Amorphous Cu / Si-LOC catalyst, preparation method thereof and application of amorphous Cu / Si-LOC catalyst in preparation of methanol through CO2 hydrogenation

Abstract

The invention discloses an amorphous Cu / Si-LOC catalyst, a preparation method thereof and application of the amorphous Cu / Si-LOC catalyst in methanol preparation through CO2 hydrogenation, and belongs to the technical field of catalysts. The invention solves the problems of difficult CO2 activation, low methanol selectivity, easy sintering inactivation and the like of the catalyst in the prior art. The preparation method of the catalyst comprises the following steps: reacting lanthanum nitrate with stronger ammonia water to generate lanthanum hydroxide, and reacting the lanthanum hydroxide with tetraethyl orthosilicate to obtain a Si-LOC carrier; and carrying out ultrasonic dispersion on the carrier, and adding a copper source to obtain the Cu / Si-LOC catalyst. The amorphous Si-LOC carrier with rich specific surface area and surface defect sites is obtained through silicon doping, adsorption and activation of CO2 are promoted, and adsorption and further hydrogenation of an intermediate are enhanced through loading of Cu. In addition, the catalyst is not easy to sinter and inactivate. The catalyst is applied to a CO2 hydrogenation reaction, and efficient conversion of CO2 can be realized at a relatively low temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to an amorphous Cu / Si-LOC catalyst, a preparation method thereof, and an application thereof in the hydrogenation of CO 2 to methanol. Background Art

[0002] In recent years, the effective conversion and utilization of carbon dioxide (CO 2 ) have become the focus of research. Many researchers have begun to explore efficient conversion routes for CO 2 to convert it into high-value-added chemicals. Among them, the hydrogenation of carbon dioxide to methanol (CH 3 OH) has received extensive attention and research as a highly potential conversion route. As a basic chemical raw material, the demand for methanol has been increasing year by year. Methanol is not only the starting material for synthesizing many organic chemicals (such as formaldehyde, acetic acid, olefins, etc.) and is widely used in multiple fields such as plastics, coatings, fibers, and pharmaceuticals, but also shows great potential in the energy field. As a kind of clean energy, methanol can be used as a fuel to directly replace or partially replace gasoline and diesel for transportation. Therefore, using CO 2 as a raw material to produce methanol by hydrogenation is a highly potential CO 2 efficient conversion route.

[0003] Cu-based catalysts are widely used in various catalytic reactions due to their low cost, easy availability, and high catalytic activity. However, there is a problem of rapid deactivation due to sintering during the reaction process. The performance regulation of catalysts is not only related to the properties of metals but also related to promoters, carrier types, and dispersion. In recent years, the metal-support interaction (MSI) has been an important means to regulate the performance of catalysts. For the commonly used Cu-based catalysts for carbon dioxide hydrogenation, regulating the MSI by surface modification of the carrier such as heteroatom doping, defect construction, and surface functionalization provides new ideas for optimizing the catalyst carrier.

[0004] Chinese Patent CN202310340392.5 provides a preparation method of a copper-zinc-aluminum-zeolite catalyst. The hydrophobic property of this catalyst improves the conversion rate and methanol selectivity of CO 2 hydrogenation, but the synthesis steps of the catalyst are relatively complex and the preparation period is long. The hydrophobicity of the material limits its stability under high-temperature reaction conditions; Chinese Patent CN202311295435.9 discloses a platinum-group metal-doped Cu-ZnO catalyst for the thermal catalytic hydrogenation of CO 2 to methanol. At T = 250 °C, H 2 / CO 2 = 3 / 1, WHSV = 16000 mL·g cat -1·h -1 Under the condition of P = 4 MPa, the 2Pd / CZ catalyst has the best catalytic activity and stability, and the methanol production reaches 0.52 g MeOH ·h -1 ·g cat -1 , However, the doping of noble metals such as Pd, Pt, and Ru, as well as the relatively high reaction temperature and reaction pressure, increase the cost of the catalyst, which is not conducive to the economical and efficient industrial production of Cu-based catalysts. In addition to the harsh preparation conditions and low high-temperature stability, the performance improvement of the commonly used Cu-based catalysts modified by the carrier surface in carbon dioxide hydrogenation is limited, and there are still problems such as difficult CO 2 activation, low methanol selectivity, and easy sintering and deactivation. Summary of the Invention

