Ruthenium grafted manganese-aluminum hydrotalcite and method for preparing formic acid by catalyzing CO2 hydrogenation

Abstract

The invention discloses ruthenium-grafted manganese-aluminum hydrotalcite and a method for preparing formic acid by catalyzing CO2 hydrogenation, and belongs to the technical field of catalysts, in the invention, under optimized reaction conditions, a mixture of methanol and water is used as a solvent (5: 1), the total pressure is 60bar, the temperature is 60 DEG C, the reaction is performed for 24 hours, and a reactor is heated to the required temperature by using a temperature controller. When the internal temperature of the reactor reaches a specified temperature, stirring is started at a fixed stirring speed (200-800 revolutions per minute), and stirring and heating are stopped after a required reaction time, so that the reactor is cooled to room temperature. A hydrogenation product is analyzed by adopting a high performance liquid chromatography, and the conversion number (TON) of formic acid reaches 8000 or above; ruMnAl-LDH is prepared through a coprecipitation method, the RuMnAl-LDH catalyst is obtained through heating activation of a muffle furnace, the preparation process is simple, and raw materials are easy to obtain. The RuMnAl-LDH catalyst prepared by the invention has good catalytic activity and catalytic stability in a reaction for preparing formic acid by catalytic hydrogenation of formic acid, and has a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and specifically relates to a ruthenium-grafted manganese-aluminum hydrotalcite and a method for catalyzing the hydrogenation of CO2 to produce formic acid. Background Art

[0002] As a potent greenhouse gas, CO2 is an important factor in global warming. Converting CO2 into useful chemicals can reduce or inhibit CO2 emissions while obtaining added value, which is a promising green process route for treating CO2. Formic acid has indispensable applications in many fields such as textile, printing and dyeing, medicine, and perfume industries, and plays an important role in chemical synthesis and hydrogen energy storage and transportation. The synthesis of formic acid by catalytic hydrogenation of CO2 can not only effectively alleviate the greenhouse effect and climate problems caused by CO2 emissions, but also produce formic acid products with high added value, which has both environmental and economic benefits. Excellent catalysts are the core factors for the hydrogenation of CO2 to produce formic acid. The catalysts used for the hydrogenation of CO2 to produce formic acid include homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts based on transition metal complexes have fast reaction rates and high catalytic activity, but have the defects of difficult separation and recovery of catalysts and poor catalytic stability, which limits their further industrial application. In contrast, heterogeneous catalysts are easy to separate and recover and have good stability. Therefore, the design of catalysts for the catalytic hydrogenation of CO2 to produce formic acid is increasingly focused on heterogeneous catalytic systems. The construction of heterogeneous catalysts usually requires a carrier, and the selection of a carrier with excellent performance is of great significance for improving catalytic activity and selectivity.

[0003] Hydrotalcite is a type of layered double metal hydroxide that is easy to prepare and easy to graft metals. It can be modified by anion intercalation, adjusting the metal molar ratio, etc. to optimize catalytic performance, and is often used to construct heterogeneous catalysts. For example, CN116174034 A uses a uniform precipitation method to prepare a catalyst precursor CaZnAl hydrotalcite, and then calcines it at high temperature to obtain a CaZnAl-O solid base to catalyze the synthesis of dodecyl alcohol esters; Catalysts2022,12,759 uses an organic base tetramethylammonium hydroxide (TMAH) to design and synthesize MgZnAl-LDH type materials for catalyzing Claisen-Schmidt condensation.

[0004] However, most carrier materials have problems such as high cost and complex synthesis routes, which are not conducive to their industrial production. Hydrotalcite has low cost, wide sources, and is easy to graft metals. Using hydrotalcite as a carrier material to graft Ru metal provides a simple, convenient and low-cost method for the synthesis of heterogeneous catalysts for CO2 hydrogenation to formic acid. Summary of the invention

[0005] The object of the present invention is to provide a ruthenium-grafted manganese-aluminum hydrotalcite and a method for catalyzing the hydrogenation of CO2 to produce formic acid in order to solve the above-mentioned problems.

[0006] The technical solution adopted by the present invention is as follows: under optimized reaction conditions, a methanol:water mixture is used as a solvent (5:1, v / v), a total pressure of 60 bar, 60° C., and a reaction time of 24 hours, and the conversion number (TON) of formic acid reaches more than 8000;

[0007] A ruthenium-grafted manganese aluminum hydrotalcite and a method for catalyzing CO2 hydrogenation to produce formic acid, comprising the following steps:

[0008] S1: RuCl3·xH2O, Mn(NO3)2 and Al(NO3)3·9H2O are mixed according to: Ru:Mn:Al=

[0009] A mixed salt solution obtained by dissolving in deionized water at a molar ratio of (0.5-2):(50-200):20;

