A catalyst applied to catalytic carbon dioxide hydrogenation to form formic acid and a preparation method thereof

Abstract

The application belongs to the technical field of carbon dioxide hydrogenation, and particularly relates to a preparation method and application of an Ir monatomic catalyst for carbon dioxide hydrogenation to produce formic acid. A metal precursor, acetylacetone iridium Ir(acac)3, is in-situ coordinated and encapsulated in a complex cavity assembled with gallic acid coordination, and is carbonized at different temperatures (800 DEG C, 900 DEG C and 1000 DEG C) respectively, thereby successfully preparing monatomic catalysts with different coordination environments (Ir-N4, Ir-N3 and Ir-N2). The method is simple in operation, the obtained material structure is controllable, the carbon skeleton has good thermal stability and has a high specific surface area, the Ir is atomically dispersed and does not agglomerate, and in addition, the metal loading is low. The precise synthesis strategy of the catalyst is simple and feasible, easy to industrial production, can meet the needs of future carbon dioxide resource utilization and industrial production of bulk chemicals formic acid, and has good application prospect.

Description

Technical Field

[0001] This invention relates to the fields of carbon dioxide resource utilization technology and catalyst synthesis technology, specifically to a method for preparing and using an Ir single-atom catalytic material for the hydrogenation of carbon dioxide to formic acid. Background Technology

[0002] Carbon dioxide (CO2) is a major greenhouse gas that contributes to climate change and related adverse environmental impacts, making the mitigation of anthropogenic CO2 production a significant challenge. CO2 capture and conversion into energy is currently considered an effective way to mitigate the effects of global warming and find alternatives to fossil fuels. Currently, catalytic hydrogenation technology can convert CO2 into various fuels such as formic acid, methanol, olefins, and aromatics. Converting atmospheric CO2 into high-value-added formic acid, and using formic acid as a hydrogen carrier, not only reduces CO2 emissions and recycles atmospheric carbon resources, alleviating climate problems, but also, as a liquid hydrogen storage carrier, formic acid can alleviate energy shortages.

[0003] Catalysts are fundamental to catalytic conversion. Carbon-based catalysts, due to their high specific surface area, good chemical stability and tunability, environmental friendliness, and low cost, can load more active sites and remain stable during reactions. Furthermore, their catalytic performance can be modulated through surface modification or doping, and their preparation is low-cost and pollution-free, making them suitable for large-scale applications. Inexpensive pyrolytic complex precursors can yield carbon materials with high specific surface areas, which is beneficial for improving metal loading, dispersibility, and stability. Gallic acid (GA) metal complexes are simple and readily available, and their diverse structures (metal nodes and organic ligands, etc.) allow for tunable structure and pore structure of their derived carbon materials, and easy functionalization (introducing heteroatoms or functional groups). Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing an Ir single-atom catalyst for the catalytic hydrogenation of CO2 to formic acid, to explore the structure-activity relationship between the catalyst's metal site structure and catalytic activity, and to successfully prepare an Ir-acac@GA precursor structure encapsulated with iridium acetylacetone through an in-situ encapsulation strategy. This precursor was then mixed with dicyandiamide as a nitrogen source and carbonized at different temperatures (800℃, 900℃, and 1000℃) to obtain Ir-N catalysts with different N coordination environments. x (x = 4, 3 and 2) Single-atom catalysts.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] One method for preparing an Ir single-atom catalyst for the catalytic hydrogenation of CO2 to formic acid involves in-situ coordination and encapsulation of the metal precursor acetylacetone Ir(acac)3 within a cavity of a complex assembled with gallic acid. Dicyandiamide is then mixed as a nitrogen source, and the catalyst is carbonized at different temperatures to prepare single-atom catalysts with different nitrogen coordination environments. The preparation method includes the following steps:

[0007] S1. Dissolve gallic acid in methanol and label the solution as solution A. Dissolve Ir(acac)3 in methanol and label the solution as solution B. Then, pour solution A into solution B, which is being stirred rapidly, and continue stirring to ensure thorough mixing.

