Catalyst for preparing methanol through carbon dioxide hydrogenation, preparation method and application

Abstract

The invention discloses a catalyst for preparing methanol through hydrogenation of carbon dioxide, a preparation method and application, the catalyst is a MoS2-O catalyst, and the catalyst comprises the following components in percentage by mass: 50-56% of SO3; moO3: 44% to 50%; the microstructure is in lamellar and petal-shaped distribution; according to the catalyst, on the basis of in-situ doping of O in MoS2, an electronic structure is effectively adjusted, a high-activity and stable hydrogen evolution MoS2-O catalyst is formed, the MoS2-O catalyst has rich catalytic edge sites due to the specific microscopic shape, and the catalytic activity is enhanced due to the increase of the electrochemical accessible surface area and the unique synergistic effect between an MGF carrier and the active catalyst; methanol can be prepared through carbon dioxide hydrogenation only under the condition of the reaction temperature of 200 DEG C, the CO2 conversion rate can reach 4.2%, and the methanol selectivity reaches up to 96.4%; the reaction temperature is low, so that the energy consumption can be greatly reduced, the service life of the reaction device can be greatly prolonged, and the industrial application potential is huge.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon emission reduction and conversion, and specifically relates to a catalyst for hydrogenating carbon dioxide to methanol, a preparation method thereof, and an application thereof. Background Art

[0002] Methanol is an important basic chemical raw material and clean energy carrier, while carbon dioxide is a greenhouse gas. Among them, the technology of directly hydrogenating carbon dioxide as a carbon source to methanol has attracted much attention. This process can not only effectively consume the CO2 emitted by industries, but also realize the recycling of carbon resources to obtain the required methanol.

[0003] At present, the metal catalysts used in methanol synthesis in industry are mainly copper-based and noble metals. These catalysts generally have problems such as the need for high-temperature reaction conditions (>300°C), low methanol selectivity, and easy deactivation due to hydrothermal environment. In particular, copper-based catalysts have insufficient activity at low temperatures and it is difficult to suppress the selectivity to by-products (such as CO, CH4), which limits the process energy efficiency and economy. In addition, although noble metal catalysts have low-temperature activity, they are costly, have insufficient selectivity, and are sensitive to sulfides, making it difficult to be applied on a large scale. In recent years, transition metal sulfides (such as MoS2) have shown potential in the field of hydrogenating carbon dioxide to methanol due to their unique electronic structure and adjustable surface active sites. The layered structure of MoS2 can expose abundant edge active sites, but its intrinsic catalytic performance is still limited by the low density of active sites, poor stability of sulfur vacancies, and insufficient selectivity to methanol at low temperatures.

[0004] Therefore, how to provide a new catalyst that can achieve high activity at low temperatures and has high CO2 conversion rate and methanol selectivity during the process of hydrogenating carbon dioxide to methanol is the research direction required by the present invention. Summary of the Invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a catalyst for hydrogenating carbon dioxide to methanol, a preparation method thereof, and an application thereof, which can achieve high activity at low temperatures and have high CO2 conversion rate and methanol selectivity during the process of hydrogenating carbon dioxide to methanol.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a catalyst for hydrogenating carbon dioxide to methanol, the catalyst is a MoS2-O catalyst, and by mass fraction, SO3: 50% - 56%; MoO3: 44% - 50%.

[0007] Further, the microstructure of the catalyst is distributed in a lamellar and petal-like shape.

[0008] The preparation method of the above-mentioned catalyst for hydrogenating carbon dioxide to methanol includes the following steps:

[0009] Step 1: Weigh (NH4)6Mo7O 24 *4H2O and thiourea (NH2CSNH2), add to deionized water and stir to form a homogeneous solution;

[0010] Step 2: Transfer the dissolved solution to a hydrothermal reactor and perform a hydrothermal synthesis reaction at 140-220° C. for 8-36 hours;

[0011] Step 3: After completion, filter with ethanol and water several times;

[0012] Step 4: Place the filtered product in a vacuum oven for drying to prepare a MoS2-O catalyst.

[0013] Furthermore, the (NH4)6Mo7O 24 *The molar ratio of 4H2O to NH2CSNH2 is 1:50.

[0014] Furthermore, the temperature of the hydrothermal synthesis reaction is 160° C., and the reaction time is 24 h.

[0015] Furthermore, in step 3, the ethanol and water are each filtered 3 times.

