Modified CeO2 catalyst for preparing methanol as well as preparation method and application of modified CeO2 catalyst

Abstract

The preparation method comprises the following steps: dissolving m-tribenzoic acid in a mixed solution of ethanol and water at room temperature, mixing with a Ce (NO3) 3 aqueous solution, fully stirring, centrifuging, collecting a white precipitate, sequentially washing with deionized water and ethanol for several times until the supernatant is neutral, drying, grinding, and drying to obtain the modified CeO2 catalyst for methanol preparation. Roasting in an air atmosphere, preserving heat, cooling and grinding to obtain faint yellow CeO2 powder; the preparation method comprises the following steps: mixing and dissolving copper nitrate, zinc nitrate, ammonium fluoride and urea in a dispersion liquid of faint yellow CeO2 powder, performing ultrasonic stirring, performing hydrothermal reaction, naturally cooling to room temperature, performing centrifugal separation, washing with water and ethanol for multiple times, and performing vacuum drying to obtain a precursor; and calcining the precursor at 400 DEG C, keeping constant temperature, cooling, and grinding to obtain the black bimetallic CuZn loaded CeO2 catalyst. The CuZn / CeO2 catalyst has the advantages of high catalytic activity and the like, the preparation method is simple, rapid and efficient, and the CuZn / CeO2 catalyst has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide hydrogenation catalytic conversion technology, specifically to a modified CeO2 catalyst for preparing methanol, its preparation method, and its application. Background Technology

[0002] CO2 is a highly attractive renewable source of C1, but large amounts are emitted into the atmosphere each year, causing serious environmental and ecological problems and wasting resources. In recent years, the reuse of CO2 has attracted great interest and significant progress has been made. To date, CO2 has been successfully converted into fuels and chemical feedstocks, such as alkanes, formic acid, and methanol. Methanol is an important chemical transported and used worldwide; therefore, converting CO2 into methanol is a very promising method for addressing CO2 emissions and energy shortages.

[0003] Due to its tunable properties, cerium oxide, as a member of the rare earth oxide family, has attracted considerable attention for its use in many environmental applications. One of the many advantages of CeO2 is its higher abundance in the Earth's crust; it is more abundant than nickel and copper metals. Promising results from CeO2-based catalysts in CO2 conversion also provide a driving force for applying this unique material to the conversion of CO2 to methanol. Furthermore, the acid-base surface properties and reversible redox properties of CeO2 have been observed. 3+ / Ce 4+ This effectively expands the scope of its catalytic applications.

[0004] CeO2, as a rare earth material, has wide applications in catalysis, fuel cells, and ultraviolet absorbers due to its unique properties, with extensive research focused on the catalytic performance of CeO2 nanomaterials. Recent studies have revealed that the morphology of nanoscale CeO2 crystals strongly influences catalyst performance. According to Wolff's rule, different crystal morphologies correspond to different exposed crystal faces, which in turn affect surface composition and geometry. Larger specific surface areas and smaller sizes often exhibit better catalytic performance. Therefore, research on synthesizing CeO2 nanostructures with different morphologies (such as CeO2 nanooctahedrons, CeO2 nanowires, and CeO2 nanocubes) under various conditions as catalysts or catalytic supports is essential. Different morphologies often represent different surface structures and active sites, resulting in varying effects on catalysis. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a modified CeO2 catalyst for methanol preparation, its preparation method, and its application. This invention improves the catalytic activity of the catalyst by modifying and altering CeO2, and simultaneously enhances the specific surface area and effective active sites of the material through Ce-MOF-derived CeO2 nanorods, effectively improving the catalyst's effective catalytic specific surface area. CuZn further enhances the catalytic activity, thereby obtaining a highly active, selective, stable, and safe CO2 hydrogenation to methanol catalyst material.

