Preparation method and application of catalyst for preparing methanol through carbon dioxide hydrogenation

Abstract

The invention relates to a preparation method and application of a catalyst for preparing methanol through carbon dioxide hydrogenation, a cobalt carbon nanotube is used as a carrier of the catalyst, has the advantage of large specific surface area, and is beneficial to uniform dispersion of indium, so that the proportion of In2O3 on the surface is high, and more oxygen vacancies can be formed on the surface of the catalyst; more active sites are provided for a reaction for preparing methanol through carbon dioxide hydrogenation, and the reaction activity of the catalyst in the reaction is improved. Besides, metal cobalt contained in the cobalt carbon nanotubes has very strong hydrogen adsorption and dissociation capabilities, so that generation of oxygen vacancies on the surface of the catalyst is promoted, the reaction activity and stability of the catalyst are further improved, and the yield of methanol prepared through carbon dioxide hydrogenation is further remarkably improved.

Description

Technical Field

[0001] The present application relates to the field of catalyst technology, and in particular to a method for preparing a catalyst for producing methanol by hydrogenating carbon dioxide and its application. Background Art

[0002] Large-scale CO2 emissions are increasingly causing problems such as the greenhouse effect, glacier melting, sea level rise, and desertification. Exploring ways to capture and utilize CO2 and convert it into high-value-added chemicals can not only reduce CO2 emissions and alleviate environmental pressures, but also recycle carbon resources. Catalytic hydrogenation of CO2 to methanol is an effective way to recycle CO2. Methanol is an important chemical raw material and can also be used directly as a fuel.

[0003] Due to the stable nature of CO2 and the difficulty in activation, the conversion rate of this reaction is generally low. The production of methanol is an exothermic reaction. Thermodynamically, low temperature is conducive to the production of methanol but not to the activation of CO2. Therefore, designing an efficient catalyst is the key to the production of methanol by hydrogenation of carbon dioxide.

[0004] At present, the catalysts widely studied for methanol synthesis include modified copper-based catalysts, precious metal catalysts and indium oxide catalysts. However, in copper-based catalytic systems, the high activity of the side reaction reverse water gas shift (RWGS), the sintering of the active phase induced by H2O, and poor stability limit its further application. In precious metal catalytic systems, the high cost of precious metals also limits the further application of such catalysts in the field of carbon dioxide catalytic hydrogenation. In2O3 has moderate CO2 and CO adsorption capacity, shows significantly better methanol selectivity than Cu-based catalysts, and has the advantage of low cost compared to precious metal catalysts. Therefore, it has attracted widespread attention from scientific researchers. However, the catalytic effect of In2O3 catalysts in the existing technology still needs to be further improved. Summary of the Invention

[0005] This application provides a method for preparing a catalyst for producing methanol from carbon dioxide hydrogenation and its application, addressing the issues of low catalytic activity and insufficient stability of In2O3 catalysts. The catalyst prepared in this application exhibits improved catalytic performance and significantly increases the yield of methanol from carbon dioxide hydrogenation.

[0006] In a first aspect, the present application provides a method for preparing a catalyst for producing methanol by hydrogenating carbon dioxide, taking the preparation method of an In2O3 catalyst supported by cobalt carbon nanotubes as an example, comprising the following steps:

[0007] Preparation of carbon nitride: calcining melamine in a muffle furnace to obtain carbon nitride;

[0008] Preparation of cobalt carbon nanotubes: The prepared carbon nitride, cobalt acetate, and melamine are mixed, anhydrous ethanol is added, and the mixture is ultrasonicated and then heated in a water bath until the ethanol is evaporated to dryness; the product is then calcined in a tube furnace under an inert atmosphere to obtain cobalt carbon nanotubes;

[0009] Shortening of cobalt carbon nanotubes: adding deionized water to the prepared cobalt carbon nanotubes and performing ultrasonic shortening;

[0010] Cobalt carbon nanotube impregnation: Dissolve indium nitrate in deionized water, add to the chopped cobalt carbon nanotubes, stir evenly, and heat in a water bath until the deionized water evaporates;

[0011] Catalyst calcination: The product impregnated with cobalt carbon nanotubes is ground, placed on a magnetic boat, and then placed in a muffle furnace for calcination to obtain a catalyst for producing methanol by hydrogenation of carbon dioxide.

