An nt-ceo2 catalyst, a preparation method and application thereof

Abstract

The application provides a kind of NT-CeO2 catalyst and its preparation method and application, belong to catalytic technology field. Its characterized in that, the catalyst is prepared using hydrothermal-microwave assisted etching method and obtains defective NT-CeO2 nanorod material. The catalyst is used for catalyzing carbon dioxide and methanol to directly synthesize dimethyl carbonate, the conversion rate of raw material methanol is high, and the selectivity of target product dimethyl carbonate is high. The NT-CeO2 catalyst prepared by the method has the advantages of large specific surface area, rich defect site, low price, simple operation, easy separation and recovery of catalyst, and its surface properties are far superior to ordinary CeO2, and has good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of NT-CeO2 Catalyst and its preparation method and application, especially to a kind of defect-rich NT-CeO2 Catalyst and its preparation method and application in catalyzing carbon dioxide and methanol direct synthesis dimethyl carbonate. BACKGROUND

[0002] Dimethyl carbonate (DMC) is an organic compound of colorless transparent liquid, in the context of green chemistry and sustainable development, because of its low toxicity, excellent environmental performance is listed as green chemicals, widely used in chemical industry, medicine, battery and other fields. Not only can and alcohol, phenol and other chemical reactions, as the raw material of synthetic polycarbonate (PC), but also can replace phosgene, dimethyl sulfate and other toxic substances, is an important organic synthesis intermediate; Because it has high oxygen content, good solubility, low viscosity and high dielectric constant and other characteristics, in addition to reactivity applications, also be used for various non-reactive applications, such as electrolyte, gasoline additive, coating additive, etc. At present, the main production process of dimethyl carbonate is phosgene method, ester exchange method, urea alcoholysis method and methanol oxidation carbonylation method and carbon dioxide and methanol direct synthesis method. Among them, phosgene method because of the toxicity of raw materials and the corrosion of by-products has been eliminated in industrial production; Ester exchange method with epoxide or cyclic carbonate as raw material, toxic raw material, high production cost, lack of market competitiveness; Liquid phase methanol oxidation carbonylation method with CO, methanol and O2 as raw material, the reaction process is easy to explode; Urea alcoholysis method with urea and methanol as raw material, low yield and selectivity, by-product NH3 easy to adhere to the surface of catalyst leading to its deactivation; Carbon dioxide and methanol direct synthesis method is still in the basic research stage, the reaction process is limited by thermodynamics, DMC yield is low, but the reaction process is green, raw material cost is low, it is a route with atomic economy and potential. Through the development of carbon capture and utilization (CCU) to alleviate the environmental problem of carbon dioxide, carbon dioxide is converted into value-added products such as dimethyl carbonate. Therefore, once the carbon dioxide and methanol direct synthesis method is industrialized, not only realizes carbon reduction, but also produces economic benefits, further promotes the development of carbon chemical industry, at present, it is widely valued in laboratory and industrial production.

[0003] Cerium dioxide (CeO2) is widely used in the synthesis of dimethyl carbonate from carbon dioxide and methanol due to its excellent oxygen storage capacity, rich oxygen vacancies and rich acid-base properties. Austrian patent EP3204350A1 describes potassium carbonate as a catalyst for the direct synthesis of carbon dioxide and methanol to produce dimethyl carbonate at 60-140℃ and 2-12MPa, but requires an iodomethane co-catalyst, with a methanol conversion rate of about 25%. Indian patent IN2014DE02734A describes a cerium metal solid solution (Ce 1-x M x O 2-dM = Zr, Al, Sn, Ga, La, Zn, Co, Cu), the mass ratio of methanol to catalyst is as low as 20, and the reaction temperature is as high as 180 DEG C. Chinese patent CN117205910A uses cerium metal as a key active site, and metal lanthanum and zirconium as an additive supported on a CeO2 carrier, and is used for a direct synthesis reaction of carbon dioxide and methanol, with a methanol conversion rate of about 50%, a selectivity of about 80%, and a 2-cyanopyridine to methanol mass ratio of up to 3. Research has found that the defect site of cerium dioxide is a key catalytic active site of the reaction. At present, common methods for defecting cerium dioxide include a transition metal doping method and a chemical etching surface etching method. The transition metal doping method promotes the formation of defects by lattice distortion caused by metal doping, but too much doping of heteroatoms can cause a significant decrease in the crystallinity of cerium dioxide, and a decrease in catalytic performance, and limited doping of heteroatoms has not yet shown obvious improvement. The chemical etching surface etching method obtains defects by etching the surface of the material with chemicals such as acids, bases and strong reducing agents, but the use of etchants often involves toxic and harmful chemicals. The microwave method not only provides radiation energy to speed up the reaction process, but also provides uniform heat distribution to realize crystallization at low temperature and in a short time, and can obtain highly uniform materials. However, there has been no report on the preparation of defect-rich cerium dioxide by the microwave-assisted etching method and its application in the catalytic direct synthesis of dimethyl carbonate from carbon dioxide and methanol. SUMMARY

