Catalyst for low-temperature synthesis of methanol by carbon dioxide hydrogenation and preparation method and application thereof

Abstract

This invention discloses a catalyst for the low-temperature synthesis of methanol from carbon dioxide via hydrogenation. The method employs a template method, using PVP as a template agent to prepare a precursor solution. Metal salts corresponding to CuO, ZnO, and Al₂O₃ or CuO, ZnO, ZrO₂, and Al₂O₃ are added to the precursor solution, and the solution is then frozen into ice by dripping in liquid nitrogen. The solution is then freeze-dried and finally calcined to obtain the two-dimensional copper-based nanocatalyst CuZnAl or CuZnAlZr. This method solves the problems of low metal oxide dispersion and low catalytic activity in copper-based nanocatalysts. Furthermore, the PVP template method can expand the thermal catalytic boundary, enabling the general and large-scale synthesis of high-entropy two-dimensional materials. It overcomes the limitations of other methods, such as high temperature (typically >1000℃), specialized equipment, and cumbersome procedures, and suppresses byproduct generation, making it easy to industrialize. The catalyst prepared by this invention has advantages such as low preparation cost, environmental friendliness, good stability, and high activity. It exhibits excellent methanol selectivity in the reaction of carbon dioxide hydrogenation to methanol.

Description

Technical Field

[0001] This invention belongs to the field of copper-based catalyst technology, and particularly relates to a catalyst for the low-temperature synthesis of methanol by hydrogenation of carbon dioxide, its preparation method and application. Background Technology

[0002] Methanol is an essential liquid fuel and chemical raw material in human production and daily life, possessing high economic value and serving as a crucial raw material for the preparation of fine chemical products. Simultaneously, methanol is also an important intermediate in the production of high-value-added chemicals. In recent years, carbon emissions have led to a continuous increase in atmospheric CO2 concentration, resulting in global warming and rising sea levels, posing a serious threat to human development. Faced with this environmental crisis, promoting carbon recycling through CO2 hydrogenation not only solves the problem of excess carbon emissions but also converts renewable hydrogen energy into liquid methanol. Therefore, the CO2 hydrogenation to methanol reaction can help address global environmental issues while simultaneously meeting the world's growing methanol demand. CO2 hydrogenation to methanol is considered one of the most promising pathways for large-scale CO2 utilization, becoming an important new route for promoting the sustainable development of the chemical industry. This not only helps alleviate climate change but is also a key step in achieving energy structure transformation.

[0003] The hydrogenation of CO2 to methanol is an exothermic reaction (CO2 + 3H2 → CH3OH, ΔH). 0 =-49.5kJ / mol) Low temperature and high pressure favor the conversion of CO2 to methanol. However, due to the inertness of CO2, it is difficult to activate or convert CO2 at low temperatures. At high temperatures, a reverse water-gas shift reaction occurs, producing CO as a byproduct. ΔH 0 =41.2 kJ / mol). Therefore, it is very important to develop a methanol catalyst with high activity and selectivity at low temperatures.

