A method for one-step preparation of methylamine by carbon dioxide hydrogenation amination

Abstract

A method for one-step preparation of methylamine by hydrogenation amination of carbon dioxide, belonging to the field of catalysis. In a fixed-bed reactor, carbon dioxide, hydrogen, and ammonia are reacted. The catalyst comprises a microporous or mesoporous silica support, and the active component includes indium, zirconium, and at least one metal promoter selected from nickel, copper, palladium, rhodium, and platinum; the In 3d... 5 / 2 The binding energy is 444.0~444.7 eV, which is more than 0.2 eV lower than that of pure indium oxide; the single-pass conversion rate of carbon dioxide is not less than 50%, the total selectivity of methylamine is not less than 80%, and the selectivity of the byproduct carbon monoxide is not higher than 20%. This invention constructs a unique In-Zr-M active center, with In, Zr, and M uniformly co-distributed at the nanoscale. By adjusting the NH3 / CO2 ratio, the ratio of dimethylamine to trimethylamine can be controlled. The catalyst of this invention exhibits excellent performance and good stability, and has broad application prospects in the fields of carbon dioxide resource utilization and green synthesis of methylamine.

Description

Technical Field

[0001] This invention relates to the field of catalysis, and more particularly to a method for one-step preparation of methylamine by hydrogenation amination of carbon dioxide. Background Technology

[0002] Methylamine, including monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA), is an indispensable key chemical raw material for the synthesis of pesticides, pharmaceuticals, dyes, solvents, and high-performance materials. Common laboratory methods for synthesizing methylamine compounds mainly involve reacting alkylating agents (such as alcohols, aldehydes, acids, and esters) with amine compounds in the presence of reducing agents and catalysts. Alternatively, nitrogen-containing compounds, such as nitro compounds and nitrile compounds, can be directly reduced to methylamine. These methods generate harmful byproducts and waste (such as salts), and the catalysts are difficult to recover and reuse, limiting their large-scale application.

[0003] Currently, the mainstream industrial method for producing methylamine is the methanol amination process. This process typically involves reacting methanol and ammonia at high temperatures (350-500℃) with acidic molecular sieves or alumina catalysts to produce a methylamine mixture. Although the technology is mature, this route relies on methanol derived from fossil resources as a carbon source and involves two separate stages: methanol synthesis and amination. The process is lengthy and energy-intensive. Utilizing carbon dioxide as a renewable carbon source, directly synthesizing methylamine in one step with green hydrogen (H2) and ammonia (NH3) through catalytic hydrogenation amination, not only provides a new pathway for the high-value utilization of CO2 resources but also holds promise for achieving green and sustainable methylamine production, possessing significant strategic importance. However, this reaction pathway is complex, involving multiple elementary steps such as CO2 hydrogenation, intermediate (e.g., formaldehyde, formamide) formation, CN-C bond coupling, and subsequent methylation. Furthermore, it faces intense competition from side reactions such as reverse water-gas shift reaction (RWGS, which produces CO). Therefore, developing highly efficient and selective multifunctional catalysts is crucial for achieving a breakthrough in this technology.

[0004] Currently, the publicly disclosed catalyst systems for the hydrogenation and amination of CO2 to produce methylamine can be mainly divided into the following two categories: (1) Modified copper-based catalysts: For example, CN110563592A discloses a core-shell structure catalyst (Cu-based core / molecular sieve shell) for the one-step production of dimethylamine from CO2, H2, and NH3. This scheme separates the hydrogenation and amination functions in space. However, its CO2 conversion rate still has room for improvement, and the preparation process of the core-shell structure is relatively complex. (2) Noble metal or transition metal-based catalysts: Early studies used metals such as Fe, Rh, and Pd supported on oxide supports. These systems tend to catalyze the deep hydrogenation of CO2 to produce methane or promote the RWGS reaction, resulting in extremely low selectivity for methylamine and excessively high selectivity for the byproduct CO.

