However, the multifunctional tandem catalyst has the phenomenon of phase separation leading to deactivation, while a single-component catalyst can effectively avoid this phenomenon. Therefore, the present invention designs a single Fe-based catalyst, and obtains a pure phase Fe5C2 by hydrothermal synthesis and in situ carbonization, which appears at 2θ=39.4°, 41.2°, 43.5°, and 44.2°. The characteristic diffraction peak of iron carbide (Fe5C2) belongs to the triclinic Fe5C2 (ICSD PDF#97-018-1367). At the same time, alkali metal is added as a promoter to induce the in-situ production of Fe3O4 phase during the reaction and maintain the dynamic balance between carbide and oxide, forming a coexistence structure of two active phases, promoting the production of low-carbon alcohols. Summary of the invention

[0004] The main purpose of the present invention is to provide an Fe-based catalyst for preparing low-carbon alcohols by hydrogenating CO2, and a preparation method and application thereof. The Fe-based catalyst provided by the present invention realizes the preparation of low-carbon alcohols by hydrogenating CO2 on a single metal, and has a high CO2 conversion rate, low-carbon alcohol selectivity and time-space yield.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] First, dissolve ferrous salt in a mixture of ethylene glycol and water and stir. Then, dissolve anhydrous oxalic acid in a mixture of ethylene glycol and water and stir. Subsequently, slowly mix the above two solutions under stirring and perform hydrothermal treatment; after the reaction, wash with water and ethanol, centrifuge, and dry. Add alkali metal salt to the dried sample, stir, evaporate the water, and dry. Add the dried sample to a fixed bed reactor, pass carbon monoxide into the reactor, and obtain Fe5C2 catalyst after carbonization.

[0007] Preferably, the ferrous salt is one of ferrous sulfate, ferrous chloride and ferrous carbonate, and the molar ratio of the ferrous salt to anhydrous oxalic acid is 1:(0.2-4).

[0008] Preferably, the volume ratio of ethylene glycol to water is 1:(0.5-4).

[0009] Preferably, the temperature of the hydrothermal reaction is 60° C. to 120° C., and the reaction time is 12 to 36 hours.

[0010] Preferably, the stirring time is 0.5 to 6 hours, the evaporation temperature is 30 to 100°C, and the drying temperature is 60 to 120°C.

[0011] Preferably, the alkali metal salt comprises one of lithium, potassium and sodium carbonates, and the amount of the alkali metal salt added is 1 to 20 wt % of the mass of the sample after hydrothermal reaction and drying.

[0012] Preferably, the carbonization reaction conditions are: heating to 250-500° C. at a heating rate of 0.1-1° C. / min, carbonization reaction for 1 h to 6 h, and a reactor pressure of 0-1 MPa.

[0013] An application of the Fe-based catalyst for preparing low-carbon alcohols by hydrogenation of CO2 as described above, further comprising loading the catalyst into a fixed bed reactor, introducing a mixed gas of CO2 and H2 under high temperature and high pressure conditions to prepare low-carbon alcohols.

[0014] Furthermore, the high temperature and high pressure are: temperature of 250-350°C, pressure of 1-6MPa; the molar ratio of CO2 to hydrogen is 1:(1-5).

[0015] Compared with the prior art, the present invention has the following excellent effects:

[0016] (1) Compared with the existing catalyst preparation method for preparing low-carbon alcohols by hydrogenating CO2, the preparation method provided by the present invention does not require the introduction of other metal element components and can prepare low-carbon alcohols on a single Fe-based catalyst modified with an alkali metal.

[0017] (2) The present invention exhibits excellent catalytic performance for the synthesis of low-carbon alcohols. Under heating and pressurizing reaction conditions (reaction temperature 320°C, 4MPa), the space-time yield of low-carbon alcohols can reach 143.9 mg g - c 1 at h -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The XRD spectra of the catalyst before and after the reaction of Example 5 are shown in FIG.

[0019] Figure 2 XRD spectra of the catalyst before and after the reaction in Comparative Example 1 DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. At the same time, the embodiments only provide some conditions for achieving this purpose, but it does not mean that these conditions must be met to achieve this purpose.