[0005] The present invention provides an amorphous Cu / Si-LOC catalyst, its preparation method, and its application in the hydrogenation of CO 2 to methanol to solve the problems of difficult CO 2 activation, low methanol selectivity, and easy sintering and deactivation existing in the catalysts of the prior art.

[0006] To solve the above technical problems, the present invention is achieved through the following technical solutions:

[0007] One of the purposes of the present invention is to provide a preparation method of an amorphous Cu / Si-LOC catalyst, including:

[0008] (1) Synthesis of the Si-LOC support: Prepare a lanthanum nitrate solution, drop the lanthanum nitrate solution into concentrated ammonia water to form a precipitate, wash, centrifuge, and dry the precipitate to obtain La(OH) 3 , Take a certain amount of La(OH) 3 Disperse it in absolute ethanol, drop tetraethyl orthosilicate, then carry out condensation reflux, dry and calcine the product to obtain the Si-LOC support;

[0009] (2) Synthesis of the Cu / Si-LOC catalyst: Prepare a copper nitrate solution, ultrasonically disperse the Si-LOC support in deionized water, then add the prepared copper nitrate solution, transfer the reaction system to an oil bath, and reduce the product after the reaction to obtain the Cu / Si-LOC catalyst.

[0010] Further limited, the volume ratio of the lanthanum nitrate solution to the concentrated ammonia water in (1) is 50:3.

[0011] Further limited, the molar ratio of Si in tetraethyl orthosilicate to La in La(OH) 3 is 0.1.

[0012] Further limitation: in (1), the calcination temperature is 500 °C and the time is 2 h.

[0013] Further limitation: in (2), when the Si-LOC support is ultrasonically dispersed and then added to the prepared copper nitrate solution, the mass ratio of the Si-LOC support to copper nitrate in the copper nitrate solution is 20:1.

[0014] Further limitation: in (2), the reduction treatment temperature is 200 - 500 °C and the time is 1 - 3 h.

[0015] The second object of the present invention is to provide an amorphous Cu / Si-LOC catalyst obtained by the above preparation method.

[0016] The third object of the present invention is to provide an application of the above amorphous Cu / Si-LOC catalyst, specifically for catalyzing the 2 hydrogenation of CO to methanol reaction.

[0017] Further limitation: for the 2 hydrogenation of CO to methanol reaction, the reaction temperature is 200 - 220 °C and the pressure is 3 MPa.

[0018] The beneficial effects of the present invention are as follows:

[0019] In the present invention, an amorphous LOC support, namely Si-LOC support, is obtained by Si doping, and then the Cu / Si-LOC catalyst is synthesized by the evaporation-drying impregnation method. Compared with the amorphous catalysts in the prior art, this catalyst is not only simple to prepare, but also remains amorphous at 500 °C calcination. Compared with the prior art, the present invention also has the following advantages:

[0020] (1) The amorphous Si-LOC support obtained by Si doping in the present invention has a large specific surface area and surface defect sites, which promotes the 2 adsorption and activation of CO. The loading of Cu generates metal-support interface sites on the Cu / Si-LOC catalyst, enhancing the adsorption and further hydrogenation of the HCOO* intermediate, thereby realizing the improvement of methanol yield and selectivity. In addition, due to the increase in the specific surface area of the amorphous support, the active metal Cu exists in a more dispersed state on the support surface, thus inhibiting Cu sintering deactivation and improving the 2 long-term stability of the CO hydrogenation reaction.

