Catalyst for preparing dimethyl carbonate from CO2 through low-pressure photo-thermal catalysis, preparation method and application

Abstract

The invention provides a catalyst for preparing dimethyl carbonate through low-pressure photo-thermal catalysis of CO2, a preparation method and application. The catalyst provided by the invention is formed by loading active metal copper on a cerium oxide substrate. The active metal copper is loaded on the surface of the cerium oxide substrate by virtue of a soft template method and then transferred into the muffle furnace, and the catalyst defects, the size and valence state of the active metal copper and the interface structure are accurately regulated and controlled by controlling the temperature, the heating rate and the heat preservation time of the muffle furnace, so that the charge transfer efficiency is greatly improved, and the catalytic activity of the catalyst is improved. The energy barrier of reactant activation is reduced, and meanwhile, the catalytic reaction of the material is promoted by light. The catalyst provided by the invention can realize low-pressure, high-efficiency and high-stability photo-thermal catalysis of methanol and CO2 to prepare dimethyl carbonate.

Description

Technical Field

[0001] The present invention relates to the field of energy catalysis technology, and in particular to a catalyst for preparing dimethyl carbonate by low-pressure photothermal catalysis of CO2, a preparation method and application thereof. Background Art

[0002] The use of excess CO2 to prepare high-value-added multi-carbon compounds has attracted widespread attention from researchers. Among various reaction pathways, the direct coupling of CO2 and methanol to prepare dimethyl carbonate (DMC), which has important industrial value and wide applications, shows great potential. As an environmentally friendly chemical, DMC is widely used as a raw material for methylation and carbonylation reactions, as well as an important monomer for the preparation of polyester materials. It is also often used as an electrolyte in high-performance batteries and is widely used in industrial production.

[0003] Carbon dioxide and methanol can directly synthesize dimethyl carbonate. This method has attracted much attention due to its high atomic utilization, avoidance of toxic reactant reactions and resource utilization. The method of synthesizing dimethyl carbonate directly from carbon dioxide and methanol provides a green chemical approach to convert greenhouse gases into valuable chemicals. This process not only helps to reduce carbon dioxide emissions, but also increases the economic value of methanol. By optimizing the catalyst and reaction conditions, increasing the yield of DMC, and realizing this process on an industrial scale, it will have a positive impact on both environmental protection and the development of the chemical industry.

[0004] In the past few years, scholars have done a lot of work in the field of thermal catalysis of methanol and carbon dioxide to dimethyl carbonate. For example, Ding Yueming's research group published a paper in Angew reporting that lattice oxygen can efficiently catalyze methanol and carbon dioxide to dimethyl carbonate, with a selectivity efficiency of nearly 100% and a yield of 22.2mmol / g. Xie Yi's research group published papers in Angew and NanoLetters reporting that Lewis acid-base pairs and grain boundary structures can achieve efficient thermal catalysis of methanol and carbon dioxide to dimethyl carbonate. Although it reduces the reaction temperature to 140°C, its reaction pressure reaches 2MPa, which still has a high energy cost.

[0005] Patent application document CN202311625858.2 discloses a method for preparing dimethyl carbonate from methanol and carbon dioxide by thermal catalysis. The catalyst uses acidic Ce-MOFs as a cerium precursor, which can utilize its ordered pore structure, large specific surface area and super strong adsorption capacity to achieve metal ion (Ce 3+ 、Ce 4+) is highly dispersed in Ce-MOF. The addition of appropriate hydroxide can reduce the adsorption that cannot react, thereby significantly improving the catalytic activity of the catalyst. The MOF (metal organic framework) structure can increase the surface area of ​​CeO2 and reduce the situation where the internal active sites cannot be activated due to the collapse of CeO2 agglomeration. At the same time, the acidic MOF can combine with the Lewis basic sites on the surface of cerium dioxide, shield the Lewis basic sites, and reduce the adsorption rate of carbon dioxide on the Lewis basic sites.

[0006] Solar energy is inexhaustible and does not pollute the environment. If it is possible to photocatalytically convert methanol and carbon dioxide into dimethyl carbonate, it will also bring about revolutionary reforms in related industries. Relevant scholars have also done a lot of research work. For example, Li Zhong's research group published a paper in Fuel on bismuth-doped cerium oxide nanorods that catalyzed the conversion of methanol and carbon dioxide into dimethyl carbonate under the synergistic effect of light and heat. The yield was 3.3 mmol / g and the selectivity efficiency was close to 100%.