[0004] An object of the present application is to improve the problems and deficiencies in the prior art and provide a defect-rich NT-CeO2 catalyst, another object of the present application is to provide a preparation method of the catalyst, and still another object of the present application is to provide the application of the catalyst in the catalytic direct synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0005] The technical scheme of the present application is as follows: an NT-CeO2 catalyst is prepared by a hydrothermal-microwave-assisted etching method. 2 / g, Ce 3+ / (Ce 3+ +Ce 4+ ) surface atomic concentration is 35% to 65%, and the NT-CeO2 has a large specific surface area and rich defect sites, and its surface properties are much better than those of ordinary CeO2.

[0006] The present application also provides a preparation method of the NT-CeO2 catalyst.

[0007] (1) Preparation of CeO2: cerium metal salt is prepared into an aqueous solution A, and an alkali solution C is prepared; the solution A and the solution C are mixed uniformly; then hydrothermal treatment is performed, cooling, filtration, washing, drying, and grinding to obtain CeO2; wherein the molar ratio of alkali to cerium metal salt is (100-140): 1.

[0008] (2) Preparation of the NT-CeO2 catalyst: a cerium metal salt is prepared into an aqueous solution B, and then CeO2 is dispersed in the solution B; subsequently, etching, oxidation, re-deposition and crystallization processes are carried out through ultrasonic and microwave treatment; cooling, filtering, washing, drying, grinding and calcining are carried out to obtain the NT-CeO2 catalyst; wherein the molar ratio of the cerium metal salt to CeO2 is (2-6):1.

[0009] Preferably, the cerium metal salt in step (1) is any one of cerium nitrate, cerium chloride or cerium sulfate; the base is any one of sodium hydroxide or potassium hydroxide; the concentration of the solution A is 0.4-0.8 mol / L, and the concentration of the solution C is 6.0-12.0 mol / L; the hydrothermal reaction temperature is 80-140℃, and the hydrothermal reaction time is 12-30 h.

[0010] Preferably, the cerium metal salt in step (2) is any one of cerium nitrate, cerium chloride or cerium sulfate; the concentration of the solution B is 0.04-0.08 mol / L; the microwave reaction temperature is 40-120℃, the microwave reaction time is 0.1-2.0 h, and the microwave reaction power is 200-800 W; the calcination temperature is 400-700℃, the heating rate is 2-10℃ / min, and the calcination time is 2-6 h.

[0011] The application further provides the use of the above-mentioned NT-CeO2 catalyst in the direct synthesis of dimethyl carbonate from carbon dioxide and methanol. In a reaction kettle, the NT-CeO2 catalyst, methanol and 2-cyanopyridine dehydrating agent are sequentially added, carbon dioxide is used to replace the air in the kettle, and then the pressure is charged and the temperature is raised to the reaction temperature to start the reaction. After the reaction is completed, the catalyst is separated by centrifugation.

[0012] Preferably, the mass ratio of methanol to the NT-CeO2 catalyst is (80-280):1, and the mass ratio of 2-cyanopyridine to methanol is (0.1-2.5):1.

[0013] Preferably, the above-mentioned reaction temperature is 110-160℃, the reaction time is 2-6 h, and the carbon dioxide pressure after the pressure is charged is 3-7 MPa.