[0008] S2. The mixed solution was transferred to a hydrothermal reactor and kept at 120 °C for 4 h in a forced-air oven. Finally, after the hydrothermal reactor cooled to room temperature, the product was filtered and washed several times with methanol. The collected Ir-acac@GA precursor was then dried overnight in a vacuum oven at 80 °C.

[0009] S3. Place the Ir-acac@GA precursor mixed with dicyandiamide in a crucible, and heat it in a tube furnace at 5 °C·min under an Ar protective atmosphere. -1 The target temperature was reached and held for 3 h to obtain the corresponding Ir SACs catalysts. The carbonization temperatures of Ir-N4 SACs, Ir-N3 SACs, and Ir-N2 SACs catalysts were 800 ℃, 900 ℃, and 1000 ℃, respectively, with all other conditions kept consistent except for the carbonization temperature.

[0010] Another object of the present invention is to provide the application of the above-described Ir single-atom catalyst in the reduction of carbon dioxide to formic acid.

[0011] The above application technology includes the following steps: placing the Ir single-atom catalyst in a pressure reactor, introducing hydrogen and carbon dioxide gases to mix them in a 1:1 volume ratio, adding the catalyst material to the reactor, sealing the reactor, maintaining a total gas pressure of 2-6 MPa, heating to 110-140℃, using a 1 M KHCO3 solution (10 ml), and reacting for 2-24 hours.

[0012] The beneficial effects of this invention are as follows:

[0013] (1) By combining the strategy of in-situ encapsulation of precursors with high-temperature pyrolysis, uniform and stable anchoring of Ir single atoms on carbon support was achieved, and the Ir coordination environment can be conveniently controlled by the pyrolysis temperature.

[0014] (2) The obtained Ir-N2 SACs catalyst has significantly enhanced adsorption and activation capacity for H2 and CO2 hydrogenation activity due to the increased electron density of the Ir center and the upward shift of the d band center caused by the low coordination structure.

[0015] (3) Ir-N2 SACs exhibit excellent catalytic activity and stability in the reaction of CO2 hydrogenation to formic acid, with TON values ​​reaching over 6154 and up to 19400, showing good prospects for industrial application. Attached Figure Description

[0016] Figure 1 Aberration-corrected electron micrograph of Ir-N2 SACs.

[0017] Figure 2 Raman spectra of Ir-N4 SACs, Ir-N3 SACs and Ir-N2 SACs

[0018] Figure 3 Synchrotron radiation diagrams of Ir, Ir-N4 SACs (a), Ir-N3 SACs (b), and Ir-N2 SACs (c).

[0019] Figure 4 The catalytic performance of Ir-N4 SACs, Ir-N3 SACs, and Ir-N2 SACs at different reaction temperatures and the corresponding Arrhenius images are shown.

[0020] Figure 5 Images showing the catalytic performance of Ir-N2 SACs under different reactant gas pressures. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, all goods or reagents in the present invention are purchased through market channels.

[0022] Example 1: Preparation of Ir-N4 SACs

[0023] Gallic acid (530 mg) was dissolved in 30 mL of methanol, denoted as solution A. Ir(acac)3 (80 mg, 0.16 mmol) was dissolved in 25 mL of methanol, denoted as solution B. Solution A was poured into solution B, and the mixture was stirred rapidly for 5 min to obtain a clear solution. This solution was then transferred to a hydrothermal reactor and reacted at 120 °C for 4 h. After cooling to room temperature, the solution was filtered, washed three times with methanol, and dried under vacuum at 80 °C to obtain the Ir-acac@GA precursor. 100 mg of the precursor was mixed with 1 g of dicyandiamide and pyrolyzed at 800 °C for 3 h under an Ar atmosphere with a heating rate of 5 °C / min to obtain Ir-N4 SACs.

[0024] Example 2: Preparation of Ir-N3 SACs

[0025] Using the same precursor preparation method as in Example 1, but with the pyrolysis temperature changed to 900℃ and all other conditions remaining unchanged, Ir-N3 SACs were obtained.