[0006] To address the shortcomings of existing technologies, the technical solution adopted by this invention is as follows:

[0007] A method for preparing a modified CeO2 catalyst for methanol production includes the following steps:

[0008] Step 1: Dissolve Ce(NO3)3·6H2O in deionized water and stir until homogeneous to obtain Ce(NO3)3 aqueous solution; dissolve m-tribenzoic acid in a mixed solution of ethanol and water at room temperature, then mix with Ce(NO3)3 aqueous solution, continue stirring until fully mixed, centrifuge to collect white precipitate, then wash several times with deionized water and ethanol until the pH of the supernatant is 7.0, then dry at 60-80 ℃ for 12 h, take it out and grind to obtain white Ce-MOF powder; calcine the ground white Ce-MOF powder in an air atmosphere in a muffle furnace and keep it at that temperature for 2 h, cool and grind to obtain light yellow CeO2 powder;

[0009] Step 2: Place the pale yellow CeO2 powder in deionized water and ultrasonically stir until homogeneous to obtain a dispersion;

[0010] Step 3: Mix copper nitrate, zinc nitrate, ammonium fluoride and urea in a dispersion, ultrasonically stir for 30 min, transfer to a stainless steel autoclave lined with polytetrafluoroethylene for hydrothermal treatment, cool naturally to room temperature, centrifuge, wash with water and ethanol several times, and vacuum dry at 60 ℃ for 12 h to obtain the catalyst precursor, wherein the mass ratio of urea to ammonium fluoride is 1:4.

[0011] Step 4: Place the precursor in a covered quartz crucible in a muffle furnace, heat it to the target temperature of 400℃ at a rate of 3-10℃ / min and maintain the constant temperature for 4h. After cooling, grind to obtain a black bimetallic CuZn supported CeO2 catalyst.

[0012] Preferably, the molar ratio of Ce(NO3)3·6H2O to m-tribenzoic acid in step 1 is 1:1.

[0013] Preferably, the roasting temperature in step 1 is 400-600℃, the program temperature is set, and the program heating rate is 5℃ / min.

[0014] Preferably, the roasting temperature in step 1 is 500℃.

[0015] The modified CeO2 catalyst prepared by the above method has a nanorod-like structure. Numerous defects are formed on the surface, which enhances the catalyst's performance.

[0016] The application of the above-mentioned modified CeO2 catalyst in the hydrogenation of carbon dioxide to methanol.

[0017] As an improvement, the reaction feed gas for the application consists of CO2 and H2.

[0018] As an improvement, the flow rate ratio of CO2 to H2 is 1:2-3, the reaction temperature is 220-320 ℃, and the reaction pressure is 2-3.5 MPa.

[0019] Further improvements were made to the flow rate ratio of CO2 to H2, the reaction temperature, and the reaction pressure, which was 3 MPa.

[0020] Beneficial effects

[0021] Compared with existing technologies, the modified CeO2 catalyst for methanol preparation, its preparation method, and its application, as described in this invention, have the following advantages:

[0022] 1) This invention uses Ce-MOF as a precursor to synthesize rod-shaped CeO2 and grows bimetallic CuZn in situ on the surface of rod-shaped CeO2, successfully preparing CuZn / CeO2 rod-shaped catalyst.

[0023] 2) The catalyst of this invention exhibits excellent catalytic performance, with superior CO2 conversion and methanol selectivity. Compared with bimetallic supported catalysts of different ratios, the Cu:Zn=5:1 loading resulted in the highest space-time yield of methanol.

[0024] 3) The catalyst prepared by this invention through scientific formulation exhibits good catalytic activity under relatively mild reaction conditions, and the preparation method is simple, rapid, and efficient. It offers broad prospects for subsequent industrial applications and coupling with subsequent methanol conversion processes (MTO, MTG). Attached Figure Description

[0025] Figure 1 The activity test results of CuZn / CeO2 catalysts prepared under different parameters are shown in (a) carbon dioxide conversion, (b) methanol selectivity, (c) carbon monoxide selectivity, and (d) space-time yield.

[0026] Figure 2 XRD patterns of catalysts prepared under different parameters;

[0027] Figure 3These are TEM images of the corresponding products prepared in Example 2 of the present invention, where (a), (b), and (c) are the obtained CuZn. 0.2 The CuZn / CeO2 images are magnified sequentially, and defects are clearly visible. (d) is a 5nm image of the prepared CuZn / CeO2, where lattice fringes are clearly visible. (e), (f), (g), (h), and (i) are images of CuZn prepared in Example 2. 0.2 The EDS plot of / CeO2 shows that the elements are evenly distributed. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The present invention can be better understood from the following embodiments. However, those skilled in the art will readily understand that the specific material ratios, process conditions, and results described in the embodiments are for illustrative purposes only and should not, and will not, limit the present invention as described in detail in the claims.

