Non-noble metal and rare earth metal composite doped oxide photocatalyst and method for preparing the same
By preparing a composite doped oxide photocatalyst of non-precious metals and rare earth metals, the problem of copper atom diffusion and aggregation under high temperature and high pressure was solved, achieving high activity and stable photocatalytic effect, which is suitable for photocatalytic preparation of products such as methane, methanol and formic acid.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YOUPENG (JIAXING) NEW MATERIALS TECH CO LTD
- Filing Date
- 2023-09-19
- Publication Date
- 2026-05-22
Smart Images
Figure CN117225395B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of photocatalyst technology, specifically relating to non-precious metal and rare earth metal composite doped oxide photocatalysts and their preparation methods. Background Technology
[0002] Reducing CO2 concentration in the air is a long-term and arduous task. Converting CO2 into energy substances such as methane, formic acid, and methanol through hydrogenation can further reduce carbon emissions while increasing product value, and has high economic potential.
[0003] Catalysts are crucial for the CO2 hydrogenation conversion. The activity, stability, and cost of a catalyst largely determine the yield and selectivity of the product. In recent years, many researchers have conducted extensive work on the preparation and modification of CO2 hydrogenation catalysts, with copper-based catalysts currently being the mainstream. However, under high temperature and pressure, copper atoms in copper-based catalysts diffuse and aggregate, leading to a reduction in catalytic active sites and a significant decrease in catalytic activity. Therefore, it is necessary to improve existing CO2 hydrogenation catalysts to expose more active sites, which is an important means of enhancing catalytic activity. By preparing materials with high specific surface area and high porosity and loading active metals onto their surfaces, the aggregation of active metals can be greatly reduced, thereby improving catalytic efficiency. Summary of the Invention
[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a non-precious metal and rare earth metal composite doped oxide photocatalyst, wherein the preparation method is a liquid-phase method or a solid-phase method.
[0005] The liquid phase method includes the following steps:
[0006] Step 1) Mixing and dissolving: Dissolve the non-precious metal source and rare earth metal source completely in anhydrous ethanol, and add the titanium source or silicon source. Stir well to obtain mixed solution A; add the pH adjuster to anhydrous ethanol, and add polyvinyl alcohol aqueous solution. Stir well to obtain mixed solution B.
[0007] Step 2) Hydrolysis of gel: Slowly add the mixed solution B obtained in step 1) to the mixed solution A, stir evenly, add a weak base solution, and let stand to hydrolyze to obtain a gel;
[0008] Step 3) High-temperature aging: Place the gel obtained in step 2) into an oven for high-temperature aging;
[0009] Step 4) Solution replacement: After aging, the gel is placed in the prepared replacement solution and soaked for a period of time;
[0010] Step 5) Drying: Dry the gel after step 4) to obtain a non-precious metal and rare earth metal composite doped oxide aerogel.
[0011] Step 6) High-temperature heat treatment: The oxide aerogel obtained in step 5) is placed in a high-temperature tube furnace for heat treatment to obtain a non-precious metal and rare earth metal composite doped oxide photocatalyst with catalytic performance.
[0012] The solid-state method includes the following steps:
[0013] Step a: Mixing: Mix the non-precious metal source and the rare earth metal source together, then add silica aerogel or titanium dioxide aerogel, and mix them evenly in a mortar or ball mill.
[0014] Step b: Drying: The mixture obtained in step a is dried to obtain an oxide that is composite doped with non-precious metals and rare earth metals.
[0015] Step c: High-temperature heat treatment: The oxide obtained in step b is placed in a high-temperature tube furnace for heat treatment to obtain a non-precious metal and rare earth metal composite doped oxide photocatalyst with catalytic properties.
[0016] As a preferred embodiment of the above technical solution, the non-precious metal source is one or more of copper, zinc, aluminum, zirconium, or indium; the rare earth metal source is one of cerium, scandium, yttrium, or lanthanum; the titanium source is at least one of tetrabutyl titanate, titanium tetrachloride, tetraisopropyl titanate, or titanium isopropoxide; the silicon source is tetraethyl silicate or silane; the pH adjuster is glacial acetic acid; the weak alkaline solution is formamide or ammonia; and the mass fraction of the polyvinyl alcohol aqueous solution is 1%-5%.