[0014] The application adopts a process harmless and green microwave method to assist in etching cerium dioxide, obtains nanorod-like cerium dioxide with a large specific surface area and rich defect sites, and applies it to the direct synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0015] Compared with the prior art, the application has the following beneficial effects:

[0016] (1) The synthesis method of the NT-CeO2 catalyst provided by the application has the advantages of simple equipment, convenient operation and mild conditions. The defective NT-CeO2 nanorod material is prepared by a microwave-assisted etching method. The NT-CeO2 has a large specific surface area and rich defects, and the surface properties are much better than those of ordinary CeO2.

[0017] (2) The NT-CeO2 catalyst provided by the application is a transition metal oxide catalyst. Compared with the existing potassium carbonate catalyst, the NT-CeO2 catalyst does not need an iodomethane promoter, reduces the production cost, and is more conducive to industrialized production.

[0018] (3) The NT-CeO2 catalyst provided by the application is used for directly synthesizing dimethyl carbonate from carbon dioxide and methanol, has a high methanol conversion rate, and is higher than 50% of the methanol conversion rate reported in the existing literature under the same reaction conditions. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is an XRD graph of NT-CeO2-1 prepared in Example 1.

[0020] Figure 2 is a TEM graph of NT-CeO2-1 prepared in Example 1.

[0021] Figure 3 is an N2 adsorption-desorption graph of NT-CeO2-1 prepared in Example 1.

[0022] Figure 4 is an XPS graph of NT-CeO2-1 prepared in Example 1. DETAILED DESCRIPTION

[0023] The application will be described in more detail by the following examples. These examples are only a description of the best mode of the application and do not have any limitation on the protection scope of the application.

[0024] Example 1

[0025] Step 1: Ce(NO3)3.6H2O was weighed and dissolved to prepare 10 mL of an aqueous solution A with a concentration of 0.40 mol / L. Then, NaOH was weighed and dissolved to prepare 62 mL of an aqueous solution C with a concentration of 9.00 mol / L. The aqueous solution A was added to the aqueous solution C and mixed uniformly, and then the solution was transferred to an autoclave, heated at 100℃ for 24 h, filtered and washed with deionized water and ethanol until the filtrate was neutral, dried, and ground in an agate mortar to obtain a CeO2 powder.

[0026] Step 2: Ce(NO3)3.6H2O was weighed and dissolved to prepare 80 mL aqueous solution B with a concentration of 0.04 mol / L. 0.001 mol CeO2 was weighed and added to solution B, and after ultrasonic dispersion, the solution was placed in a microwave reactor and reacted at 200 W and 100 ℃ for 0.5 h. The obtained solid was washed and dried, calcined in a muffle furnace at 500 ℃ for 5 h (the heating rate was 5 ℃ / min), and ground in an agate mortar to obtain NT-CeO2-1 powder.

[0027] The XRD characterization of the NT-CeO2-1 catalyst is shown in Figure 1 From the XRD pattern, it can be seen that NT-CeO2-1 has a standard cubic fluorite structure. Characteristic diffraction peaks appear at 28.5°, 33.1°, 47.5° and 56.3°, corresponding to (111), (200), (220) and (311) crystal face characteristic diffraction peaks, respectively, indicating that microwave-assisted etching does not change the crystal structure of CeO2. The TEM characterization of the NT-CeO2-1 catalyst is shown in Figure 2 From the TEM, it can be seen that the morphology of the prepared NT-CeO2-1 catalyst is nanorod-like. The N2 adsorption and desorption characterization of the NT-CeO2-1 catalyst is shown in Figure 3 From the BET, it can be seen that the prepared NT-CeO2-1 catalyst has a type II isotherm and a H3 type hysteresis loop, and is a typical mesoporous material. The specific surface area of NT-CeO2-1 is 157 m 2 / g. The XPS characterization of the NT-CeO2-1 catalyst is shown in Figure 4 The atomic concentration of Ce 3+ / (Ce 3+ +Ce 4+ ) on the surface of NT-CeO2-1 is 65%, which is much higher than the atomic concentration of Ce 3+ / (Ce 3+ +Ce 4+ ) on the surface of ordinary CeO2, indicating that the surface of NT-CeO2-1 has more abundant oxygen vacancies, and a defect-rich NT-CeO2 catalyst is successfully prepared.

