Preparation method and application method of copper-zinc-based catalyst for preparing methanol through CO2 hydrogenation

Abstract

The invention discloses a preparation method of a copper-zinc-based catalyst for preparing methanol through CO2 hydrogenation in the technical field of catalysts, which comprises the following steps: (1) precipitation reaction: in a precipitation reactor, dissolving a metal oxide precursor, urea and a template agent in a water and ethanol azeotrope in proportion, and refluxing for set time; (2) solid-liquid separation: in solid-liquid separation equipment, washing the material obtained in the previous step with absolute ethyl alcohol, and entering the next step of the dried material; and (3) calcining the precursor, namely calcining the material obtained in the previous step for 5 hours in a muffle furnace in calcining equipment to obtain the copper-zinc-based catalyst, and obtaining the copper-zinc-based catalyst which is mild in reaction condition, simple in preparation method, environment-friendly, energy-saving, low in preparation cost and high in economic benefit.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a method for preparing a copper-zinc based catalyst. Background Art

[0002] With the continuous utilization of energy and the increase of human activities, the solubility of CO2 in the atmosphere has increased year by year, seriously affecting the balance of the natural carbon cycle and posing a threat to the earth's ecological environment system. In this context, CO2 capture and conversion technology has attracted people's attention, among which CO2 hydrogenation to methanol (CO2+ 3H2→ CH3OH + H2O) has been widely studied by scientific researchers. In recent years, based on the concept of "methanol economy", combined with green energy H2, CO2 is converted into methanol through thermal catalytic technology, providing a renewable carbon source for subsequent chemical production, which is conducive to energy storage and transportation, and helps to alleviate the greenhouse effect.

[0003] Among them, copper-zinc-based catalysts have been widely studied as a commonly used catalyst for CO2 hydrogenation to methanol. Commonly used copper-zinc-based catalysts are prepared by co-precipitation, and the activity and stability of CO2 hydrogenation to methanol are improved by adding promoters (Zn, Al, Zr, etc.). Cu / ZnO / Al2O3 catalysts have been put into production, but there are still some shortcomings. The co-precipitation method produces a large amount of wastewater (residual Na + 、NO3 - ), Na + It will poison the catalyst, thereby reducing the catalyst activity and reducing the methanol yield. Al2O3 is a hydrophilic oxide, which makes the byproduct water of the CO2 hydrogenation reaction enriched on the catalyst surface, thus affecting the stability of the catalyst.

[0004] As we all know, traditional copper-based catalysts usually need to operate under high temperature (280-300℃) and high pressure (3-10MPa) conditions to obtain sufficient catalytic activity. Wang et al. prepared ZnO / Cu catalyst for methanol synthesis by emulsion method. At 250℃, the selectivity of methanol was only 59.2%, while the selectivity of carbon monoxide (CO) was as high as 40.8% (Wang, G et al. Reaction Kinetics, Mechanisms and Catalysis 2021, 132 (1), 155-170).

[0005] Related studies have reported that the interaction between manganese and other metals can regulate particle size and resist aggregation, significantly affecting catalytic activity and selectivity for higher alcohols. Wang et al. prepared a Cu-Mn-Zn / ZrO2 series catalyst by sol-gel method with a space-time yield of 69.2 mg·mL methanol at 260 °C. cat-1 ·h -1 (Wang S et al. FuelProcessing Technology 2023; 247: 107789). As a result, the space-time yield of the target product is low. Although the catalytic activity of CO2 hydrogenation to methanol is improved when the reaction temperature is higher than 260°C, a lower space-time yield of methanol is inevitably obtained. High temperature is conducive to the activation of CO2, but a large amount of by-products (CO and H2O) will be produced. The presence of H2O will accelerate the deactivation of copper-zinc-based catalysts at high temperatures, causing a sudden drop in CO2 conversion rate and methanol yield. Therefore, controlling the reaction temperature is crucial for the synthesis of methanol. Jia et al. prepared LaCu by sol-gel method 0.5 Mn 0.5 O3 catalyst, the preparation process of this method is time-consuming, uneconomical and difficult to scale up (Jia S et al. Journal of rare earths, vol.28. No. 5, Oct. 2010).

