A catalyst for CO / CO2 hydrogenation to aromatics, its preparation method and application

Abstract

A catalyst for the hydrogenation of CO / CO2 to aromatics, its preparation method, and its application are disclosed, belonging to the field of catalysis. It comprises a sulfur-modified composite oxide and an H-ZSM-5 molecular sieve. The sulfur-modified composite oxide contains sulfur (S), a first metal, and a second metal. The molar percentage of S in the sulfur-modified composite oxide is 0.1%–5.0%. The first metal is Zn, and the second metal is selected from at least one of Mg, Zr, Cr, Al, and Ga. The molar ratio of Zn to the second metal component is 1:(1–500). The doping of sulfur reduces the average particle size, significantly increases the specific surface area, and significantly enhances the surface acidity of the composite oxide. The bifunctional catalyst formed by combining the sulfur-modified composite oxide with the H-ZSM-5 molecular sieve can be applied to the efficient hydrogenation of CO / CO2 to aromatics. The preparation process of the sulfur-modified composite oxide and its coupling process with the molecular sieve are simple and controllable, easily scaled up, and have good application prospects.

Description

Technical Field

[0001] This invention relates to the field of industrial catalysis, and more particularly to a catalyst for the hydrogenation of CO / CO2 to aromatics, its preparation method, and its application. Background Technology

[0002] Aromatic hydrocarbons, as one of the most important basic chemical raw materials, are widely used in the production of fragrances, pharmaceuticals, dyes, and high molecular weight polymers, accounting for nearly one-third of the petrochemical market. At the same time, the environmental problems caused by increasing carbon emissions are receiving significant attention, and CO2, while a major greenhouse gas, is also the largest renewable carbon resource in terms of reserves. Therefore, given my country's abundant coal resources, researching the efficient conversion and utilization of C1 molecules, especially CO and CO2, and developing new alternatives to petrochemicals is of great strategic importance for ensuring my country's energy security and achieving its "dual carbon" goals.

[0003] In recent years, the direct preparation of aromatics from CO / CO2 hydrogenation via relay catalysis has been widely applied. This process uses a bifunctional metal oxide-molecular sieve catalyst, and the reaction mechanism is generally as follows: CO / CO2 is activated on the metal oxide and hydrogenated to form an oxygen-containing intermediate (methanol / dimethyl ether). The oxygen-containing intermediate is then transferred to the molecular sieve for dehydration and C / C coupling to generate low-carbon olefins, which are then aromatized to form aromatics.

[0004] CC coupling and aromatization are typical acid-catalyzed reactions that require catalysts with sufficient strength and density of acidic sites. However, if the strength or density of acidic sites is too high, it can lead to hydrogenation of intermediates to form saturated alkanes or carbon deposition on the catalyst, which is not conducive to the formation of aromatic products and the construction of highly stable catalysts. Therefore, the regulation of catalyst acidity is very important.

[0005] In current technologies, the control of catalyst acidity almost entirely focuses on molecular sieves, and CO / CO2 conversion and aromatic product selectivity still need to be improved. Therefore, developing catalysts that combine high activity with suitable acidity is a key research focus in this area. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems in the prior art and provide a catalyst for the hydrogenation of CO / CO2 to produce aromatics, its preparation method and application. The composite oxide used in this catalyst has a reduced average particle size, a significantly increased specific surface area and a significantly enhanced surface acidity after being modified with sulfur. When combined with H-ZSM-5 molecular sieve to form a bifunctional catalyst, it can be applied to the efficient hydrogenation of CO / CO2 to produce aromatics.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A catalyst for the hydrogenation of CO / CO2 to aromatics comprises a sulfur-modified composite oxide and an H-ZSM-5 molecular sieve;

[0009] The sulfur-modified composite oxide comprises S, a first metal, and a second metal. The molar percentage of S in the sulfur-modified composite oxide is 0.1% to 5.0%. The first metal is Zn, and the second metal is selected from at least one of Mg, Zr, Cr, Al, and Ga. The molar ratio of Zn to the second metal component is 1:(1 to 500).

[0010] The method for preparing a catalyst for the hydrogenation of CO / CO2 to aromatics includes the following steps:

[0011] 1) Dissolve the first metal salt, the second metal salt, and the foaming agent in deionized water, stir under water bath heating until a thick gel appears, place the resulting gel in an oven to foam, then mix sulfur powder into the foamed solid and grind it, and finally calcine to obtain sulfur-modified composite oxide.