[0029] Example 1

[0030] A method for preparing a modified CeO2 catalyst for methanol production includes the following steps:

[0031] Step 1: Dissolve 2.5 mM Ce(NO3)3·6H2O in 50 mL of deionized water and stir to obtain an aqueous solution of Ce(NO3)3. Then, add an equal volume (50 mL) of 2.5 mM m-tribenzoic acid to the solution at room temperature. Next, mix the two solutions and stir for 90 min. Centrifuge to collect the white precipitate. Wash the white precipitate several times with deionized water and ethanol until the pH of the supernatant is 7.0. Finally, dry at 60 °C for 12 h to obtain Ce-MOF.

[0032] The prepared Ce-MOF was placed in a muffle furnace under air atmosphere and calcined at 500 ℃. The programmed temperature was set with a heating rate of 5 ℃ / min. The calcination temperature was maintained for 2 h. After cooling, the mixture was ground to obtain a light yellow CeO2 powder.

[0033] Step 2: Take 0.2g of the pale yellow CeO2 powder obtained in Step 1, place it in deionized water, sonicate and stir to obtain a uniform dispersion.

[0034] Step 3: Mix 0.132g copper nitrate, 0.0132g zinc nitrate, 0.099g ammonium fluoride and 0.396g urea into the dispersion in Step 2, sonicate for 30 min, then transfer to a polytetrafluoroethylene-lined stainless steel high-pressure reactor and hydrothermally heat at 90 ℃ for 18 h. After naturally cooling to room temperature, centrifuge, wash several times with water and ethanol, and vacuum dry at 60 ℃ for 12 h to obtain the catalyst precursor.

[0035] Step 4: Place the precursor in a covered quartz crucible in a muffle furnace, heat it to the target temperature of 400℃ at a rate of 5℃ / min, and maintain the constant temperature for 4 h. After cooling, grind to obtain the catalyst, denoted as CuZn. 0.1 / CeO2.

[0036] Experiment Example 2

[0037] A method for preparing a modified CeO2 catalyst for methanol production includes the following steps:

[0038] Step 1: Dissolve 2.5 mM Ce(NO3)3·6H2O in 50 mL of deionized water and stir to obtain an aqueous solution of Ce(NO3)3. Then, add an equal volume (50 mL) of 2.5 mM m-tribenzoic acid to the solution at room temperature. Next, mix the two solutions and stir for 90 min. Centrifuge to collect the white precipitate, and wash it several times with deionized water and ethanol until the pH of the supernatant is 7.0. Finally, dry at 60 °C for 12 h to obtain Ce-MOF.

[0039] The prepared Ce-MOF was calcined in a muffle furnace under air atmosphere at 500 °C with a programmed temperature and a heating rate of 5 °C / min. The calcination was maintained at this temperature for 2 hours, followed by cooling and grinding to obtain a pale yellow CeO2 powder.

[0040] Step 2: Take 0.2g of the pale yellow CeO2 powder obtained in Step 1, place it in deionized water, sonicate and stir to obtain a uniform dispersion.

[0041] Step 3: Mix 0.132g copper nitrate, 0.0264g zinc nitrate, 0.108g ammonium fluoride and 0.432g urea into the dispersion in Step 2, sonicate for 30 min, then transfer to a polytetrafluoroethylene-lined stainless steel high-pressure reactor and hydrothermally heat at 90 ℃ for 18 h. After naturally cooling to room temperature, centrifuge and wash several times with water and ethanol, then vacuum dry at 60 ℃ for 12 h to obtain the catalyst precursor.

[0042] Step 4: Place the precursor in a covered quartz crucible in a muffle furnace, heat it to the target temperature of 400℃ at a rate of 5℃ / min, and maintain the constant temperature for 4 h. After cooling, grind to obtain the catalyst, denoted as CuZn. 0.2 / CeO2.

[0043] The catalyst prepared in this embodiment was tested, and the results are as follows: Figure 3 The TEM image shown. Among them, Figure 3 (a), (b), (c) and (d) are the obtained CuZn 0.2As the CeO2 crystal is magnified sequentially, defects become clearly visible, and lattice fringes are clearly discernible. Figure 3 (e), (f), (g), (h), and (i) are CuZn samples prepared in Example 2. 0.2 The EDS plot of / CeO2 shows that the elements are evenly distributed.

