A modified Cu2O / SiTiO4 catalyst for catalytic hydrogenation of CO2 to ethanol and its preparation method

Abstract

The present invention discloses a modified Cu2O / SiTiO4 catalyst for catalytic hydrogenation of CO2 to produce ethanol and a preparation method thereof, relating to the technical field of carbon dioxide hydrogenation reaction catalyst preparation. The present invention uses a specific organic substance, tetradecyltrimethylammonium bromide, as a soft template, specific tetraethyl orthosilicate and tetraethyl titanate, a copper ammonia complex, and a treatment process to prepare the Cu2O / SiTiO4 catalyst. The catalyst can increase the CO2 conversion rate to 69% and the ethanol selectivity to 88% in the catalytic hydrogenation of CO2 to produce ethanol.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide hydrogenation reaction catalyst preparation, and in particular to a modified Cu2O / SiTiO4 catalyst for CO2 catalytic hydrogenation to ethanol and a preparation method thereof. Background Art

[0002] Industrial production and human life inevitably release large amounts of carbon dioxide into the atmosphere. Authoritative organizations estimate that by around 2050, the "greenhouse effect" caused by greenhouse gases such as carbon dioxide could cause global temperatures to rise by two degrees Celsius. Effectively addressing this serious problem poses a daunting challenge for scientists worldwide. To this end, in 2015, officials, climatologists, chemists, and economists from 118 countries and regions collaborated to formulate the Paris Agreement to jointly address the greenhouse effect. The agreement aims to limit the rising global average temperature to below 28°C and ultimately achieve zero greenhouse gas emissions.

[0003] As a non-toxic, clean, and abundant C1 raw material, CO2 is widely used in industrial processes, such as the synthesis of urea and its derivatives, salicylic acid, carbonates, and other industrial synthesis processes. However, due to the extremely stable chemical properties of carbon dioxide and its difficulty in activation, other energy sources must be introduced into the system to overcome its conversion energy barrier, and temperature and catalytic conditions must be used to overcome the kinetic barriers in its conversion process, which also poses great difficulties for its application. In 1902, Sabatier proposed the technical feasibility of converting CO and CO2 into methane. Since then, a large number of studies have selected hydrogen as a high-energy substance to activate and convert carbon dioxide through catalytic processes, and "carbon dioxide hydrogenation" has become an important research direction.

[0004] Currently, there are three main bottlenecks hindering the development of CO2 hydrogenation to C2 products. The first is the overly complex catalyst interface. The second is the difficulty in characterizing the intermediates. Finally, the unclear catalytic mechanism due to the first two factors leads to low product selectivity. CO2 hydrogenation reactions and related synthesis gas conversions have long attracted attention. Many researchers have developed a variety of metal and support-metal heterogeneous catalysts and summarized relevant empirical conclusions. However, to this day, understanding the CO2 gas-solid phase reaction from a molecular perspective remains a major challenge. Summary of the Invention

[0005] The present invention aims to provide a modified Cu2O / SiTiO4 catalyst for catalytic hydrogenation of CO2 to ethanol and a preparation method thereof, so as to further improve the yield of existing catalysts.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a modified Cu2O / SiTiO4 catalyst for catalytic hydrogenation of CO2 to ethanol comprises the following steps:

[0008] (1) dissolving tetradecyltrimethylammonium bromide in isopropyl alcohol to obtain a solution for later use;

[0009] (2) dissolving tetraethyl orthosilicate and tetraethyl titanate in a molar ratio of 8:1 to 10:1 in the solution obtained in step (1) to obtain a mixed solution, wherein the total mass of tetraethyl orthosilicate and tetraethyl titanate is 1.5 to 3 times the mass of tetradecyltrimethylammonium bromide;

[0010] (3) adding deionized water dropwise to the mixed solution obtained in step (2) under stirring until no excess precipitate is produced, then controlling the pH value of the system to 7.5-8.5 and stirring the reaction for 2 h;

[0011] (4) separating the white precipitate produced in step (3) and placing it in a copper ammonia complex solution and ultrasonically immersing it for 6 hours;

[0012] (5) Add dilute hydrochloric acid to the system obtained by impregnation in step (4) and continue impregnation for 1 hour;

[0013] (6) The precipitate obtained by impregnation was filtered and then calcined in air in two steps: first, the temperature was increased to 450°C at a heating rate of 5°C / min and calcined for 1 h; then, the temperature was increased to 800°C at a heating rate of 10°C / min and calcined for 2 h;

[0014] (7) The powder obtained by calcining step (6) is dispersed in deionized water, and zinc borohydride solution is added for reduction to obtain Cu2O / SiTiO4 catalyst.