[0012] 2) Grind and mix the sulfur-modified composite oxide and H-ZSM-5 molecular sieve.

[0013] In step 1), the water bath heating temperature is 50-100℃.

[0014] In step 1), the foaming temperature is 150-200℃ and the time is 3-10 hours.

[0015] In step 1), the heating rate during calcination is 1–5 °C / min. -1 The temperature is 400-600℃, and the roasting time is 5-15 hours.

[0016] The first metal salt and the second metal salt are selected from at least one of nitrates, hydrochlorides, sulfates, and acetates.

[0017] The foaming agent is citric acid monohydrate, and the molar ratio of citric acid monohydrate to the sum of the first metal salt and the second metal salt is 1:(2-5).

[0018] In step 2), the mass ratio of the sulfur-modified composite oxide and the H-ZSM-5 molecular sieve is 1:(1~3); the H-ZSM-5 molecular sieve is an industrial H-ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 100~400.

[0019] The catalyst for the hydrogenation of CO / CO2 to aromatics is applied to the hydrogenation of CO / CO2 to aromatics.

[0020] Before the reaction, the catalyst was pretreated with nitrogen at 300–500 °C for 1–2 h to activate it.

[0021] The reaction temperature for CO / CO2 hydrogenation to produce aromatics is 280–450℃, the reaction pressure is 1–6 MPa, and the space velocity is 1000–10000 mL h⁻¹. -1 g -1 ;

[0022] The volume ratio of hydrogen to CO in the feed gas for CO hydrogenation is (1-3):1, and the volume ratio of hydrogen to CO2 in the feed gas for CO2 hydrogenation is (1-4):1. The reaction time is 10-50 h.

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

[0024] (1) The catalyst provided by the present invention includes sulfur-modified composite oxide and H-ZSM-5 molecular sieve. After sulfur modification, the average particle size of the composite oxide is smaller, the specific surface area is significantly increased, and more active sites are exposed.

[0025] (2) In the catalyst provided by the present invention, the surface acidity of the composite oxide is significantly enhanced after sulfur modification. Therefore, when combined with H-ZSM-5 molecular sieve to form a bifunctional catalyst, it can not only provide methanol intermediate, but also assist the molecular sieve in dehydration and CC coupling reaction, thereby achieving efficient preparation of aromatics by CO / CO2 hydrogenation.

[0026] (3) The preparation process of sulfur-modified composite oxide and its coupling process with H-ZSM-5 molecular sieve provided by the present invention are simple and controllable, easy to scale up further, and have good application prospects. Attached Figure Description

[0027] Figure 1 Example 2: Sulfur-modified composite oxide S-ZnZr 16 O x HAADF-STEM and EDX characterization images; where (a) is S-ZnZr 16 O x The HAADF-STEM characterization diagrams are shown in (b) to (d), and the EDX characterization diagrams of elements Zr, Zn, and S are shown in (d).

[0028] Figure 2 Example 2: Sulfur-modified composite oxide S-ZnZr 16 O x TEM characterization images and their particle size distribution.

[0029] Figure 3 Comparative Example 2: Composite Oxide ZnZr 16 O x TEM characterization images and their particle size distribution.

[0030] Figure 4Example 2: Sulfur-modified composite oxide S-ZnZr 16 O x Comparative Example 2: Composite Oxide ZnZr 16 O x A comparison chart of specific surface areas.

[0031] Figure 5 Example 2: Sulfur-modified composite oxide S-ZnZr 16 O x Comparative Example 2: Composite Oxide ZnZr 16 O x The NH3-TPD curve. Detailed Implementation

[0032] To make the technical problems, technical solutions, and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0033] Example 1

[0034] Weigh 0.036g Zn(NO3)2·6H2O, 10.30g Zr(NO3)4·5H2O, and 9.3g citric acid monohydrate and dissolve them in 100mL deionized water. Stir the solution in an 80℃ water bath until a transparent, viscous gel forms. Place the resulting gel in an oven at 180℃ for 3 hours to foam. Weigh 0.02g sulfur powder, mix it into the solid, and grind it evenly. Transfer the solid to a muffle furnace for calcination at a heating rate of 2℃ / min. -1 The temperature was 500℃, and the calcination time was 5 hours. The resulting sulfur-modified composite oxide was denoted as S-ZnZr. 200 O x .