[0021] (2) The amorphous Cu / Si-LOC catalyst provided by the present invention is applied to the 2 hydrogenation of CO to methanol reaction, and efficient 2 CO conversion is achieved at a relatively low reaction temperature. This catalyst significantly improves the selectivity of the hydrogenation product methanol and enhances the 2The ability to hydrogenate to high - value - added products achieved a methanol selectivity of up to 67.2%. In addition, Si doping improved the structural stability of the catalyst during the reaction. After continuous reaction, the amorphous structure of the Cu / Si - LOC catalyst remained in good condition, and there was no obvious agglomeration of Cu nanoparticles.

[0022] (3) The loading amount of the active metal Cu significantly affects the conversion rate and selectivity of CO 2 hydrogenation. The active sites formed with a lower Cu loading have insufficient activation ability for CO 2 , resulting in poor CO 2 conversion rate; while when the Cu loading is very high, the dispersion degree of the active Cu in the catalyst decreases, and the particles increase, leading to a decrease in the selectivity of the target product methanol. Therefore, the Cu loading of the amorphous Cu / Si - LOC catalyst provided by the present invention is 5 wt%, and the catalyst shows a high methanol yield at this loading. The doping of Si in the present invention increases the specific surface area of the catalyst support. Compared with the catalyst without Si doping, the presence of Si promotes the adsorption of CO 2 and thus improves the CO 2 conversion rate.

[0023] (4) The reaction of CO 2 hydrogenation to methanol is an exothermic reaction with a decrease in the number of molecules. Although increasing the reaction temperature can increase the CO 2 conversion rate, it will also lead to the formation of by - product CO. Therefore, under the condition of using the amorphous Cu / Si - LOC catalyst provided by the present invention, adopting a lower reaction temperature (200 - 220 °C) is beneficial to the improvement of methanol selectivity. Description of the Drawings

[0024] Figure 1 is the TEM image (magnified 8700 times) of the Cu / Si - LOC catalyst prepared in Example 1;

[0025] Figure 2 is the TEM image (magnified 174000 times) of the Cu / Si - LOC catalyst prepared in Example 1;

[0026] Figure 3 is the XRD pattern of the Si - LOC support prepared in Example 1;

[0027] Figure 4 is the BET test result of the Cu / Si - LOC catalyst prepared in Example 1;

[0028] Figure 5 is the test result of methanol selectivity and CO 2 conversion rate in the reaction of CO 2 hydrogenation to methanol for Example 1 and Comparative Examples 1 - 2;

[0029] Figure 6 For the CO in Examples 1-2 and Comparative Examples 3-4 2 The test results of methanol selectivity and CO 2 conversion rate in the hydrogenation reaction of methanol;

[0030] Figure 7 For the CO in Example 1 and Comparative Examples 5-6 2 The test results of methanol selectivity and CO 2 conversion rate in the hydrogenation reaction of methanol;

[0031] Figure 8 For the CO in Example 1 and Comparative Examples 7-9 2 The test results of methanol selectivity and CO 2 conversion rate in the hydrogenation reaction of methanol. Detailed implementation manners

[0032] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe in detail the specific implementation manners of the present invention in combination with the embodiments of the specification.

[0033] In the following description, many specific details are set forth to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0034] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation manner of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or selectively exclusive embodiment from other embodiments.

[0035] The experimental methods used in the following embodiments are all conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used, unless otherwise specified, are all conventional materials, reagents, methods, and instruments in the art, and those skilled in the art can obtain them through commercial channels.

