Preparation and application of non-metal modified single-atom catalyst for co2 hydrogenation to ethanol

Abstract

The application discloses a preparation and application of a non-metal modified single-atom catalyst for CO2 hydrogenation to ethanol, and belongs to the field of carbon dioxide conversion applications. The catalyst is composed of an active component and a non-metal modified carrier, wherein the active component comprises one or more of Rh, Pd, Ir, Fe, Co, Ni and Cu; and the non-metal modified carrier comprises one or more of P, B and S modified CN carriers. The single-atom Rh catalyst constructed by embedding a single atom of Rh into the non-metal modified carrier shows excellent CO2 hydrogenation performance, and the ethanol selectivity reaches 81.8%, and the stability is relatively high. The active sites are modified by non-metals, so that the coordination environment and electronic properties of the active sites are regulated, and an effective site pair catalytic system is provided for high selectivity of CO2 hydrogenation to form ethanol.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation and application of a non-metal modified single-atom catalyst for CO2 hydrogenation to ethanol, and belongs to the field of carbon dioxide conversion. BACKGROUND

[0002] With the massive consumption of chemical fuels and the excessive emission of greenhouse gas CO2 in the atmosphere, fuel shortage and environmental problems seriously affect the survival and development of human society. Therefore, the capture and utilization of CO2 have attracted the attention of researchers. As a safe and renewable C1 resource, the activation of CO2 and its hydrogenation to prepare high-value chemicals such as CO, CH4, olefins, aromatic hydrocarbons and alcohols has important significance for realizing carbon neutralization and promoting the development of circular economy. Ethanol (EtOH) is an important chemical raw material, which can be converted into other chemical substances such as ethylene and its derivatives. At present, ethanol is mainly produced by grain fermentation, which not only consumes grain resources, but also lacks environmental sustainability. Therefore, the development of syngas (CO2 / H2) to produce ethanol has great application prospects. However, since CO2 is a completely oxidized, thermodynamically stable and chemically inert molecule, the formation of ethanol requires C-C coupling, and the C-C coupling process is difficult to control, so it is still a great challenge to directly convert CO2 into ethanol with high activity and high selectivity.

[0003] At present, the catalytic systems for CO2 hydrogenation to ethanol reported in the literature mainly include noble metal-based, Fischer-Tropsch-based and multi-element composite catalysts. Among them, Rh-based catalysts have attracted widespread attention in the production of ethanol with high selectivity. However, the high cost of Rh limits its practical application, so strategies need to be taken to maximize its use. Single-atom catalysts (SACs) have attracted great attention due to their 100% atom utilization. In recent years, metal-organic framework materials (MOFs) and their derived carbon materials have been widely used in the field of catalysis due to their unique pore characteristics, which can effectively confine metal nanoparticles in the pores. Zinc-based zeolitic imidazolate framework (ZIF-8) is a typical MOF material, which can be converted into nitrogen-doped porous carbon material after pyrolysis under inert atmosphere. The coordination structure of the carbon material can be regulated by replacing the coordination N atom in the metal-N4 with a heteroatom (such as sulfur, boron or phosphorus). However, the research on the reaction path of non-metal modified single-atom catalysts in CO2 hydrogenation has not been reported so far. In addition, due to the lack of proper interaction between the active metal and the support, the catalyst is prone to agglomeration and deactivation.

[0004] Therefore, it is still a research difficulty to develop a non-metal modified single-atom catalyst with high activity, high selectivity and excellent stability for CO2 hydrogenation to ethanol. SUMMARY

[0005] To solve the above problems, the application adopts a non-metal modification strategy to regulate the coordination environment and electronic structure of active metal sites, thereby affecting CO2 activation and reaction path. The catalyst can effectively convert CO2 hydrogenation products from methanol to ethanol and effectively inhibit the formation of by-products (such as CO and CH4) in the process of CO2 hydrogenation to ethanol, and the catalyst has excellent stability.