[0021] Example 1

[0022] Weigh 4.448g of ferrous sulfate heptahydrate and dissolve it in a mixture of 32mL ethylene glycol and 128mL deionized water and stir evenly. Then weigh 1.44g of anhydrous oxalic acid and dissolve it in a mixture of 32mL ethylene glycol and 128mL deionized water and stir evenly. Then, add the anhydrous oxalic acid solution dropwise to the ferrous sulfate heptahydrate solution, stir evenly, pour the solution into the polytetrafluoroethylene liner of a 500mL hydrothermal kettle, tighten it and put it in an oven, keep it at 60℃ for 24h; after the reaction is completed, wash and centrifuge it with water and ethanol three times respectively, and place the sample in a 60℃ oven to dry for 12h. Weigh 1g of the dried sample, add 3.6mL of 0.01g / mL potassium carbonate solution, stir evenly, evaporate to dryness at 60℃, and place the sample in a 60℃ oven to dry for 12h. Weigh 1g of the dried sample and put it into a fixed bed reactor quartz tube. At a pressure of 0.3MPa, introduce 100% CO gas. At a gas flow rate of 80mL / min, heat it to 350℃ at a heating rate of 0.5℃ / min for 6h. After cooling to room temperature, collect the Fe5C2 powder and record it as (HT-60℃-24h)Fe5C2. Then carry out the CO2 hydrogenation catalytic performance test. Catalytic test conditions: take 0.2g of catalyst, at 320℃, 4MPa, 6000mL g - c 1 at h -1Under the conditions, a CO2 / H2 mixed gas was used to carry out the reaction of CO2 hydrogenation to prepare low-carbon alcohols, and the gas used was CO2 / H2 / N2 (24 / 72 / 4).

[0023] Example 2

[0024] Weigh 4.448g of ferrous sulfate heptahydrate and dissolve it in a mixture of 32mL ethylene glycol and 128mL deionized water and stir evenly. Then weigh 1.44g of anhydrous oxalic acid and dissolve it in a mixture of 32mL ethylene glycol and 128mL deionized water and stir evenly. Then, add the anhydrous oxalic acid solution dropwise to the ferrous sulfate heptahydrate solution, stir evenly, pour the solution into the polytetrafluoroethylene liner of a 500mL hydrothermal kettle, tighten it and put it in an oven, keep it at 80℃ for 24h; after the reaction is completed, wash and centrifuge it with water and ethanol three times respectively, and place the sample in a 60℃ oven to dry for 12h. Weigh 1g of the dried sample, add 3.6mL of 0.01g / mL potassium carbonate solution, stir evenly, evaporate to dryness at 60℃, and place the sample in a 60℃ oven to dry for 12h. Weigh 1g of the dried sample and put it into a fixed bed reactor quartz tube. At a pressure of 0.3MPa, introduce 100% CO gas. At a gas flow rate of 80mL / min, heat it to 350℃ at a heating rate of 0.5℃ / min for carbonization for 6h. After cooling to room temperature, collect Fe5C2 powder and record it as (HT-80℃-24h)Fe5C2. Then, carry out the CO2 hydrogenation catalytic performance test. The catalytic test conditions are the same as those in Example 1.

[0025] Example 3

[0026] Weigh 4.448g of ferrous sulfate heptahydrate and dissolve it in a mixture of 32mL ethylene glycol and 128mL deionized water and stir evenly. Then weigh 1.44g of anhydrous oxalic acid and dissolve it in a mixture of 32mL ethylene glycol and 128mL deionized water and stir evenly. Then, add the anhydrous oxalic acid solution dropwise to the ferrous sulfate heptahydrate solution, stir evenly, pour the solution into the polytetrafluoroethylene liner of a 500mL hydrothermal kettle, tighten it and put it in an oven, keep it at 100℃ for 8h; after the reaction is completed, wash and centrifuge it with water and ethanol three times respectively, and place the sample in a 60℃ oven to dry for 12h. Weigh 1g of the dried sample, add 3.6mL of 0.01g / mL potassium carbonate solution, stir evenly, evaporate to dryness at 60℃, and place the sample in a 60℃ oven to dry for 12h. Weigh 1g of the dried sample and put it into a fixed bed reactor quartz tube. At a pressure of 0.3MPa, introduce 100% CO gas. At a gas flow rate of 80mL / min, heat it to 350℃ at a heating rate of 0.5℃ / min for carbonization for 6h. After cooling to room temperature, collect Fe5C2 powder and record it as (HT-100℃-8h)Fe5C2. Then, carry out the CO2 hydrogenation catalytic performance test. The catalytic test conditions are the same as those in Example 1.