[0010] S2: Add dropwise to 1.6M NaNO3 solution and continue stirring for about 45 minutes;

[0011] S3: Use 1M NaOH solution to keep the pH constant at 10;

[0012] S4: The resulting mixture was transferred to a stainless steel autoclave coated with polytetrafluoroethylene, aged at 80 °C for 16 h, filtered and washed;

[0013] S5: drying the solid material at 80° C., grinding it and preserving it in vacuum to obtain a RuMnAl hydrotalcite solid powder, and then activating it in a muffle furnace at 500° C. for 4 hours to obtain a RuMnAl-LDH heterogeneous catalyst;

[0014] S6: Fill the reactor with a proper amount of catalyst, a mixed solution of methanol and deionized water, flush the reactor with CO2 three times to remove air, introduce CO2 / H2 (1:1, p / p) to a suitable pressure, and then raise the temperature to start the reaction;

[0015] S7: After the reaction is completed, the obtained products are collected together to obtain the prepared formic acid, and then the entire process of ruthenium grafted manganese aluminum hydrotalcite and catalytic C02 hydrogenation to produce formic acid can be completed.

[0016] In a preferred embodiment, in step S1, the molar ratio of Ru, Mn and Al is 1:100:28.

[0017] In a preferred embodiment, in step S6, the volume ratio of methanol to deionized water in a 100 ml autoclave is 5:1, and the amount of catalyst used is 60-100 mg.

[0018] In a preferred embodiment, in step S6, the volume ratio of methanol and deionized water in a 100 ml autoclave is 5:1, and the amount of catalyst used is 90 mg.

[0019] In a preferred embodiment, in step S6, the reaction temperature is 60° C. during the process of introducing CO 2 / H 2 (1:1, p / p) to a suitable pressure and then heating to start the reaction.

[0020] In a preferred embodiment, in step S6, after CO2 / H2 (1:1, p / p) is introduced to a suitable pressure and the temperature is raised to start the reaction, the stirring rate is 800 rpm.

[0021] In a preferred embodiment, in step S6, after CO2 / H2 (1:1, p / p) is introduced to a suitable pressure and the temperature is raised to start the reaction, the final pressure is pCO2=30 bar, pH2=30 bar.

[0022] In a preferred embodiment, the RuMnAl-LDH catalyst is used in the catalytic hydrogenation of CO2 to produce formic acid. The hydrogenation of carbon dioxide needs to be carried out under high pressure and high temperature. A 100 ml autoclave is used. All operations involving gas injection are carried out in a well-ventilated fume hood. The specific steps are as follows:

[0023] A certain amount of catalyst, methanol and deionized water solution mixed in a required volume ratio are filled into the reactor.

[0024] The vessel was sealed, the reactor was flushed three times with CO2 to remove air, and then pressurized with CO2 / H2 (1:1, p / p) to the final desired total pressure (p / p).

[0025] The reactor is heated to the required temperature using a temperature controller. When the temperature inside the reactor reaches the specified temperature, stirring is started at a fixed stirring speed (200-800 rpm), which is considered the start of the reaction.

[0026] After the desired reaction time, stirring and heating were stopped and the reactor was allowed to cool to room temperature.

[0027] The reactor was depressurized at room temperature, the vessel was opened, and the reaction solution was collected by simple filtration to separate the catalyst.

[0028] The hydrogenation products were analyzed by HPLC and their concentrations were determined by a standard calibration curve plotted between area and formic acid concentration at a wavelength of 190 nm.

[0029] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0030] In the present invention, under optimized reaction conditions, a methanol: water mixture is used as a solvent (5:1), a total pressure of 60 bar, 60°C, and a reaction time of 24 hours, and the conversion number (TON) of formic acid reaches more than 8000; RuMnAl-LDH is prepared by a coprecipitation method, and a RuMnAl hydrotalcite catalyst is obtained by heating and activating in a muffle furnace. The preparation process is simple and the raw materials are easily available. The RuMnAl-LDH catalyst prepared by the present invention has good catalytic activity and catalytic stability in the reaction of catalytic hydrogenation of formic acid to produce formic acid, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the process principle of the present invention;

[0032] Figure 2 It is the SEM picture of the RuMnAl-LDH catalyst in the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] Reference Figure 1-2 ,

[0035] Embodiment 1:

[0036] A preparation method of a RuMnAl-LDH catalyst comprises the following steps:

[0037] (1) Prepare solution A: Dissolve 6.8 g of NaNO3 in 50 ml of deionized water to obtain a 1.6 M NaNO3 solution for use. Solution B is a mixed salt solution obtained by dissolving RuCl3·xH2O, Mn(NO3)2 and Al(NO3)3·9H2O in deionized water at a certain molar ratio.