[0006] The first object of the application is to provide a preparation method of a non-metal modified single-atom catalyst for catalyzing CO2 hydrogenation to ethanol, comprising the following steps:

[0007] (1) Dissolve 2-methylimidazole in a certain amount of methanol to form solution A; dissolve zinc salt, active metal precursor and non-metallic additive precursor in a certain amount of methanol to form solution B, quickly add solution A to solution B, stir uniformly at room temperature, and obtain a mixed solution;

[0008] (2) Transfer the obtained mixed solution to a high-pressure hydrothermal kettle for solvothermal reaction. After the reaction is completed, the solvothermal product is washed, dried and calcined to obtain the catalyst.

[0009] In an embodiment of the application, the concentration of solution A in step (1) is 0.1-2.0 mol / L; specifically, 0.5 mol / L can be selected.

[0010] In an embodiment of the application, the concentration of zinc nitrate in solution B in step (1) is 0.1-2.0 mol / L; specifically, 0.27 mol / L can be selected.

[0011] In an embodiment of the application, the concentration of active metal precursor in solution B in step (1) is 0.001-2.0 mol / L; specifically, 0.008 mol / L can be selected.

[0012] In an embodiment of the application, the concentration of non-metallic additive precursor in solution B in step (1) is 0.1-2.0 mol / L; specifically, 0.23 mol / L can be selected.

[0013] In an embodiment of the application, the zinc salt in step (1) can be zinc nitrate.

[0014] In an embodiment of the application, the active metal in step (1) is one or more of rhodium, palladium, iridium, cobalt, copper, iron and nickel.

[0015] In an embodiment of the application, the active metal precursor in step (1) is one or more of rhodium nitrate, palladium nitrate, chloroiridic acid, cobalt nitrate, copper nitrate, iron nitrate and nickel nitrate.

[0016] In an embodiment of the present application, the non-metallic additive precursor in step (1) is one or more of triphenylphosphine, phenylphosphine, dimethylphenylphosphine, trimethylphosphine, diphenyldisulfide, and boric acid.

[0017] In an embodiment of the present application, the stirring time in step (1) is 5-720 min.

[0018] In an embodiment of the present application, the conditions for the solvothermal reaction in step (2) are as follows: heating to 60-180℃ in an autoclave for 1-12 h.

[0019] In an embodiment of the present application, the drying temperature in step (2) is 40-120℃, and the drying time is 1-24 h.

[0020] In an embodiment of the present application, the atmosphere for the calcination in step (2) is any one of nitrogen, argon, hydrogen, and air.

[0021] In an embodiment of the present application, the calcination temperature in step (2) is 400-1200℃, and the calcination time is 1-12 h.

[0022] The present application provides a preparation method of the above-mentioned catalyst, specifically comprising the following steps:

[0023] (1) dissolving 2-methylimidazole in a certain amount of methanol to form solution A; dissolving zinc nitrate, an active metal precursor, and a non-metallic additive precursor in a certain amount of methanol to form solution B, and rapidly adding solution A to solution B, and stirring at room temperature for 5-720 min;

[0024] (2) after the stirring is completed, transferring the mixed solution to an autoclave for hydrothermal reaction at 60-180℃ for 1-12 h, washing the obtained hydrothermal product, and vacuum drying at 40-120℃ for 1-24 h. Finally, calcining the sample in different atmospheres at 400-1200℃ for 1-12 h to obtain the catalyst.

[0025] The present application provides a non-metallic modified single-atom catalyst for catalyzing CO2 hydrogenation to ethanol based on the above-mentioned method.

[0026] In an embodiment of the present application, the non-metallic modified single-atom catalyst is composed of an active component and a non-metallic modified carrier; wherein the active component comprises one or more of Rh, Pd, Ir, Fe, Co, Ni, and Cu; and the non-metallic modified carrier comprises one or more of P, B, and S modified CN carriers.

[0027] In an embodiment of the present application, the active component is highly dispersed on the non-metallic modified carrier at an atomic level.

[0028] In one embodiment of the present application, the non-metal includes one or more of triphenylphosphine, phenylphosphine, dimethylphenylphosphine, trimethylphosphine, diphenyldisulfide, boric acid.

[0029] In one embodiment of the present application, the content of the active component in the catalyst is 0.01% to 10% of the total mass of the catalyst; and the carrier is 90% to 99.99% of the total mass of the catalyst.