[0027] Example 4

[0028] Weigh 4.448g of ferrous sulfate heptahydrate and dissolve it in a mixture of 32mL ethylene glycol and 128mL deionized water and stir evenly. Then weigh 1.44g of anhydrous oxalic acid and dissolve it in a mixture of 32mL ethylene glycol and 128mL deionized water and stir evenly. Then, add the anhydrous oxalic acid solution dropwise to the ferrous sulfate heptahydrate solution, stir evenly, pour the solution into the polytetrafluoroethylene liner of a 500mL hydrothermal kettle, tighten it and put it in an oven, keep it at 100℃ for 16h; after the reaction is completed, wash and centrifuge it with water and ethanol three times respectively, and place the sample in a 60℃ oven to dry for 12h. Weigh 1g of the dried sample, add 3.6mL of 0.01g / mL potassium carbonate solution, stir evenly, evaporate to dryness at 60℃, and place the sample in a 60℃ oven to dry for 16h. Weigh 1g of the dried sample and put it into a fixed bed reactor quartz tube. At a pressure of 0.3MPa, introduce 100% CO gas. At a gas flow rate of 80mL / min, heat it to 350℃ at a heating rate of 0.5℃ / min for carbonization for 6h. After cooling to room temperature, collect Fe5C2 powder and record it as (HT-100℃-16h)Fe5C2. Then, carry out the CO2 hydrogenation catalytic performance test. The catalytic test conditions are the same as those in Example 1.

[0029] Example 5

[0030] Weigh 4.448g of ferrous sulfate heptahydrate and dissolve it in a mixture of 32mL ethylene glycol and 128mL deionized water and stir evenly. Then weigh 1.44g of anhydrous oxalic acid and dissolve it in a mixture of 32mL ethylene glycol and 128mL deionized water and stir evenly. Then, add the anhydrous oxalic acid solution dropwise to the ferrous sulfate heptahydrate solution, stir evenly, pour the solution into the polytetrafluoroethylene liner of a 500mL hydrothermal kettle, tighten it and put it in an oven, keep it at 100℃ for 24h; after the reaction is completed, wash and centrifuge it with water and ethanol three times respectively, and place the sample in a 60℃ oven to dry for 12h. Weigh 1g of the dried sample, add 3.6mL of 0.01g / mL potassium carbonate solution, stir evenly, evaporate to dryness at 60℃, and place the sample in a 60℃ oven to dry for 12h. Weigh 1g of the dried sample and put it into a fixed bed reactor quartz tube. At a pressure of 0.3MPa, introduce 100% CO gas. At a gas flow rate of 80mL / min, heat it to 350℃ at a heating rate of 0.5℃ / min for carbonization for 6h. After cooling to room temperature, collect Fe5C2 powder and record it as (HT-100℃-24h)Fe5C2. Then, carry out the CO2 hydrogenation catalytic performance test. The catalytic test conditions are the same as those in Example 1.

[0031] The XRD patterns of the Fe5C2 catalyst prepared in Example 5 before and after the reaction are as follows: Figure 1As shown, the Fe5C2 catalyst is a triclinic (ICSD PDF#97-018-1367) Fe5C2 phase before the reaction, and is a mixture of Fe5C2 and Fe3O4 after the reaction.