[0038] (2) Prepare solution B: Mix 0.1 g RuCl3·xH2O, 9 g Mn(NO3)2, and 3.5 g Al(NO3)3·9H2O and dissolve them in 50 ml deionized water.

[0039] (3) Solution B was added dropwise to solution A at room temperature and stirred for about 45 minutes. 1 M NaOH solution was used to maintain a constant pH of 10.

[0040] (4) The resulting mixture was transferred to a stainless steel autoclave coated with polytetrafluoroethylene and aged at 80°C for 16 hours.

[0041] (5) The precipitate is filtered and washed with hot distilled water to remove unreacted ions.

[0042] (6) The solid material obtained in step (5) is dried in a vacuum drying oven at 80° C., ground and stored in a vacuum oven to obtain a RuMnAl hydrotalcite solid powder.

[0043] (7) Activate the solid powder obtained in step (6) in a muffle furnace at 500° C. for 4 hours to obtain a RuMnAl hydrotalcite catalyst.

[0044] Embodiment 2:

[0045] A method for preparing formic acid by catalyzing CO2 hydrogenation with ruthenium-grafted manganese-aluminum hydrotalcite, comprising the following steps:

[0046] (1) A mixed solution of 60 mg of catalyst, 10 ml of methanol and 1 ml of deionized water was injected into an autoclave reactor.

[0047] (2) Seal the container, flush the reactor with CO2 three times to remove air, and then pressurize it with CO2 / H2 (1:1, p / p) to pCO2 = 30 bar, pH2 = 30 bar.

[0048] (3) Heat the reactor to 60°C using a temperature controller. When the temperature inside the reactor reaches the specified temperature, stir at 800 rpm, and the reaction is considered to have started.

[0049] (4) After the desired reaction time, stop stirring and heating and allow the reactor to cool to room temperature.

[0050] (5) The reactor is depressurized at room temperature, the container is opened, and the reaction solution is collected by simple filtration to separate the catalyst.

[0051] (6) The hydrogenation products were analyzed by high performance liquid chromatography, and the concentration of the hydrogenation products was determined by a standard calibration curve plotted against formic acid concentration at a wavelength of 190 nm.

[0052] Embodiment 3:

[0053] A ruthenium-grafted manganese-aluminum hydrotalcite and a method for catalyzing the hydrogenation of CO2 to produce formic acid, which differs from Example 2 in that the amount of catalyst used is different. The amount of catalyst used in this example is 70 mg, and the rest is the same as Example 2, and a catalytic experiment is carried out.

[0054] Embodiment 4:

[0055] A ruthenium-grafted manganese-aluminum hydrotalcite and a method for catalyzing the hydrogenation of CO2 to produce formic acid, which differs from Example 2 in that the amount of catalyst used is different. The amount of catalyst used in this embodiment is 80 mg, and the rest is the same as Example 2, and a catalytic experiment is carried out.

[0056] Embodiment 5:

[0057] A ruthenium-grafted manganese-aluminum hydrotalcite and a method for catalyzing the hydrogenation of CO2 to produce formic acid, which differs from Example 2 in that the amount of catalyst used is different. The amount of catalyst used in this example is 90 mg, and the rest is the same as Example 2, and a catalytic experiment is carried out.

[0058] Embodiment 6:

[0059] A ruthenium-grafted manganese-aluminum hydrotalcite and a method for catalyzing the hydrogenation of CO2 to produce formic acid, which differs from Example 2 in that the amount of catalyst used is different. The amount of catalyst used in this example is 100 mg, and the rest is the same as Example 2, and a catalytic experiment is carried out.

[0060] The formic acid yields of Examples 2 to 6 are shown in Table 1 below:

[0061]

[0062] It can be seen from Table 1 that when the catalyst dosage is 90 mg and 100 mg, the formic acid generation rate is the highest, so Example 5 with a smaller catalyst dosage is selected to carry out the cycle stability experiment, see Example 7 for details.

[0063] Example 7: Recovery and recycling of a RuMnAl-LDH catalyst after a catalytic CO2 hydrogenation to formic acid, the steps are as follows:

[0064] (1) The catalyst obtained in Example 5 was separated, washed with deionized water and dried at 80°C.

[0065] (2) The dried catalyst is further used to catalyze the hydrogenation of CO2 to produce formic acid, and the operating steps are the same as those in Example 2.

[0066] (3) Determine and record the formic acid generation rate during each cycle, and obtain Table 2.

[0067]

[0068] From the above experimental results, we can know that:

[0069] In the present invention, under optimized reaction conditions, a methanol: water mixture is used as a solvent (5:1), a total pressure of 60 bar, 60°C, and a reaction time of 24 hours, and the conversion number (TON) of formic acid reaches more than 8000; RuMnAl-LDH is prepared by a coprecipitation method, and a RuMnAl hydrotalcite catalyst is obtained by heating and activating in a muffle furnace. The preparation process is simple and the raw materials are easily available. The RuMnAl-LDH catalyst prepared by the present invention has good catalytic activity and catalytic stability in the reaction of catalytic hydrogenation of formic acid to produce formic acid, and has broad application prospects.

