Catalyst for preparing methanol through hydrogenation of carbon dioxide as well as preparation method and application of catalyst

Abstract

The invention discloses a catalyst for preparing methanol through carbon dioxide hydrogenation as well as a preparation method and application of the catalyst. The catalyst provided by the invention is prepared from the following components: CuO, ZnO and ZnGa2O4, wherein the ZnGa2O4 has a spinel structure. When the catalyst is used for a reaction for preparing methanol through CO2 hydrogenation, a reduction reaction is firstly carried out, and CuO exists in the form of elemental Cu after being reduced. The simple substance Cu is taken as a main active component, and Zn and Ga elements are introduced, so that the electronic structure and the surface property of the catalyst are optimized, copper particles are dispersed more uniformly, and the dispersity is greatly improved, and therefore, the catalyst shows higher activity and longer catalytic activity life in a reaction for preparing methanol through CO2 hydrogenation; meanwhile, the CO2 conversion rate of the catalyst is high, a more efficient and more economical solution is provided for reactions such as methanol preparation through carbon dioxide hydrogenation, and the catalyst is expected to play an important role in industrial application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon dioxide hydrogenation to methanol catalyst, in particular to a carbon dioxide hydrogenation to methanol catalyst and a preparation method thereof, and application of the catalyst in carbon dioxide hydrogenation to methanol. BACKGROUND

[0002] Methanol, as a clean energy carrier and green fuel, is an important way of consumption and storage medium of green hydrogen, and can realize high value-added utilization of carbon dioxide, and has a wide application in fine chemical industry, industrial production and green fuel. Methanol is easier to store and transport than hydrogen, and has higher safety.

[0003] The synthesis of green methanol from carbon dioxide obtained by carbon capture technology and hydrogen generated by renewable energy power generation has become an important direction for future industrial development. CO2+H2 direct one-step methanol synthesis is also an advanced route for green methanol preparation, and Cu-based catalyst plays an important role. CO2 hydrogenation reaction on Cu-based catalyst is a structure-sensitive reaction, and the selection of preparation method and the control of preparation conditions are very important.

[0004] Traditional Cu-based catalyst preparation methods mainly include co-precipitation method, sol-gel method and impregnation method, among which the co-precipitation method is the most common. In addition, some novel preparation methods such as low-temperature combustion synthesis method and solid-phase synthesis method are also applied to the preparation of Cu-based catalyst. As one of the main preparation methods of Cu-based catalyst, the main advantage of co-precipitation method is that the prepared catalyst can achieve molecular-level mixing and nanoscale particle size, and the elements of the catalyst have strong interaction. At the same time, the co-precipitation method also has the advantage of easy industrial production. However, the co-precipitation method also has some obvious shortcomings, such as long preparation period, precise pH control and heavy washing process.

[0005] The existing Cu-based catalysts have some obvious shortcomings. First, they are prone to sintering at high temperatures, which will lead to a decrease in specific surface area and active sites, thereby significantly reducing the catalytic activity. Second, their CO2 conversion efficiency is usually low, which limits their application effect in CO2 hydrogenation reaction. In addition, the activity and selectivity of Cu-based catalysts will gradually decrease during long-term use, and the reaction conditions are relatively high, which increases the complexity and cost of the reaction process. Moreover, the modification elements of Cu-based catalysts in existing patents are mostly concentrated in a few kinds such as Zn, Al, Zr and In, the types of modification agents are relatively few, and the preparation method of the catalyst is relatively complex, which also limits the further improvement of its performance to some extent.

[0006] To achieve high catalytic performance in the CO2 hydrogenation to methanol process, it is necessary to develop an efficient, simple, and mild catalyst preparation method and to broaden the range of modifying elements for Cu-based catalysts. Summary of the Invention

[0007] The purpose of this invention is to provide a gallium-modified copper-based methanol catalyst with high catalytic activity and stability, which can be prepared by a conventional and controllable one-pot method. This catalyst exhibits advantages such as good catalytic performance and high stability in the CO2 hydrogenation to methanol process.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a copper-based methanol synthesis catalyst comprising the following components: CuO, ZnO and ZnGa2O4; wherein the ZnGa2O4 has a spinel structure.

[0009] The catalyst provided by this invention uses elemental Cu as the main active component and introduces Ga for certain modifications, wherein Zn and Ga form a ZnGa2O4 spinel structure. This structure enhances the ability of Cu-based catalysts to activate CO2 and improves methanol selectivity.