[0007] The conventional reaction temperature of methanol and carbon dioxide is 100-250℃ and the reaction pressure is 2-8MPa, which has high energy cost and requires the device to withstand huge pressure, which is not conducive to industrial production. Therefore, it is necessary to develop a method for efficiently catalyzing methanol and carbon dioxide to produce dimethyl carbonate under mild conditions. Summary of the invention

[0008] The purpose of the present invention is to provide a catalyst, preparation method and application of low-pressure photothermal catalysis of CO2 to dimethyl carbonate. The catalyst provided by the present invention can efficiently catalyze methanol and carbon dioxide to produce dimethyl carbonate through thermal effect and photothermal synergy under relatively mild conditions, and the catalyst preparation method is simple, easy to operate, and can be mass-produced.

[0009] The present invention is achieved in that:

[0010] The catalyst for preparing dimethyl carbonate from CO2 with low pressure photothermal catalysis provided by the present invention is an active metal Cu loaded on a CeO2 substrate. At the same time, a PVP soft template is used to adjust the appropriate sintering temperature, heating rate and holding time of the muffle furnace, and the structural defects of the catalyst, the state of the active metal and the interface structure are precisely regulated. With the help of a high-pressure reactor (although the catalyst of the present application can react under low pressure, a high-pressure reactor is still used for safety), the catalyst can efficiently catalyze methanol and carbon dioxide to prepare dimethyl carbonate under relatively mild conditions through thermal effect and photothermal synergy, and the catalyst preparation method is simple, easy to operate, and can be mass-produced.

[0011] The present invention provides a method for preparing a catalyst for catalyzing methanol and carbon dioxide to produce dimethyl carbonate, comprising the following steps:

[0012] Step 1: Use 80 mL of deionized water to prepare a precursor solution of soft template PVP with a concentration of 0.13-0.21 mg / mL, mix and stir for 1.5-2.5 hours, add 0.9-1.2 g of the first metal salt, stir for 0.5-2.0 hours, add 20-200 mg of the second metal salt, stir for 0.5-1.0 hours, and obtain a mixed solution.

[0013] Step 2, freeze-drying the mixed solution with liquid nitrogen, and placing it in a freeze dryer for 48 to 72 hours to obtain a catalyst precursor;

[0014] Step 3: Place the catalyst precursor in a muffle furnace, heat the muffle furnace from room temperature to 100-700° C., at a heating rate of 1-6° C. / min, keep the temperature for 1-5 hours, and then take it out to obtain coarse catalyst sample particles.

[0015] Preferably, the coarse particles of the catalyst sample can be subsequently ground into powder, evacuated with a vacuum packaging bag and labeled with the sample name.

[0016] In step 1, the first metal salt is a cerium salt, specifically cerium nitrate hexahydrate; the second metal salt is a copper salt, specifically anhydrous copper nitrate.

[0017] In step 2, after the mixed solution is freeze-dried with liquid nitrogen, it is first placed in the freezer layer of a refrigerator to allow the liquid nitrogen to evaporate completely, and then the sample is placed in a freeze dryer for freeze drying.

[0018] In step 3, the catalyst precursor fixes the morphology of the catalyst and creates defects and interface structures at the corresponding heating temperature, holding time and heating rate. In the heating process of the muffle furnace in step 3, the temperature is first raised from room temperature to 100°C and kept for a period of time; then raised from 100°C to 200°C and kept for a period of time; then raised from 200°C to 300°C and kept for a period of time; then raised from 300°C to 450°C to 700°C and kept for 1 to 5 hours.

[0019] According to the catalyst prepared by the above method, the loading amount of active metal copper is 0.2-2.0%, and the rest is CeO2 substrate.

[0020] The catalyst prepared by the above method can be used to catalyze methanol and CO2 to produce dimethyl carbonate. Specifically, the catalyst and anhydrous methanol are loaded into the reactor, and then the reactor is purged with the reaction gas CO2 for 60 minutes; the power is turned on, the reactor is heated to 70-260°C, and the pressure is set at 0.1-1.0MPa. The catalyst catalyzes methanol and CO2 to produce dimethyl carbonate under thermal conditions or photothermal synergistic conditions. Photothermal synergistic conditions refer to a light source irradiated by a xenon lamp in addition to a heat source. The xenon lamp is a full-spectrum reflector with a current of 5-15A.