[0036] Example 1

[0037] In this example, Si-doped amorphous LOC (Si-LOC) was used as the catalyst support, and anhydrous Cu(NO 3 ) 2 was used as the metal salt precursor, with a Cu loading of 5 wt%, that is, Cu accounted for 5 wt% of the Si-LOC support. The specific steps for preparing the Cu / Si-LOC catalyst are as follows:

[0038] (1) Weigh 2.0 g of lanthanum nitrate and dissolve it in 100 mL of deionized water to form a lanthanum nitrate solution. Drop the lanthanum nitrate solution into 6 mL of concentrated ammonia water. After magnetic stirring at 150 rpm at room temperature for 1 h, the obtained precipitate is centrifugally washed with deionized water multiple times (5500 rpm) until the pH of the supernatant is 7. Then the precipitate is placed in an oven at 70 °C for overnight drying to obtain La(OH) 3 , and grind it into powder. Take a certain amount of La(OH) 3 and disperse it in 50 mL of absolute ethanol. Dropwise add 1 mL of tetraethyl orthosilicate (TEOS) under vigorous stirring at 300 rpm, so that the molar ratio of Si in tetraethyl orthosilicate to La in La(OH) 3 is 0.1. Then transfer it to a round-bottom flask and carry out condensation reflux at 60 °C for 4 h. After the reaction is completed, centrifuge the product (5500 rpm), and the solid substance collected by centrifugation is dried overnight at 70 °C. Finally, calcine it in a muffle furnace at 500 °C for 2 h to obtain an amorphous Si-LOC support;

[0039] (2) Weigh 563 mg of anhydrous Cu(NO 3 ) 2 and dissolve it in 30 mL of deionized water to obtain a 0.1 mol / L Cu(NO 3 ) 2 solution. Ultrasonically disperse 200 mg of amorphous Si-LOC support in 20 mL of deionized water, and then add Cu(NO 3 ) 2 solution to it. The mass ratio of the amorphous Si-LOC support to Cu(NO 3 ) 2 in the added copper nitrate solution is 20:1. After stirring for 30 min, transfer the reaction system to an 80 °C oil bath at room temperature until all the water has evaporated. Collect the product and grind it thoroughly. Heat the ground product to 300 °C at a rate of 10 °C / min in a H 2 / Ar = 1:9 (v / v) mixed gas and hold for 2 h for reduction treatment to obtain an amorphous Cu / Si-LOC catalyst.

[0040] The TEM images of the amorphous Cu / Si-LOC catalyst prepared in this example are as shown in Figure 1 and Figure 2 . It can be seen that the amorphous Cu / Si-LOC catalyst is composed of irregularly stacked nanoparticles. As found from Figure 2 , the overall surface of the catalyst shows an amorphous state, and the alternating arrangement of crystal domains and amorphous domains appears in local areas, indicating that the catalyst is in an amorphous state. Figure 3XRD pattern of the Si-LOC support. The pattern shows two broad diffraction peaks, demonstrating that the Si-LOC support prepared in this example has an amorphous nature. Figure 4 Physical adsorption (BET) data of the amorphous Cu / Si-LOC catalyst. The Si-LOC support is a mesoporous material with a pore diameter of about 30 nm, indicating that the support has a rich pore structure and a high specific surface area, and can effectively promote the adsorption of CO 2 in the reaction of hydrogenation of CO to methanol. 2

[0041] The above-prepared amorphous Cu / Si-LOC catalyst was used to catalyze the reaction of hydrogenation of CO 2 to methanol. The reaction process is as follows: 100 mg of the Cu / Si-LOC catalyst was added to a fixed-bed reactor, and 3 MPa of CO 2 / H 2 = 1:3 (v / v) was introduced as the reaction gas. The reaction was carried out at a reaction temperature of 220 °C and a catalyst weight hourly space velocity (WHSV) of 12000 mL g cat -1 h -1 .

[0042] Qualitative and quantitative analysis was carried out by a gas chromatograph-mass spectrometer. The methanol selectivity in the reaction of hydrogenation of CO 2 to methanol over the amorphous Cu / Si-LOC catalyst was calculated to reach 67.2%, and the CO 2 conversion was 1.7%.

[0043] Example 2

[0044] The difference between this example and Example 1 is that: in the reaction of hydrogenation of CO 2 to methanol, the reaction temperature is 200 °C, and the other process steps and parameter settings are the same as those in Example 1.