[0010] The molar ratio of Cu, Zn, and Ga in the copper-based methanol synthesis catalyst is 6:(2.5-4):(0-1.5).

[0011] In one specific embodiment of the present invention, the molar ratio of Cu, Zn, and Ga in the copper-based methanol synthesis catalyst is 6:3.5:0.5.

[0012] In one specific embodiment of the present invention, the molar ratio of Cu, Zn, and Ga in the copper-based methanol synthesis catalyst is 6:3:1.

[0013] In one specific embodiment of the present invention, the molar ratio of Cu, Zn, and Ga in the copper-based methanol synthesis catalyst is 6:2.5:1.5.

[0014] Secondly, the present invention provides a method for preparing the copper-based methanol synthesis catalyst, comprising: S1. Add the metal salt to water, disperse it by ultrasonication, and stir to obtain the precursor salt solution; S2. The precursor salt solution and alkaline solution are subjected to co-precipitation by parallel-flow titration, stirred, allowed to stand for aging, filtered and dried to obtain the precursor. S3. The precursor is calcined to obtain a copper-based methanol synthesis catalyst.

[0015] The application adopts one-pot method to prepare copper-based methanol synthesis catalysts modified by metal gallium by co-precipitation method, no new ions are introduced in the co-precipitation process, and the hydroxide is decomposed into gas in the calcination process, which is beneficial to improve the dispersion of the active component and the catalytic hydrogenation capacity of the catalyst.

[0016] In step S1, the metal salt is one or more of nitrate, chloride, phosphate, acetate and sulfate; preferably nitrate.

[0017] The ultrasonic dispersion time is 0.5-2 h; preferably 1 h.

[0018] The stirring time is 2-2.5 h; The concentration of the metal element in the precursor salt solution is 0.1-0.15 mol / L.

[0019] In step S2, the base is Na2CO3, (NH4)2CO3, NaOH or NH3·H2O. The concentration of the base solution is 0.1-0.15 mol / L. The conditions of the parallel flow titration co-precipitation are as follows: water bath condition, drop rate of 1-2 mL / min, temperature of 60-90 ℃, preferably 70 ℃, time of 0.5-2 h, preferably 1 h, and pH value of the system solution of 7.0-7.2.

[0020] In step S2, the stirring time is 1-1.5 h, and the standing aging time is 1-1.5 h; the drying temperature is 40-150 ℃, and the time is 6-24 h. The preferred temperature is 110 ℃, and the time is 10-12 h.

[0021] In step S3, the calcination conditions are as follows: temperature of 300-800 ℃, and time of 1-10 h. The more preferred temperature is 450-600 ℃, and the time is 3-6 h.

[0022] In a third aspect, the application provides a method for preparing methanol by CO2 hydrogenation, which comprises using the above-mentioned copper-based methanol synthesis catalyst.

[0023] In one specific embodiment of the application, the method for preparing methanol by CO2 hydrogenation comprises the following steps: first reducing the catalyst at 350-450 ℃ for 2-4 h, and then introducing reaction gas with a H2 / CO2 volume ratio of 3 / 1 into a high-pressure fixed bed reactor to start the reaction of CO2 hydrogenation to methanol.

[0024] The CO2 hydrogenation to prepare methanol is carried out at a reaction pressure of 0-5 MPa, preferably 4 MPa, a space velocity of 4500-9000 mL / g / h, preferably 7500 mL / g / h, and a reaction temperature of 200-320 DEG C.

[0025] In one specific embodiment of the present application, the catalyst is used in a proportion of 0.1-0.5 g.

[0026] Compared with the prior art, the present application has the following beneficial effects: 1. The present application uses elemental Cu as the main active component, and by introducing Zn and Ga elements, the electronic structure and surface properties of the catalyst are optimized, the copper particles are more uniformly dispersed, the dispersion degree is greatly improved, and therefore higher activity and longer catalytic activity life are exhibited in the CO2 hydrogenation to prepare methanol, and the catalyst can be stably operated for more than 100 h.

[0027] 2. The catalyst provided by the present application also has good carbon deposition resistance, can effectively inhibit the carbon deposition phenomenon on the surface of the catalyst, and further improves the long-term stability of the catalyst.

[0028] 3. The catalyst provided by the present application has high CO2 conversion rate, provides a more efficient and more economical solution for the CO2 hydrogenation to prepare methanol, and is expected to play an important role in industrial applications.