[0021] Preferably, before the catalyst is loaded into the reactor, the catalyst is placed in a glass dish for drying, and the water in the catalyst is removed before the catalyst is placed in the reactor.

[0022] The power supply under the above thermal conditions is 220V.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] The present invention provides a catalyst for catalyzing methanol and CO2 to produce dimethyl carbonate, which is prepared by freeze drying and sintering processes, and the active metal copper in the obtained catalyst is loaded on the substrate cerium oxide in the form of a single atom. The present invention freeze-dries the copper and cerium solution by liquid nitrogen freeze drying and fixes it, and then transfers it to a freeze dryer, and after the freeze dryer is evacuated to vacuum, freeze-drying is performed at -56°C, so that the position of the metal ions in the solution remains relatively stable, and then the sample is ground and transferred to a muffle furnace, and the muffle furnace is heated from room temperature to 100-700°C, and kept warm at 100°C, 200°C and 300°C for a period of time, and finally heated from 300°C to the sintering temperature, the heating rate is 1-6°C / min, and the temperature is kept warm for 1-5h, and finally the catalyst sample coarse particles are obtained.

[0025] The present invention precisely regulates catalyst defects, active metal copper size and valence, and interface structure by controlling the temperature, heating rate, holding time, and precursor concentration of the muffle furnace. The effect of the loaded active metal improves the adsorption capacity, adsorption characteristics, and charge transfer efficiency of the catalyst, and realizes efficient and high-stability coupled catalysis of methanol and CO2 to produce dimethyl carbonate. At the same time, the catalyst can photothermally catalyze methanol and CO2 to produce dimethyl carbonate. Light energy causes the catalyst to produce high-energy electrons and holes, selectively activates adsorbed molecules, and contributes to reactant adsorption and desorption reactions, thereby improving reaction efficiency and reducing reaction temperature. In addition, the catalyst raw materials are easily available, the metal loading is extremely low, the preparation steps are simple and easy, the conditions are mild, and it can be prepared in large quantities in a short time.

[0026] The catalyst provided by the present invention is used for the thermal catalysis of methanol and CO2 to produce dimethyl carbonate, with a yield of up to 22.9 mmol / g. During the reaction, heat causes the catalyst to selectively activate the adsorbed molecules, and thermal energy enhances the mass transfer of the reactants and promotes product desorption. By thermally catalyzing methanol and CO2 to produce dimethyl carbonate, the goal of efficiently and low-costly producing dimethyl carbonate is achieved. At the same time, the material can improve the yield of methanol and CO2 to produce dimethyl carbonate and reduce the reaction temperature through photothermal synergy. Moreover, the catalyst provided by the present invention can achieve catalytic reaction under relatively low pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The flowchart of the preparation method of the catalyst for preparing dimethyl carbonate from methanol and CO2 provided in an embodiment of the present invention is shown.

[0028] Figure 2 A flow chart showing the use of the catalyst provided in an embodiment of the present invention for catalyzing methanol and CO2 to produce dimethyl carbonate.

[0029] Figure 3 The TEM image of the catalyst 0.8% Cu-CeO2 prepared in Example 1 of the present invention is shown.

[0030] Figure 4 The high-resolution element distribution map of the catalyst 0.8% Cu-CeO2 prepared in Example 1 of the present invention is shown.

[0031] Figure 5 The XRD patterns of the catalysts Cu-CeO2 prepared in Examples 1 to 6 of the present invention are shown.

[0032] Figure 6 The in-situ infrared image of the catalyst 0.8% Cu-CeO2 prepared in Example 1 of the present invention is shown.

[0033] Figure 7 The ESR graphs of the catalysts Cu-CeO2 prepared in Examples 1 to 6 of the present invention are shown.

[0034] Figure 8 The XPS graph of the catalyst 0.8% Cu-CeO2 prepared in Example 1 of the present invention is shown.

[0035] Fig. 9 The graph shows the reaction performance data of the catalyst Cu-CeO2 prepared in Examples 1 to 6 of the present invention for the thermal catalysis of methanol and CO2.

[0036] Fig.10 The graph shows the performance data of the thermal catalytic reaction of methanol and CO2 of the catalyst 0.8% Cu-CeO2 prepared in Example 1 of the present invention and several catalysts in the prior art.

[0037] Fig.11 The performance data of the catalyst 0.8% Cu-CeO2 prepared in Example 1 of the present invention for thermally catalyzing methanol and CO2 at different reaction temperatures is shown.