[0016] The catalyst is used in the production of methanol by hydrogenation of carbon dioxide. The catalyst is placed in a reactor and carbon dioxide and hydrogen are introduced. The carbon dioxide is hydrogenated to produce methanol at a temperature of 200-300°C.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. The catalyst prepared by the present invention has been shown in experiments to require only a reaction temperature of 200°C for the hydrogenation of carbon dioxide to produce methanol, with a CO2 conversion rate of up to 4.2% and a methanol selectivity of up to 96.4%. Under the same conditions, the CO2 conversion rate of the MoS2 catalyst is only 2.9%, and the methanol selectivity is 70.9%. This shows that the present invention is more conducive to methanol synthesis than existing catalysts. Moreover, since the catalyst of the present invention can produce methanol at a lower temperature, it can greatly save energy consumption and extend the life of the reaction device, and has great industrial application potential.

[0019] 2. The catalyst of the present invention effectively regulates the electronic structure based on the in-situ incorporation of O into MoS2, forming a highly active and stable hydrogen evolution MoS2-O catalyst. The specific microscopic shape gives it abundant catalytic edge sites, an increase in the electrochemically accessible surface area, and a unique synergistic effect between the MGF support and the active catalyst, which enhances the catalytic activity, thereby effectively ensuring the effect of subsequent methanol production.

[0020] 3. The whole process of preparing the catalyst of the present invention is simple and easy to operate, which is convenient for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the X-ray diffraction (XRD) pattern in the experimental proof of the present invention;

[0022] Figure 2 is the EPR scan in the experimental proof of the present invention;

[0023] Figure 3 is the binding energy spectrum of the 3d orbital of the Mo element in the X-ray photoelectron spectroscopy (XPS) in the experimental proof of the present invention;

[0024] Figure 4 is the binding energy spectrum of the 2P orbital of the S element in the X-ray photoelectron spectroscopy (XPS) in the experimental proof of the present invention;

[0025] Figure 5 is the scanning electron microscope (SEM) image of the catalyst of Example 1 of the present invention at a resolution of 500 μm;

[0026] Figure 6 is the scanning electron microscope (SEM) image of the catalyst of Example 1 of the present invention at a resolution of 5 μm. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be further described below.

[0028] Example 1: The catalyst is MoS2-O catalyst. By mass fraction, SO3: 52.4%; MoO3: 47.6%; the microstructure of the catalyst is distributed in a lamellar and petal-like shape as shown in Figure 5 and Figure 6 shown.

[0029] The preparation method of the above catalyst includes the following steps:

[0030] Step 1: Weigh 2.0385 g of (NH4)6Mo7O 24 *4H2O (M = 1235.857) and 3.768 g of thiourea (NH2CSNH2) respectively, so that the molar ratio of (NH4)6Mo7O 24 *4H2O to NH2CSNH2 is 1:50, and add them to 57 ml of deionized water, and stir into a homogeneous solution;

[0031] Step 2: Transfer the dissolved solution to a hydrothermal reactor, and carry out hydrothermal synthesis reaction at 160 °C for 24 h;

[0032] Step 3: After completion, filter with ethanol and water three times each;

[0033] Step 4: After putting the product obtained by suction filtration into a vacuum oven at 80 °C for drying, the MoS2-O catalyst of Example 1 was prepared.

[0034] Example 2: Its preparation process is the same as that of Example 1, except that the temperature of the hydrothermal synthesis reaction is 180 °C and the reaction time is 30 h, thereby preparing the MoS2-O catalyst of Example 2.

[0035] Example 3: Its preparation process is basically the same as that of Example 1, except that the temperature of the hydrothermal synthesis reaction is 220 °C and the reaction time is 18 h, thereby preparing the MoS2-O catalyst of Example 3.

[0036] Experimental verification:

[0037] 1. The MoS2-O catalyst prepared in Example 1 and the existing MoS2 catalyst were both subjected to X-ray diffraction and EPR analysis (i.e., electron paramagnetic resonance analysis) to observe the oxygen vacancy signal peak. The analysis results are shown in Appendices Figure 1 and 2 . It can be seen from the figure that the signal peak intensity of MoS2 is lower than that of MoS2-O, and MoS2-O has more oxygen, indicating that the incorporation of O into the MoS2 lattice reduces its vacancy concentration.

[0038] 2. The performance of the catalysts prepared in Examples 1 to 3 was tested:

[0039] The catalysts of Examples 1 to 3 were respectively used in a 100 ml hydrothermal autoclave at a reaction temperature of 200 °C, a pressure of 5 MPa, and a CO2 / H2 flow rate of 20 ml / min for the hydrogenation of carbon dioxide to methanol. The catalyst dosage for each example was 0.2 g, and the catalyst performance evaluation results are shown in Table 1.

[0040] Table 1 Performance results of MoS2-O catalysts

[0041]

[0042] It can be seen from Table 3 that the CO2 conversion rate and methanol selectivity of Example 1 are the highest, and it is the optimal example.