[0028] Example 2

[0029] Step 1: Ce(SO4)2 was weighed and dissolved to prepare 10 mL aqueous solution A with a concentration of 0.53 mol / L. Then, K(OH) was weighed and dissolved to prepare 70 mL aqueous solution C with a concentration of 9.00 mol / L. Aqueous solution A was added to aqueous solution C and mixed uniformly, and then the solution was transferred to an autoclave and crystallized at 80 ℃ for 30 h. After filtration, the filtrate was washed with deionized water and ethanol until it was neutral, and then dried and ground in an agate mortar to obtain CeO2 powder.

[0030] Step 2: Weigh cerium nitrate hexahydrate and dissolve it to prepare 80 mL of aqueous solution B with a concentration of 0.07 mol / L. Weigh 0.0028 mol of CeO2 and add it to solution B. After ultrasonic dispersion, place it in a microwave reactor and react at 200 W and 80°C for 2 h. Wash and dry the obtained solid, calcine it in a muffle furnace at 400°C for 5 h (the heating rate is 10°C / min), and grind it in an agate mortar to obtain NT-CeO2-2 powder.

[0031] NT-CeO2-2 has a nanorod-like morphology and typical mesoporous structure, and its specific surface area is 120 m 2 / g, the surface Ce 3+ / (Ce 3 + +Ce 4+ atomic concentration is 35%.

[0032] Example 3

[0033] Step 1: Weigh cerium chloride and dissolve it to prepare 10 mL of aqueous solution A with a concentration of 0.63 mol / L. Then, weigh sodium hydroxide and dissolve it to prepare 126 mL of aqueous solution C with a concentration of 6.00 mol / L. Add aqueous solution A to aqueous solution C and mix well, and then transfer the solution to an autoclave and heat it at 120°C for crystallization for 20 h. Filter and wash with deionized water and ethanol until the filtrate is neutral. Dry and grind in an agate mortar to obtain CeO2 powder.

[0034] Step 2: Weigh cerium nitrate hexahydrate and dissolve it to prepare 60 mL of aqueous solution B with a concentration of 0.06 mol / L. Weigh 0.0012 mol of CeO2 and add it to solution B. After ultrasonic dispersion, place it in a microwave reactor and react at 800 W and 40°C for 1.5 h. Wash and dry the obtained solid, calcine it in a muffle furnace at 600°C for 2 h (the heating rate is 2°C / min), and grind it in an agate mortar to obtain NT-CeO2-3 powder.

[0035] NT-CeO2-3 has a nanorod-like morphology and typical mesoporous structure, and its specific surface area is 134 m 2 / g, the surface Ce 3+ / (Ce 3 + +Ce 4+ atomic concentration is 40%.

[0036] Example 4

[0037] Step 1 : Ce(N03)3.6H20 was weighed and dissolved to prepare 10 mL of aqueous solution A with a concentration of 0.50 mol / L. Then, NaOH was weighed and dissolved to prepare 63 mL of aqueous solution C with a concentration of 8.00 mol / L. Aqueous solution A was added to aqueous solution C and mixed uniformly, and then the solution was transferred to an autoclave, heated at 140 °C for crystallization for 12 h, filtered and washed with deionized water and ethanol until the filtrate was neutral, dried, and ground in a maroon mortar to obtain Ce02 powder.

[0038] Step 2: CeCl3 was weighed and dissolved to prepare 60 mL of aqueous solution B with a concentration of 0.08 mol / L. 0.0008 mol of Ce02 was added to solution B, ultrasonically dispersed, and then placed in a microwave reactor, reacted at 600 W and 110 °C for 0.1 h, and the obtained solid was washed and dried, calcined in a muffle furnace at 400 °C for 6 h with a temperature rising rate of 2 °C / min, and ground in a maroon mortar to obtain NT-Ce02-4 powder.

[0039] NT-Ce02-4 has a nanorod-like morphology and a typical mesoporous structure, and the specific surface area is 141 m 2 / g, the surface Ce 3+ / (Ce 3 + +Ce 4+ atomic concentration is 52%.

[0040] Example 5

[0041] Step 1 : Ce(N03)3.6H20 was weighed and dissolved to prepare 6 mL of aqueous solution A with a concentration of 0.60 mol / L. Then, K02 was weighed and dissolved to prepare 63 mL of aqueous solution C with a concentration of 8.00 mol / L. Aqueous solution A was added to aqueous solution C and mixed uniformly, and then the solution was transferred to an autoclave, heated at 100 °C for crystallization for 24 h, filtered and washed with deionized water and ethanol until the filtrate was neutral, dried, and ground in a maroon mortar to obtain Ce02 powder.