[0070] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the term "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0071] The above description enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing formic acid by catalyzing CO2 hydrogenation and ruthenium-grafted manganese-aluminum hydrotalcite, characterized in that: The steps include: S1: RuCl3·xH2O, Mn(NO3)2 and Al(NO3)3·9H2O are mixed according to: Ru:Mn:Al= A mixed salt solution obtained by dissolving in deionized water at a molar ratio of (0.5-2):(50-200):20; S2: Add dropwise to 1.6M NaNO3 solution and continue stirring for about 45 minutes; S3: Use 1M NaOH solution to keep the pH constant at 10; S4: The resulting mixture was transferred to a stainless steel autoclave coated with polytetrafluoroethylene, aged at 80 °C for 16 h, filtered and washed; S5: drying the solid material at 80° C., grinding it and preserving it in vacuum to obtain a RuMnAl hydrotalcite solid powder, and then activating it in a muffle furnace at 500° C. for 4 hours to obtain a RuMnAl-LDH heterogeneous catalyst; S6: Fill the reactor with a proper amount of catalyst, a mixed solution of methanol and deionized water, flush the reactor with CO2 three times to remove air, introduce CO2 / H2 (1:1, p / p) to a suitable pressure, and then raise the temperature to start the reaction; S7: After the reaction is completed, the obtained products are collected together to obtain the prepared formic acid, and then the entire process of ruthenium grafted manganese aluminum hydrotalcite and catalytic C02 hydrogenation to produce formic acid can be completed.

2. A ruthenium-grafted manganese aluminum hydrotalcite and a method for catalyzing CO2 hydrogenation to prepare formic acid as claimed in claim 1, characterized in that: In the step S1, the molar ratio of Ru, Mn and Al is 1:100:

28.

3. A ruthenium-grafted manganese aluminum hydrotalcite and a method for catalyzing CO2 hydrogenation to prepare formic acid as claimed in claim 1, characterized in that: In the step S6, the volume ratio of methanol to deionized water in the 100 ml autoclave is 5:1, and the amount of catalyst used is 60-100 mg.

4. A ruthenium-grafted manganese aluminum hydrotalcite and a method for catalyzing CO2 hydrogenation to prepare formic acid as claimed in claim 1, characterized in that: In the step S6, the volume ratio of methanol to deionized water in the 100 ml autoclave is 5:1, and the amount of catalyst used is 90 mg.

5. A ruthenium-grafted manganese aluminum hydrotalcite and a method for catalyzing CO2 hydrogenation to prepare formic acid as claimed in claim 1, characterized in that: In the step S6, the reaction temperature is 60° C. after CO 2 / H 2 (1:1, p / p) is introduced to a suitable pressure and the temperature is raised to start the reaction.

6. A ruthenium-grafted manganese aluminum hydrotalcite and a method for catalyzing CO2 hydrogenation to prepare formic acid as claimed in claim 1, characterized in that: In the step S6, after CO2 / H2 (1:1, p / p) is introduced to a suitable pressure, the temperature is raised and the stirring rate is 800 rpm during the reaction.

7. A ruthenium-grafted manganese aluminum hydrotalcite and a method for catalyzing CO2 hydrogenation to prepare formic acid as claimed in claim 1, characterized in that: In step S6, CO2 / H2 (1:1, p / p) is introduced to a suitable pressure and then the temperature is raised to start the reaction, and the final pressure is pCO2=30 bar, pH2=30 bar.

8. A ruthenium-grafted manganese aluminum hydrotalcite and a method for catalyzing CO2 hydrogenation to prepare formic acid as claimed in claim 1, characterized in that: In step S6, the specific steps are as follows: (1) Filling a reactor with a certain amount of catalyst, methanol and deionized water mixed in a required volume ratio; (2) Seal the container, flush the reactor with CO2 three times to remove air, and then pressurize it with CO2 / H2 (1:1, p / p) to the final required total pressure (p / p); (3) Using a temperature controller to heat the reactor to the desired temperature; when the temperature inside the reactor reaches the specified temperature, stirring is started at a fixed stirring speed (200-800 rpm), which is considered the start of the reaction; (4) After the desired reaction time, stop stirring and heating and allow the reactor to cool to room temperature; (5) The reactor is depressurized at room temperature, the container is opened, and the reaction solution is collected by simple filtration to separate the catalyst; (6) The hydrogenation products were analyzed by high performance liquid chromatography, and the concentration of the hydrogenation products was determined by a standard calibration curve plotted against formic acid concentration at a wavelength of 190 nm.

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