[0005] In summary, existing catalysts used in the CO2 hydrogenation amination reaction generally suffer from one or more of the following technical defects: (1) The conversion rate of CO2 is generally low, which is difficult to meet industrial needs; (2) Severe side reactions such as RWGS result in high selectivity of CO by-product (usually >50%), which not only reduces carbon atom economy but also burdens subsequent product separation and tail gas treatment; (3) The preparation method of the catalyst is complex and not conducive to industrial scale-up; (4) There is a lack of systematic research and effective control strategies on the ratio of monomethylamine, dimethylamine and trimethylamine in the reaction products.

[0006] Therefore, there is an urgent need in this field to develop a novel catalyst that can not only achieve efficient CO2 conversion but also strongly suppress CO formation while selectively directing the methylamine product. Furthermore, if the distribution of different methylamine products can be flexibly controlled through simple process parameter adjustments, it will have even greater application value. Summary of the Invention

[0007] The purpose of this invention is to solve the above-mentioned problems in the prior art and provide a method for one-step preparation of methylamine by carbon dioxide hydrogenation amination, which can simultaneously achieve high activity, high methylamine selectivity and extremely low CO selectivity.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for one-step preparation of methylamine by carbon dioxide hydrogenation amination, comprising reacting a feed gas containing carbon dioxide, hydrogen, and ammonia in a fixed-bed reactor under the following conditions: reaction temperature 250–350 °C; reaction pressure 1–8 MPa; feed gas molar ratio CO2 : H2 : NH3 = 1 : (2–9) : (0.1–2); space velocity 6000–24000 mL·g -1 ·h -1 The catalyst used comprises a support and an active component supported on the support. The support is microporous or mesoporous silica, and the active component comprises indium (In), zirconium (Zr), and at least one metal promoter M selected from nickel (Ni), copper (Cu), palladium (Pd), rhodium (Rh), and platinum (Pt). In the catalyst, In 3d... 5 / 2 The binding energy is between 444.0 eV and 444.7 eV, and this binding energy is lower than that of the In 3dO3 standard of pure indium oxide. 5 / 2 The binding energy is 0.2 eV or lower; the single-pass conversion rate of carbon dioxide is not less than 50%, the total selectivity of methylamine products is not less than 80%, and the selectivity of the by-product carbon monoxide is not higher than 20%.

[0010] By adjusting the molar ratio of ammonia to carbon dioxide in the feed gas, the molar ratio of dimethylamine to trimethylamine in the reaction products can be controlled. When the molar ratio of ammonia to carbon dioxide is in the range of 0.1 to 0.8, the molar ratio of dimethylamine / trimethylamine is less than 1; when the molar ratio of ammonia to carbon dioxide is in the range of 1.0 to 2.0, the molar ratio of dimethylamine / trimethylamine is between 1 and 2.

[0011] When the molar ratio of CO2 : H2 : NH3 = 1 : (6~9) : (1~2), the reaction pressure is 1~3MPa, and the reaction temperature is 270℃~310℃, dimethylamine becomes the main methylamine product in the reaction products, and the molar ratio of dimethylamine to trimethylamine is greater than 1.

[0012] In the catalyst, indium, zirconium, and metal additive M are spatially uniformly distributed within a region of at least 50 nm × 50 nm.

[0013] The dispersion of the metal promoter M in the catalyst is not less than 40%.

[0014] The mass content of the metal promoter M in the catalyst is 0.1% to 8.0% based on the total mass of the catalyst.

[0015] In the catalyst, the mass ratio of indium to zirconium, calculated as metal oxides, is 10:1 to 1:1; and the total mass content of indium and zirconium oxides, calculated as the total mass of the catalyst, is 5% to 60%.

[0016] In the catalyst, the specific surface area of ​​the support is not less than 150 m². 2 g -1 .