[0045] The methanol selectivity of the catalyst obtained in this example in the reaction of hydrogenation of CO 2 to methanol was tested. The results are shown in Figure 6 . The CO 2 conversion was 0.6%, and the methanol selectivity was 70.1%.

[0046] Comparative Example 1

[0047] The difference between this comparative example and Example 1 is that: (1) tetraethyl orthosilicate was not used, and the obtained support was the LOC support. Correspondingly, in (2), the used support was the LOC support, and the catalyst used in the reaction of hydrogenation of CO 2 to methanol was the Cu-LOC catalyst, that is, Si in tetraethyl orthosilicate and La(OH) 3 ​The molar ratio of La in it is 0, and the remaining process steps and parameter settings are the same as those in Example 1.

[0048] The methanol selectivity of the catalyst obtained in this comparative example was tested in the reaction of catalytic hydrogenation of CO 2 to methanol, and the results are shown in Figure 5 , CO 2 conversion rate was 0.8%, and methanol selectivity was 46.6%.

[0049] Comparative Example 2

[0050] The difference between this comparative example and Example 1 is that: (1) in it, the molar ratio of Si in tetraethyl orthosilicate to La in La(OH) 3 is 0.5, and the remaining process steps and parameter settings are the same as those in Example 1.

[0051] The methanol selectivity of the catalyst obtained in this comparative example was tested in the reaction of catalytic hydrogenation of CO 2 to methanol, and the results are shown in Figure 5 , CO 2 conversion rate was 1.5%, and methanol selectivity was 39.1%.

[0052] Comparative Example 3

[0053] The difference between this comparative example and Example 1 is that: in the reaction of catalytic hydrogenation of CO 2 to methanol, the reaction temperature is 240 °C, and the remaining process steps and parameter settings are the same as those in Example 1.

[0054] The methanol selectivity of the catalyst obtained in this comparative example was tested in the reaction of catalytic hydrogenation of CO 2 to methanol, and the results are shown in Figure 6 , CO 2 conversion rate was 2.1%, and methanol selectivity was 59.5%.

[0055] Comparative Example 4

[0056] The difference between this comparative example and Example 1 is that: in the reaction of catalytic hydrogenation of CO 2 to methanol, the reaction temperature is 260 °C, and the remaining process steps and parameter settings are the same as those in Example 1.

[0057] The methanol selectivity of the catalyst obtained in this comparative example was tested in the reaction of catalytic hydrogenation of CO 2 to methanol, and the results are shown in Figure 6 , CO 2 conversion rate was 3.9%, and methanol selectivity was 46.7%.

[0058] Comparative Example 5

[0059] The difference between this comparative example and Example 1 is that: in CO2 In the hydrogenation reaction to produce methanol, the reaction gas pressure is 1 MPa, and the remaining process steps and parameter settings are the same as those in Example 1.

[0060] The catalyst obtained in this comparative example was tested for the methanol selectivity in the catalytic CO 2 hydrogenation reaction to produce methanol. The results are shown in Figure 7 , CO 2 The conversion rate was 0.9%, and the methanol selectivity was 25.7%.

[0061] Comparative Example 6

[0062] The difference between this comparative example and Example 1 is that: in the hydrogenation reaction to produce methanol, the reaction gas pressure is 2 MPa, and the remaining process steps and parameter settings are the same as those in Example 1. 2 In the hydrogenation reaction to produce methanol, the reaction gas pressure is 2 MPa, and the remaining process steps and parameter settings are the same as those in Example 1.

[0063] The catalyst obtained in this comparative example was tested for the methanol selectivity in the catalytic CO 2 hydrogenation reaction to produce methanol. The results are shown in Figure 7 , CO 2 The conversion rate was 1.4%, and the methanol selectivity was 46.5%.

[0064] Comparative Example 7

[0065] The difference between this comparative example and Example 1 is that: the Cu loading is 2 wt% (Cu accounts for 2 wt% of the Si-LOC support), that is, the mass ratio of the Si-LOC support to Cu(NO 3 ) 2 is 50:1, and the remaining process steps and parameter settings are the same as those in Example 1.