[0029] 4. The catalyst preparation method provided by the present application adopts the coprecipitation method, the raw materials are cheap and easy to obtain, the process is simple, no other metal impurity ions are introduced, the hydroxide metal precursor is decomposed into gas in the calcination process, and there is no environmental pollution, so the method is suitable for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Fig. 1 is an XRD pattern of a catalyst with different molar ratios; from top to bottom in the figure are XRD patterns of CuZn (molar ratio 6:4), CuZnGa (molar ratio 6:3.5:0.5), CuZnGa (molar ratio 6:3:1) and CuZnGa (molar ratio 6:2.5:1.5).

[0031] Figure 2 Fig. 2 is a TEM and EDS pattern of the catalyst CuZnGa (molar ratio 6:3:1).

[0032] Figure 3 Fig. 3 is a catalytic activity data graph of the catalyst CuZn (molar ratio 6:4).

[0033] Figure 4 Fig. 4 is a catalytic activity data graph of the catalyst CuZnGa (molar ratio 6:3.5:0.5).

[0034] Figure 5 Catalytic activity data graph of CuZnGa (molar ratio 6:3:1) as catalyst.

[0035] Figure 6 Catalytic activity data graph of CuZnGa (molar ratio 6:2.5:1.5) as catalyst.

[0036] Figure 7 Catalytic activity data graph of CuZnGa (molar ratio 6:3:1) as catalyst under different pressures.

[0037] Figure 8 Catalytic activity data graph of CuZnGa (molar ratio 6:3:1) as catalyst under different space velocities. DETAILED DESCRIPTION

[0038] The application will be further described in conjunction with specific examples, but the application is not limited to the following examples.

[0039] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0040] The reagents, materials, instruments, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0041] The source of raw materials used in the following examples is described as follows: Copper nitrate, zinc nitrate, gallium nitrate: provided by Shanghai Maikelin Biochemical Technology Co., Ltd.

[0042] Sodium hydroxide: provided by Shanghai Aldrin Biochemical Technology Co., Ltd.

[0043] The source of equipment used in the following examples is described as follows: High-pressure fixed-bed reactor: built by Xiamen Hande Engineering Co., Ltd.

[0044] Online gas chromatograph: Shanghai Shimin GC2060.

[0045] Example 1, ternary CuZnGa (molar ratio 6:3.5:0.5) catalyst The ternary CuZnGa catalyst was prepared by coprecipitation method, and the preparation steps were as follows: (1) Taking Cu / Zn / Ga atomic ratio of 6:3.5:0.5 as an example, 7.248 g of Cu(NO3)2·3H2O, 5.2057 g of Zn(NO3)2·6H2O and 0.6394 g of Ga(NO3)3· x The metal nitrate was dissolved in deionized water, ultrasonically dispersed for 1 h, and stirred for 2 h to obtain a nitrate solution; (2) In a constant temperature water bath at 70 ℃, the above nitrate solution and 0.1 mol / L Na2CO3 solution are titrated in parallel flow, the drop rate is 1 mL / min, and the pH value of the solution during titration is kept near 7.0; the solution after titration is continuously stirred in a 70 ℃ water bath for 1 h, and then aged for 1 h to cool to room temperature; after filtration and sufficient washing for multiple times, the impurity Na + , dried at 110 ℃ overnight to obtain a precursor; (3) The precursor is ground and calcined in a vertical tube furnace at 450 ℃ for 3 h to obtain a ternary CuZnGa catalyst.

[0046] Example 2, ternary CuZnGa (molar ratio 6:3:1) catalyst The preparation steps are the same as those in Example 1, except that the amount of the corresponding nitrate is changed when the Cu / Zn / Ga atomic ratio is changed. CuZnGa is weighed in the proportion of 7.248 g of Cu(NO3)2·3H2O, 4.4621 g of Zn(NO3)2·6H2O and 1.2787 g of Ga(NO3)3· x The H2O metal nitrate is dissolved in deionized water.

[0047] Example 3, ternary CuZnGa (molar ratio 6:2.5:1.5) catalyst The preparation steps are the same as those in Example 1, except that the amount of the corresponding nitrate is changed when the Cu / Zn / Ga atomic ratio is changed. CuZnGa is weighed in the proportion of 7.248 g of Cu(NO3)2·3H2O, 3.7184 g of Zn(NO3)2·6H2O and 1.9181 g of Ga(NO3)3· x The H2O metal nitrate is dissolved in deionized water.