[0004] Domestic researchers have developed various catalysts for the hydrogenation of carbon dioxide to methanol. Hu et al. proposed that, at room temperature, sulfur vacancies in MoS2 nanosheets promote CO2 dissociation while inhibiting methane hydrogenolysis, thus achieving high activity in the low-temperature hydrogenation of CO2 to methanol. At 180℃, the catalyst showed a methanol selectivity of 94.3% and a CO2 conversion rate of 12.5% ​​on sulfur-vacancy-rich MoS2 nanosheets. This catalyst exhibited high stability over more than 3000 hours without any deactivation, demonstrating promising prospects for industrial application. (Nat. Catal., 2021, 4(3): 242-250.) Wang et al. reported a binary metal oxide ZnO-ZrO2 solid solution catalyst, which, under high pressure and high reactant space-time velocity reaction conditions, achieved a methanol selectivity of 86%-91% at 315-320℃ and a CO2 single-pass conversion rate exceeding 10% (Sci. Adv., 2017, 3(10): 1701-290.) Maxim et al. found that Pd / ZnO catalysts exhibited good activity and high selectivity for methanol during the catalytic hydrogenation of CO2. In the absence of ZnO coexistence, the Pd-Zn alloy phase does not provide active sites for direct CO2 hydrogenation to methanol, but mainly produces CO. The presence of the ZnO phase in contact with the Pd-Zn phase is essential for efficient methanol production. (Angew. Chem. Int. Ed., 2021, 60: 17053-17059) Lee et al. prepared a Pd-doped catalyst for ZnZrOx solid solution. This catalyst has atomically dispersed Pd species, with Pd substituting up to 0.6 wt% of lattice Zn or Zr atoms. Although Pd doping did not significantly alter the structural properties of ZnZrOx, it generated more oxygen vacancies on its surface, thereby increasing the CO2 adsorption capacity. Structural and electronic characterization combined with DFT calculations showed that Pd atoms promote H2 activation on the catalyst surface, causing hydrogen spillover to adjacent Zn sites, thus accelerating the selective hydrogenation of CO2. (Appl. Catal., B., 2022, 304: 120994) Toyir et al. optimized Cu-based catalysts by adding Ga. 0 / Cu +The ratio improves catalytic performance. (Appl. Catal., B 34(2001)255–266). Gao et al. reported that an appropriate amount of ZrO2 in CuO / ZnO / Al2O3 / ZrO2 can increase the surface area and surface basicity of Cu, resulting in high activity and selectivity. (J. Catal. 298(2013)51–60) Numerous studies have found that Cu-based catalysts are still at the core of research. Using a suitable support and adding promoters can improve the activity and stability of Cu-based catalysts. Traditional Cu-Zn-Al catalysts, as commercial methanol production catalysts, have good activity when using syngas as a reaction feedstock, but they have disadvantages such as low methanol selectivity, poor stability, and easy poisoning in the CO2 hydrogenation to methanol reaction. Noble metal catalysts and metal oxide catalysts have disadvantages such as high cost, high reaction temperature, and easy decomposition at high temperature.

[0005] Currently, the challenge lies in precisely controlling the morphology of the catalyst, the exposed surface area of ​​copper, the dispersion of copper, and the surface basicity and Cu content through suitable synthesis methods and mature processes. 0 / (Cu 0 +Cu + However, achieving the desired high selectivity and activity for methanol production via carbon dioxide hydrogenation remains a challenge. Catalysts with high activity, high selectivity, low cost, high stability, and suppression of byproduct formation, along with simple preparation processes, easy operation, and reproducibility for industrial production, are still the focus of future research and development and have promising application prospects. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a catalyst for the low-temperature synthesis of carbon dioxide hydrogenation to methanol that is simple in process, convenient in operation, and has good effect, as well as its preparation method and application. The obtained two-dimensional copper-based nanocatalyst product has the advantages of low preparation cost, green and environmentally friendly, good stability and high activity.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for preparing catalysts for the low-temperature synthesis of carbon dioxide to methanol via hydrogenation employs a template method. A precursor solution is prepared using PVP as a template agent. Metal salts corresponding to CuO, ZnO, and Al2O3 or CuO, ZnO, ZrO2, and Al2O3 are added to the precursor solution, and liquid nitrogen is dripped into the solution to freeze it into ice. The solution is then freeze-dried and finally calcined to obtain two-dimensional copper-based nanocatalysts CuZnAl or CuZnAlZr.

[0009] In the two-dimensional copper-based nanocatalyst CuZnAl, the mass percentages of Al2O3, ZnO, and CuO in the catalyst are 15.0 wt%, 25.0 wt%, and 60.0 wt%, respectively; in the two-dimensional copper-based nanocatalyst CuZnAlZr, the mass percentages of Al2O3, ZnO, ZrO2, and CuO in the catalyst are 10–15.0 wt%, 20–25.0 wt%, 4–16 wt%, and 55–60.0 wt%, respectively.

[0010] The metal salts corresponding to CuO, ZnO, ZrO2, and Al2O3 are Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O, and Zr(NO3)4·5H2O, respectively.