[0006] Therefore, using manganese as an auxiliary metal can not only solve the above-mentioned defects well, but also reduce the reaction temperature and increase the methanol yield during the CO2 hydrogenation reaction. However, the catalyst prepared by the sol-gel method cannot obtain an excellent methanol space-time yield. Since CO2 molecules are highly oxidized and thermodynamically stable, it is challenging to achieve the conversion of CO2 into methanol. Therefore, exploring efficient catalysts to activate CO2 at lower temperatures has always been a key process in this reaction.

[0007] In summary, in the process of CO2 hydrogenation to methanol using copper-zinc-based catalysts prepared by existing technology, the excessively high reaction temperature not only easily produces by-products (such as CO, H2O and CH4), reduces the methanol yield, but also increases energy consumption, resulting in poor economic benefits. Summary of the invention

[0008] In view of the deficiencies in the prior art, the present invention provides a method for preparing a copper-zinc-based catalyst for producing methanol by hydrogenation of CO2, thereby obtaining a copper-zinc-based catalyst with mild reaction conditions, simple preparation method, environmental protection and energy saving, low preparation cost and high economic benefit.

[0009] The object of the present invention is achieved as follows: A method for preparing a copper-zinc-based catalyst for producing methanol by hydrogenating CO2, using ammonia water generated by urea hydrolysis to react with metal nitrates, adopting precipitation reaction-solid-liquid separation-calcination of the precursor to obtain a copper-zinc-manganese catalyst, the method steps are as follows: (1) Precipitation reaction: In a precipitation reactor, the metal oxide precursor, urea and template are dissolved in water and ethanol azeotrope in a certain proportion and refluxed for a set time; (2) Solid-liquid separation: In the solid-liquid separation equipment, the material obtained in the previous step is washed with anhydrous ethanol, and the material after the drying operation enters the next step; (3) Calcination of precursor: In a calcination device, the material obtained in the previous step is calcined in a muffle furnace to obtain a copper-zinc-based catalyst.

[0010] Furthermore, the metal oxide precursors are copper nitrate, zinc nitrate and manganese nitrate.

[0011] Furthermore, the template agent is D-anhydrous glucose, and the solubility of the glucose solution is 0-1 mol / L.

[0012] Furthermore, in step (1), the reflux operation temperature is 80° C. and the reflux time is 3-5 h.

[0013] Furthermore, in step (2), the drying condition is drying at 80-120° C. for 12 h in an air atmosphere.

[0014] Furthermore, in step (3), the calcination condition is to increase the temperature to 300-400° C. at 2° C. / min in an air atmosphere and maintain for 5 hours.

[0015] Furthermore, the molar ratio of copper, zinc and manganese is 1.0: (0-5%).

[0016] A method for preparing methanol by hydrogenating CO2, using the copper-zinc-based catalyst obtained by the above preparation method at a temperature of 220°C, a pressure of 3MPa, and a space velocity of 3600mL·g cat -1 ·h -1 The CO2 hydrogenation to methanol reaction was carried out under the conditions of .

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) Compared with the Cu-based catalyst prepared by the traditional co-precipitation method, the present invention successfully prepared a Na-free Cu-based catalyst by the reflux-assisted uniform precipitation method. + The copper-zinc-based catalyst is produced without wasting a lot of water, and this method is environmentally friendly and simple, which is an attractive new route to prepare highly active catalysts.

[0018] (2) The present invention successfully prepared a series of novel and efficient Cu-based catalysts through a reflux-assisted uniform precipitation method. The catalysts have unique properties and can significantly improve the selectivity of methanol and promote the activation of CO2 and its conversion into methanol.

[0019] (3) The copper-zinc-based catalyst of the present invention, due to the complementary chemical properties formed by the combination of metal oxide and Cu, can change the electronic properties of the adsorbed metal, promote the binding strength between CO2 and the metal catalyst, and open up a reaction pathway for the synthesis of methanol. Its catalytic performance is shown in Appendix 1.

[0020] (4) The copper-zinc-based catalyst of the present invention exhibits better CO2 conversion rate, methanol selectivity and methanol space-time yield in CO2 hydrogenation to methanol than the Cu-based catalysts prepared by conventional co-precipitation and sol-gel methods. Its catalytic performance is shown in Appendix 1.

[0021] (5) Due to the chemical inertness of CO2 molecules, a low reaction temperature is not conducive to the activation and conversion of CO2 molecules into methanol. The copper-zinc-based catalyst of the present invention promotes CO2 to have a higher catalytic activity at a mild reaction temperature (220°C), so that the reaction proceeds in the direction of methanol production, thereby increasing the methanol yield.