[0012] In some embodiments of the present application, in the step of preparing carbon nitride:

[0013] The heating rate of the calcination is 1-10°C / min, the calcination temperature is 500-1800°C, and the calcination time is 0.5-8h.

[0014] In some embodiments of the present application, in the step of preparing cobalt carbon nanotubes:

[0015] Carbon nitride: 1.2g; melamine: 0.6g; cobalt nitrate hexahydrate: 0.2-0.6g; ethanol solution: 20-50ml;

[0016] The ultrasonic time is 30 to 60 minutes, the water bath temperature is 40 to 70°C, and the water bath time is 6 to 8 hours;

[0017] The inert gas under the inert atmosphere is nitrogen or argon, and the inert gas flow rate is 20-300 mL / min;

[0018] The roasting process includes a first roasting process and a second roasting process, wherein the first roasting process has a heating rate of 1 to 10°C / min, a roasting temperature of 400 to 600°C, and a roasting time of 0.5 to 3h; the second roasting process has a heating rate of 1 to 10°C / min, a roasting temperature of 700 to 1100°C, and a roasting time of 0.5 to 3h.

[0019] In some embodiments of the present application, in the step of shortening the cobalt carbon nanotubes:

[0020] The amount of deionized water is 20-40 mL, and the ultrasonic time is 1-4 h.

[0021] In some embodiments of the present application, during the step of impregnating cobalt carbon nanotubes:

[0022] Indium nitrate is 0.3-0.6 g; deionized water is 20-30 ml; cobalt carbon nanotubes are 1 g; stirring time is 8-12 h; water bath temperature is 60-80° C., and water bath time is 4-6 h.

[0023] In some embodiments of the present application, during the step of calcining the catalyst:

[0024] The calcination temperature is 300-500°C, and the calcination time is 2-4 hours.

[0025] In a second aspect, the present application further provides an application of the catalyst prepared according to the above preparation method, specifically:

[0026] The catalyst was loaded into the reaction tube, and after nitrogen was passed through to check air tightness, a mixture of hydrogen and nitrogen was passed through and reduced at 300-600°C for 1-4 hours.

[0027] Then, a reaction mixture of hydrogen, nitrogen and carbon dioxide is introduced, and the carbon dioxide is hydrogenated to produce methanol under the conditions of 200-400° C. and 2-8 MPa.

[0028] The present application provides a method for preparing a catalyst for producing methanol by hydrogenating carbon dioxide and its application. Cobalt carbon nanotubes are used as catalyst carriers, which have the advantage of a large specific surface area, facilitating uniform dispersion of indium, resulting in a high proportion of surface In2O3, and facilitating the formation of more oxygen vacancies on the catalyst surface. This provides more active sites for the reaction of producing methanol by hydrogenating carbon dioxide, thereby increasing the reactivity of the catalyst in the reaction. In addition, the metallic cobalt contained in the cobalt carbon nanotubes has a strong ability to adsorb and dissociate hydrogen, which also promotes the generation of oxygen vacancies on the catalyst surface, further improving the reactivity and stability of the catalyst, and thus significantly improving the yield of producing methanol by hydrogenating carbon dioxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 XRD pattern of cobalt carbon nanotubes as the support of the catalyst used for the hydrogenation of carbon dioxide to produce methanol in this application.

[0030] Figure 2 This is the XRD pattern of the catalyst used in this application for the hydrogenation of carbon dioxide to produce methanol.

[0031] Figure 3 TEM image of cobalt carbon nanotubes as the support of the catalyst used for the hydrogenation of carbon dioxide to produce methanol in this application.

[0032] Figure 4 This is a partially enlarged TEM image of the cobalt carbon nanotubes as the support of the catalyst used in the present application for producing methanol by hydrogenation of carbon dioxide.

[0033] Figure 5This is a TEM image of the cobalt carbon nanotubes supported by the catalyst used in this application for preparing methanol by hydrogenation of carbon dioxide after ultrasonic cutting.

[0034] Figure 6 This is a partially enlarged TEM image of the cobalt carbon nanotubes, the carrier of the catalyst used in the present application for preparing methanol by hydrogenation of carbon dioxide, after ultrasonic cutting. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the present invention more apparent, the present invention will be described in further detail below. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, rather than all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0036] The preparation method of the catalyst for producing methanol by hydrogenation of carbon dioxide and its application will be described in detail below with reference to specific examples.