[0017] The preparation of the catalyst includes the following steps:

[0018] 1) Provide a first precursor solution containing an indium source and a zirconium source;

[0019] 2) The first precursor solution is loaded onto the carrier and subjected to a first-stage heat treatment to obtain an intermediate containing indium-zirconium composite oxide;

[0020] 3) Provide a second precursor solution containing a metal auxiliary source M;

[0021] 4) The second precursor solution is loaded onto the intermediate and subjected to a second-stage reducing heat treatment to obtain the catalyst.

[0022] The first stage of heat treatment is carried out in an air atmosphere at a temperature of 300°C to 500°C for 1 to 4 hours; the second stage of reducing heat treatment is carried out in a hydrogen-containing atmosphere at a temperature of 200°C to 400°C for 1 to 4 hours.

[0023] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0024] 1. A breakthrough improvement in the performance of carbon dioxide hydrogenation amination: This invention, by constructing a unique In-Zr-M active center, simultaneously achieves high carbon dioxide conversion, high selectivity for methylamine products, and extremely low selectivity for the byproduct carbon monoxide on a single catalyst. Under optimal conditions, CO2 conversion can reach over 50%, the total selectivity for methylamine (MMA, DMA, TMA) can reach over 80%, while CO selectivity can be significantly suppressed to below 20%, achieving excellent technical results.

[0025] 2. The catalyst possesses a unique and stable active center structure: The catalyst of this invention is not a simple combination or physical mixture of active components. XPS characterization confirmed that the electronic state of indium in the active center undergoes a significant change (a negative shift in the In 3d binding energy), indicating that strong electronic interactions are formed between In, Zr, and the metal promoter M. This is considered the essential reason for its high activity and high selectivity. TEM-EDX mapping further confirmed the uniform co-distribution of active elements at the nanoscale. This structural characteristic enables the catalyst to exhibit excellent stability during continuous reactions lasting up to 100 hours.

[0026] 3. Provides a flexible means of controlling the distribution of methylamine products: Under the catalyst system described in this invention, the ratio of dimethylamine to trimethylamine (DMA / TMA) in the reaction products can be effectively controlled by simply adjusting the molar ratio of ammonia to carbon dioxide in the feed gas (NH3 / CO2). For example, by using a higher NH3 / CO2 feed ratio, a product distribution dominated by dimethylamine can be preferentially obtained. This controllability provides great process flexibility to meet the differentiated needs of downstream markets for different methylamine products.

[0027] 4. The catalyst preparation method is efficient, controllable, and easy to scale up: The sequential assembly method and other preparation methods provided by this invention have clear process steps and mild and controllable conditions. This method can directionally construct the desired In-Zr-M active structure, avoiding the preparation difficulties caused by complex core-shell structures or harsh hydrothermal synthesis, and has good potential for industrial scale-up. Attached Figure Description

[0028] Figure 1 The image shows the XPS In 3d spectrum of the catalyst prepared in Example 2.

[0029] Figure 2 The images show HAADF images and EDX elemental analysis diagrams of the In-Zr-Pd / SiO2 catalyst prepared in Example 2.

[0030] Figure 3The graph shows the stability test results of the In-Zr-Pd / SiO2 catalyst prepared in Example 2 for the carbon dioxide to methylamine reaction. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments and comparative examples, but the present invention is not limited to the following embodiments. The embodiments are intended to help those skilled in the art to better understand and implement the present invention, and do not constitute a limitation on the scope of protection of the present invention. Unless otherwise specified, the reagents used in the following embodiments are all commercially available analytical grade, and the gas purity is ≥99.99%.

[0032] Example 1: Preparation of In-Zr-Ni / SiO2 catalyst

[0033] This embodiment uses a sequential assembly method to prepare the catalyst, including the following steps:

[0034] (1) Take 5g of mesoporous SiO2 with a specific surface area of ​​about 300 m² / g and dry it at 120 ℃ for 6 h for later use;

[0035] (2) Dissolve 6.02g In(NO3)3 xH2O (molecular weight 300.83) and 1.06g ZrO(NO3)2 in 15 mL of deionized water and stir at room temperature for 30 min until completely dissolved to obtain the first precursor solution. The mass ratio of In:Zr oxide is approximately 5:1 based on the metal oxide feeding ratio.