[0030] The present application also provides a method for preparing ethanol by hydrogenation of CO2, wherein the above non-metal modified single-atom catalyst is used as the hydrogenation catalyst.

[0031] In one embodiment of the present application, the method is to introduce CO2 / H2 synthesis gas into the catalyst for preparing ethanol by hydrogenation of CO2, and to perform the reaction of preparing ethanol by hydrogenation of CO2 in a reactor.

[0032] In one embodiment of the present application, the reactor is a batch tank reactor, a fixed bed or a slurry bed.

[0033] In one embodiment of the present application, the catalyst needs to be activated and pretreated before use, the pretreatment atmosphere is hydrogen or carbon monoxide, the pressure is 0.1 to 2 MPa, the temperature is 300 to 600℃, and the time is 1 to 10 h.

[0034] In one embodiment of the present application, the reaction conditions for preparing ethanol by hydrogenation of CO2 are as follows: CO2:H2=1:1 to 8, the reaction temperature is 100 to 350℃, and the reaction pressure is 1 to 10 MPa.

[0035] In one embodiment of the present application, the reaction temperature is further preferably 250 to 350℃.

[0036] In one embodiment of the present application, the reaction pressure is further preferably 3 to 10 MPa.

[0037] Compared with the prior art, the present application has the following beneficial effects:

[0038] (1) The present application introduces a non-metal modification concept to regulate the coordination environment and electronic structure of the active metal site. The modified catalyst has more defects and a larger specific surface area, can effectively anchor active component atoms and adsorb reactants and reaction intermediates, and obtains a highly dispersed single-atom catalyst. The catalyst of the present application realizes the conversion of the product of CO2 hydrogenation from methanol to ethanol by constructing a Rh single-atom catalyst with Rh anchored on a non-metal modified carrier, and the selectivity of ethanol reaches 81.8%, and the catalyst has excellent stability.

[0039] (2) The non-metal modification strategy proposed by the present application emphasizes the importance of regulating the coordination and electronic environment of the active metal sites, and provides insights for the design of site pair synergistic catalysis of metal sites and non-metal sites. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 Structure diagram of the non-metal modified monatomic catalyst of the present application.

[0041] Figure 2 Scanning electron microscope image of the Rh / CNP monatomic catalyst obtained in Example 1.

[0042] Figure 3 Spherical aberration electron microscope image of the Rh / CNP monatomic catalyst obtained in Example 1. DETAILED DESCRIPTION

[0043] In order to more clearly illustrate the present application, the present application will be further described below in conjunction with specific examples. It should be understood by those skilled in the art that the specific descriptions below are illustrative rather than limiting, and should not limit the protection scope of the present application.

[0044] The catalyst performance evaluation was carried out in a batch reactor. The specific catalyst performance evaluation method is as follows: the catalyst was subjected to reduction pre-activation treatment. The catalyst activation pre-treatment conditions were as follows: the pre-treatment atmosphere was high-purity hydrogen, the pressure was 0.1 MPa, the temperature was 300℃, and the time was 1 h. After reduction, the raw material gas of CO2:H2=1:3 was charged into the reactor to 3 MPa, the reaction temperature was raised to 250℃, and then the reaction was started. The catalyst mass was 30 mg, the solvent was water, the solvent volume was 20 mL, the rotation speed was 400 rpm, and the reaction time was 5 h. The gaseous product after reaction was subjected to online analysis by chromatography, and the liquid phase product was analyzed by nuclear magnetic resonance spectrum.

[0045] CO2 conversion rate = (moles of CO2 before reaction - moles of CO2 after reaction) / moles of CO2 before reaction x 100%;

[0046] Product selectivity = (moles of product x number of carbon atoms in product molecule) / (moles of CO2 before reaction - moles of CO2 after reaction) x 100%.