[0026] Example 3: Preparation of Ir-N2 SACs

[0027] Using the same precursor preparation method as in Example 1, but with the pyrolysis temperature changed to 1000℃ and all other conditions remaining unchanged, Ir-N2 SACs were obtained.

[0028] Test Example 1:

[0029] Five mg of the obtained Ir-N2 SACs catalyst and 10 mL of 1.0 M KHCO3 solution were added to a high-pressure reactor, and a H2 / CO2 mixture (volume ratio 1:1) was introduced to a total pressure of 6.0 MPa. The reactor was reacted at 110℃, 120℃, 130℃, and 140℃ for 24 h, respectively. High-performance liquid chromatography (HPLC) analysis of the products showed that the formic acid yield catalyzed by Ir-N2 was superior to that of Ir-N4 and Ir-N3 at different temperatures, with a very significant performance difference. The total oxygen ionization (TON) of formic acid from Ir-N2 could reach as high as 6154.

[0030] Test Example 2:

[0031] Five mg of the obtained Ir-N2 SACs catalyst and 10 mL of 1.0 M KHCO3 solution were added to a high-pressure reactor. A H2 / CO2 mixture (volume ratio 1:1) was introduced to a total pressure of 2.0 MPa, 3.0 MPa, 4.0 MPa, 5.0 MPa, and 6.0 MPa, respectively, and the reaction was carried out at 150 °C for 24 h. High-performance liquid chromatography (HPLC) analysis showed that the formic acid yield was positively correlated with the pressure of the reaction gas. Increasing the reaction gas pressure helped improve the solubility of the two gaseous reactants in the reaction solution, thereby promoting the forward reaction and increasing the formic acid yield. The formic acid TON reached as high as 10691.

[0032] Calculate the TON and TOF of the catalyst using the following formulas:

[0033] TON = (Formic acid concentration in the reaction solution * volume of the reaction solution) / (molar amount of active sites of the metal in the catalyst)

[0034] TOF = TON / Reaction Time

[0035] The present invention is illustrated by the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of individual raw materials (gallic acid, noble metal Ir) in the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0036] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing an Ir single-atom catalyst for the catalytic hydrogenation of CO2 to formic acid, characterized in that, First, the metal precursor acetylacetone iridium Ir(acac)3 is in situ coordinated and encapsulated in the cavity of a complex assembled with gallic acid. Then, carbon material in the form of Ir single atoms is obtained after high-temperature pyrolysis. Carbonization at different temperatures yields single-atom catalysts with different N coordination environments.

2. The method for preparing an Ir single-atom catalyst for the catalytic hydrogenation of CO2 to formic acid according to claim 1, characterized in that: Gallic acid was completely dissolved in methanol, and the solution was denoted as solution A. Ir(acac)3 was completely dissolved in methanol, and the solution was denoted as solution B. Then, solution A was poured into solution B, which was being stirred rapidly, and stirring was continued after pouring to ensure that the solutions were fully mixed.

3. The method for preparing an Ir single-atom catalyst for the catalytic hydrogenation of CO2 to formic acid according to claim 2, characterized in that: The mixed solution was transferred to a hydrothermal reactor and kept at 120 °C for 4 h in a forced-air oven. Finally, after the hydrothermal reactor cooled to room temperature, the product was filtered and washed several times with methanol. The collected Ir-acac@GA precursor was then dried overnight in a vacuum oven at 80 °C.

4. The method for preparing an Ir single-atom catalyst for the catalytic hydrogenation of CO2 to formic acid according to claim 3, characterized in that: The Ir-acac@GA precursor and a measured amount of dicyandiamide were placed in a crucible and heated to the target temperature in a tube furnace under an Ar protective atmosphere to obtain the corresponding Ir SACs catalyst.

5. The method for preparing an Ir single-atom catalyst for the catalytic hydrogenation of CO2 to formic acid according to claim 4, characterized in that: The heating rate is 5 °C·min -1 The holding time was 3 h; the corresponding carbonization temperatures of Ir-N4 SACs, Ir-N3 SACs and Ir-N2 SACs catalysts were 800 ℃, 900 ℃ and 1000 ℃, respectively, and all other conditions were kept consistent except for the carbonization temperature.

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