[0048] Comparative Example 1, binary CuZn (molar ratio 6:4) catalyst The binary CuZn catalyst is prepared by coprecipitation method, and the preparation steps are as follows: (1) Cu / Zn is weighed in the proportion of 7.248 g of Cu(NO3)2·3H2O and 5.9494 g of Zn(NO3)2·6H2O metal nitrate, and dissolved in deionized water, ultrasonic dispersion for 1 h, stirring for 2 h, to obtain a nitrate solution; (2) In a constant temperature water bath at 70 ℃, the above nitrate solution and 0.1 mol / L Na2CO3 solution are titrated in parallel flow, the drop rate is 1 mL / min, and the pH value of the solution during titration is kept near 7.0; the solution after titration is continuously stirred in a 70 ℃ water bath for 1 h, and is aged for 1 h to cool to room temperature; after filtration and multiple sufficient washing, the impurity Na + , is washed off, and the catalyst is dried at 110 ℃ overnight to obtain a precursor; (3) The precursor is ground and calcined in a vertical tube furnace at 450 ℃ for 3 h to obtain a binary CuZn catalyst.

[0049] Example 4, a method for preparing methanol by hydrogenation of CO2 The steps are as follows: The catalysts obtained in Examples 1-3 and Comparative Example 1 (the catalyst usage amount is 0.24 g) are first reduced in a 10% H2 / Ar atmosphere at 400 ℃ for 3 h, then the reaction gas with a H2 / CO2 volume ratio of 3 / 1 is introduced into a high-pressure fixed bed reactor, the space velocity condition is 7500 mL / g / h, then the pressure is increased to the reaction pressure of 4 MPa, and the temperature is increased to the reaction temperature, and the reaction is started to prepare methanol.

[0050] Test Example 1, structure of the catalyst The catalysts prepared in Examples 1-3 and Comparative Example 1 are detected, and the results are shown in Figure 1 , Figure 2

[0051] Figure 1 The XRD patterns of catalysts with different molar ratios are shown.

[0052] Figure 2 The TEM and EDS patterns of the catalyst CuZnGa (molar ratio 6:3:1) are shown.

[0053] Test Example 2, catalytic activity of the catalyst The catalysts prepared in Examples 1-3 are tested for activity to explore the optimal activity data conditions under different ratios.

[0054] ​The hydrogenation activity evaluation method of the catalyst: first, the catalyst is reduced at 400 ℃ for 3 h in a 10% H2 / Ar atmosphere, and the catalyst usage is fixed at 0.24 g; then the reaction gas with a H2 / CO2 volume ratio of 3 / 1 is introduced into the high-pressure fixed bed reactor, the pressure is increased to 4 MPa, and the temperature is increased to the required reaction temperature, and the CO2 hydrogenation to methanol reaction is started; wherein, the reaction temperature is 200 ℃, 220 ℃, 240 ℃, 260 ℃ and 280 ℃ respectively; online gas chromatograph equipped with thermal conductivity detector (TCD) and flame ionization detector (FID) is used for detection.

[0055] TCD analysis of Ar, CO and CO2 using a packed column (TDX-01) with H2 as carrier gas. Capillary column FID (TG-BOND Q) with Ar as carrier gas for analysis of hydrocarbons, alcohols and other carbon-containing products. All data were collected within 2 h after the start of the reaction (unless otherwise specified). Each activity test data was tested 3 times for average value to seek experimental repeatability.

[0056] The test results are shown in Figures 3-6 .

[0057] As can be seen from Figure 3 , the conversion rate of CuZn (molar ratio 6:4) catalyst increases from 2.56% to 14.12% as the temperature increases (220-280 ℃), and the methanol selectivity decreases from 50.87% to 26.83%.

[0058] As can be seen from Figure 4 , the conversion rate of CuZnGa (molar ratio 6:3.5:0.5) catalyst increases from 2.91% to 17.07% as the temperature increases (220-280 ℃), and the methanol selectivity decreases from 69.22% to 51.22%.

[0059] As can be seen from Figure 5 , the conversion rate of CuZnGa (molar ratio 6:3:1) catalyst increases from 3.36% to 18.42% as the temperature increases (220-280 ℃), and the methanol selectivity decreases from 61.1% to 51.44%.

[0060] As can be seen from Figure 6 , the conversion rate of CuZnGa (molar ratio 6:2.5:1.5) catalyst increases from 1.8% to 14.01% as the temperature increases (220-280 ℃), and the methanol selectivity decreases from 69.14% to 54.07%.