[0047] Catalyst system for hydrogenation of CO2 to ethanol and preparation method thereof

[0048] Example 1

[0049] First step, 2.62 g 2-methylimidazole was dissolved in 60 mL methanol to form solution A; 2.38 g zinc nitrate, 0.073 g rhodium nitrate and 1.829 g triphenylphosphine were mixed and dissolved in 30 mL methanol to form solution B, solution A was quickly added to solution B, and stirred at room temperature for 30 min;

[0050] Second step, after stirring, the mixed solution was transferred to a high-pressure hydrothermal kettle for solvothermal reaction, and reacted at 120°C for 4h, the obtained solvothermal product was centrifuged, washed with methanol three times, and the filter cake was vacuum dried at 70°C for 12h. Finally, the sample was calcined at 950°C for 3h under nitrogen atmosphere, to obtain the catalyst Rh / CNP. The Rh element content in the catalyst was 0.09wt%, and the P element content was 1.43wt%. The scanning electron microscope and spherical aberration electron microscope images of the obtained Rh / CNP single-atom catalyst are shown in Figure 2 and 3 .

[0051] Example 2

[0052] The active metal precursor of the first step of Example 1 was changed to equimolar amount of palladium nitrate, and the remaining steps and operations were unchanged, to obtain Pd / CNP catalyst.

[0053] Example 3

[0054] The active metal precursor of the first step of Example 1 was changed to equimolar amount of iridic chloride, and the remaining steps and operations were unchanged, to obtain Ir / CNP catalyst.

[0055] Example 4

[0056] The active metal precursor of the first step of Example 1 was changed to equimolar amount of iron nitrate, and the remaining steps and operations were unchanged, to obtain Fe / CNP catalyst.

[0057] Example 5

[0058] The active metal precursor of the first step of Example 1 was changed to equimolar amount of cobalt nitrate, and the remaining steps and operations were unchanged, to obtain Co / CNP catalyst.

[0059] Example 6

[0060] The active metal precursor of the first step of Example 1 was changed to equimolar amount of copper nitrate, and the remaining steps and operations were unchanged, to obtain Cu / CNP catalyst.

[0061] Example 7

[0062] The active metal precursor of the first step of Example 1 was changed to equimolar amount of nickel nitrate, and the remaining steps and operations were unchanged, to obtain Ni / CNP catalyst.

[0063] Example 8

[0064] The triphenylphosphine in the first step of Example 1 was replaced by equimolar amount of phenylphosphine, and the rest of the steps and operations were unchanged, i.e. Rh / CNP-2 catalyst was obtained.

[0065] Example 9

[0066] The triphenylphosphine in the first step of Example 1 was replaced by equimolar amount of trimethylphosphine, and the rest of the steps and operations were unchanged, i.e. Rh / CNP-3 catalyst was obtained.

[0067] Example 10

[0068] The triphenylphosphine in the first step of Example 1 was replaced by equimolar amount of diphenyl disulfide, and the rest of the steps and operations were unchanged, i.e. Rh / CNS catalyst was obtained.

[0069] Example 11

[0070] The triphenylphosphine in the first step of Example 1 was replaced by equimolar amount of boric acid, and the rest of the steps and operations were unchanged, i.e. Rh / CNB catalyst was obtained.

[0071] Application of catalysts for hydrogenation of CO2 to ethanol:

[0072] The catalysts obtained in the above examples were placed in a batch reactor for reduction pre-activation treatment. After reduction treatment, the reaction conditions were 250℃, 3MPa, the catalyst mass was 30mg, the solvent was water, the solvent volume was 20mL, the rotation speed was 400rpm, and the reaction time was 5h. The conversion rate and the selectivity or distribution of each product were shown in Table 1. The catalysts after reaction were recovered and marked as runN (N was the number of cycles) for the next cycle test. The catalytic performance of the catalysts was shown in Table 1.

[0073] Example 12

[0074] The Rh / CNP catalyst was placed in a batch reactor, and the reaction temperature was changed to 175℃, and the rest of the parameters were unchanged. The conversion rate and the selectivity or distribution of each product were shown in Table 1.

[0075] Example 13

[0076] The Rh / CNP catalyst was placed in a batch reactor, and the reaction pressure was changed to 1MPa, and the rest of the parameters were unchanged. The conversion rate and the selectivity or distribution of each product were shown in Table 1.