[0011] The above preparation method includes the following steps:

[0012] The template agent was dissolved in deionized water and stirred until completely dissolved to obtain the precursor solution;

[0013] Then, the metal salt was added to the precursor solution from step (1) under a magnetic stirrer;

[0014] The mixed solution obtained in stirring step (2) is dropped into liquid nitrogen to freeze it rapidly into ice.

[0015] The frozen product obtained in step (3) was freeze-dried to remove H2O for 24 to 48 hours.

[0016] The freeze-dried product obtained in calcination step (4) yielded a two-dimensional CuZnAl catalyst, with a calcination time of 6 h.

[0017] The calcined material obtained in step (5) is pressed into tablets and sieved.

[0018] The weight ratio of the template agent in step (1) to the metal salt in step (2) is 1 to 2.

[0019] The stirring time in step (3) is 0.5h to 1h; the freeze-drying time in step (4) is 24 to 48h; and the calcination temperature in step (5) is 450℃ and the calcination time is 6h.

[0020] In step (6), the sample is sieved to 100-120 mesh.

[0021] The two-dimensional copper-based nanocatalyst was prepared by the above method.

[0022] The above-mentioned two-dimensional copper-based nanocatalysts are used in the catalytic hydrogenation of carbon dioxide to methanol.

[0023] To address the current problems in the preparation of copper-based nanocatalysts, the inventors have established a method for preparing a catalyst for the low-temperature synthesis of methanol via carbon dioxide hydrogenation. This method employs a template method, using PVP as a template agent to prepare a precursor solution. Corresponding metal salts of CuO, ZnO, and Al₂O₃ or CuO, ZnO, ZrO₂, and Al₂O₃ are added to the precursor solution, and the solution is then frozen into ice by dripping in liquid nitrogen. The solution is then freeze-dried and finally calcined to obtain the two-dimensional copper-based nanocatalyst CuZnAl or CuZnAlZr. This method, through a flexible and efficient PVP template preparation method, can prepare two-dimensional copper-based nanocatalysts, solving the problems of low metal oxide dispersion and low catalytic activity in copper-based nanocatalysts. Furthermore, the PVP template method can expand the thermocatalytic boundary, enabling the general and large-scale synthesis of high-entropy two-dimensional materials. This overcomes the limitations of other methods, such as high temperatures (typically >1000℃), specialized equipment, and cumbersome procedures, and suppresses byproduct generation, making it easily industrializable.

[0024] In summary, the preparation method of this invention provides a new approach for achieving synergistic catalytic stability and activity of copper-based nanocatalysts through low-temperature synthesis of metal oxide nanocatalysts. The catalyst prepared by this invention has advantages such as low preparation cost, environmental friendliness, good stability, and high activity. It exhibits excellent methanol selectivity and a high space-time yield in the reaction of carbon dioxide hydrogenation to methanol, and can selectively reduce carbon dioxide to methanol at low temperature (200℃). Under optimized reaction conditions, a methanol selectivity of 87.28% can be achieved, with a STY of 873.15g. MeOH kg -1 cat h -1 . Attached Figure Description

[0025] Figure 1 This is a flowchart of the preparation method of the catalyst for the low-temperature synthesis of methanol from carbon dioxide by hydrogenation according to the present invention.

[0026] Figure 2 These are the XRD patterns of the two-dimensional copper-based nanocatalyst CuZnAlZr obtained in this invention and a commercial catalyst after calcination.

[0027] Figure 3 The figure shows the stability test results of the two-dimensional copper-based nanocatalyst obtained by the present invention. In the figure: a) stability test results of the commercial catalyst CuZnAl, b) stability test results of the two-dimensional copper-based nanocatalyst CuZnAlZr.

[0028] Figure 4 These are SEM images of the two-dimensional copper-based nanocatalyst obtained in this invention. In the images: a and b are morphology images of the two-dimensional copper-based nanocatalyst CuZnAl; c and d are morphology images of the two-dimensional copper-based nanocatalyst CuZnAlZr.

[0029] Figure 5 This is a performance diagram of the two-dimensional copper-based nanocatalyst CuZnAlZr obtained in this invention.