[0042] Step 2: Ce(S04)2 was weighed and dissolved to prepare 100 mL of aqueous solution B with a concentration of 0.05 mol / L. 0.001 mol of Ce02 was added to solution B, ultrasonically dispersed, and then placed in a microwave reactor, reacted at 400 W and 80 °C for 0.2 h, and the obtained solid was washed and dried, calcined in a muffle furnace at 500 °C for 5 h with a temperature rising rate of 5 °C / min, and ground in a maroon mortar to obtain NT-Ce02-5 powder.

[0043] NT-Ce02-5 has a nanorod-like morphology and a typical mesoporous structure, and the specific surface area is 155 m 2 / g, the surface Ce 3+ / (Ce 3 + +Ce4+ ) atomic concentration of 61%.

[0044] Example 6

[0045] Step 1 : Ce(NO3)3.6H2O was weighed and dissolved to prepare 4 mL of aqueous solution A with a concentration of 0.80 mol / L. Then, NaOH was weighed and dissolved to prepare 32 mL of aqueous solution C with a concentration of 10.0 mol / L. Aqueous solution A was added to aqueous solution C and mixed uniformly, and then the solution was transferred to an autoclave, heated at 100°C for crystallization for 24 h, filtered and washed with deionized water and ethanol until the filtrate was neutral, dried, and ground in a marver to obtain a CeO2 powder.

[0046] Step 2: Ce(NO3)3.6H2O was weighed and dissolved to prepare 80 mL of aqueous solution B with a concentration of 0.04 mol / L. 0.001 mol of CeO2 was added to solution B, ultrasonically dispersed, and then placed in a microwave reactor, reacted at 800 W and 100°C for 0.1 h, the obtained solid was washed and dried, calcined in a muffle furnace at 500°C for 5 h with a temperature rising rate of 5°C / min, and ground in a marver to obtain NT-CeO2-6 powder.

[0047] NT-CeO2-6 has a nanorod-like morphology and a typical mesoporous structure, and a specific surface area of 165 m 2 / g, a surface Ce 3+ / (Ce 3 + +Ce 4+ ) atomic concentration of 63%.

[0048] Example 7

[0049] Step 1 : Ce(NO3)3.6H2O was weighed and dissolved to prepare 15 mL of aqueous solution A with a concentration of 0.40 mol / L. Then, KOH was weighed and dissolved to prepare 65 mL of aqueous solution C with a concentration of 12.0 mol / L. Aqueous solution A was added to aqueous solution C and mixed uniformly, and then the solution was transferred to an autoclave, heated at 100°C for crystallization for 24 h, filtered and washed with deionized water and ethanol until the filtrate was neutral, dried, and ground in a marver to obtain a CeO2 powder.

[0050] Step 2: CeCl3 was weighed and dissolved to prepare 80 mL of aqueous solution B with a concentration of 0.04 mol / L. 0.001 mol of CeO2 was added to solution B, ultrasonically dispersed, and then placed in a microwave reactor, reacted at 500 W and 120°C for 0.3 h, the obtained solid was washed and dried, calcined in a muffle furnace at 500°C for 5 h with a temperature rising rate of 5°C / min, and ground in a marver to obtain NT-CeO2-7 powder.

[0051] NT-CeO2-6 has nanorod morphology and typical mesoporous structure, and the specific surface area is 180 m 2 / g, surface Ce 3+ / (Ce 3 + +Ce 4+ ) atomic concentration is 64%.

[0052] The NT-CeO2 is used as a catalyst to catalyze direct synthesis of dimethyl carbonate from carbon dioxide and methanol.

[0053] Application Example 1

[0054] 10 g of methanol, 0.05 g of NT-CeO2-2 catalyst and 2 g of 2-cyanopyridine dehydrating agent, i.e. the mass ratio of methanol to catalyst is 200:1, and the mass ratio of dehydrating agent to methanol is 0.2:1, are sequentially weighed and added into a high-pressure reaction kettle, carbon dioxide is used to replace air in the reaction kettle for 3 times, carbon dioxide is filled into the reaction kettle to a pressure of 4 MPa, the stirring speed is adjusted to 400 r / min, the temperature is increased to a reaction temperature of 120°C, the reaction is started, the reaction is carried out for 4 h, and the catalyst is separated by centrifugation after the reaction is completed. Gas chromatography analysis is performed on the liquid obtained in the reaction, the methanol conversion rate is 68.96%, and the dimethyl carbonate selectivity is 99.32%.