[0061] Wherein: The CO2 conversion rate is calculated on the basis of carbon atoms according to the following equation:

[0062] CO is formed through a reverse water-gas shift reaction. The CO selectivity is calculated based on the following equation on the carbon atom basis:

[0063] CO inlet and CO out These represent the number of CO moles at the inlet and outlet, respectively. 2outlet This indicates the number of moles of CO2 at the outlet.

[0064] Based on CO-free single hydrocarbon product C n H m The selectivity is calculated according to the following formula:

[0065] Where C n H m The export term indicates the number of moles (C) of a single hydrocarbon product at the export point.

[0066] Test Example 3: Optimal Reaction Pressure of Catalyst The CuZnGa (molar ratio 6:3:1) catalyst from Example 2 was used for activity testing to explore the optimal activity data conditions under different pressures. The catalyst activity evaluation method was the same as that in Example 2.

[0067] like Figure 7 As shown, the optimal pressure condition for the catalyst CuZnGa (molar ratio 6:3:1) is 4 MPa.

[0068] Test Example 4: Optimal space velocity conditions for the catalyst Activity tests were conducted using CuZnGa (molar ratio 6:3:1) from Example 2 to explore the optimal activity data conditions under different space velocities. The catalyst activity evaluation method was the same as that used in Example 2.

[0069] Depend on Figure 8 It can be seen that the optimal space velocity condition for the catalyst CuZnGa (molar ratio 6:3:1) is 7500 mL / g / h.

[0070] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A copper-based methanol synthesis catalyst, comprising the following components: CuO, ZnO and ZnGa 2O 4; the ZnGa 2O 4 has a spinel structure.

2. The copper-based methanol synthesis catalyst according to claim 1, characterized in that The molar ratio of Cu, Zn and Ga in the copper-based methanol synthesis catalyst is 6: (2.5-4) : (0-1.5).

3. The copper-based methanol synthesis catalyst according to claim 1, characterized in that The molar ratio of Cu, Zn and Ga in the copper-based methanol synthesis catalyst is preferably 6:3.5:0.5, 6:3:1 or 6:2.5:1.

5. 4.A method for preparing the copper-based methanol synthesis catalyst according to any one of claims 1-3, comprising the following steps: S1, adding metal salts into water, ultrasonic dispersion, stirring to obtain a precursor salt solution; S2, carrying out co-precipitation by parallel flow titration of the precursor salt solution and an alkali solution, stirring, standing and aging, filtering and drying to obtain a precursor; S3, calcining the precursor to obtain the copper-based methanol synthesis catalyst.

5. The preparation method according to claim 4, characterized in that, In step S1, the metal salts are one or more of nitrate, chloride, phosphate, acetate and sulfate; The ultrasonic dispersion time is 0.5-2 h; The stirring time is 2-2.5 h; The concentration of metal elements in the precursor salt solution is 0.1-0.15 mol / L.

6. The production method according to claim 4 or 5, characterized by, In step S2, the alkali is one or more of Na 2CO 3, (NH 4) 2CO 3, NaOH and NH 3·H 2O; The concentration of the alkali solution is 0.1-0.15 mol / L; The conditions for the co-precipitation by parallel flow titration are as follows: water bath, drop rate of 1-2 mL / min, temperature of 60-90 ℃, time of 0.5-2 h, and pH value of the system solution of 7.0-7.

2.

7. The production method according to any one of claims 4 to 6, characterized by, In step S2, the stirring time is 1-1.5 h, the standing and aging time is 1-1.5 h, the drying temperature is 40-150 ℃, and the drying time is 6-24 h.

8. The production method according to any one of claims 4 to 7, characterized by, In step S3, the calcination conditions are as follows: temperature of 300-800 ℃, and time of 1-10 h. 9.A method for preparing methanol by CO 2 hydrogenation, comprising using the copper-based methanol synthesis catalyst according to any one of claims 1-3.

10. The method of claim 9, wherein, The method comprises the following steps: first reducing the catalyst at 350-450 ℃ for 2-4 h, then introducing a reaction gas with a H 2 / CO 2 volume ratio of 3 / 1 into a high-pressure fixed-bed reactor to start the reaction of CO 2 hydrogenation to prepare methanol; In the method for preparing methanol by CO 2 hydrogenation, the reaction pressure is 0-5 MPa, the space velocity is 4500-9000 mL / g / h, and the reaction temperature is 200-320 ℃.

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