[0030] Figure 6 This is a TEM image of the two-dimensional copper-based nanocatalyst CuZnAlZr obtained in this invention. In the image: the top row, left, right and center show the distribution of Cu, Zn and Al in the two-dimensional copper-based nanocatalyst CuZnAlZr, respectively; the bottom row, left, right and center show the distribution of Zr and the HADDF diagram of the two-dimensional copper-based nanocatalyst CuZnAlZr, respectively.

[0031] Figure 7 This is a TEM image of the two-dimensional copper-based nanocatalyst CuZnAlZr obtained in this invention. In the image, the top left and right, and the bottom left and right are lattice fringe patterns of the reduced two-dimensional copper-based nanocatalyst CuZnAlZr. The lattice fringes corresponding to 0.182 nm and 0.208 nm correspond to the Cu (200) and (111) planes, respectively. A lattice fringe of 0.281 nm was also observed, corresponding to ZnO (100).

[0032] Figure 8 The figure shows the activation energy and STY diagram of the two-dimensional copper-based nanocatalyst obtained in this invention. In the figure: (a) activation energy diagram of two-dimensional copper-based nanocatalysts CuZnAlZr, CuZnAl and commercial CuZnAl; (b) ZrO2 content and STY diagram of two-dimensional copper-based nanocatalyst CuZnAlZr.

[0033] Figure 9 The figures show the in-situ infrared spectra of the catalytic reactions of the two-dimensional copper-based nanocatalysts obtained in this invention. In the figures: (a) and (b) are the CO2 + H2 reaction of the CuZnAlZr catalyst, and (c) and (d) are the Ar + H2 reaction of the CuZnAlZr catalyst. Reaction conditions: 240℃, 75% H2 / CO2 (25mL / min). Detailed Implementation

[0034] Example 1

[0035] According to the specified proportions of each element, 6.5 g of PVP was weighed and dissolved in 20 ml of deionized water. Then, 3.14 g of Cu(NO3)2·3H2O, 1.785 g of Zn(NO3)2·6H2O, and 0.375 g of Al(NO3)3·9H2O were added to the solution using a magnetic stirrer, with a PVP / metal salt weight ratio of 1.2. After stirring for 0.5 hours, the homogeneous solution was dropped into liquid nitrogen and rapidly frozen into ice. The solution was then freeze-dried for 30 hours to remove H2O. The dried product was calcined in a muffle furnace at 450℃ (heating rate 1℃ / min) for 6 hours, and the resulting product was named two-dimensional CuZnAl. The prepared two-dimensional CuZnAl was mixed evenly, pressed into tablets, and sieved to 100–120 mesh to prepare a two-dimensional CuZnAl catalyst with methanol catalytic activity.

[0036] Example 2

[0037] The preparation method is basically the same as in Example 1, except that the mass of the metal salts is different, namely 3.14g Cu(NO3)2·3H2O, 1.78494g Zn(NO3)2·6H2O, 0.375g Al(NO3)3·9H2O, and 1.116g Zr(NO3)4·5H2O.

[0038] Example 3

[0039] The preparation method is basically the same as in Example 1, except that the mass of the metal salts is different, namely 3.14g Cu(NO3)2·3H2O, 1.78494g Zn(NO3)2·6H2O, 0.375g Al(NO3)3·9H2O, and 0.857g Zr(NO3)4·5H2O.

[0040] Example 4

[0041] The preparation method is basically the same as in Example 1, except that the mass of the metal salts is different, namely 3.14g Cu(NO3)2·3H2O, 1.78494g Zn(NO3)2·6H2O, 0.375g Al(NO3)3·9H2O, and 0.643g Zr(NO3)4·5H2O.

[0042] Example 5

[0043] The preparation method is basically the same as in Example 1, except that the mass of the metal salts is different, namely 3.14g Cu(NO3)2·3H2O, 1.78494g Zn(NO3)2·6H2O, 0.375g Al(NO3)3·9H2O, and 0.423g Zr(NO3)4·5H2O.