[0044] Example 3

[0045] A method for preparing a modified CeO2 catalyst for methanol production includes the following steps:

[0046] Step 1: Dissolve 2.5 mM Ce(NO3)3·6H2O in 50 mL of deionized water and stir to obtain an aqueous solution of Ce(NO3)3. Then, add an equal volume (50 mL) of 2.5 mM m-tribenzoic acid to the solution at room temperature. Next, mix the two solutions and stir for 90 min. Centrifuge to collect the white precipitate, and wash it several times with deionized water and ethanol until the pH of the supernatant is 7.0. Finally, dry at 60 °C for 12 h to obtain Ce-MOF. Place the prepared Ce-MOF in a muffle furnace under air atmosphere and calcine at 500 °C with a programmed temperature increase rate of 5 °C / min. Hold at the calcination temperature for 2 h, cool, and then grind to obtain a pale yellow CeO2 powder.

[0047] Step 2: Take 0.2g of the pale yellow CeO2 powder obtained in Step 1, place it in deionized water, sonicate and stir to obtain a uniform dispersion.

[0048] Step 3: 0.132g copper nitrate, 0.066g zinc nitrate, 0.135g ammonium fluoride and 0.54g urea were mixed and dissolved in the dispersion in Step 2. After ultrasonic stirring for 30 min, the mixture was transferred to a polytetrafluoroethylene-lined stainless steel high-pressure reactor and hydrothermally heated at 90 ℃ for 18 h. After naturally cooling to room temperature, the mixture was centrifuged, washed several times with water and ethanol, and vacuum dried at 60 ℃ for 12 h to obtain the catalyst precursor.

[0049] Step 4: Place the precursor prepared in Step 4 into a covered quartz crucible in a muffle furnace, heat it to the target temperature of 400℃ at a rate of 5℃ / min, and maintain the constant temperature for 4 h. After cooling, grind to obtain the catalyst, denoted as CuZn. 0.5 / CeO2.

[0050] The catalysts prepared in different embodiments of the present invention were tested, and the XRD test results are shown in Figure 2. The X-ray diffraction peaks of the CuZn / CeO2 powder are consistent with those of PDF#34-0394, and the material has a good crystal structure, indicating that the bimetallic CuZn loading does not affect CeO2. Furthermore, in Figure 2It can be seen that for different CuZn / CeO2 parameters, the diffraction peaks of CuO in the sample are present, while those of ZnO are absent. As Zn increases, the diffraction peaks of CuO shift to the right. Simultaneously, the sample exhibits the (111) peak of CeO2, and no other impurity phase diffraction peaks are observed, indicating that CuZn was successfully composited. x / CeO2 catalytic material.

[0051] Comparative Example 1

[0052] A method for preparing a Cu-supported CeO2 catalyst includes the following steps:

[0053] Step 1: Dissolve 2.5 mM Ce(NO3)3·6H2O in 50 mL of deionized water and stir to obtain an aqueous solution of Ce(NO3)3. Then, add an equal volume (50 mL) of 2.5 mM m-tribenzoic acid to the solution at room temperature. Next, mix the two solutions and stir for 90 min. Centrifuge to collect the white precipitate, and wash it several times with deionized water and ethanol until the pH of the supernatant is 7.0. Finally, dry at 60 °C for 12 h to obtain Ce-MOF. Place the prepared Ce-MOF in a muffle furnace under air atmosphere and calcine at 500 °C with a programmed temperature increase rate of 5 °C / min. Hold at the calcination temperature for 2 h, cool, and then grind to obtain a pale yellow CeO2 powder.

[0054] Step 2: Take 0.2g of the pale yellow CeO2 powder obtained in Step 1, place it in deionized water, sonicate and stir to obtain a uniform dispersion.

[0055] Step 3: Mix 0.132g copper nitrate, 0.09g ammonium fluoride and 0.36g urea in the dispersion from Step 2, sonicate for 30 min, transfer to a polytetrafluoroethylene-lined stainless steel high-pressure reactor and hydrothermally heat at 90 ℃ for 18 h. After naturally cooling to room temperature, centrifuge, wash several times with water and ethanol, and vacuum dry at 60 ℃ for 12 h to obtain the catalyst precursor.

[0056] Step 4: Place the precursor prepared in Step 3 into a covered quartz crucible in a muffle furnace, heat it to the target temperature of 400℃ at a rate of 5℃ / min, and maintain the constant temperature for 4 h. After cooling, grind to obtain the catalyst, denoted as Cu / CeO2.