[0038] Fig.12 The performance data diagrams of thermal catalysis and photothermal synergistic catalysis of the catalysts prepared in Examples 1 to 6 of the present invention are shown. DETAILED DESCRIPTION

[0039] The catalyst provided by the present invention is a catalyst of a substrate-loaded active metal, which can prepare dimethyl carbonate by heat and photothermal synergistic catalysis of methanol and carbon dioxide. Under the action of heat, the catalyst substrate is excited to produce high-energy electron-hole pairs with reduction-oxidation ability, and the active metal adsorbs and activates the reactants (methanol and carbon dioxide molecules) as active sites, while receiving electrons or holes, promoting the separation of electron-hole pairs, and causing the adsorbed reactant molecules to undergo redox reactions. Under the conditions of photothermal synergy, the reaction temperature and pressure can be reduced, and the low-temperature catalytic effect can be improved under illumination.

[0040] Specifically, Figure 1 The flow chart of the catalyst preparation method for preparing dimethyl carbonate by catalyzing methanol and carbon dioxide provided in an embodiment of the present invention is shown. The catalyst preparation method comprises the following steps:

[0041] S1. Use 80 mL of deionized water to prepare a precursor solution of soft template PVP with a concentration of 0.13-0.21 mg / mL, and stir for 1.5-2.5 h; add 0.9-1.2 g of the first metal salt, stir for 0.5-2.0 h, add 20-200 mg of the second metal salt, stir for 0.5-1.0 h, and obtain a mixed solution.

[0042] As an example, the first metal salt is a cerium salt, specifically cerium nitrate hexahydrate, and the concentration of cerium nitrate hexahydrate in the precursor solution is 0.1-0.5 g / mL; the second metal salt is a copper salt, specifically anhydrous copper nitrate, and the concentration of anhydrous copper nitrate in the precursor solution is 1.8-2.5 mg / mL; in the final catalyst, copper is the active metal and cerium oxide is the substrate.

[0043] S2, freeze-drying the mixed solution with liquid nitrogen to fix the solution into a fixed shape. Liquid nitrogen is placed in a plastic beaker, and the mixed solution is dripped into the liquid nitrogen drop by drop.

[0044] S3. Put the fixed and formed sample together with the plastic beaker into the freezer layer of the refrigerator to evaporate the liquid nitrogen in the beaker, and then quickly transfer it to a freeze dryer and keep it at -56°C for 48 to 72 hours, and then take it out to obtain the catalyst precursor.

[0045] The sample must be moved to the freeze dryer quickly to ensure that it does not melt, because the catalyst obtained after melting is not only not conducive to improving the efficiency of catalyzing methanol and carbon dioxide to produce dimethyl carbonate, but also affects the catalytic efficiency due to the poor uniformity between the Cu active metal and the CeO2 substrate.

[0046] S4. Grind the catalyst precursor into powder, spread it into a quartz boat, and then put it into a muffle furnace. Heat the muffle furnace from room temperature to 100-700°C at a heating rate of 1-6°C / min. Keep it warm for 1-5 hours and take it out to obtain catalyst sample particles.

[0047] The sample is taken out of the freeze dryer and placed in a muffle furnace to set the heating program. It must be kept warm after the temperature reaches 100°C. The purpose is to remove the water in the sample and prevent excessive water vapor in the heating environment from being unable to accurately control the defects of the CeO2 substrate and the size and valence of the Cu active metal. In addition, insulation is also required at 200°C and 300°C to release water vapor and fix the original soft template structure to be stable. After 300°C, the temperature can be directly raised to the sintering temperature, and the sintering temperature can be, for example, 450°C to 700°C. After a large number of experimental explorations, the embodiments of the present invention have found that the freeze-drying method is adopted and the stirring time after adding copper salt is controlled to be no more than 1h to control the fusion of the precursor solution and the catalytic substrate.

[0048] In the catalyst prepared by the above method, the loading amount of active metal copper is 0.2-2%, and the rest is cerium oxide substrate.

[0049] The catalyst for catalyzing methanol and carbon dioxide to produce dimethyl carbonate provided by the present invention, under the action of heat, excites the catalyst substrate to produce high-energy electron-hole pairs with reduction and oxidation capabilities, promotes the separation of electron-hole pairs between methanol and carbon dioxide molecules, and thermal energy is beneficial to the mass transfer between methanol and carbon dioxide molecules, and promotes the timely desorption of products. At the same time, the life of the charge is extended by thermal excitation to maintain the high efficiency and stability of the catalyst, and to achieve the purpose of producing dimethyl carbonate with high yield and high selectivity. In addition to thermal catalysis, the catalyst provided by the present invention can also perform photothermal synergistic catalysis.