[0035] Weigh out 1.0g of S-ZnZr 200 O x The oxide and 2.0 g of industrial H-ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 240 were placed in a mortar and ground for 10 min to ensure thorough mixing. The mixture was then compressed into tablets, and the resulting catalyst was denoted as S-ZnZr. 200 O x / H-ZSM-5.

[0036] Weigh out 1.2g of S-ZnZr 200 O x The / H-ZSM-5 catalyst was loaded into a quartz reaction tube; before the reaction, the tube was pretreated with nitrogen at 30 mL / min at 400 °C for 1 h; after pretreatment, the tube was cooled to room temperature, and a feed gas was introduced, with a hydrogen to CO volume ratio of 2:1. The reaction pressure was 3 MPa, the reaction temperature was 400 °C, and the space velocity was 1000 mL / h. -1 g -1The reaction time was 20 hours. The reaction products and feed gas were analyzed online by gas chromatography.

[0037] The reaction evaluation results of the catalytic CO hydrogenation to aromatics in this embodiment are shown in Table 1. It can be seen that the CO conversion rate is high when the CO hydrogenation reaction occurs on this catalyst, and the products are mainly aromatics.

[0038] Table 1

[0039] <![CDATA[CH₄ Selectivity (%),]]> 1.9 <![CDATA[C 2-4 Selectivity %) 15.4 Aromatic selectivity (%) 80.2 <![CDATA[Other C 5+ Selectivity (%)]]> 2.5

[0040] Note: C 2-4 These are C2-C4 hydrocarbons, including aromatic hydrocarbons such as benzene, toluene, xylene, and polymethylbenzene. 5+ Alkanes and alkenes with ≥5 carbon atoms.

[0041] Example 2

[0042] Weigh 0.45g Zn(NO3)2·6H2O, 10.30g Zr(NO3)4·5H2O, and 9.8g citric acid monohydrate and dissolve them in 100mL deionized water. Stir the solution in an 80℃ water bath until a transparent, viscous gel forms. Place the resulting gel in an oven at 180℃ for 3 hours to foam. Weigh 0.02g sulfur powder, mix it into the solid, and grind it evenly. Transfer the solid to a muffle furnace for calcination at a heating rate of 2℃ / min. -1 The temperature was 500℃, and the calcination time was 5 hours. The resulting sulfur-modified composite oxide was denoted as S-ZnZr. 16 O x .

[0043] Weigh out 0.5g of S-ZnZr 16 O x The oxide and 1.0 g of industrial H-ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 240 were placed in a mortar and ground for 10 min to ensure thorough mixing. The mixture was then compressed into tablets, and the resulting catalyst was denoted as S-ZnZr. 16 O x / H-ZSM-5.

[0044] Weigh 0.6g of S-ZnZr 16 O x The / H-ZSM-5 catalyst was loaded into a quartz reaction tube; before the reaction, the tube was pretreated with nitrogen at 30 mL / min at 400 °C for 1 h; after pretreatment, the tube was cooled to room temperature, and a feed gas was introduced, with a hydrogen to CO2 volume ratio of 2:1. The reaction pressure was 3 MPa, the reaction temperature was 340 °C, and the space velocity was 3000 mL / h. -1 g -1The reaction time was 10 h. The reaction products and feed gas were analyzed online by gas chromatography. The evaluation results of the catalytic CO2 hydrogenation to aromatics reaction are shown in Table 2. It can be seen that the CO2 conversion rate is high during the CO2 hydrogenation reaction on this catalyst, and the main product is aromatics.

[0045] Table 2

[0046] <![CDATA[CH₄ Selectivity (%)]]> 0.5 <![CDATA[C 2-4 Selectivity (%) 22.8 Aromatic selectivity (%) 70.1 <![CDATA[Other C 5+ Selectivity (%)]]> 6.6

[0047] Comparative Example 1

[0048] Weigh 0.036 g Zn(NO3)2·6H2O, 10.30 g Zr(NO3)4·5H2O, and 9.3 g citric acid monohydrate and dissolve them in 100 mL of deionized water. Stir the solution in an 80°C water bath until a transparent, viscous gel forms. Place the resulting gel in an oven at 180°C for 3 hours to allow it to foam. Grind the resulting solid into a fine powder and transfer it to a muffle furnace for calcination at a heating rate of 2°C / min, a temperature of 500°C, and a calcination time of 5 hours. The resulting unmodified sulfur-containing composite oxide is denoted as ZnZr. 200 O x .