[0055] Application Example 2

[0056] 10 g of methanol, 0.05 g of NT-CeO2-2 catalyst and 2 g of 2-cyanopyridine dehydrating agent, i.e. the mass ratio of methanol to catalyst is 200:1, and the mass ratio of dehydrating agent to methanol is 0.2:1, are sequentially weighed and added into a high-pressure reaction kettle, carbon dioxide is used to replace air in the reaction kettle for 3 times, carbon dioxide is filled into the reaction kettle to a pressure of 4 MPa, the stirring speed is adjusted to 400 r / min, the temperature is increased to a reaction temperature of 120°C, the reaction is started, the reaction is carried out for 4 h, and the catalyst is separated by centrifugation after the reaction is completed. Gas chromatography analysis is performed on the liquid obtained in the reaction, the methanol conversion rate is 68.96%, and the dimethyl carbonate selectivity is 99.32%.

[0057] Application Example 3

[0058] Take 8 g of methanol, 0.05 g of NT-CeO2-3 catalyst and 4 g of 2-cyanopyridine dehydrating agent, i.e. the mass ratio of methanol to catalyst is 160:1 and the mass ratio of dehydrating agent to methanol is 0.5:1, in sequence, and add them into a high-pressure reaction kettle. Replace the air in the reaction kettle with carbon dioxide for 3 times. Fill carbon dioxide into the reaction kettle until the pressure is 5 MPa. Adjust the stirring speed to 400 r / min. Increase the temperature until the reaction temperature is 140 ℃. Start the reaction. After 3 h of reaction, separate the catalyst by centrifugation. Perform gas chromatography analysis on the obtained liquid. The methanol conversion rate is 77.31% and the dimethyl carbonate selectivity is 99.46%.

[0059] Application Example 4

[0060] Take 5 g of methanol, 0.05 g of NT-CeO2-4 catalyst and 5 g of 2-cyanopyridine dehydrating agent, i.e. the mass ratio of methanol to catalyst is 100:1 and the mass ratio of dehydrating agent to methanol is 1:1, in sequence, and add them into a high-pressure reaction kettle. Replace the air in the reaction kettle with carbon dioxide for 3 times. Fill carbon dioxide into the reaction kettle until the pressure is 6 MPa. Adjust the stirring speed to 400 r / min. Increase the temperature until the reaction temperature is 150 ℃. Start the reaction. After 2 h of reaction, separate the catalyst by centrifugation. Perform gas chromatography analysis on the obtained liquid. The methanol conversion rate is 85.78% and the dimethyl carbonate selectivity is 99.15%.

[0061] Application Example 5

[0062] Take 10 g of methanol, 0.08 g of NT-CeO2-5 catalyst and 16 g of 2-cyanopyridine dehydrating agent, i.e. the mass ratio of methanol to catalyst is 125:1 and the mass ratio of dehydrating agent to methanol is 1.6:1, in sequence, and add them into a high-pressure reaction kettle. Replace the air in the reaction kettle with carbon dioxide for 3 times. Fill carbon dioxide into the reaction kettle until the pressure is 7 MPa. Adjust the stirring speed to 400 r / min. Increase the temperature until the reaction temperature is 160 ℃. Start the reaction. After 3 h of reaction, separate the catalyst by centrifugation. Perform gas chromatography analysis on the obtained liquid. The methanol conversion rate is 80.72% and the dimethyl carbonate selectivity is 99.26%.

[0063] Application Example 6

[0064] Take 4 g of methanol, 0.05 g of NT-CeO2-6 catalyst and 8 g of 2-cyanopyridine dehydrating agent, i.e. the mass ratio of methanol to catalyst is 80:1 and the mass ratio of dehydrating agent to methanol is 2:1, in sequence, and add them into a high-pressure reaction kettle. Replace the air in the reaction kettle with carbon dioxide for 3 times. Fill the reaction kettle with carbon dioxide to a pressure of 6 MPa. Adjust the stirring speed to 400 r / min. Increase the temperature to a reaction temperature of 140°C. Start the reaction. After 5 h of reaction, separate the catalyst by centrifugation. Perform gas chromatography analysis on the obtained liquid. The conversion rate of methanol is 95.37% and the selectivity of dimethyl carbonate is 99.35%.