[0066] The catalyst obtained in this comparative example was tested for the methanol selectivity in the catalytic CO 2 hydrogenation reaction to produce methanol. The results are shown in Figure 8 , CO 2 The conversion rate was 1.3%, and the methanol selectivity was 33.3%.

[0067] Comparative Example 8

[0068] The difference between this comparative example and Example 1 is that: the Cu loading is 8 wt% (Cu accounts for 8 wt% of the Si-LOC support), that is, the mass ratio of the Si-LOC support to Cu(NO 3 ) 2 is 25:2, and the remaining process steps and parameter settings are the same as those in Example 1.

[0069] The catalyst obtained in this comparative example was tested for the methanol selectivity in the catalytic CO 2 hydrogenation reaction to produce methanol. The results are shown in Figure 8 , CO2 The conversion rate is 1.8%, and the methanol selectivity is 45.9%.

[0070] Comparative Example 9

[0071] The difference between this comparative example and Example 1 is that the Cu loading is 10 wt% (Cu accounts for 10 wt% of the Si-LOC support), that is, the mass ratio of the Si-LOC support to Cu(NO 3 ) 2 is 10:1, and the remaining process steps and parameter settings are the same as those in Example 1.

[0072] The methanol selectivity of the catalyst obtained in this comparative example was tested in the reaction of catalytic hydrogenation of CO 2 to methanol, and the results are shown in Figure 8 , CO 2 The conversion rate is 2.0%, and the methanol selectivity is 38.3%.

[0073] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for preparing an amorphous Cu / Si-LOC catalyst, comprising: (1) Synthesis of Si-LOC carrier: Lanthanum nitrate is prepared into a lanthanum nitrate solution, and the lanthanum nitrate solution is added dropwise into concentrated ammonia water to form a precipitate. The precipitate is washed, centrifuged and dried to obtain La(OH)3, La(OH)3 is dispersed in anhydrous ethanol, tetraethyl orthosilicate is added dropwise, and then condensed and refluxed. The product is dried and calcined to obtain a Si-LOC carrier; (2) Synthesis of Cu / Si-LOC catalyst: Copper nitrate was prepared into a copper nitrate solution, and the Si-LOC carrier was ultrasonically dispersed in deionized water. The prepared copper nitrate solution was then added, and the reaction system was transferred to an oil bath. After the reaction was completed, the product was reduced to obtain a Cu / Si-LOC catalyst.

2. The preparation method according to claim 1, characterized in that: (1) The volume ratio of lanthanum nitrate solution to concentrated ammonia water is 50:

3.

3. The preparation method according to claim 1, characterized in that: (1) The molar ratio of Si in tetraethyl orthosilicate to La in La(OH)3 is 0.

1.

4. The preparation method according to claim 1, characterized in that: (1) The calcination temperature is 500°C and the time is 2 h.

5. The preparation method according to claim 1, characterized in that: (2) When the Si-LOC carrier is ultrasonically dispersed and then added to the prepared copper nitrate solution, the mass ratio of the Si-LOC carrier to the copper nitrate in the copper nitrate solution is 20:

1.

6. The preparation method according to claim 1, characterized in that: (2) The reduction treatment temperature is 200-500°C and the time is 1-3h.

7. Amorphous Cu / Si-LOC catalyst, characterized in that The method is prepared by any one of claims 1 to 6.

8. Use of the amorphous Cu / Si-LOC catalyst according to claim 7, characterized in that: The catalyst is used for catalyzing the CO2 hydrogenation reaction to produce methanol.

9. The use according to claim 8, characterized in that The reaction temperature of CO2 hydrogenation to produce methanol is 200-220°C.

10. The use according to claim 8, characterized in that The reaction pressure of CO2 hydrogenation to produce methanol is 3MPa.

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