[0036] (3) The above solution was added dropwise to 5 g of pretreated SiO2 support while stirring to ensure uniform impregnation of the support. After stirring for 2 h, the solution was dried at 120 °C for 12 h. The dried solid was then transferred to a muffle furnace and dried at 5 °C for 1 min. -1 The temperature was raised to 300℃ and calcined in air atmosphere for 1 h, then naturally cooled to obtain an In-Zr / SiO2 oxide intermediate.

[0037] (4) Dissolve 1.44 g of Ni(NO3)2·6H2O in 10 mL of deionized water and stir to dissolve to obtain the second precursor solution;

[0038] (5) The above-mentioned second precursor solution was added dropwise to the In-Zr / SiO2 intermediate, impregnated at room temperature for 2 h, most of the water was evaporated at 80 ℃, and then dried at 120 ℃ for 6 h. After drying, the sample was placed in a tube furnace under a 5% H2 / Ar mixed atmosphere (flow rate 50 mL / min). -1 In ), at 5℃ min -1The catalyst was reduced at 300℃ for 2 hours and then naturally cooled to room temperature to obtain the In-Zr-Ni / SiO2 catalyst. The metal contents of In, Zr, and Ni were determined by ICP to be 24.0%, 4.5%, and 3.6% (based on the total mass of the catalyst).

[0039] The catalytic reaction was carried out in a fixed-bed reactor. The catalyst loading was 0.3 g (20-40 mesh), with quartz wool filling both the top and bottom. The feed gas flow rate was controlled by a mass flow meter, and the pressure was controlled by a back pressure valve. Typical evaluation conditions: reaction temperature 310℃, pressure 6 MPa, molar ratio CO2 : H2 : NH3 = 1 : 9 : 0.5, total space velocity 12000 mL·g -1 ·h -1 The reaction products were introduced into the gas chromatograph for online analysis via an insulated pipeline (150 °C). CO, CO2, and N2 (internal standard) were analyzed using a TDX-01 column (2 m × 2 mm) and a TCD detector; methane, methylamine (monomethylamine, dimethylamine, trimethylamine), methanol, etc., were analyzed using a PC-1Amine capillary column (30 m × 0.32 mm) and an FID detector.

[0040] Example 2: Preparation of In-Zr-Pd / SiO2 catalyst

[0041] The preparation method was the same as in Example 1, except that the Ni source was replaced with Pd(NO3)2. 0.21 g of Pd(NO3)2·2H2O was weighed and dissolved in 10 mL of deionized water, and the subsequent steps were the same. ICP analysis showed that the In, Zr, and Pd metal contents were 24.6%, 4.4%, and 0.8%, respectively.

[0042] The catalyst evaluation method is the same as in Example 1.

[0043] Example 3: Preparation of In-Zr-Cu / SiO2 catalyst

[0044] The preparation method was the same as in Example 1, except that the Ni source was replaced with Cu(NO3)2. 1.35 g of Cu(NO3)2·3H2O (containing approximately 26.0 wt% Cu) was weighed and dissolved in 10 mL of deionized water, and the subsequent steps were the same. ICP analysis showed that the In, Zr, and Cu metal contents were 25.0%, 4.6%, and 3.5%, respectively.

[0045] The catalyst evaluation method is the same as in Example 1.

[0046] Example 4: Preparation of In-Zr-Rh / SiO2 catalyst

[0047] The preparation method was the same as in Example 1, except that the Ni source was replaced with Rh(NO3)3. 0.08 g of Rh(NO3)3·2H2O (containing approximately 32.0 wt% Rh) was weighed and dissolved in 10 mL of deionized water, and subsequent steps were the same. ICP analysis revealed that the In, Zr, and Rh metal contents were 24.0%, 4.6%, and 0.2%, respectively.

[0048] The catalyst evaluation method is the same as in Example 1.