[0015] More preferably, in step (2), the molar ratio of aluminum isopropoxide to zirconium propoxide is 10:1.

[0016] More preferably, in step (5), the concentration of the dilute hydrochloric acid is 0.5 mol / L.

[0017] More preferably, in step (7), the concentration of the zinc borohydride solution is 0.1 mol / L.

[0018] A modified Cu2O / SiTiO4 catalyst for catalytic hydrogenation of CO2 to produce ethanol prepared by any of the preparation methods described above.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The Cu2O / SiTiO4 catalyst prepared by the present invention by using specific organic matter as a soft template, specific additives and treatment can increase the CO2 conversion rate in CO2 catalytic hydrogenation to ethanol to 69% and the ethanol selectivity to 88%.

[0021] In the catalyst prepared by the present invention, the doping of Ti can change the surface structure of SiO2, making it easy for the SiO2 surface to form -OH in an alkaline environment, which is conducive to the anchoring of the copper ammonia complex on the SiO2 surface to form highly dispersed Cu active sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A line graph showing the carbon dioxide conversion rate and ethanol selectivity of the catalyst prepared in Example 1 at different catalytic temperatures;

[0023] Figure 2 A line graph showing carbon dioxide conversion and ethanol selectivity of the catalyst prepared in Example 1 at different reaction pressures;

[0024] Figure 3 This is a bar chart comparing carbon dioxide conversion rates in multiple cycle catalytic activity tests of the catalyst prepared in Example 1;

[0025] Figure 4 A bar chart comparing the carbon dioxide conversion rates in the catalytic reactions of the catalyst prepared in Example 1 with those of Cu2O / SiO2, Cu2O / TiO2, Cu2O / AC, and Cu2O / Al2O3;

[0026] Figure 5 The line graphs are for carbon dioxide conversion and ethanol yield of catalysts prepared with different Si:Ti ratios;

[0027] Figure 6 Line graphs of carbon dioxide conversion and ethanol yield for catalysts prepared under different pH control conditions;

[0028] Figure 7 The bar graph shows the carbon dioxide conversion rate of catalysts prepared at different calcination heating rates;

[0029] Figure 8 Bar graph of carbon dioxide conversion of catalysts prepared at different calcination temperatures;

[0030] Figure 9 This is a bar chart comparing the carbon dioxide conversion rates in the catalytic reactions of catalysts prepared by the two-step calcination method and the one-step calcination method.

[0031] Figure 10 A bar chart comparing the carbon dioxide conversion rates in catalytic reactions of catalysts prepared using different preparation processes. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention is further described below in conjunction with various embodiments and drawings. The implementation of the present invention includes but is not limited to the following embodiments.

[0033] Throughout this specification, unless otherwise specified, the terms used herein should be understood as having the same meaning as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the event of any conflict, the present specification shall take precedence.

[0034] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0035] In the following examples, different catalysts were prepared under different reaction conditions and their catalytic activities were verified.

[0036] The catalytic process of the catalyst prepared in the following example is:

[0037] 0.5g of catalyst was loaded into a Beijing Aerospace Century Star GCZX-011-01 fixed-bed reactor and heated to the target temperature for reaction. The reactor inlet gas flow rate was 200mL / min, and the gas composition was 70% H2 and 30% CO2. The post-reaction gas composition at the reactor outlet was analyzed using gas chromatography.

[0038] Example 1

[0039] The preparation process of the catalyst of this embodiment is as follows:

[0040] (1) Dissolve 1 g of tetradecyltrimethylammonium bromide in 20 ml of isopropanol to obtain a solution for later use;

[0041] (2) dissolving 2.10 g of tetraethyl orthosilicate and 0.23 g of tetraethyl titanate in the solution obtained in step (1) to obtain a mixed solution;

[0042] (3) Add deionized water dropwise to the mixed solution obtained in step (2) under stirring until no excess precipitation is produced, then control the pH value of the system to about 8 (±0.1), and stir the reaction for 2 hours;

[0043] (4) The white precipitate produced in step (3) was separated and placed in 10 ml of copper ammonia complex solution and immersed in ultrasound for 6 h;

[0044] (5) Add 20 ml of 0.5 mol / L dilute hydrochloric acid to the system obtained by impregnation in step (4) and continue impregnation for 1 hour;

[0045] (6) The precipitate obtained by impregnation was filtered and then calcined in air in two steps: first, the temperature was increased to 450°C at a heating rate of 5°C / min and calcined for 1 h; then, the temperature was increased to 800°C at a heating rate of 10°C / min and calcined for 2 h;

[0046] (7) The powder obtained by calcining step (6) was dispersed in deionized water, and 30 ml of 0.1 mol / L zinc borohydride solution was added for reduction to obtain a Cu2O / SiTiO4 catalyst.