[0077] Table 1 Catalytic performance of different catalysts

[0078]

[0079]

[0080] From the results in Table 1, it can be seen that the catalyst prepared by the catalyst preparation method of the present application exhibits high ethanol selectivity (81.8%) in the CO2 hydrogenation to ethanol, and the catalyst can still maintain good catalytic performance after five cycle tests, showing good catalytic stability.

[0081] Comparative Example 1

[0082] Only zinc nitrate and rhodium nitrate were added to solution B of the first step of Example 1, and other catalyst preparation steps were the same as those of Example 1, to obtain a Rh / CN catalyst, which was subjected to CO2 hydrogenation performance evaluation in a batch reactor at 250°C and 3 MPa. The conversion rate and product selectivity distribution results are shown in Table 2.

[0083] Comparative Example 2

[0084] Only zinc nitrate and palladium nitrate were added to solution B of the first step of Example 1, and other catalyst preparation steps were the same as those of Example 1, to obtain a Pd / CN catalyst, which was subjected to CO2 hydrogenation performance evaluation in a batch reactor at 250°C and 3 MPa. The conversion rate and product selectivity distribution results are shown in Table 2.

[0085] Comparative Example 3

[0086] Only zinc nitrate and chloroiridic acid were added to solution B of the first step of Example 1, and other catalyst preparation steps were the same as those of Example 1, to obtain an Ir / CN catalyst, which was subjected to CO2 hydrogenation performance evaluation in a batch reactor at 250°C and 3 MPa. The conversion rate and product selectivity distribution results are shown in Table 2.

[0087] Comparative Example 4

[0088] Only zinc nitrate and iron nitrate were added to solution B of the first step of Example 1, and other catalyst preparation steps were the same as those of Example 1, to obtain an Fe / CN catalyst, which was subjected to CO2 hydrogenation performance evaluation in a batch reactor at 250°C and 3 MPa. The conversion rate and product selectivity distribution results are shown in Table 2.

[0089] Comparative Example 5

[0090] Only zinc nitrate and cobalt nitrate were added to solution B of the first step of Example 1, and other catalyst preparation steps were the same as those of Example 1, to obtain a Co / CN catalyst, which was subjected to CO2 hydrogenation performance evaluation in a batch reactor at 250°C and 3 MPa. The conversion rate and product selectivity distribution results are shown in Table 2.

[0091] Comparative Example 6

[0092] The solution B of the first step of Example 1 was added with only zinc nitrate and copper nitrate, and other catalyst preparation steps were the same as Example 1, i.e. Cu / CN catalyst was obtained, and its CO2 hydrogenation performance was evaluated in a batch reactor, and the evaluation conditions were 250℃, 3MPa. The conversion rate and the product selectivity distribution results are shown in Table 2.

[0093] Comparative Example 7

[0094] The solution B of the first step of Example 1 was added with only zinc nitrate and nickel nitrate, and other catalyst preparation steps were the same as Example 1, i.e. Ni / CN catalyst was obtained, and its CO2 hydrogenation performance was evaluated in a batch reactor, and the evaluation conditions were 250℃, 3MPa. The conversion rate and the product selectivity distribution results are shown in Table 2.

[0095] Table 2 Catalytic performance of different catalysts for CO2 hydrogenation

[0096]

[0097] From the results in Table 2, it can be seen that the CO2 conversion rate of the catalyst loaded on the non-metal unmodified CN carrier is low, and only methanol is generated in the alcohol product, without ethanol.

[0098] Comparative Example 8

[0099] First step, 2.62g 2-methylimidazole was dissolved in 60mL methanol to form solution A; 2.38g zinc nitrate and 1.829g triphenylphosphine were mixed and dissolved in 30mL methanol to form solution B, and solution A was quickly added to solution B, and stirred at room temperature for 30min;

[0100] Second step, after stirring, the mixed solution was transferred to a high-pressure hydrothermal kettle for solvothermal reaction, and the reaction was carried out at 120℃ for 4h, and the obtained solvothermal product was centrifuged, washed with methanol three times, and the filter cake was vacuum dried at 70℃ for 12h to obtain a P-containing MOF material PPh3@ZIF-8;

[0101] Third step, 0.073g rhodium nitrate precursor was weighed in a flask, and methanol was added to dissolve it to obtain a brown solution, and PPh3@ZIF-8 was added to the flask and stirred for 1h. Then the impregnated sample was rotary evaporated at 60℃, and then vacuum dried at 70℃ for 12h. Finally, the sample was calcined at 950℃ for 3h under nitrogen atmosphere, and a catalyst Rh / CNP(IM) was obtained.