[0049] Weigh out 1.0g of ZnZr 200 O x The oxide and 2.0 g of industrial H-ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 240 were placed in a mortar and ground for 10 min to ensure thorough mixing. The mixture was then compressed into tablets, and the resulting catalyst was denoted as ZnZr. 200 O x / H-ZSM-5.

[0050] ZnZr 200 O x The reaction evaluation steps for CO hydrogenation to aromatics on the / H-ZSM-5 catalyst are the same as in Example 1. The reaction results are shown in Table 3. It can be seen that when this catalyst is used for CO hydrogenation to aromatics, the CO conversion rate and the selectivity of aromatics are both low.

[0051] Table 3

[0052] <![CDATA[CH4 Selectivity (%)]]> 2.6 <![CDATA[C 2-4 Selectivity %) 27.4 Aromatic selectivity (%) 67.1 <![CDATA[Other C 5+ Selectivity (%)]]> 2.9

[0053] Comparative Example 2

[0054] Weigh 0.45g Zn(NO3)2·6H2O, 10.30g Zr(NO3)4·5H2O, and 9.8g citric acid monohydrate and dissolve them in 100mL deionized water. Stir the solution in an 80℃ water bath until a transparent, viscous gel forms. Place the resulting gel in an oven at 180℃ for 3 hours to allow it to foam. Grind the resulting solid into a fine powder and transfer it to a muffle furnace for calcination at a heating rate of 2℃ / min, a temperature of 500℃, and a calcination time of 5 hours. The resulting unmodified sulfur-containing composite oxide is denoted as ZnZr. 16 O x .

[0055] Weigh out 0.5g of ZnZr 16 O x The oxide and 1.0 g of industrial H-ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 240 were placed in a mortar and ground for 10 min to ensure thorough mixing. The mixture was then compressed into tablets, and the resulting catalyst was denoted as ZnZr. 16 O x / H-ZSM-5.

[0056] ZnZr 16 O x The reaction evaluation steps for CO hydrogenation to aromatics on the / H-ZSM-5 catalyst are the same as in Example 2. The reaction results are shown in Table 4. It can be seen that when this catalyst is used for CO2 hydrogenation to aromatics, the CO2 conversion rate and the selectivity of aromatics are both low.

[0057] Table 4

[0058] <![CDATA[CH₄ Selectivity (%)]]> 0.6 <![CDATA[C 2-4 Selectivity (%) 32.4 Aromatic selectivity (%) 65.0 <![CDATA[Other C 5+ Selectivity (%)]]> 2.0

[0059] In Example 2, the sulfur-modified composite oxide S-ZnZr 16 O x The HAADF-STEM characterization map and EDX characterization map are as follows: Figure 1 As shown, by Figure 1 It can be seen that S is uniformly dispersed in the oxide.

[0060] In Example 2, S-ZnZr 16 O x In Comparative Example 2, ZnZr 16 O x The TEM characterization images and their particle size distributions are as follows: Figure 2 and Figure 3 As shown, by Figure 2 It can be known that S-ZnZr 16 O x The morphology consists of nanoparticles with an average particle size of 5.2 nm, composed of... Figure 3 It can be seen that the unmodified sulfur-containing composite oxide ZnZr 16 O xThe morphology consists of nanoparticles with an average particle size of 7.6 nm, indicating that the particle size of the composite oxide is reduced after sulfur modification.

[0061] In Example 2, S-ZnZr 16 O x In Comparative Example 2, ZnZr 16 O x The specific surface area comparison chart is as follows Figure 4 As shown, by Figure 4 It can be seen that S-ZnZr 16 O x Its specific surface area is 66m² 2 g -1 ZnZr 16 O x Its specific surface area is 20m² 2 g -1 This indicates that the specific surface area of ​​the composite oxide increased significantly after sulfur modification.

[0062] In Example 2, S-ZnZr 16 O x In Comparative Example 2, ZnZr 16 O x The NH3-TPD curve is as follows Figure 5 As shown, by Figure 5 It can be seen that S-ZnZr 16 O x The desorption peak area of ​​the basic molecule NH3 is significantly larger, and the temperature corresponding to the peak center is higher, indicating that the acidity of the composite oxide surface is significantly enhanced after sulfur modification.