[0043] 3. The MoS2-O catalyst prepared in Example 1 and the existing MoS2 catalyst were subjected to XPS analysis (i.e., X-ray photoelectron spectroscopy analysis) to observe the characteristic peaks. The results are shown in Appendices Figure 3 and 4 ; The evaluation results are shown in Table 2.

[0044] Table 2 Evaluation results of X-ray photoelectron spectroscopy (XPS) orbital binding energy spectra

[0045]

[0046] As can be seen from Table 2, Mo dominates in the MoS2-O catalyst; the surface O of the MoS2-O catalyst is inserted into the MoS2 lattice, and the electrons of the lattice oxygen are transferred to Mo and S, increasing the local electron density. In addition, the increase in the O / Mo ratio also proves the successful incorporation of O again.

[0047] 4. Performance comparison of the catalyst prepared in this invention with other existing catalysts:

[0048] Take 0.2 g each of the MoS2-O catalyst prepared in Example 1 and the existing MoS2, MoS2-O-H2R-500, and MoS2-O-H2R-300 catalysts, and carry out the carbon dioxide hydrogenation reaction under the conditions of a reaction temperature of 200 °C, a reaction pressure of 5 MPa, and a CO2 / H2 flow rate of 20 ml / min. The catalyst evaluation results are shown in Table 3.

[0049] Table 3 Performance comparison of different catalysts

[0050]

[0051] As can be seen from Table 2, the CO2 conversion rate and methanol selectivity of Example 1 are the highest, indicating that the catalyst prepared in this invention has better effects compared with the existing catalysts.

[0052] 5. Test on the reaction temperature of the catalyst prepared in Example 1 for carbon dioxide hydrogenation to methanol:

[0053] Weigh 0.2 g of the catalyst in Example 1 and put it into a reaction kettle for the carbon dioxide hydrogenation to methanol reaction. The CO2 / H2 flow rate is 20 ml / min, the reaction pressure is 5 Mpa, heat up to the reaction temperature of 200 - 300 °C to start the reaction, analyze the reaction products and calculate the conversion rate and selectivity. The catalyst evaluation results are shown in Table 4.

[0054] Table 4 Reaction performance of the catalyst at different temperatures

[0055]

[0056] As can be seen from Table 4, the comprehensive effects of the CO2 conversion rate and methanol selectivity of the catalyst prepared in Example 1 for carbon dioxide hydrogenation to methanol are the best under the condition of a temperature of 200 °C, indicating that the catalyst prepared in this invention can have high-performance CO2 conversion rate and methanol selectivity under low-temperature conditions.

[0057] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A catalyst for hydrogenating carbon dioxide to methanol, characterized in that, The catalyst is MoS2-O catalyst. By mass fraction, SO3: 50% - 56%; MoO3: 44% - 50%.

2. The catalyst for hydrogenating carbon dioxide to methanol according to claim 1, characterized in that, The microstructure of the catalyst is distributed in a lamellar and petal-like shape.

3. A method for preparing a catalyst for hydrogenating carbon dioxide to methanol according to claim 1 or 2, characterized in that, It includes the following steps: Step 1. Weigh a certain amount of (NH4)6Mo7O 24 *4H2O and NH2CSNH2 respectively, add them into deionized water, and stir to form a homogeneous solution; Step 2: Transfer the dissolved solution into a hydrothermal autoclave and conduct a hydrothermal synthesis reaction at 140 - 220 °C for 8 - 36 h; Step 3: After completion, filter with ethanol and water by suction for multiple times respectively; Step 4: Put the product after suction filtration into a vacuum oven for drying, and then prepare the MoS2-O catalyst.

4. The preparation method according to claim 3, wherein The molar ratio of (NH4)6Mo7O 24 *4H2O to NH2CSNH2 is 1:

50.

5. The preparation method according to claim 3, characterized in that, The temperature of the hydrothermal synthesis reaction is 160 °C, and the reaction time is 24 h.

6. The preparation method according to claim 3, characterized in that, In Step 3, filter with ethanol and water by suction 3 times respectively.

7. An application of the catalyst according to claim 1 or 2 in the hydrogenation of carbon dioxide to methanol. Put the catalyst into a reaction kettle, introduce carbon dioxide and hydrogen, and conduct the hydrogenation of carbon dioxide to methanol under the condition that the temperature is 200 - 300 °C.

8. The application according to claim 7, characterized in that During the reaction process, the temperature of the reaction kettle is 200 °C, the pressure is 5 MPa, and the flow rates of carbon dioxide and hydrogen introduced are both 20 ml / min.

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