[0044] Evaluation of Catalytic Performance Testing Machine

[0045] 0.1 g of each of the two-dimensional catalysts obtained in the examples were placed in the isothermal zone of a fixed-bed reactor for catalytic evaluation of the carbon dioxide hydrogenation to methanol reaction. Activation conditions: Under a 10% H2 / Ar argon atmosphere with a space velocity of 15000 mL / gcat / h, the temperature was increased from room temperature to 300°C at a rate of 10°C / min for 2 h. After activation, the 10% H2 / Ar activation gas was switched to the feed gas and introduced into the fixed-bed reactor. The reaction temperature was adjusted to 240°C and the reaction pressure to 4 MPa for catalytic evaluation. Gaseous reaction products were directly analyzed online by chromatography. H2, N2, and CO2 were detected by a TCD detector, while CO and methanol products were detected by an FID detector. The results are shown in Table 1.

[0046] Table 1 Catalytic performance of samples from different embodiments for CO2 hydrogenation to methanol

[0047]

[0048] like Figure 2 As shown, XRD analysis revealed that the calcined catalysts of Examples 1, 2, 3, 4, and 5 were characterized by CuO (2θ = 35.5°, 38.7°, 48.7°, and 61.5°) and ZnO (2θ = 31.8°, 34.4°, and 36.3°). Furthermore, characteristic diffraction peaks of ZnO (100), (002), and (101) at 2θ = 31.7°, 34.4°, and 36.3° were observed. However, no diffraction peaks of Al2O3 or ZrO2 were observed in the calcined catalysts, indicating that Al2O3 and ZrO2 are amorphous or highly dispersed.

[0049] like Figure 3 As shown, the long-term stability of commercial copper-based catalysts and two-dimensional copper-based nanocatalysts was investigated. The CZA-4%ZrO2 catalyst remained stable in terms of initial loss conversion, methanol selectivity, and STY over 200 h. Figure 3 The two-dimensional CuZnAlZr catalyst exhibits good stability. Compared with commercial catalysts, it demonstrates superior performance, while the STY of methanol produced by the two-dimensional CuZnAlZr catalyst remains at 254.89 g. MeOH kg Cu -1 h -1 Its thermal stability was confirmed after 200 hours.

[0050] like Figure 4 As shown, the morphology of the reduced two-dimensional copper-based nanocatalyst was analyzed by transmission electron microscopy. The catalyst exhibits a two-dimensional morphology, with flakes approximately 200 nm in size, producing significant shadows. EDS mapping was used to observe the distribution of Cu, Zn, Al, and Zr. Figure 6Cu, Zn, Al, and Zr are evenly distributed without obvious aggregation. Figure 3 As shown, lattice fringes of 0.182 nm and 0.208 nm were observed in the reduced two-dimensional copper-based nanocatalyst. Figure 7 The lattice fringes at 0.281 nm were also observed, corresponding to the Cu(200) and (111) planes.

[0051] like Figure 5 As shown, under optimized reaction conditions (4 MPa, 45000 mL / gcat / h, 200℃-300℃), the two-dimensional copper-based nanocatalyst can achieve a methanol selectivity of 87.28%, with a styrotoxicity (STY) of 873.15 g. MeOH kg -1 cat h -1

[0052] like Figure 8 As shown, kinetic studies revealed that the apparent activation energy for methanol formation on the two-dimensional copper-based nanocatalyst was significantly lower than that of commercial CZA. The ZrO2 content in the two-dimensional copper-based nanocatalyst was optimized. With increasing ZrO2 content, the space-time yield (STY) gradually decreased, and CZA-4%Z exhibited the best catalytic performance.