[0032] Comparative Example 1

[0033] Weigh 3.976g of ferrous chloride tetrahydrate and dissolve it in a mixture of 32mL ethylene glycol and 8mL deionized water and stir for 30min. Then weigh 2.52g of anhydrous oxalic acid and dissolve it in a mixture of 32mL ethylene glycol and 8mL deionized water and stir for 30min. Then, add the anhydrous oxalic acid solution dropwise to the ferrous chloride tetrahydrate solution, stir for 30min, wash and centrifuge twice with water and ethanol respectively, and place the sample in a 60℃ oven to dry for 12h. Weigh 1g of the dried sample, add 3.6mL of 0.01g / mL potassium carbonate solution, stir for 6h, evaporate to dryness at 60℃, and place the sample in a 60℃ oven to dry for 12h. Weigh 0.4g of the dried sample and 4ml of ethylenediamine and add them to two porcelain boats respectively, put them into a tube furnace, and heat them to 520℃ at a heating rate of 20℃ / min under 80mL / min N2 atmosphere, keep it for 1h, and collect Fe5C2 powder after cooling to room temperature, which is recorded as (EDA)Fe5C2. Then, the catalytic performance of CO2 hydrogenation is tested. The catalytic test conditions are the same as those in Example 1.

[0034] The XRD patterns of the Fe5C2 catalyst prepared in Comparative Example 1 before and after the reaction are as follows: Figure 2 As shown, it can be seen that the Fe5C2 catalyst is a monoclinic (ICSD PDF#97-042-3887) Fe5C2 phase before the reaction, and the main phase after the reaction is also a monoclinic Fe5C2 phase, and no peak of the Fe3O4 phase is observed. Its evaluation performance is also much lower than that of the catalyst in Example 5, which indicates that the coexistence structure of the triclinic Fe5C2 phase and the Fe3O4 phase is beneficial to the production of low-carbon alcohols.

[0035] Table 1

[0036]

[0037] The catalytic performance evaluation results in the examples and comparative examples are shown in Table 1. The above results indicate that the preparation method in the examples of the present invention can exhibit excellent low-carbon alcohol preparation performance by reasonably optimizing the reaction conditions.

Claims

1. An Fe-based catalyst for preparing low-carbon alcohols by hydrogenation of CO2, characterized in that: The catalyst is pure phase triclinic Fe5C2.

2. A method for preparing a Fe-based catalyst for preparing low-carbon alcohols by hydrogenation of CO2 as claimed in claim 1, characterized in that: The catalyst is obtained by the following steps: First, ferrous salt is dissolved in a mixture of ethylene glycol and water and stirred; anhydrous oxalic acid is dissolved in a mixture of ethylene glycol and water and stirred; the ferrous salt is one of ferrous sulfate, ferrous chloride and ferrous carbonate, and the molar ratio of the ferrous salt to the anhydrous oxalic acid is 1:(0.2-4); the volume ratio of ethylene glycol to water is 1:(0.5-4); Subsequently, the two solutions are mixed under stirring and subjected to hydrothermal treatment; the temperature of the hydrothermal reaction is 60° C. to 120° C., and the reaction time is 12 to 36 hours; After the reaction is completed, the sample is washed with water and ethanol, centrifuged, and dried; an alkali metal salt is added to the dried sample, and the amount of the alkali metal salt is 1wt% to 20wt% of the mass of the sample after the hydrothermal reaction and drying; Stir, The water is evaporated and dried; the dried sample is added into a fixed bed reactor, carbon monoxide is introduced into the reactor, and Fe5C2 catalyst is obtained after carbonization.

3. The method according to claim 2, characterized in that The stirring time for both times is 0.5 to 6 hours.

4. The method according to claim 2, characterized in that: The evaporation temperature is 30-100°C.

5. The method according to claim 2, characterized in that: The drying temperature is 60℃~120℃.

6. The method according to claim 2, characterized in that The alkali metal salt includes one of lithium, potassium and sodium carbonates.

7. The method according to claim 2, characterized in that The conditions of the carbonization reaction are: heating to 250-500° C. at a heating rate of 0.1-1° C. / min, a carbonization reaction time of 1 h-6 h, and a reactor pressure of 0-1 MPa.

8. The use of an Fe-based catalyst for preparing low-carbon alcohols by hydrogenation of CO2 as claimed in claim 1, characterized in that: The catalyst is loaded into a fixed bed reactor at a temperature of 250-350°C and a pressure of 1-6MPa; a mixed gas of CO2 and H2 is introduced, wherein the molar ratio of CO2 to H2 is 1:(1-5), to obtain low-carbon alcohols.

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