A Zr / CuZnO catalyst for CO2 hydrogenation to produce methyl ether and its preparation method

Abstract

The present invention discloses a Zr / CuZnO catalyst for CO2 hydrogenation to produce methyl ether and its preparation method, relating to the field of novel catalyst synthesis for producing methyl ether from carbon dioxide. The present invention first utilizes tetradecyltrimethylammonium bromide, potassium hydroxide, copper nitrate, and zinc nitrate to prepare a two-dimensional flaky CuZnO oxide using a soft template method. Zr is then loaded onto the two-dimensional flaky CuZnO oxide to form a Zr / CuZnO oxide catalyst. This catalyst achieves a larger specific surface area, better exposes active centers, and enhances catalytic reaction activity.

Description

Technical Field

[0001] The present invention relates to the field of novel catalyst synthesis for preparing methyl ether from carbon dioxide, and in particular to a Zr / CuZnO catalyst for preparing methyl ether from CO2 hydrogenation and a preparation method thereof. Background Art

[0002] CO2, as a widely available, abundant, and inexpensive carbon source, is often used to prepare some of the simplest organic substances, such as methanol and dimethyl ether (also called dimethyl ether, or DME). The most common research is the hydrogenation of CO2 to produce methanol, but the production of dimethyl ether is equally important. The catalytic hydrogenation of CO2 to synthesize dimethyl ether is an effective way to fully utilize CO2 as a renewable resource, develop new energy, obtain bulk chemicals, and achieve a virtuous cycle of carbon elements in nature. The combustion process of dimethyl ether is sulfur-free, NOX-free, and dust-free. It has low ozone depletion potential (ODP) and global warming potential (GWP), and can replace liquefied petroleum gas as an eco-friendly fuel.

[0003] Currently, the direct synthesis of DME from CO2 hydrogenation is still in the exploratory stage. This process utilizes a bifunctional catalyst composed of two active centers: one for methanol synthesis and one for methanol dehydration. In these bifunctional composite catalysts, the methanol synthesis active component is primarily a Cu-based catalyst, while the methanol dehydration active component is primarily a solid acid such as HZS M-5 and γ-Al2O3. However, conventional Cu-based catalysts offer low single-pass yields for both methanol and DME. Furthermore, the catalyst composition and ratio affect catalytic performance to varying degrees. Further improvements in Cu-based catalysts are crucial for the direct synthesis of DME from CO2 hydrogenation. Summary of the Invention

[0004] The present invention aims to provide a Zr / CuZnO catalyst for CO2 hydrogenation to produce methyl ether and a preparation method thereof, so as to solve the technical problem that the yield of the existing catalyst for CO2 hydrogenation to produce methyl ether is low.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a Zr / CuZnO catalyst for CO2 hydrogenation to produce methyl ether comprises the following steps:

[0007] (1) Dissolve tetradecyltrimethylammonium bromide and potassium hydroxide in deionized water and stir to dissolve in a water bath at 70-90°C;

[0008] (2) dissolving copper nitrate and zinc nitrate in the solution obtained in step (1);

[0009] (3) The solution obtained in step (2) was kept at a constant temperature of 70-80°C in a water bath for 1 hour, and then the solution was transferred to an oven and dried at 100-120°C;

[0010] (4) calcining the precipitate after drying in step (3) at 600° C. in air atmosphere for 3 h;

[0011] (5) washing the powder obtained by calcining step (4) with excess deionized water and ethanol to obtain flaky Cu ZnO oxide;

[0012] (6) Dispersing the obtained CuZnO oxide in propanol, adding zirconium propoxide, and stirring to dissolve;

[0013] (7) adding deionized water dropwise to the solution obtained in step (6) until no precipitation is produced;

[0014] (8) filtering the precipitate obtained in step (7) and washing with excess deionized water and ethanol;

[0015] (9) The powder obtained by washing in step (8) was heated to 500-600° C. in an air atmosphere and calcined for 2 h to obtain a Zr / CuZnO catalyst.

[0016] Preferably, the molar ratio of copper nitrate to zinc nitrate in step (2) is 3:2.