[0037] Example 1

[0038] A method for preparing a catalyst for preparing methanol by hydrogenating carbon dioxide comprises the following steps:

[0039] Melamine was calcined at 550°C in a muffle furnace for 1 hour to obtain carbon nitride.

[0040] 1.2g of carbon nitride, 0.4g of cobalt acetate, and 0.6g of melamine were mixed and added to 30mL of anhydrous ethanol. After sonication for 40 minutes, the mixture was placed in a water bath at 70°C until the ethanol evaporated to dryness. The product was transferred to a corundum magnetic boat and placed in a tube furnace. A temperature ramp was set and high-purity argon gas was introduced to purge the air from the furnace tube at an inert gas flow rate of 20mL / min for 1 hour. The mixture was then heated at a rate of 5°C / min to 500°C and held at that temperature for 2 hours. The temperature was then increased to 700°C at a rate of 5°C / min and held at that temperature for 2 hours. Argon was then continued to flow until the furnace tube temperature naturally cooled to room temperature, yielding cobalt carbon nanotubes.

[0041] 20 mL of deionized water was added to the prepared cobalt carbon nanotubes, and ultrasonic treatment was performed for 2 h to obtain shortened cobalt carbon nanotubes.

[0042] Dissolve 0.6 g of indium nitrate in 20 mL of deionized water, add to 1 g of cobalt carbon nanotubes, stir for 12 h, and place in a water bath at 80° C. until the deionized water is evaporated.

[0043] The product was ground and placed on a magnetic boat and then placed in a muffle furnace and calcined at 400° C. for 2 h to obtain a catalyst for producing methanol from carbon dioxide hydrogenation.

[0044] Example 2

[0045] The same method as in Example 1 was used, and other conditions were the same as in Example 1, except that 0.5 g of indium nitrate was added during the impregnation of the cobalt carbon nanotubes.

[0046] Example 3

[0047] The same method as in Example 1 was used, and other conditions were the same as in Example 1, except that 0.4 g of indium nitrate was added during the impregnation of the cobalt carbon nanotubes.

[0048] Example 4

[0049] The same method as in Example 1 was used, and other conditions were the same as in Example 1, except that 0.3 g of indium nitrate was added during the impregnation of the cobalt carbon nanotubes.

[0050] An application of a catalyst for preparing methanol by hydrogenating carbon dioxide comprises the following steps:

[0051] Take 0.2g of catalyst and pour the pellets into a stainless steel reaction tube with an inner diameter of 10mm. Use a rubber hammer to compact the tube while filling it to prevent the bed from dropping during the reaction. Use quartz wool to plug the front and back of the tube.

[0052] Install the reaction tube, open the N2 valve, adjust the cylinder pressure so that there is 3MPa N2 in the reaction tube, close the cylinder pressure reducing valve outlet and the reactor outlet valve, and check each interface of the device with soapy water in turn; then wait for 1 hour and observe that the pressure display of the reactor does not change, which means the device is considered to be airtight.

[0053] 30 mL·min -1 Purge with 10% H2 / N2 for 30 minutes, and exhaust the N2 used for leak testing. Raise the temperature of the reactor to 300°C at a heating rate of 2°C / min-1 and maintain for 1 hour to reduce the catalyst. After the reduction is complete, lower the temperature to 280°C and begin catalyst evaluation.

[0054] After cooling is completed, the reaction gas composition is: N2:H2:CO2=30:30:10 (ml·min -1 The test results are shown in Table 1.

[0055] Table 1. Activity of the catalysts obtained in Examples 1 to 4

[0056]

[0057]

[0058] As can be seen from Table 1, the catalysts prepared by the preparation method of the present application have a high CO2 conversion rate and a high methanol selectivity, among which Example 3 shows the highest CO2 conversion rate, and Example 2 shows the highest methanol selectivity.

[0059] Figure 1 This is the XRD pattern of the cobalt-carbon nanotubes as the support of the catalyst used for the hydrogenation of carbon dioxide to produce methanol in this application. Figure 1 The three characteristic peaks at 44.20°, 51.34° and 75.78° all correspond to the characteristic peaks of cobalt, indicating that cobalt exists in the carbon nanotubes in the form of a single substance.

[0060] Figure 2 This is the XRD pattern of the catalyst used in this application for producing methanol by hydrogenation of carbon dioxide. Figure 2 The characteristic peaks at 30.74°, 36.01°, 51.60° and 61.14° are consistent with those of In2O3.