[0022] (6) The copper-zinc-based catalyst of the present invention has high methanol selectivity and its activity remains unchanged after a long period of reaction, showing excellent stability.

[0023] (7) Compared with the references in Table 1, the reaction at 220 °C can save energy and reduce costs, thus achieving a more environmentally friendly and economical process. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0025] Embodiment 1: 3.4 g of copper nitrate trihydrate, 1.8 g of zinc nitrate hexahydrate and 1.086 mL of manganese nitrate aqueous solution were weighed and dissolved in 40 g of deionized water and 60 g of anhydrous ethanol to form a mixed solution. Then, 3.0 g of glucose and 3.0 g of urea were added to the above solution and refluxed at 80 ° C for 4 h. After the reflux was completed, it was washed with anhydrous ethanol, dried at 100 ° C for 12 h, and calcined in a muffle furnace at 350 ° C for 5 h to obtain the required catalyst.

[0026] A fixed bed stainless steel reactor was used to test the activity of the catalyst in CO2 catalytic hydrogenation. First, the catalyst was pressed into tablets by a tablet press, crushed and sieved to obtain a 20-40 mesh catalyst. Before the test, 0.5 g of catalyst and 1.0 g of quartz sand were weighed and mixed, and then loaded into the constant temperature section of the fixed bed reactor. At a reduction temperature of 300 ° C, atmospheric pressure (0.1 MPa), 25% H2 / 75% N2 reducing mixed gas and an air velocity of 4800 mL g cat -1 ·h -1After the reduction was completed, the temperature was naturally cooled to below 50°C, and then the reaction gas was switched to pass into the reactor, and then at 220°C, 3.0MPa and 3600mL·g cat -1 ·h -1 The methanol synthesis reaction was carried out under the following conditions. The activity evaluation of the catalyst in the production of methanol by hydrogenation of CO2 and the evaluation results are shown in Appendix 1.

[0027] Example 2 The 1.086 mL manganese nitrate aqueous solution in Example 1 was replaced with 10.86 mL manganese nitrate aqueous solution, and the remaining steps were the same as in Example 1. The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Appendix 1, and the specific steps are shown in Example 1.

[0028] Example 3 1.086 mL of manganese nitrate aqueous solution in Example 1 was removed, and the remaining steps were the same as in Example 1. The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Appendix 1, and the specific steps are shown in Example 1.

[0029] Example 4 The calcination temperature of 350°C in the example is replaced by 300°C, and the remaining steps are the same as those in Example 1. The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Attached Table 1, and the specific steps are shown in Example 1.

[0030] Embodiment 5: The calcination temperature of 350°C in the example is replaced by 400°C, and the remaining steps are the same as those in Example 1. The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Attached Table 1, and the specific steps are shown in Example 1.

[0031] Embodiment 6: The reflux time of 4 h in the example was replaced by 5 h, and the remaining steps were the same as in Example 1. The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Appendix 1, and the specific steps are shown in Example 1.

[0032] Embodiment 7: The reflux time of 4 h in the example was replaced by 3 h, and the remaining steps were the same as those in Example 1. The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Attached Table 1, and the specific steps are shown in Example 1.

[0033] Embodiment 8: The concentration of the glucose solution in the example was changed from 0.5 mol / L to 1 mol / L, and the remaining steps were the same as in Example 1. The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Appendix 1, and the specific steps are shown in Example 1.

[0034] Embodiment 9: Glucose was removed from the example, and the remaining steps were the same as in Example 1. The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Attached Table 1, and the specific steps are shown in Example 1.

[0035] Embodiment 10: A method for preparing methanol by catalyzing CO2 hydrogenation using the catalyst prepared in Example 1, comprising the steps of: cat -1 ·h -1 Change to 24000mL·g cat -1 ·h -1 The remaining steps are the same as those in Example 1. The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Attached Table 1.

[0036] Comparative Example 1 Weigh 3.4g of copper nitrate trihydrate and 1.8g of zinc nitrate hexahydrate to a concentration of 1.0 mol·L -1 At the same time, weigh 6.0g of ammonia water to make 1.0mol·L -1 The solution was recorded as solution B. Then, the two solutions were simultaneously added dropwise to 30 mL of deionized water in a 500 mL beaker, and the pH of the solution was maintained at about 6.0. After the addition was completed, the mixture was aged at room temperature for 12 h, the precipitate was filtered, washed with anhydrous ethanol, and dried at 100 ° C for 12 h. The precursor was calcined at 350 ° C for 5 h in a muffle furnace to obtain the desired catalyst.