[0050] like Figure 2 As shown, Figure 2 The process of using the catalyst provided by the present invention to catalyze methanol and carbon dioxide to produce dimethyl carbonate is shown as follows:

[0051] S11, loading methanol and catalyst into a reaction kettle reactor, and then purging the reactor with reaction gas (CO2) for 60 minutes;

[0052] S12, introducing 0.1-1.0 MPa of carbon dioxide, turning on the power, raising the temperature of the reactor to 70-260° C., so that the catalyst catalyzes methanol and carbon dioxide to produce dimethyl carbonate under thermal conditions or photothermal synergistic conditions. The light source under photothermal synergistic conditions is irradiated by a xenon lamp.

[0053] In specific implementation, before the catalyst is loaded into the reaction kettle reactor, the catalyst can be placed in a water-free glass dish and placed in a vacuum drying oven for drying. After the moisture of the catalyst is removed, it can be placed in the reactor.

[0054] In some embodiments, carbon dioxide is introduced into a closed reactor to exhaust other gases in the reactor. Carbon dioxide is fed into the reactor from the air inlet, and the carbon dioxide inlet flow rate is controlled by a flow meter at the air outlet at 1 to 15 mL / min to ensure that volatilization of anhydrous methanol aqueous solution is reduced.

[0055] In some embodiments, the power supply is 220V; the xenon lamp current is 5-15A.

[0056] In order to enable those skilled in the art to more clearly understand the present invention, the catalyst for preparing dimethyl carbonate from methanol and carbon dioxide, the preparation method and application thereof are described in detail through the following examples.

[0057] Example 1

[0058] Preparation of catalyst for the production of dimethyl carbonate from methanol and carbon dioxide:

[0059] 1) Add 12 g of PVP to 80 mL of deionized water and stir for 2.5 h as a catalyst PVP soft template, also known as a precursor solution;

[0060] 2) Add 1.1897 g of cerium nitrate hexahydrate to the above precursor solution and stir for 1.0 h; then add 0.0103 g of anhydrous copper nitrate and stir for 0.5 h to obtain a mixed solution;

[0061] 3) At room temperature, the mixed solution obtained in step 2) is evenly dropped into liquid nitrogen to fix the mixed solution instantly. After completion, the sample is placed in the freezer layer of a refrigerator to wait for the liquid nitrogen to evaporate;

[0062] 4) placing the mixture obtained in step 3) into a freeze dryer, evacuating to 20 Pa, cooling, and maintaining at -56°C for 72 h;

[0063] 5) Grind the solid obtained in step 4) into powder, transfer it to a muffle furnace, heat the muffle furnace from room temperature to 100°C, keep it warm for 3 hours; then heat it from 100°C to 200°C, keep it warm for 3 hours; then heat it from 200°C to 300°C, keep it warm for 3 hours; then heat it from 300°C to 500°C, keep it warm at 500°C for 6 hours, and obtain a catalyst (0.8% Cu-CeO2) for catalyzing methanol and carbon dioxide to produce dimethyl carbonate. The doping amount of Cu in the catalyst obtained in this embodiment is 0.8%. The heating rate is 2°C / min.

[0064] Figure 3 The TEM image of the catalyst 0.8% Cu-CeO2 prepared in this example is shown. Figure 3 The morphology of 0.8% Cu-CeO2 can be seen intuitively. The catalyst presents a lamellar structure and has a large specific surface area.

[0065] Figure 4 A high-resolution element distribution map of the catalyst 0.8% Cu-CeO2 prepared in this embodiment is shown. It can be seen from the figure that Cu is attached to the surface of cerium oxide in the form of single atoms, forming a unique microstructure. This highly dispersed single-atom structure greatly increases the number of catalytic active sites and provides a basis for efficient catalytic reactions.

[0066] Example 2

[0067] Compared with Example 1, the masses of cerium nitrate hexahydrate and anhydrous copper nitrate used in step 2) of this example are 1.17 g and 0.03 g respectively, and the doping amount of Cu in the final catalyst is 2.0%. Others are the same as in Example 1.

[0068] Example 3

[0069] Compared with Example 1, the masses of cerium nitrate hexahydrate and anhydrous copper nitrate used in step 2) of this example are 1.1796 g and 0.0204 g respectively, and the doping amount of Cu in the final catalyst is 1.6%. Others are the same as in Example 1.