[0049] Example 5: Preparation of catalysts with different In / Zr ratios

[0050] Following the preparation method of Example 2, the amount of support was fixed at 5 g, and the total mass fraction of In and Zr oxides was maintained at approximately 40% (based on the total mass of the catalyst). The In:Zr mass ratio was adjusted to 10:1, 5:1, 2:1, and 1:1, and the amount of Pd added was fixed at 0.21 g Pd(NO3)2·2H2O. Subsequent steps were the same as in Example 2. The specific amounts of Pd added are shown in Table 1 below.

[0051] Table 1

[0052]

[0053] The catalyst evaluation method is the same as in Example 1.

[0054] Comparative Example 1: Preparation of In-Pd / SiO2 catalyst

[0055] Weigh 6.02 g In(NO3)3·2H2O and 0.21 g Pd(NO3)2·2H2O, dissolve them in 15 mL of deionized water, add 5 g SiO2 support, stir and impregnate at room temperature for 2 h, dry at 120 °C for 12 h, and then calcine in a muffle furnace at 400 °C for 4 h (heating rate 5 °C / min). -1 Finally, the catalyst was reduced at 250°C for 2 hours in a 5% H2 / Ar atmosphere to obtain the In-Pd / SiO2 catalyst.

[0056] The catalyst evaluation method is the same as in Example 1.

[0057] Comparative Example 2: Preparation of Zr-Pd / SiO2 catalyst

[0058] The procedure is the same as in Comparative Example 1, except that the In source is replaced with ZrO(NO3)2. 1.06 g of ZrO(NO3)2 and 0.21 g of Pd(NO3)2·2H2O were weighed and dissolved in 15 mL of deionized water, then impregnated with 5 g of SiO2. Subsequent drying, calcination, and reduction were performed in the same manner. The catalyst evaluation method was the same as in Example 1.

[0059] Comparative Example 3: Preparation of In-Rh@S-1 catalyst

[0060] Weigh 9g of ultrapure water, 2g of tetrapropylammonium hydroxide (TPAOH, 25wt%), and 4g of tetraethyl orthosilicate (TEOS) and add them sequentially to a 100mL beaker, stirring for 10min. Add 0.3mL of In metal solution (0.1g / mL). -1 (In source: indium nitrate, solvent: water) and 0.5 mL of Rh metal solution (0.01 g / mL) -1 (Rh source: rhodium chloride, solvent: water) Stirring continued for 8 hours. The mixture was then transferred to a hydrothermal reactor and placed in an oven at 5°C for 1 minute. -1 The heating rate was increased to 180℃, and the hydrothermal reaction was carried out for 72 hours. The resulting solid product was centrifuged, washed, filtered, dried overnight at 80℃, and calcined at 550℃ for 4 hours to obtain the In-Rh@S-1 catalyst.

[0061] The catalyst evaluation method is the same as in Example 1.

[0062] Comparative Example 4: Preparation of In-Zr-Pd / SiO2 catalyst

[0063] In(NO3)3 (6.02 g), ZrO(NO3)2 (1.06 g) and Pd(NO3)2 (0.21 g) were dissolved together in 20 mL of deionized water, and 5 g of SiO2 support was added at once. The mixture was stirred and impregnated for 2 h, dried at 120 °C for 12 h, calcined in air at 400 °C for 4 h, and finally reduced at 250 °C for 2 h in 5% H2 / Ar.

[0064] The catalyst evaluation method is the same as in Example 1.

[0065] Comparative Example 5: Preparation of In-Zr-Pd@S-1 catalyst

[0066] The assembly method was exactly the same as in Example 2, but the mesoporous SiO2 support was replaced with an all-silica molecular sieve S-1 (MFI structure, specific surface area 400 m²). 2 / g).

[0067] The catalyst evaluation method is the same as in Example 1.