[0065] Application Example 7

[0066] Take 5 g of methanol, 0.05 g of NT-CeO2-7 catalyst and 12.5 g of 2-cyanopyridine dehydrating agent, i.e. the mass ratio of methanol to catalyst is 100:1 and the mass ratio of dehydrating agent to methanol is 2.5:1, in sequence, and add them into a high-pressure reaction kettle. Replace the air in the reaction kettle with carbon dioxide for 3 times. Fill the reaction kettle with carbon dioxide to a pressure of 6 MPa. Adjust the stirring speed to 400 r / min. Increase the temperature to a reaction temperature of 150°C. Start the reaction. After 4 h of reaction, separate the catalyst by centrifugation. Perform gas chromatography analysis on the obtained liquid. The conversion rate of methanol is 97.22% and the selectivity of dimethyl carbonate is 99.14%.

[0067] The results of the application examples are shown in Table 1.

[0068] Table 1. Results of application examples

[0069]

Claims

1. An NT-CeO2 catalyst, characterized in that... Defective NT-CeO2 nanorods were prepared using a hydrothermal-microwave assisted etching method; the specific surface area was 120–180 m². 2 / g,Ce 3+ / (Ce 3+ + Ce 4+ The surface atomic concentration is 35%~65%; it is prepared by the following method, the specific steps of which are as follows: (1) Preparation of CeO2: Prepare an aqueous solution A of cerium metal salt and then prepare an alkaline solution C; mix solution A and solution C evenly; then perform hydrothermal reaction, cooling, filtration, washing, drying, and grinding to obtain CeO2; wherein the molar ratio of alkali to cerium metal salt is (100~140):1; the hydrothermal reaction temperature is 80~140 ℃, and the hydrothermal reaction time is 12~30 h; (2) Preparation of NT-CeO2 catalyst: Prepare aqueous solution B with cerium metal salt, and then disperse CeO2 in solution B; Subsequently, ultrasound and microwave treatment occur, resulting in etching, oxidation, recrystallization, and crystallization processes. The catalyst was obtained by cooling, filtering, washing, drying, grinding, and calcining; wherein the molar ratio of cerium metal salt to CeO2 was (2~6):1; the microwave reaction temperature was 40~120 ℃, the microwave reaction time was 0.1~2.0 h, the microwave reaction power was 200~800 W; the calcination temperature was 400~700 ℃, the heating rate was 2~10 ℃ / min, and the calcination time was 2~6 h.

2. The NT-CeO2 catalyst according to claim 1, characterized in that, The cerium metal salt mentioned in step (1) is any one of cerium nitrate, cerium chloride, or cerium sulfate; the alkali is any one of sodium hydroxide or potassium hydroxide; the concentration of solution A is 0.4~0.8 mol / L, and the concentration of solution C is 6.0~12.0 mol / L.

3. The NT-CeO2 catalyst according to claim 1, characterized in that... The cerium metal salt mentioned in step (2) is any one of cerium nitrate, cerium chloride, or cerium sulfate; the concentration of solution B is 0.04~0.08 mol / L.

4. The application of the NT-CeO2 catalyst as described in claim 1 in the direct synthesis of dimethyl carbonate from carbon dioxide and methanol.

5. The application according to claim 4, characterized in that... NT-CeO2 catalyst, methanol, and 2-cyanopyridine dehydrating agent were added sequentially to the reactor. After replacing the air in the reactor with carbon dioxide, the reactor was pressurized and heated to the reaction temperature to start the reaction. After the reaction was completed, the catalyst was separated by centrifugation.

6. The application according to claim 5, characterized in that: The mass ratio of methanol to NT-CeO2 catalyst is (80~280):1, and the mass ratio of 2-cyanopyridine to methanol is (0.1~2.5):

1.

7. The application according to claim 5, characterized in that: The reaction temperature is 110~160 ℃, the reaction time is 2~6 h, and the carbon dioxide pressure after pressurization is 3~7 MPa.

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