[0047] like Figure 1 The figure below shows a line graph of CO2 conversion and ethanol selectivity over the Cu2O / SiTiO4 catalyst at different catalytic temperatures. At low reaction temperatures, CO2 conversion is low and ethanol selectivity is high. As the reaction temperature increases, CO2 conversion gradually increases, while ethanol selectivity decreases slightly. CO2 conversion reaches its maximum at 400°C. As the reaction temperature continues to rise, CO2 conversion remains essentially unchanged.

[0048] like Figure 2 Figure 2 shows a line graph of CO2 conversion and ethanol selectivity over the Cu2O / SiTiO4 catalyst at different reaction pressures. As the reaction pressure increases, CO2 conversion and selectivity both increase. At low pressures, most CO2 is converted to CO. As pressure increases, ethanol selectivity gradually increases.

[0049] like Figure 3 The chart below shows a comparison of carbon dioxide conversion rates obtained from five 1000-hour activity tests of the Cu2O / SiTiO4 catalyst. After each 1000-hour test, the catalyst was regenerated. As can be seen from the chart, the catalyst activity recovered approximately 95% after regeneration.

[0050] Example 2

[0051] In this example, the catalytic performance of the catalyst prepared in Example 1 was compared with that of Cu2O / SiO2, Cu2O / TiO2, Cu2O / AC, and Cu2O / Al2O3 catalysts prepared by the traditional impregnation method. Figure 4 As shown, it is not difficult to find that the catalytic activity prepared in Example 1 is much higher than that of other catalysts.

[0052] Example 3

[0053] This example discusses the effect of the Si:Ti ratio on the catalytic performance of the catalyst.

[0054] The other steps are the same as those in Example 1, except that the Si:Ti ratio is adjusted. The addition conditions of tetraethyl orthosilicate and tetraethyl titanate are shown in Table 1:

[0055] Table 1 Feeding conditions of aluminum propoxide and zirconium propoxide

[0056] Si:Ti Tetraethyl orthosilicate / g Tetraethyl titanate / g 20:1 4.16 0.23 15:1 3.12 0.23 10:1 (Example 1) 2.10 0.23 8:1 1.67 0.23 5:1 1.04 0.23

[0057] The catalysts prepared according to the feed in Table 1 were used in the catalytic experiment. Figure 5 As shown in the figure, when the Si:Ti ratio is 10:1, the carbon dioxide conversion rate can reach 69% and the ethanol selectivity performance reaches 88%. When the Si:Ti ratio is larger, the yield and selectivity are lower, especially the selectivity for ethanol drops sharply. When the Si:Ti ratio is less than 10:1, the conversion rate and selectivity are also lower.

[0058] Example 3

[0059] This example discusses the effect of different pH control conditions on the catalytic efficiency of the catalyst.

[0060] The other steps were the same as in Example 1, except that the pH value in step (2) was replaced by 6 / 7 / 9 / 10. The prepared catalysts were used in catalytic experiments. The test results were as follows: Figure 6 As shown in the figure, by comparison, it was found that when the pH value was 8, the activity of the catalyst reached the highest value. It may be that under this pH environment, the copper ammonia complex can form highly dispersed small-particle Cu active centers on the surface of SiTiO4, which is beneficial to improve the catalytic activity.

[0061] Example 4

[0062] This example discusses the effects of different calcination temperatures and calcination temperature increase rates on the catalytic effect of the catalyst.

[0063] The other steps were the same as in Example 1, except that the two-stage calcination temperature was replaced and the heating rate was changed. The prepared catalysts were used in the catalytic experiment. The test results are shown in FIG. Figure 7 / 8 shows that, by comparison, it is found that both the calcination temperature and the calcination temperature heating rate will affect the catalytic performance of the catalyst.