[0068] Comparative Example 6: Preparation of In-Zr-Pd Catalyst

[0069] In-Zr-Pd oxide powder was prepared by co-precipitation. 6.02 g In(NO3)3, 1.06 g ZrO(NO3)2 and 0.21 g Pd(NO3)2 were dissolved in 50 mL of deionized water. 1 M (NH4)2CO3 solution was added dropwise under vigorous stirring until the pH reached 8.5. The precipitate was aged for 2 h, dried at 120 °C for 12 h, then calcined in air at 400 °C for 4 h, and finally reduced at 300 °C for 2 h in 5% H2 / Ar.

[0070] The catalyst evaluation method is the same as in Example 1.

[0071] XPS analysis: XPS analysis of the catalyst in Example 2 showed that In 3d 5 / 2 The binding energy is 444.3 eV, a negative shift of 0.6 eV compared to pure In₂O₃ (444.9 eV) (see...). Figure 1 The valence state of In in the catalysts synthesized by the methods in Comparative Examples 1 and 3 remained almost unchanged.

[0072] TEM-EDX elemental distribution: HAADF images and EDX surface scans of the catalyst in Example 2 show that In, Zr, and Pd are uniformly distributed within the 150×150 nm region, with no segregation (see...). Figure 2 ).

[0073] N2 physical adsorption-desorption and M metal dispersion test results: N2 adsorption-desorption tests were performed on the support of Example 2, the catalysts of Example 2, Comparative Example 1, and Comparative Example 3. The specific surface area of ​​the support of Example 2 was 305 m². 2 g -1 The catalyst in Example 2 has a specific surface area of ​​255 m². 2 g -1 All are no less than 150m 2 g -1 (See Table 2). Furthermore, the metal dispersion in Example 2 is greater than 50%.

[0074] Table 2

[0075]

[0076] The catalytic activity of each example and comparative example was tested under the following reaction conditions: the CO2 to methylamine reaction was carried out in a fixed-bed reactor with a catalyst loading of 0.3 g, a reaction temperature of 310 °C, a pressure of 6 MPa, a CO2 : H2 : NH3 ratio of 1 : 9 : 0.5, and a total space velocity of 12000 mL·g. −1 ·h −1 The performance test results of each catalyst are shown in Table 3:

[0077] Table 3

[0078]

[0079] Taking the catalyst of Example 2 as an example, the catalyst loading was fixed at 0.3 g, the reaction temperature was 310 °C, the pressure was 2.5 MPa, and the total space velocity was 12000 mL·g. -1 ·h -1With CO2 : H2 = 1 : 9, the molar ratio of NH3 / CO2 was adjusted, and the change in the ratio of dimethylamine to trimethylamine in the product was investigated. The results are shown in Table 4.

[0080] Table 4

[0081]

[0082] The catalyst from Example 2 was loaded at a concentration of 0.3 g, a reaction temperature of 310 °C, a pressure of 6 MPa, a CO2:H2:NH3 ratio of 1:9:0.5, and a total space velocity of 12000 mL·g. -1 ·h -1 Under these conditions, after 100 hours of continuous operation, the CO2 conversion rate remained at 57%–62%, the methylamine selectivity was above 80%, the CO selectivity was less than 16%, and no significant inactivation was observed (see...). Figure 3 ).

[0083] This invention presents an In-Zr-M / SiO2 (M = Ni, Cu, Pd, Rh, Pt) catalyst prepared via a sequential assembly method, which exhibits excellent catalytic performance in the one-step synthesis of methylamine via CO2 hydrogenation and ammoniation. XPS and TEM-EDX characterization confirmed the formation of unique In-Zr-M electronic interactions and a uniformly distributed nanoscale structure, which are key to the catalyst's high activity, high methylamine selectivity, and low CO selectivity. The ratio of dimethylamine to trimethylamine can be flexibly controlled by simply adjusting the NH3 / CO2 feed ratio to meet market demands. This catalyst preparation method is simple, highly stable, and has broad application prospects.