[0070] Example 4

[0071] Compared with Example 1, the masses of cerium nitrate hexahydrate and anhydrous copper nitrate used in step 2) of this example are 1.1846 g and 0.0154 g respectively, and the doping amount of Cu in the final catalyst is 1.2%. Others are the same as in Example 1.

[0072] Example 5

[0073] Compared with Example 1, the masses of cerium nitrate hexahydrate and anhydrous copper nitrate used in step 2) of this example are 1.1948 g and 0.0052 g respectively, and the doping amount of Cu in the final catalyst is 0.4%. Others are the same as in Example 1.

[0074] Example 6

[0075] Compared with Example 1, in step 2), only 1.2 g of cerium nitrate hexahydrate is added, and anhydrous copper nitrate is not added, and the Cu doping amount in the final catalyst is 0%. Others are the same as in Example 1.

[0076] Figure 5 The XRD patterns of the catalysts Cu-CeO2 prepared in Examples 1 to 6 are shown. Figure 5 It can be seen that as the Cu doping amount in the catalyst changes, the crystal structure of the catalyst does not change.

[0077] Figure 6The in-situ infrared image of the catalyst 0.8% Cu-CeO2 prepared in Example 1 of the present invention is shown. Figure 6 It can be seen that as the temperature increases, the catalytic reaction capacity increases.

[0078] Figure 7 The ESR diagram of the catalyst Cu-CeO2 prepared in Examples 1 to 6 of the present invention is shown. Figure 7 The changes in oxygen vacancies after the introduction of Cu can be seen.

[0079] Figure 8 The XPS graph of the catalyst 0.8% Cu-CeO2 prepared in Example 1 of the present invention is shown. Figure 8 It can be seen that Ce in 0.8% Cu-CeO2 is Ce 4+ and Ce 3+ of mixed state.

[0080] Example 7

[0081] Performance test of the catalyst for the production of dimethyl carbonate from thermal catalysis of methanol and carbon dioxide:

[0082] The Cu-CeO2 catalysts prepared in Examples 1 to 6 were selected to verify the performance of catalyzing methanol and carbon dioxide to produce dimethyl carbonate:

[0083] The yield test of dimethyl carbonate produced by the reaction of methanol and carbon dioxide with Cu-CeO2 catalyst under thermal catalysis:

[0084] 50 mg of CeO2 catalyst prepared in Examples 1 to 6 were placed in the reactors respectively, anhydrous methanol was added and the reactors were sealed, CO2 was purged for 60 min, and after the purging, CO2 was introduced to raise the internal pressure of the reactor to 0.9 MPa. The power was turned on and the temperature was raised to 160°C. After the reaction was completed, the liquid phase product was collected, filtered, and then injected into the gas chromatograph with a syringe for detection.

[0085] Fig. 9 The thermal catalytic reaction performance data of methanol and carbon dioxide of the catalyst prepared in Examples 1 to 6 of the present invention are shown. Fig. 9 It can be seen that compared with the catalyst CeO2 in Example 6, the yield of the thermal catalytic reaction of methanol and carbon dioxide by the catalyst 0.8% Cu-CeO2 in Example 1 increased by 1.5 times to 29.9mmol / g, the selectivity was greater than 99%, and the yield was relatively stable in the experiment, indicating that the 0.8% Cu-CeO2 provided by the present invention has excellent catalytic activity and reaction stability. Under the condition of thermal catalysis, the yield of CeO2 is only 20.8mmol / g, which shows that the active metal Cu has a great promoting effect on the reaction of methanol and carbon dioxide to dimethyl carbonate catalyzed by 0.8% Cu-CeO2.

[0086] Example 8

[0087] The performance test of the catalyst 0.8% Cu-CeO2 prepared in Example 1 of the present application is compared with the catalyst prepared by the hydrothermal method in the prior art in the thermal catalysis of methanol and carbon dioxide to dimethyl carbonate. The catalysts prepared by the hydrothermal method in the prior art are CeO2-600, P-CeO2-NR, Fe / CeO2, and CeO2-ZrO2. The process of thermal catalysis of methanol and carbon dioxide to dimethyl carbonate by each catalyst is the same as that in Example 7.

[0088] Preparation of CeO2-600 catalyst, reference: Dimethyl Carbonate Synthesis from CO2 over CeO2 with Electron-Enriched Lattice Oxygen Species, Guoqiang Hou et al. Angewandte Chemie International Edition.