[0017] As a preferred embodiment of the above technical solution, the copper source is at least one of copper nitrate, copper sulfate, and copper chloride; the zinc source is at least one of zinc nitrate, zinc sulfate, and zinc chloride; the aluminum source is at least one of aluminum nitrate, aluminum sulfate, and aluminum chloride; the zirconium source is at least one of zirconium nitrate, zirconium sulfate, and zirconium chloride; the indium source is at least one of indium nitrate, indium sulfate, and indium chloride; the cerium source is cerium nitrate or cerium sulfate; the lanthanum source is lanthanum nitrate or lanthanum sulfate; the scandium source is scandium nitrate or scandium sulfate; and the yttrium source is yttrium nitrate or yttrium sulfate.
[0018] As a preferred embodiment of the above technical solution, the molar ratio of non-precious metals to titanium or silicon in the mixed solution A is 1:1 to 10, the molar ratio of rare earth metals to titanium or silicon is 1:1 to 10, and the pH of the mixed solution B is adjusted to 4 to 5.
[0019] As a preferred embodiment of the above technical solution, the high-temperature aging temperature in step 3) is 60-80°C, and the aging time is at least 6 hours.
[0020] As a preferred embodiment of the above technical solution, the replacement solution is a 40% (v / v) aqueous solution of tert-butanol or a 50% (v / v) aqueous solution of ethanol.
[0021] As a preferred embodiment of the above technical solution, the drying in step 5) or the drying in step b is drying at room temperature and pressure, or freeze drying, or supercritical drying.
[0022] As a preferred embodiment of the above technical solution, the drying time at room temperature and pressure is 24h to 30h, the freeze-drying time is 20h to 24h, and the supercritical drying time is 7h to 10h.
[0023] As a preferred embodiment of the above technical solution, the temperature of the high-temperature heat treatment in step 6) or step c is 200℃~800℃, and the holding time is 2h~6h.
[0024] The non-precious metal and rare earth metal composite doped oxide photocatalyst was prepared by the above-described preparation method.
[0025] The beneficial effects of this invention are: This invention uses a liquid-phase method or a solid-phase method to achieve uniform doping of metal elements into oxides, resulting in a photocatalyst with a high specific surface area, uniform metal element dispersion, high photocatalytic activity, and long service life. It is particularly suitable for photocatalytic reaction processes and has good application prospects in the fields of photocatalytic preparation of methane, methanol, and formic acid. Attached Figure Description
[0026] Figure 1 This is a scanning electron microscope image of the prepared copper and cerium-doped titanium dioxide photocatalyst;
[0027] Figure 2 This is the XRD pattern of the prepared copper and cerium-doped titanium dioxide photocatalyst. Detailed Implementation
[0028] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0029] Example 1
[0030] In this embodiment, the molar ratio of copper:cerium:titanium is 3:2:5. 1.066g of copper nitrate trihydrate and 1.277g of cerium nitrate hexahydrate were added to 5ml of anhydrous ethanol, along with 2.5ml of tetrabutyl titanate. The mixture was stirred until homogeneous, yielding solution A. 0.1ml of glacial acetic acid was added to 5ml of anhydrous ethanol, along with 0.8ml of a 1% (w / w) polyvinyl alcohol aqueous solution. The mixture was stirred until homogeneous, yielding solution B. Solution B was slowly added to solution A, and after stirring until homogeneous, 1ml of formamide solution was added. The mixture was allowed to stand for 30 minutes before hydrolyzing the gel. The hydrolysis equation for tetrabutyl titanate is as follows:
[0031] Ti(O-CH4)4+H2O→Ti(O-CH4)3(OH)+C4H9OH
[0032] Ti(O-CH4)3(OH)+H2O→Ti(O-CH4)2(OH)2+C4H9OH
[0033] Ti(O-CH4)2(OH)2+H2O→Ti(O-CH4)(OH)3+C4H9OH
[0034] Ti(O-CH4(OH)3+H2O→Ti(OH)4+C4H9OH
[0035] The overall reaction equation is as follows:
[0036] Ti(O-CH4)4+4H2O→Ti(OH)4+4C4H9OH
[0037] The obtained gel was subjected to high-temperature aging in an oven at 60°C for 6 hours. After aging, the gel was placed in a 40% (v / v) tert-butanol aqueous solution, and the solution was replaced every 12 hours for a total of three times. After replacement, the resulting gel was freeze-dried in a vacuum freeze dryer for 12 hours to obtain titanium dioxide aerogel. The titanium dioxide aerogel was then heat-treated in a high-temperature tube furnace at 500°C for 3 hours to obtain a copper and cerium-doped titanium dioxide photocatalyst with catalytic properties.
[0038] Scanning electron microscope images of copper and cerium-doped titanium dioxide photocatalysts are shown below. Figure 1 As shown, its XRD pattern is as follows. Figure 2 As shown.