Claims

1. A method for one-step preparation of methylamine by carbon dioxide hydrogenation amination, characterized in that, In a fixed-bed reactor, a feed gas containing carbon dioxide, hydrogen, and ammonia is reacted under the following conditions: reaction temperature 250–350 °C; reaction pressure 1–8 MPa; feed gas molar ratio CO2 : H2 : NH3 = 1 : (2–9) : (0.1–2); the catalyst used comprises a support and an active component supported on the support, wherein the support is microporous or mesoporous silica, and the active component comprises indium, zirconium, and at least one metal auxiliary M selected from nickel, copper, palladium, rhodium, and platinum; wherein, in the catalyst, In 3d 5 / 2 The binding energy is between 444.0 eV and 444.7 eV, and this binding energy is lower than that of the In 3dO3 standard of pure indium oxide. 5 / 2 The binding energy is 0.2 eV or lower; the single-pass conversion rate of carbon dioxide is not less than 50%, the total selectivity of methylamine products is not less than 80%, and the selectivity of the by-product carbon monoxide is not higher than 20%.

2. The method for one-step preparation of methylamine by carbon dioxide hydrogenation amination as described in claim 1, characterized in that: By adjusting the molar ratio of ammonia to carbon dioxide in the feed gas, the molar ratio of dimethylamine to trimethylamine in the reaction products can be controlled. When the molar ratio of ammonia to carbon dioxide is in the range of 0.1 to 0.8, the molar ratio of dimethylamine / trimethylamine is less than 1; when the molar ratio of ammonia to carbon dioxide is in the range of 1.0 to 2.0, the molar ratio of dimethylamine / trimethylamine is between 1 and 2.

3. The method for one-step preparation of methylamine by carbon dioxide hydrogenation amination as described in claim 1, characterized in that: When the molar ratio of CO2 : H2 : NH3 = 1 : (6~9) : (1~2), the reaction pressure is 1~3 MPa, and the reaction temperature is 270℃~310℃, dimethylamine becomes the main methylamine product in the reaction products, and the molar ratio of dimethylamine to trimethylamine is greater than 1.

4. The method for one-step preparation of methylamine by carbon dioxide hydrogenation amination as described in claim 1, characterized in that: In the catalyst, indium, zirconium, and metal additive M are spatially uniformly distributed within a region of at least 50 nm × 50 nm.

5. The method for one-step preparation of methylamine by carbon dioxide hydrogenation amination as described in claim 1, characterized in that: The dispersion of the metal promoter M in the catalyst is not less than 40%.

6. The method for one-step preparation of methylamine by carbon dioxide hydrogenation amination as described in claim 1, characterized in that: The mass content of the metal promoter M in the catalyst is 0.1% to 8.0% based on the total mass of the catalyst.

7. The method for one-step preparation of methylamine by carbon dioxide hydrogenation amination as described in claim 1, characterized in that: In the catalyst, the mass ratio of indium to zirconium, calculated as metal oxides, is 10:1 to 1:1; and the total mass content of indium and zirconium oxides, calculated as the total mass of the catalyst, is 5% to 60%.

8. The method for one-step preparation of methylamine by carbon dioxide hydrogenation amination as described in claim 1, characterized in that: In the catalyst, the specific surface area of ​​the support is not less than 150 m². 2 g -1 .

9. The method for one-step preparation of methylamine by carbon dioxide hydrogenation amination as described in claim 1, characterized in that, The preparation of the catalyst includes the following steps: 1) Provide a first precursor solution containing an indium source and a zirconium source; 2) The first precursor solution is loaded onto the carrier and subjected to a first-stage heat treatment to obtain an intermediate containing indium-zirconium composite oxide; 3) Provide a second precursor solution containing a metal auxiliary source M; 4) The second precursor solution is loaded onto the intermediate and subjected to a second-stage reducing heat treatment to obtain the catalyst.

10. The method for one-step preparation of methylamine by carbon dioxide hydrogenation amination as described in claim 9, characterized in that: The first stage of heat treatment is carried out in an air atmosphere at a temperature of 300°C to 500°C for 1 to 4 hours; the second stage of reducing heat treatment is carried out in a hydrogen-containing atmosphere at a temperature of 200°C to 400°C for 1 to 4 hours.

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