[0089] Preparation of P-CeO2-NR catalyst, reference: Atom-Economical Synthesis of DimethylCarbonate from CO2: Engineering Reactive Frustrated Lewis Pairs on Ceria with Vacancy Clusters. Lei Li et al. Angew. Chem. Int. Ed. 2022, 61, e202214490 (1 of 8).

[0090] Preparation of Fe / CeO2 catalyst, reference: Improvement of surface properties of metal doped-CeO2 nanospindle catalysts for direct synthesis of dimethylcarbonate from CO2 and methanol, Panpailin Seeharaj et al. Journal of Environmental Chemical Engineering 11 (2023) 109813.

[0091] Preparation of CeO2-ZrO2 catalyst, reference: CeO2–ZrO2 solid solution catalyst for selective synthesis of dimethyl carbonate from methanol and carbondioxide. Keiichi Tomishige et al. Catalysis Letters Vol.76,No.1–2,2001.

[0092] Fig.10 The performance data of each catalyst for thermal catalysis of methanol and carbon dioxide are shown in FIG. Fig.10 It can be seen that the catalytic reaction activities of the catalysts in the prior art are all lower than the performance of the catalyst of the present invention, which shows that the catalyst provided by the present invention has significant advantages.

[0093] Example 9

[0094] Take 50mg of 0.8% Cu-CeO2 prepared in Example 1 as a catalyst, fill it into an anhydrous glass dish and put it into a vacuum drying oven for drying. After removing the moisture of the catalyst, put it into a reactor. After adding 30mL of anhydrous methanol to the reactor and sealing it, purge the reactor with carbon dioxide for 60min, then pass into 0.9MPa of carbon dioxide, which is sent into the reactor from the air inlet. The carbon dioxide inlet flow rate is controlled at 10mL / min by the flow meter at the air outlet to ensure that the anhydrous methanol aqueous solution is reduced. The reactor is heated to 80°C and the pressure is set at 0.9MPa. After the end, the liquid product at the reactor outlet is collected and the product is injected into a gas chromatograph for detection with an injection.

[0095] Example 10

[0096] Compared with Example 9, in this embodiment, the reactor temperature is set to 100° C., and the rest is the same as Example 9.

[0097] Embodiment 11

[0098] Compared with Example 9, the reactor temperature in this embodiment is raised to 120° C., and the rest is the same as Example 9.

[0099] Example 12

[0100] Compared with Example 9, the reactor temperature in this embodiment is raised to 140° C., and the rest is the same as Example 9.

[0101] Example 13

[0102] Compared with Example 9, the reactor temperature in this example is raised to 180° C., and the rest is the same as Example 9.

[0103] Embodiment 14

[0104] Compared with Example 9, in this embodiment, the reactor temperature is set to rise to 200° C., and the rest is the same as Example 9.

[0105] The results of the comparison of the reaction performance of the catalyst 0.8% Cu-CeO2 prepared in Example 1 for the thermal catalysis of methanol and carbon dioxide to dimethyl carbonate at different temperatures are shown in Fig.11 .Depend on Fig.11 It can be seen that the DMC yields in Example 9 (80°C), Example 12 (140°C) and Example 13 (180°C) are 0.27, 22.7 and 24.4 mmol / g, respectively, while the DMC yield in Example 7 (160°C) is 29.9 mmol / g.

[0106] Embodiment 15

[0107] Take 50mg of Cu-CeO2 prepared in Examples 1 to 6 as a catalyst, fill it into anhydrous glass dishes and put it into a vacuum drying oven for drying. After removing the moisture of the catalyst, put it into a reactor, add 30mL of anhydrous methanol to the reactor and seal it. Then, purge the reactor with carbon dioxide for 60min, and then pass 0.9MPa of carbon dioxide. Carbon dioxide is sent into the reactor from the air inlet. The carbon dioxide inlet flow rate is controlled by the flow meter at the air outlet at 10mL / min and sent into the reactor to ensure that the anhydrous methanol aqueous solution is reduced. The reactor is heated to 100°C and the pressure is set at 0.9MPa. After the temperature stabilizes, the xenon lamp is turned on and the current is adjusted to 15A. Under separate thermal catalysis and photothermal synergistic catalysis, the reactions are carried out respectively. After the reaction, the liquid product at the reactor outlet is collected, and the product is injected into the gas chromatograph for detection with an injection.