[0064] The present invention comprises two stages of heating. The first stage involves the formation of Cu active centers and the conversion of mixed Si(OH)4 and Ti(OH)4 into SiTiO4. The second stage involves the calcination of the SiTiO4 to strengthen the structural skeleton. The heating rate should be kept constant, as this would cause the skeleton to collapse. The calcination temperatures in both stages have a certain influence on the catalytic activity. Calcining the catalyst at an appropriate temperature allows for the complete oxidation of Cu, Si, and Ti, strengthening the skeleton structure.

[0065] Example 5

[0066] This example discusses the effects of a two-step calcination method and a one-step calcination method on the catalytic effect of the catalyst.

[0067] The two-step calcination method is the preparation process of Example 1.

[0068] The other steps of the one-step calcination method are the same as those in Example 1, but in step (6), the temperature is directly raised to 800° C. without stopping.

[0069] like Figure 9 As shown in the figure, it is a bar chart comparing the carbon dioxide conversion rates in the catalytic reactions of the catalysts prepared by the two methods. It can be seen that the catalytic performance of the one-step calcination method is significantly worse. It is possible that the direct one-step heating method will cause the Cu active center to form too quickly, resulting in agglomeration to form large particles, reducing the dispersion of the active center and finally leading to a decrease in catalytic activity.

[0070] Example 6

[0071] This example discusses the effect of the organic soft template on the catalytic efficiency of the catalyst.

[0072] a. The other steps are the same as in Example 1, except that poly F127 is used to replace tetradecyltrimethylammonium bromide to prepare Cu2O / SiTiO4-1 catalyst.

[0073] b. The other steps are the same as in Example 1, using poly P123 to replace tetradecyltrimethylammonium bromide to prepare Cu2O / SiTiO4-2 catalyst:

[0074] c. The other steps were the same as in Example 1, omitting step (1) to prepare a Cu2O / SiTiO4-3 catalyst.

[0075] The prepared catalysts were used in catalytic experiments and compared with those in Example 1. Figure 10 As shown in the results, tetradecyltrimethylammonium bromide has obvious advantages over poly P123 and poly F127, and compared with not adding organic matter, adding organic matter can obviously achieve better results.

[0076] The above embodiment is only one of the preferred implementation methods of the present invention and should not be used to limit the scope of protection of the present invention. Any changes or modifications that have no substantive meaning made to the main design concept and spirit of the present invention, as long as the technical problems solved are still consistent with the present invention, should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a modified Cu2O / SiTiO4 catalyst for catalytic hydrogenation of CO2 to ethanol, characterized in that: The steps include: (1) dissolving tetradecyltrimethylammonium bromide in isopropyl alcohol to obtain a solution for later use; (2) dissolving tetraethyl orthosilicate and tetraethyl titanate in a molar ratio of 8:1 to 10:1 in the solution obtained in step (1) to obtain a mixed solution, wherein the total mass of tetraethyl orthosilicate and tetraethyl titanate is 1.5 to 3 times the mass of tetradecyltrimethylammonium bromide; (3) adding deionized water dropwise to the mixed solution obtained in step (2) under stirring until no excess precipitate is produced, then controlling the pH value of the system to 7.5-8.5 and stirring the reaction for 2 h; (4) separating the white precipitate produced in step (3) and placing it in a copper ammonia complex solution and ultrasonically immersing it for 6 hours; (5) Add dilute hydrochloric acid to the system obtained by impregnation in step (4) and continue impregnation for 1 hour; (6) The precipitate obtained by impregnation was filtered and then calcined in air in two steps: first, the temperature was increased to 450°C at a heating rate of 5°C / min and calcined for 1 h; then, the temperature was increased to 800°C at a heating rate of 10°C / min and calcined for 2 h; (7) The powder obtained by calcining step (6) is dispersed in deionized water, and zinc borohydride solution is added for reduction to obtain Cu2O / SiTiO4 catalyst.

2. The preparation method according to claim 1, wherein In step (2), the molar ratio of tetraethyl orthosilicate to tetraethyl titanate is 10:

1.

3. The preparation method according to claim 1, wherein In step (5), the concentration of the dilute hydrochloric acid is 0.5 mol / L.

4. The preparation method according to claim 1, wherein In step (7), the concentration of the zinc borohydride solution is 0.1 mol / L.

5. A modified Cu2O / SiTiO4 catalyst for catalytic hydrogenation of CO2 to ethanol prepared by the preparation method according to any one of claims 1 to 4.

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