[0017] Preferably, the Zr content in the Zr / CuZnO catalyst in step (9) is 1 to 1.5 wt%.

[0018] Preferably, step (9) is carried out by heating the temperature to 500-600°C at a heating rate of 10°C / min.

[0019] A Zr / CuZnO catalyst prepared by any of the preparation methods described above.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention first uses tetradecyltrimethylammonium bromide, potassium hydroxide, copper nitrate and zinc nitrate to prepare a two-dimensional flaky CuZnO oxide by a soft template method, and then loads Zr on the two-dimensional flaky CuZnO oxide to form a Zr / CuZnO oxide catalyst, which can obtain a larger specific surface area, better expose active centers, and improve catalytic reaction activity. The present invention greatly improves the yield of methyl ether through a specific CuZn ratio and a specific Zr loading amount. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a SEM electron microscope image of Zr / CuZnO obtained in the present invention;

[0023] Figure 2 This is a line graph showing the effect of CuZnO with different CuZn ratios on the catalytic hydrogenation activity of CO2;

[0024] Figure 3 The line graph shows the effect of different Zr loadings on the CO2 catalytic hydrogenation activity of Zr / CuZnO catalysts;

[0025] Figure 4 It is a line graph showing the effect of different supports on catalytic activity;

[0026] Figure 5 The line graph shows the effect of different preparation methods on the catalytic activity of Zr / CuZnO catalysts;

[0027] Figure 6 1wt% Zr / Cu 0.6 Zn 0.4 Line graph showing the effect of catalyst O on the catalytic activity of CO2 hydrogenation to methyl ether at different temperatures;

[0028] Figure 7 1wt% Zr / Cu 0.6 Zn 0.4 A line graph showing the effect of catalyst O-1's catalytic activity on CO2 hydrogenation to methyl ether at different temperatures;

[0029] Figure 8 1wt% Zr / Cu 0.6 Zn 0.4 Line graph showing the effect of O-2 catalyst's catalytic activity on CO2 hydrogenation to produce methyl ether at different temperatures. DETAILED DESCRIPTION

[0030] 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.

[0031] 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.

[0032] 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.

[0033] In the following examples, except for the conditions clearly stated, the catalyst preparation process was carried out as follows:

[0034] (1) Dissolve tetradecyltrimethylammonium bromide (1 mol) and potassium hydroxide (0.1 mol) in deionized water (1 L) and stir in a water bath at 70-90°C to dissolve.

[0035] (2) dissolving copper nitrate (6 g) and zinc nitrate (4 g) in the solution obtained in step (1);

[0036] (3) The solution obtained in step (2) was kept at a constant temperature of 70-80°C in a water bath for 1 hour, and then the solution was transferred to an oven and dried at 100-120°C;

[0037] (4) calcining the precipitate after drying in step (3) at 600° C. in air atmosphere for 3 h;

[0038] (5) washing the powder obtained by calcining step (4) with excess deionized water and ethanol to obtain flaky Cu ZnO oxide;

[0039] (6) The prepared CuZnO oxide (1 g) was dispersed in propanol, zirconium propoxide (0.03 g) was added, and stirred to dissolve;

[0040] (7) adding deionized water dropwise to the solution obtained in step (6) until no precipitation is produced;

[0041] (8) filtering the precipitate obtained in step (7) and washing with excess deionized water and ethanol;

[0042] (9) The powder obtained by washing in step (8) was heated to 500-600°C in an air atmosphere and calcined for 2 hours to obtain a Zr / CuZnO catalyst. The SEM electron microscope image is shown in FIG. Figure 1 shown.

[0043] The catalyst activity of each example was verified as follows: 0.5 g of catalyst was loaded into a 1 cm diameter straight quartz reactor and heated to the target temperature for reaction. The reactor inlet gas flow rate was 200 mL / min, and the gas composition was CO₂:H₂ = 3:1 (molar ratio). The post-reaction gas composition was analyzed at the reactor outlet using a mass spectrometer.

[0044] In the following examples, different catalysts were prepared under different reaction conditions and their catalytic activities were verified.