[0108] Fig.12 The reaction performance data of the x% Cu-CeO2 (x=0, 0.4, 0.8, 1.2, 1.6, 2.0) catalysts provided in Examples 1 to 6 as well as the photothermal catalytic performance of methanol and carbon dioxide are shown. Fig.12 As shown, compared with the single thermal catalysis, under the photothermal synergistic catalysis, different contents of x% Cu-CeO2 cause the product yield to increase by 1.07, 1.01, 1.2, 1.1, 1.06 and 1.02 respectively (corresponding to x=0, 0.4, 0.8, 1.2, 1.6, 2.0 respectively). Obviously, the yield of the 0.8% Cu-CeO2 catalyst in Example 1 increased the most, indicating that the catalyst can generate more high-energy electrons and holes, selectively activate adsorbed molecules, promote product desorption, and at the same time prolong the life of photogenerated charges, increase the adsorption and desorption of carbon dioxide, and the interface structure of the catalyst is optimized, thereby having excellent efficiency.

[0109] In addition, the catalyst of the present invention has almost no catalytic activity decrease after repeated use, showing good repeatability and stability. This feature makes it have great advantages in practical applications and can bring long-term economic benefits to industrial production.

Claims

1. A method for preparing a catalyst for preparing dimethyl carbonate by low-pressure photothermal catalysis of CO2, characterized in that: The steps include: S1, prepare a soft template PVP solution with a concentration of 0.13-0.21 mg / mL; S2, adding cerium salt and copper salt to the soft template PVP solution, stirring evenly to obtain a mixed solution; S3, freeze-drying the mixed solution in liquid nitrogen to obtain a fixed sample; S4. Place the fixed sample in the freezer to allow the liquid nitrogen to evaporate completely; S5, transferring the fixed sample to a freeze dryer, keeping it at -56°C for 48 to 72 hours, and taking it out to obtain a catalyst precursor; S6. Grind the catalyst precursor into powder, then put it into a muffle furnace, heat the muffle furnace to 100-700°C at a heating rate of 1-6°C / min, keep it warm for 1-5 hours and then take it out to obtain a catalyst for low-pressure photothermal catalysis of CO2 to produce dimethyl carbonate.

2. The method for preparing a catalyst for preparing dimethyl carbonate by low-pressure photothermal catalysis of CO2 according to claim 1, characterized in that: When preparing the soft template PVP solution in step S1, stir for 1.5 to 2.5 hours.

3. The method for preparing a catalyst for preparing dimethyl carbonate by low-pressure photothermal catalysis of CO2 according to claim 1, characterized in that: In step S2, the cerium salt is cerium nitrate hexahydrate, and the copper salt is anhydrous copper nitrate.

4. The method for preparing a catalyst for preparing dimethyl carbonate by low-pressure photothermal catalysis of CO2 according to claim 1, characterized in that: In step S6, during the heating process of the muffle furnace, the temperature is raised from room temperature to 100°C and kept for 3 hours; then the temperature is raised from 100°C to 200°C and kept for 3 hours; then the temperature is raised from 200°C to 300°C and kept for 3 hours; then the temperature is raised from 300°C to 450°C~700°C and kept for 6 hours; the heating rate is 2°C / min.

5. A catalyst for preparing dimethyl carbonate from CO2 using low-pressure photothermal catalysis prepared by the method according to any one of claims 1 to 4.

6. The catalyst according to claim 5, characterized in that The proportion of copper in the catalyst is 0.2 to 2.0%.

7. Use of the catalyst according to claim 5 or 6 in catalyzing methanol and CO2 to produce dimethyl carbonate under thermal catalysis and photothermal catalysis conditions.

8. The use according to claim 7, characterized in that: The specific application steps are: loading the catalyst into a high-pressure reactor, then adding anhydrous methanol, purging the reactor with reaction gas CO2 for 60 minutes, heating the reactor to 70-260°C and setting the pressure at 0.1-1.0MPa; the catalyst catalyzes methanol and carbon dioxide to produce dimethyl carbonate under thermal conditions or photothermal conditions.

9. The use according to claim 8, characterized in that: Before the catalyst is loaded into the autoclave, the catalyst is vacuum dried at 60°C in a glass dish and then placed in the autoclave.

10. The use according to claim 8, characterized in that: The light source used in the photothermal condition is a xenon lamp, and the current of the xenon lamp is controlled to be 5-15A.

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