[0037] The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Appendix 1, and the specific steps are shown in Example 1.

[0038] Comparative Example 2 Weigh 3.4g of copper nitrate trihydrate, 1.8g of zinc nitrate hexahydrate and 1.086mL of manganese nitrate aqueous solution and dissolve them in 50mL of deionized water to form a mixed solution. Then, weigh 5.91g of citric acid and add it to the mixed solution, and adjust the pH of the solution to 6.0 with ammonia water. Then, stir in an 80℃ oil bath for 4h, and then stir at 80℃ until it becomes a colloid. The colloid is dried at 100℃ for 12h, and the precursor is calcined at 350℃ for 5h to obtain the desired catalyst.

[0039] A series of copper-zinc-based catalysts prepared by the present invention were subjected to CO2 hydrogenation reaction in a fixed bed reactor equipped with a gas chromatograph (GC). The specific steps for evaluating the catalytic activity were as follows: In the catalytic reaction process, the catalyst was heated at 200-400℃, 0.1MPa, 40mL·min before the reaction. -1The reaction was carried out under a reducing atmosphere of (25% H2 / 75% N2) for 1-4 hours. Then, the mixture was naturally cooled to 50°C. Subsequently, the reaction gas (V(H2) / V(CO2) / V(Ar) = 72.0%:24.3%:3.62%) was switched to a fixed bed reactor. Afterwards, different catalysts, reaction pressures (1-5 MPa), reaction temperatures (200-280°C) and space velocities (2400-24000 mL·g cat -1 ·h -1 ). During the reaction, in order to prevent product condensation, all pipelines used before the tail gas enters the chromatograph are kept warm (120°C) and the product immediately enters the chromatograph equipped with a thermal conductivity detector (TCD) and a flame ionization detector (FID) for analysis. All data collection began 3 hours after the reaction started.

[0040] The activity evaluation conditions and evaluation results of the catalyst in CO2 hydrogenation to methanol are shown in Appendix 1, and the specific steps are shown in Example 1.

[0041] As shown in Table 1, Examples 1 to 9 show that the catalytic reaction test shows that the catalytic activity and methanol selectivity of the copper-zinc-based catalysts in the reaction process are different. As shown in Table 1, Examples 1 to 9 have different catalytic activities and methanol selectivity at 220°C, 3.0 MPa and 3600 mL·g cat -1 ·h -1 The CO2 hydrogenation reaction was carried out under the following conditions. Compared with Example 1, Examples 2-9 showed relatively lower CO2 conversion, methanol selectivity and methanol space-time yield. For example, the highest methanol space-time yield of Example 1 was 175.14 g·kg cat -1 ·h -1 , and its performance is obviously better than that of Examples 2-9, which are 36.35g·kg cat -1 ·h -1 , 103.42g·kg cat -1 ·h -1 , 124.02g·kg cat -1 ·h -1 , 99.45g·kg cat -1 ·h -1 、89.42g·kg cat -1 ·h -1 , 111.45g·kg cat -1 ·h -1 , 26.74g·kg cat-1 ·h -1 and 107.81 g kg cat -1 ·h -1 . This phenomenon indicates that the amount of manganese added in Example 1 regulates the copper-zinc catalyst, and the surface structure of the metal oxide changes, resulting in a sudden drop in catalytic performance. Interestingly, the change in the amount of manganese added in Examples 1-3 also has a considerable impact on the methanol space-time yield. The results confirm that the different strong interactions between metal oxides and metals in copper-zinc-based catalysts cause different effective active sites produced at the interface, which greatly affects the binding strength of CO2 with the catalyst. On the other hand, with the change of reflux time and calcination temperature, the particle size changes, thereby causing the interaction between the metal oxide and the metal to increase. Therefore, excessively strong interactions change the reaction path for the formation of methanol, and the results are consistent with Table 1. In addition, the electron transfer between Cu and ZnO during the CO2 hydrogenation reaction helps to form the oxygen-deficient active phase ZnO x (or Cu x Zn (1-x) O y ), which helps in the synthesis of methanol.

[0042] Compared with Comparative Examples 1 and 2, Example 1 has the highest methanol space-time yield, which is attributed to the unique strong metal-support interaction effect of Cu and ZnO in Example 1 prepared by the reflux-assisted uniform precipitation method, which can effectively promote the activation of CO2 and convert it into methanol, but Comparative Examples 1 and 2 prepared by the traditional method cannot obtain such results. In summary, in Table 1, Example 1 has the best methanol selectivity and methanol space-time yield.