[0053] like Figure 9 As shown, the evolution of intermediate substances during the CZA-4%ZrO2 reaction was observed using in-situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). The catalyst was reduced in situ at 300℃ in the sample cell, and then the feed gas was introduced into the cell to simulate the actual reaction conditions at 240℃ and 1.0 MPa. In the spectrum of CZA-4%ZrO2, formate (HCOO) species were observed at 1386 cm⁻¹. -1 1590cm -1 The characteristic bands can correspond to the asymmetric OCO stretching νas(OCO), the symmetric OCO stretching vibration νas(OCO), and the OCO vibration of CH stretching ν(CH) formate (denoted as C=O). At 2935 cm⁻¹ -1 and 2878cm -1 The observed signals correspond to νas(CH3) and νs(CH3) of the methoxy (H3CO) species. With increasing reaction time, the signals of formate and methoxy groups increased with the accumulation of surface species, reaching a stable state at 20 min. No CO was detected during the reaction (1900-2000 cm⁻¹). -1After 50 min of reaction, the sample was scanned with 75% H2 / He. The characteristic peak intensity of formate gradually decreased while that of methoxy group gradually increased, indicating that the formate was hydrogenated to methoxy group and further hydrogenated to methanol. There are two main reaction mechanisms for the hydrogenation of CO2 to methanol: the RWGS pathway and the formate pathway. CO is the main intermediate in the RWGS pathway, and methanol is produced by hydrogenating CO. The formate pathway involves the conversion of CO2 to HCOO and the further hydrogenation of HCOO to H2COO. * →H2CO * →H3CO * →CH3OH. During the reaction, formate and methoxy compounds are mainly produced on the catalyst surface; CO was not detected. * Therefore, methoxylated substances are formed by the hydrogenation of formate substances. After switching to 75% H2 / He gas, through a series of hydrogenation steps (HCOO) * →H2CO * →H3CO * →CH3OH) transforms formate and methoxy compounds accumulated on the surface. Therefore, the CZA-xZrO2 catalyst follows the formate pathway in the methanol synthesis reaction. The CO in the reaction may be caused by the decomposition of formate esters.

Claims

1. A method for preparing a catalyst for the low-temperature synthesis of methanol by hydrogenation of carbon dioxide, characterized in that... A precursor solution was prepared using a template method with PVP as the template agent. Metal salts corresponding to CuO, ZnO, and Al2O3, or CuO, ZnO, ZrO2, and Al2O3, were added to the precursor solution, and liquid nitrogen was added dropwise to freeze it into ice. The solution was then freeze-dried and finally calcined to obtain two-dimensional copper-based nanocatalysts CuZnAl or CuZnAlZr. In the two-dimensional copper-based nanocatalyst CuZnAl, the mass percentages of Al2O3, ZnO, and CuO in the catalyst were 15.0 wt%, 25.0 wt%, and 60.0 wt%, respectively. In the two-dimensional copper-based nanocatalyst CuZnAlZr, the mass percentages of Al2O3, ZnO, ZrO2, and CuO in the catalyst were 10–15.0 wt%, 20–25.0 wt%, 4–16 wt%, and 55–60.0 wt%, respectively. The weight ratio of the template agent to the metal salt was 1–2.

2. The method of claim 1, wherein: The metal salts corresponding to CuO, ZnO, ZrO2, and Al2O3 are Cu(NO3)2·3H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O, and Zr(NO3)4·5H2O, respectively.

3. The method of claim 2, wherein Includes the following steps: (1) Dissolve the template agent in deionized water and stir until completely dissolved to obtain a precursor solution; (2) Then, the metal salt is added to the precursor solution from step (1) under a magnetic stirrer; (3) Stir the mixed solution obtained in step (2), and drop the uniform solution into liquid nitrogen to freeze it into ice quickly; (4) Freeze-dry the frozen material obtained in step (3) to remove H2O for 24 to 48 hours; (5) The freeze-dried product obtained from the calcination step (4) yields a two-dimensional CuZnAl catalyst, and the calcination time is 6h; (6) Press and sieve the calcined material obtained in step (5).

4. The method of claim 3, wherein The stirring time in step (3) is 0.5h to 1h; the freeze-drying time in step (4) is 24 to 48h; and the calcination temperature in step (5) is 450℃ and the calcination time is 6h.

5. The method of claim 3, wherein In step (6), the sample is sieved to 100-120 mesh.

6. The two-dimensional copper-based nanocatalyst prepared by any one of the preparation methods described in claims 1 to 5.

7. The application of the two-dimensional copper-based nanocatalyst according to claim 6 in the catalytic hydrogenation of carbon dioxide to methanol.