[0045] Example 1

[0046] This example discusses the effect of different CuZn ratios on catalytic activity. Therefore, steps (6) to (9) are omitted in this example, and CuZnO oxide is directly used as the catalyst.

[0047] According to the above experimental steps, the molar ratio of CuZn was changed to 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, and 10:0. The catalytic activity of each group of CuZnO oxide catalysts at about 275°C is shown in the following table. Figure 2 As shown in the figure, it is not difficult to see the effect of the CuZn ratio on the catalytic activity in the absence of Zr. When the CuZn molar ratio is 6:4, the unmarked Cu 0.6 Zn 0.4 The conversion rate of O and carbon dioxide reached 50%, and the yield of dimethyl ether DME reached 46%.

[0048] We also verified the effect of different CuZn ratios on Zr / CuZnO catalysts. The results were the same as those of CuZnO oxide. The yield of dimethyl ether (DME) was the highest when the CuZn molar ratio was less than 6:4.

[0049] Example 2

[0050] This example explores the effect of the Zr content of the additive on the catalytic activity: the molar ratio of Cu to Zn is fixed at 6:4, and the Zr loading amounts of 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0% are explored. The catalytic activity results of each group of Zr / CuZnO oxide catalysts at around 275°C are as follows: Figure 3 As shown in Figure 2, when the Zr content reaches 1.5 wt%, the catalytic activity reaches its highest, with a carbon dioxide conversion rate of 53% and a dimethyl ether selectivity of 73%. When the Zr content exceeds 1.5-2 wt%, the dimethyl ether selectivity begins to decline.

[0051] The corresponding materials of Zr(C3H7O)4 in this embodiment are shown in Table 1:

[0052] Table 1 Zr(C3H7O)4 dosage corresponding to different Zr loadings

[0053] Zr loading <![CDATA[Zr(C3H7O)4]]> 0.5％ 0.01g 1％ 0.02g 1.5％ 0.03g 2.5％ 0.05g 3％ 0.06g

[0054] Example 3

[0055] This example explores the effect of different active centers (promoters) on catalytic activity: The molar ratio of Cu to Zn was fixed at 6:4, and zirconium propoxide was replaced with corresponding promoter metal salts of Cr, Ti, Fe, and Mn. 1 wt% of Zr, Cr, Ti, Fe, and Mn promoter metals were loaded onto the CuZnO surface, respectively, and their catalytic activities were compared. The catalytic activity results of the various groups of Zr / CuZnO oxide catalysts at around 275°C are shown in Figure 2. Figure 4As shown, it can be seen that after adding Fe and Mn additives, the selectivity of dimethyl ether is not significantly improved. After adding Cr and Ti, the selectivity of dimethyl ether is improved to a certain extent, but is significantly lower than that of Zr.

[0056] In this embodiment, the corresponding materials of copper nitrate (6g) and zinc nitrate (4g) are shown in Table 2:

[0057] Table 1 Amounts of Cu(NO3)2 and Zn(NO3)2 corresponding to different CuZn molar ratios

[0058]

[0059]

[0060] Example 4

[0061] This example discusses the effect of different carriers on catalytic activity: CuO, ZnO, Al2O3, CeO2, TiO2 and other carriers are compared. Zr is loaded on CuO, ZnO, Al2O3, CeO2, TiO2 and other carriers according to steps (6) to (9). The catalytic activity of each group of Zr / CuZnO oxide catalysts at about 275°C is shown in the following figure. Figure 5 The catalytic activity of CuO and ZnO alone is not high, but it is still better than that of supports such as Al2O3, CeO2, and TiO2. After CuO and ZnO are combined, defect sites are formed, which is conducive to the adsorption and conversion of CO2.

[0062] Example 5

[0063] This example also explores the effect of different preparation methods on the catalytic activity of Zr / CuZnO catalysts. 0.6 Zn 0.4 O catalyst, 1wt% Zr / Cu was prepared by step precipitation method 0.6 Zn 0.4 O-1 catalyst, 1wt% Zr / Cu prepared by coprecipitation 0.6 Zn 0.4 O-2 catalyst.