[0063] In summary, this invention reduces the average particle size, significantly increases the specific surface area, and significantly enhances the surface acidity of the composite oxide through sulfur doping. The bifunctional catalyst formed by combining it with H-ZSM-5 molecular sieves can be applied to the efficient production of aromatics from CO / CO2 hydrogenation. The preparation process of the sulfur-modified composite oxide and its coupling process with the molecular sieve are simple and controllable, easily scaled up for further development, and have promising application prospects.

Claims

1. A catalyst for the hydrogenation of CO / CO2 to aromatics, characterized in that: The product includes a sulfur-modified composite oxide and an H-ZSM-5 molecular sieve. The sulfur-modified composite oxide contains sulfur (S), a first metal, and a second metal. The molar percentage of S in the sulfur-modified composite oxide is 0.1% to 5.0%. The first metal is Zn, and the second metal is selected from at least one of Mg, Zr, Cr, Al, and Ga. The molar ratio of Zn to the second metal component is 1:(1 to 500). The method for preparing the catalyst includes the following steps: 1) Dissolve the first metal salt, the second metal salt, and the foaming agent in deionized water, and stir under water bath heating until a thick gel appears. Place the resulting gel in an oven to foam, then mix sulfur powder into the foamed solid and grind it. Finally, calcine to obtain sulfur-modified composite oxide; wherein the calcine temperature is 400-600℃ and the calcine time is 5-15h. 2) Grind and mix the sulfur-modified composite oxide and H-ZSM-5 molecular sieve.

2. The method for preparing a catalyst for CO / CO2 hydrogenation to aromatics according to claim 1, characterized in that, Includes the following steps: 1) Dissolve the first metal salt, the second metal salt, and the foaming agent in deionized water, and stir under water bath heating until a thick gel appears. Place the resulting gel in an oven to foam, then mix sulfur powder into the foamed solid and grind it. Finally, calcine to obtain sulfur-modified composite oxide. 2) Grind and mix the sulfur-modified composite oxide and H-ZSM-5 molecular sieve.

3. The method for preparing a catalyst for CO / CO2 hydrogenation to aromatics as described in claim 2, characterized in that: The water bath heating temperature is 50–100℃.

4. The method for preparing a catalyst for CO / CO2 hydrogenation to aromatics as described in claim 2, characterized in that: The foaming temperature is 150–200℃, and the time is 3–10 hours.

5. The method for preparing a catalyst for CO / CO2 hydrogenation to aromatics as described in claim 2, characterized in that: The heating rate for roasting is 1–5 °C / min. -1 The temperature is 400-600℃, and the roasting time is 5-15 hours.

6. The method for preparing a catalyst for CO / CO2 hydrogenation to aromatics as described in claim 2, characterized in that: The first metal salt and the second metal salt are selected from at least one of nitrate, hydrochloride, sulfate and acetate.

7. The method for preparing a catalyst for CO / CO2 hydrogenation to aromatics as described in claim 2, characterized in that: The foaming agent is citric acid monohydrate, and the molar ratio of citric acid monohydrate to the sum of the first metal salt and the second metal salt is 1:(2-5).

8. The method for preparing a catalyst for CO / CO2 hydrogenation to aromatics as described in claim 2, characterized in that: The mass ratio of the sulfur-modified composite oxide and the H-ZSM-5 molecular sieve is 1:(1~3); the H-ZSM-5 molecular sieve is an industrial H-ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 100~400.

9. The application of the catalyst for CO / CO2 hydrogenation to aromatics according to claim 1, or the catalyst for CO / CO2 hydrogenation to aromatics prepared by any one of claims 2 to 8, characterized in that: It is used in the production of aromatics from CO / CO2 hydrogenation.

10. The application as described in claim 9, characterized in that: Before the reaction, the catalyst is pretreated with nitrogen at 300–500 °C for 1–2 h to activate it; the reaction temperature for CO / CO2 hydrogenation to produce aromatics is 280–450 °C, the reaction pressure is 1–6 MPa, and the space velocity is 1000–10000 mL / h. -1 g -1 The volume ratio of hydrogen to CO in the feed gas for the CO hydrogenation reaction is (1-3):1, and the volume ratio of hydrogen to CO2 in the feed gas for the CO2 hydrogenation reaction is (1-4):

1. The reaction time is 10-50 h.

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