[0043] Changing the space velocity to optimize Example 1. It is concluded from Table 1 that Example 10 has a reaction temperature of 220°C, a pressure of 3.0 MPa, and a space velocity of 24000 mL·g cat -1 ·h -1 The selectivity of methanol was as high as 88.24% and the space-time yield was significantly increased to 367.82 g·kg. cat -1 ·h -1 .

[0044] Table 1 Results of product selectivity of Examples 1-9 and Comparative Examples 1-2 and Literature Comparison 1-3

[0045] It should be noted that Example 10 is more suitable for CO2 hydrogenation to methanol in a series of catalysts (Table 1). In order to further evaluate the catalytic performance of Example 10, Example 10 was compared with the reported copper-zinc-based catalyst in the process of CO2 hydrogenation to methanol. All the results are listed in Table 1. It can be clearly seen that compared with Example 10, the catalysts of Comparative Documents 1 and 2 exhibit lower methanol space-time yields (Wang S et al. FuelProcessing Technology 2023; 247: 107789; KohM et al. Journal of Industrialand Engineering Chemistry 62 (2018) 156-165). On the contrary, Comparative Document 3 has a higher CO2 conversion rate, but lower methanol selectivity and methanol space-time yield (Jia S et al. Journal of rare earths, vol.28. No. 5, Oct. 2010). Most importantly, the reaction temperatures of copper-zinc-based catalysts reported in the literature are all higher than 250°C, but the reaction temperature of Example 10 studied in this paper achieved higher methanol selectivity and methanol space-time yield at 220°C.

[0046] Therefore, it is worth emphasizing that Example 10 has great application prospects as a catalyst for industrial CO2 hydrogenation to methanol due to its superior catalytic performance at mild reaction temperatures.

[0047] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a copper-zinc-based catalyst for CO2 hydrogenation to methanol, characterized in that: Ammonia water generated by urea hydrolysis is reacted with metal nitrate, and a precipitation reaction-solid-liquid separation-calcination of the precursor is used to obtain a copper-zinc-manganese catalyst. The method steps are as follows: (1) Precipitation reaction: In a precipitation reactor, the metal oxide precursor, urea and template are dissolved in water and ethanol azeotrope in a certain proportion and refluxed for a set time; (2) Solid-liquid separation: In the solid-liquid separation equipment, the material obtained in the previous step is washed with anhydrous ethanol, and the material after the drying operation enters the next step; (3) Calcination of precursor: In a calcination device, the material obtained in the previous step is calcined in a muffle furnace to obtain a copper-zinc-based catalyst.

2. The method for preparing a copper-zinc-based catalyst for preparing methanol by hydrogenation of CO2 according to claim 1, characterized in that: The metal oxide precursors are copper nitrate, zinc nitrate and manganese nitrate.

3. The method for preparing a copper-zinc-based catalyst for CO2 hydrogenation to methanol according to claim 1 or 2, characterized in that: The template agent is D-anhydrous glucose, and the solubility of the glucose solution is 0-1 mol / L.

4. The method for preparing a copper-zinc-based catalyst for CO2 hydrogenation to methanol according to claim 1 or 2, characterized in that: In step (1), the reflux operation temperature is 80°C and the reflux time is 3-5h.

5. The method for preparing a copper-zinc-based catalyst for CO2 hydrogenation to methanol according to claim 1 or 2, characterized in that: In step (2), the drying condition is drying at 80-120° C. for 12 h in an air atmosphere.

6. The method for preparing a copper-zinc-based catalyst for CO2 hydrogenation to methanol according to claim 1 or 2, characterized in that: In step (3), the calcination condition is to increase the temperature to 300-400°C at 2°C / min in an air atmosphere and maintain it for 5 hours.

7. The method for preparing a copper-zinc-based catalyst for CO2 hydrogenation to methanol according to claim 1 or 2, characterized in that: The molar ratio of copper, zinc and manganese is 1.0:(0-5%).

8. A method for preparing methanol by hydrogenating CO2, characterized in that: The copper-zinc-based catalyst obtained by the preparation method according to any one of claims 1 to 7 is heated to 220°C, 3MPa and 3600mL / g cat -1 ·h -1 The CO2 hydrogenation to methanol reaction was carried out under the conditions of .

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