[0057] For the catalysts CuZn in Examples 1-3 x Activity tests were performed on / CeO2 (x=0.1, 0.2, 0.5), and the specific experimental methods and results are as follows:

[0058] The catalyst activity was tested in a fixed-bed reactor (10 mm inner diameter stainless steel reaction tube). 0.1 g of catalyst and 1 g of quartz sand were weighed and mixed thoroughly before being placed in the reaction tube. Before the reaction, the catalyst was reduced at atmospheric pressure for 3 h under H2 gas at a flow rate of 50 mL / min. The reduction temperature was slightly higher than the reaction temperature. After reduction, the mixture was cooled to 150 °C, and a H2:CO2 volume ratio of 3:1 was introduced at a reaction pressure of 3 MPa and GHSV = 12000 mL / (g·h). The temperature was then increased to 220 °C, 240 °C, 260 °C, 280 °C, and 300 °C. After the reaction stabilized at each temperature, performance tests were performed. The reaction products were analyzed by gas chromatography. CO and CO2 were detected using a TCD detector, and methanol and other hydrocarbon gases were detected using an FID detector. The content of each component in the tail gas was quantitatively analyzed using the corrected area normalization method. The activity test results are as follows: Figure 1 As shown in the figure, the CuZn prepared in Example 2... 0.2 / CeO2 exhibits good catalytic activity.

[0059] In summary, this invention utilizes Ce-MOF-derived CeO2 nanorods to modify and enhance CuZn, thereby increasing the specific surface area and effective active sites of the material and effectively improving the catalyst's effective catalytic specific surface area. CuZn enhances catalytic activity, resulting in a highly active, selective, stable, and safe CO2 hydrogenation to methanol catalyst.

Claims

1. A method for preparing a modified CeO2 catalyst for methanol production, characterized in that, Includes the following steps: Step 1: Dissolve Ce(NO3)3·6H2O in deionized water and stir until homogeneous to obtain Ce(NO3)3 aqueous solution; dissolve m-tribenzoic acid in a mixed solution of ethanol and water at room temperature, then mix with Ce(NO3)3 aqueous solution, continue stirring until fully mixed, centrifuge to collect white precipitate, then wash several times with deionized water and ethanol until the pH of the supernatant is 7.0, then dry at 60-80℃ for 12 h, take it out and grind to obtain white Ce-MOF powder; calcine the ground white Ce-MOF powder in an air atmosphere in a muffle furnace and keep it at that temperature for 2 h, cool and grind to obtain light yellow CeO2 powder; Step 2: Place the pale yellow CeO2 powder in deionized water and ultrasonically stir until homogeneous to obtain a dispersion; Step 3: Mix copper nitrate, zinc nitrate, ammonium fluoride and urea in a dispersion, ultrasonically stir for 30 min, transfer to a stainless steel autoclave lined with polytetrafluoroethylene for hydrothermal treatment, cool naturally to room temperature, centrifuge, wash with water and ethanol several times, and vacuum dry at 60 ℃ for 12 h to obtain the catalyst precursor, wherein the mass ratio of urea to ammonium fluoride is 1:

4. Step 4: Place the precursor in a covered quartz crucible in a muffle furnace, heat it to the target temperature of 400℃ at a rate of 3-10℃ / min and maintain the constant temperature for 4h. After cooling, grind to obtain a black bimetallic CuZn supported CeO2 catalyst.

2. The method for preparing a modified CeO2 catalyst for methanol according to claim 1, characterized in that: In step 1, the molar ratio of Ce(NO3)3·6H2O to m-tribenzoic acid is 1:

1.

3. The method for preparing a modified CeO2 catalyst for methanol according to claim 1, characterized in that: In step 1, the roasting temperature is 400-600℃, the program temperature is set, and the program heating rate is 5℃ / min.

4. The method for preparing a modified CeO2 catalyst for methanol according to claim 1, characterized in that: The roasting temperature in step 1 is 500℃.

5. The modified CeO2 catalyst prepared by the method according to claim 1, characterized in that, The modified CeO2 catalyst has a nanorod-like structure.

6. The application of the modified CeO2 catalyst according to claim 5 in the hydrogenation of carbon dioxide to methanol, characterized in that, The reaction feed gas for the application consists of CO2 and H2.

7. The application according to claim 6, characterized in that, The flow rate ratio of CO2 to H2 is 1:2-3, the reaction temperature is 220-320 ℃, and the reaction pressure is 2-3.5 MPa.

8. The application according to claim 7, characterized in that, The flow rate ratio of CO2 to H2 is 1:3, the reaction temperature is 260℃, and the reaction pressure is 3 MPa.

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