[0102] The Rh / CNP(IM) catalyst was evaluated for CO2 hydrogenation performance in a batch reactor, and the evaluation conditions were 250℃, 3MPa. The conversion rate and the product selectivity distribution results are shown in Table 3.

[0103] Table 3 Catalytic performance of Rh / CNP(IM) catalyst for CO2 hydrogenation

[0104]

[0105] As can be seen from the results in Table 3, both CO2 conversion and ethanol selectivity are low over Rh / CNP(IM) catalyst.

[0106] The above examples of the present application are merely illustrative for the sake of clarity of the present application, and are not intended to limit the present application. Various changes or modifications can be made by those skilled in the art based on the above description. It is impossible to enumerate all the embodiments here. Therefore, the scope of protection of the present application should be defined by the claims.

Claims

1. A method for preparing a non-metal modified single-atom catalyst for catalyzing the hydrogenation of CO2 to ethanol, characterized in that, The method comprises the following steps: (1) dissolving 2-methylimidazole in methanol to form solution A; dissolving a zinc salt, an active metal precursor and a non-metallic additive precursor in methanol to form solution B, rapidly adding solution A into solution B, stirring and mixing at room temperature to obtain a mixed solution; (2) transferring the mixed solution into a high-pressure hydrothermal kettle to perform a solvothermal reaction, after the reaction is completed, performing washing, drying and calcination on the solvothermal product to obtain a catalyst; In step (1), the active metal is rhodium; the non-metallic additive precursor is one or more of triphenylphosphine, phenylphosphine, dimethylphenylphosphine and trimethylphosphine.

2. The method of claim 1, wherein, In step (1), the concentration of solution A is 0.1-2.0 mol / L; the concentration of the zinc salt in solution B is 0.1-2.0 mol / L, the concentration of the active metal precursor is 0.001-2.0 mol / L, and the concentration of the non-metallic additive precursor is 0.1-2.0 mol / L.

3. The method according to any one of claims 1-2, in step (2), the solvothermal reaction is performed under the following conditions: heating in a high-pressure kettle to 60-180 ℃ for 1-12 h; the drying is performed at a temperature of 40-120 ℃ for 1-24 h; the calcination is performed in an atmosphere of any one of nitrogen and argon at a temperature of 400-1200 ℃ for 1-12 h.

4. A non-metallic modified single-atom catalyst for catalyzing CO2 hydrogenation to prepare ethanol, which is prepared by the method according to any one of claims 1-3.

5. A process for the production of ethanol by the hydrogenation of CO2, characterized in that, In the method, the non-metallic modified single-atom catalyst according to claim 4 is used as a hydrogenation catalyst.

6. The method of claim 5, wherein, The reaction of CO2 hydrogenation to prepare ethanol is performed in a reactor containing the non-metallic modified single-atom catalyst by introducing CO2 / H2 synthesis gas.

7. The method of claim 6, wherein, The reactor is a batch kettle reactor, a fixed bed or a slurry bed; the non-metallic modified single-atom catalyst needs to be activated and pretreated before use, the pretreatment atmosphere is hydrogen or carbon monoxide, the pressure is 0.1-2 MPa, the temperature is 300-600 °C, and the time is 1-10 h.

8. The method according to any one of claims 5-7, characterized in that, The reaction conditions of the CO2 hydrogenation to prepare ethanol are as follows: CO2:H2=1:1-8, the reaction temperature is 100-350 °C, and the reaction pressure is 1-10 MPa.

9. The method of claim 8, wherein, The reaction temperature is 250-350 °C, and the reaction pressure is 3-10 MPa.

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