[0061] Figure 3 This is a TEM image of the cobalt-carbon nanotubes as a support for the catalyst used in this application for the hydrogenation of carbon dioxide to produce methanol. Figure 3 It can be seen that this material has unique structural characteristics: Co nanoparticles are encapsulated in carbon nanotubes.

[0062] Figure 4 This is a partially enlarged TEM image of the cobalt carbon nanotubes as the support of the catalyst for preparing methanol from carbon dioxide hydrogenation in this application.

[0063] Figure 5 This is a TEM image of the cobalt carbon nanotubes used as the catalyst for preparing methanol from carbon dioxide hydrogenation in this application after ultrasonic cutting. Figure 5 It can be seen that the cobalt carbon nanotubes are obviously shortened.

[0064] Figure 6 This is a partially enlarged TEM image of the cobalt carbon nanotubes supported by the catalyst for preparing methanol from carbon dioxide hydrogenation in this application after ultrasonic cutting.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a catalyst for producing methanol by hydrogenating carbon dioxide, characterized in that: The steps include: Preparation of carbon nitride: calcining melamine in a muffle furnace to obtain carbon nitride; Preparation of cobalt carbon nanotubes: The prepared carbon nitride, cobalt acetate, and melamine are mixed, anhydrous ethanol is added, and the mixture is ultrasonicated and then heated in a water bath until the ethanol is evaporated to dryness; the product is then calcined in a tube furnace under an inert atmosphere to obtain cobalt carbon nanotubes; Shortening of cobalt carbon nanotubes: adding deionized water to the prepared cobalt carbon nanotubes and performing ultrasonic shortening; Cobalt carbon nanotube impregnation: Dissolve indium nitrate in deionized water, add to the chopped cobalt carbon nanotubes, stir evenly, and heat in a water bath until the deionized water evaporates; Catalyst calcination: The product impregnated with cobalt carbon nanotubes is ground, placed on a magnetic boat, and then placed in a muffle furnace for calcination to obtain a catalyst for producing methanol by hydrogenation of carbon dioxide.

2. The preparation method according to claim 1, characterized in that In the steps of preparing carbon nitride: The heating rate of the calcination is 1-10°C / min, the calcination temperature is 500-1800°C, and the calcination time is 0.5-8h.

3. The preparation method according to claim 1, characterized in that In the steps of preparing cobalt carbon nanotubes: Carbon nitride: 1.2g; melamine: 0.6g; cobalt nitrate hexahydrate: 0.2-0.6g; ethanol solution: 20-50ml; The ultrasonic time is 30 to 60 minutes, the water bath temperature is 40 to 70°C, and the water bath time is 6 to 8 hours. The inert gas under the inert atmosphere is nitrogen or argon, and the inert gas flow rate is 20-300 mL / min; The roasting process includes a first roasting process and a second roasting process, wherein the first roasting process has a heating rate of 1 to 10°C / min, a roasting temperature of 400 to 600°C, and a roasting time of 0.5 to 3h; the second roasting process has a heating rate of 1 to 10°C / min, a roasting temperature of 700 to 1100°C, and a roasting time of 0.5 to 3h.

4. The preparation method according to claim 1, characterized in that In the step of shortening cobalt carbon nanotubes: The amount of deionized water is 20-40 mL, and the ultrasonic time is 1-4 h.

5. The preparation method according to claim 1, characterized in that In the step of cobalt carbon nanotube impregnation: Indium nitrate is 0.3-0.6 g; deionized water is 20-30 ml; cobalt carbon nanotubes are 1 g; stirring time is 8-12 h; water bath temperature is 60-80° C., and water bath time is 4-6 h.

6. The preparation method according to claim 1, characterized in that During the catalyst calcination step: The calcination temperature is 300-500°C, and the calcination time is 2-4 hours.

7. Use of a catalyst prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The steps include: The catalyst was loaded into the reaction tube, and after nitrogen was passed through to check air tightness, a mixture of hydrogen and nitrogen was passed through and reduced at 300-600°C for 1-4 hours. Then, a reaction mixture of hydrogen, nitrogen and carbon dioxide is introduced, and the carbon dioxide is hydrogenated to produce methanol under the conditions of 200-400° C. and 2-8 MPa.

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