[0064] (1) The Zr / CuZnO catalyst prepared by the step-by-step precipitation method is as follows:

[0065] a. Disperse a certain amount of commercial nano-CuO into deionized water.

[0066] b. Dissolve a certain amount of zinc nitrate into the above solution, then transfer the solution to an oven and dry it at 100°C.

[0067] c. The dried precipitate was calcined at 600°C in air atmosphere for 3 h.

[0068] d. Disperse the above powder into deionized water and add a certain amount of zirconium nitrate.

[0069] e. Transfer the above to an oven and dry at 100°C.

[0070] f. The dried precipitate was calcined at 600°C in an air atmosphere for 3h to obtain Zr / CuZnO-1.

[0071] (2) The Zr / CuZnO catalyst prepared by co-precipitation is as follows:

[0072] a. Disperse a certain amount of commercial nano-CuO into deionized water.

[0073] b. Dissolve a certain amount of zinc nitrate and zirconium nitrate into the above solution, then transfer the solution to an oven and dry it at 100°C.

[0074] c. The dried precipitate was calcined at 600°C in air atmosphere for 3 h to obtain Zr / CuZnO-2.

[0075] 1wt% Zr / Cu 0.6 Zn 0.4 O catalyst, 1wt% Zr / Cu 0.6 Zn 0.4 O-1 catalyst, 1wt% Zr / Cu 0.6 Zn 0.4 O-2 catalyst was put into the experiment, and the catalytic activity of different catalysts on CO2 catalytic hydrogenation to methyl ether at different temperatures was obtained. Figures 6-8 As shown in the figure below, Zr / CuZnO-1 and Zr / CuZnO-2 prepared by step precipitation and co-precipitation methods have small specific surface areas, large particles, and difficulty in exposing active sites, resulting in low catalytic activity of Zr / CuZnO-1 and Zr / CuZnO-2. 0.6 Zn 0.4 At 275℃, the carbon dioxide conversion rate of the catalyst reaches 53% and the selectivity of methyl ether reaches 73%. With further temperature increase, the carbon dioxide conversion rate does not increase much, but the selectivity of methyl ether decreases significantly. 0.6 Zn 0.4 O-1 and 1wt%Zr / Cu 0.6 Zn 0.4 The trend of the catalytic activity of O-2 with temperature is similar to that of 1wt% Zr / Cu 0.6 Zn 0.4The catalysts are similar, and the carbon dioxide conversion rate and methyl ether selectivity reach the highest value at 275℃. The selectivity of methyl ether decreases significantly with further temperature increase, but its activity is significantly lower than that of 1wt% Zr / Cu 0.6 Zn 0.4 catalyst.

[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 Zr / CuZnO catalyst for CO2 hydrogenation to methyl ether, characterized in that: The steps include: (1) Dissolve tetradecyltrimethylammonium bromide and potassium hydroxide in deionized water and stir to dissolve in a water bath at 70-90°C; (2) dissolving copper nitrate and zinc nitrate in a molar ratio of 3:2 in the solution obtained in step (1); (3) The solution obtained in step (2) was kept at a constant temperature of 70-80°C in a water bath for 1 hour, and then the solution was transferred to an oven and dried at 100-120°C; (4) calcining the precipitate after drying in step (3) at 600° C. in air atmosphere for 3 h; (5) washing the powder obtained by calcining step (4) with excess deionized water and ethanol to obtain flaky CuZnO oxide; (6) Dispersing the obtained CuZnO oxide in propanol, adding zirconium propoxide, and stirring to dissolve; (7) adding deionized water dropwise to the solution obtained in step (6) until no precipitation is produced; (8) filtering the precipitate obtained in step (7) and washing with excess deionized water and ethanol; (9) The powder obtained by washing in step (8) is heated to 500-600° C. in an air atmosphere and calcined for 2 h to obtain a Zr / CuZnO catalyst, wherein the Zr content in the Zr / CuZnO catalyst is 1-1.5 wt %.

2. The preparation method according to claim 1, wherein Step (9) is carried out by heating the temperature to 500-600°C at a heating rate of 10°C / min.

3. The Zr / CuZnO catalyst prepared by the preparation method according to claim 1 or 2.

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