[0039] Using the copper and cerium-doped titanium dioxide photocatalyst prepared in the above examples, an experiment was conducted to produce methanol via carbon dioxide hydrogenation. The CO2 inlet rate was 20 ml / min, the H2 inlet rate was 60 ml / min, the reaction temperature was 300℃, and the reaction pressure was 5 MPa. The CO2 conversion rate was measured to be 30%, and the methanol selectivity was 62%. Titanium dioxide itself is an excellent photocatalyst with a band gap of 3.2 eV, capable of absorbing photons, exciting electron transitions, and forming electrons and holes. Titanium dioxide exhibits synergistic effects with rare earth metals, resulting in excellent catalytic performance.
[0040] Example 2
[0041] In this embodiment, the molar ratio of zinc:lanthanum:titanium is 3:2:5. 1.325g of zinc nitrate hexahydrate and 1.273g of lanthanum nitrate hexahydrate were added to 5ml of anhydrous ethanol, along with 2.5ml of tetraisopropyl titanate. The mixture was stirred until homogeneous to obtain mixed solution A. 0.1ml of glacial acetic acid was added to 5ml of anhydrous ethanol, along with 1ml of a 2% (w / w) polyvinyl alcohol aqueous solution. The mixture was stirred until homogeneous to obtain mixed solution B. Mixed solution B was slowly added to mixed solution A. After stirring until homogeneous, 1.2ml of formamide solution was added. The mixture was allowed to stand for 20 minutes before hydrolyzing the gel.
[0042] The obtained gel was subjected to high-temperature aging in an oven at 70°C for 7 hours. After aging, the gel was placed in a 40% (v / v) tert-butanol aqueous solution, and the solution was replaced every 12 hours for a total of three times. After replacement, the resulting gel was freeze-dried in a vacuum freeze dryer for 12 hours to obtain titanium dioxide aerogel. The titanium dioxide aerogel was then heat-treated in a high-temperature tube furnace at 200°C for 2 hours to obtain a zinc and lanthanum-doped titanium dioxide photocatalyst with catalytic properties.
[0043] Using the zinc and lanthanum-doped titanium dioxide photocatalysts prepared in the above examples, experiments were conducted on the hydrogenation of carbon dioxide to methanol. The CO2 inlet rate was 20 ml / min, the H2 inlet rate was 60 ml / min, the reaction temperature was 300℃, and the reaction pressure was 5 MPa. The CO2 conversion rate was measured to be 27%, and the methanol selectivity was 55%. Compared with Example 1, the catalytic performance of the zinc and lanthanum-doped titanium dioxide photocatalyst was not as good as that of the copper and cerium-doped titanium dioxide photocatalyst. This is because the incorporation of cerium atoms can introduce oxygen vacancies, as cerium atoms possess Ce. 3+ and Ce 4+During the conversion of two ions, holes are generated, forming oxygen vacancies. An oxygen atom on CO2 readily occupies an oxygen vacancy, leading to CO2 adsorption. This increases the adsorption energy of CO2, making it easier to activate and reduce, ultimately increasing the CO2 conversion rate. Simultaneously, copper atoms act as the active phase in the hydrogenation of carbon dioxide to methanol; increasing the amount of copper incorporated will improve the methanol yield.
[0044] Example 3
[0045] In this embodiment, the molar ratio of zirconium:yttrium:titanium is 1:1:10. 0.46 g of zirconium nitrate pentahydrate and 0.71 g of yttrium nitrate hexahydrate were added to 5 ml of anhydrous ethanol, followed by 5 ml of titanium tetrachloride. The mixture was stirred until homogeneous to obtain mixed solution A. 0.1 ml of glacial acetic acid was added to 5 ml of anhydrous ethanol, followed by 0.8 ml of a 3% (w / w) polyvinyl alcohol aqueous solution. The mixture was stirred until homogeneous to obtain mixed solution B. Mixed solution B was slowly added to mixed solution A, and after stirring until homogeneous, 1 ml of formamide solution was added. The mixture was allowed to stand for 50 min before hydrolyzing the gel.
[0046] The obtained gel was subjected to high-temperature aging in an oven at 80°C for 8 hours. After aging, the gel was placed in a 50% (v / v) ethanol aqueous solution, and the tert-butanol aqueous solution was replaced every 12 hours for a total of three replacements. After replacement, the resulting gel was dried in air at room temperature and pressure for 24 hours to obtain titanium dioxide aerogel. The titanium dioxide aerogel was then heat-treated in a high-temperature tube furnace at 400°C for 4 hours to obtain a zirconium and yttrium-doped titanium dioxide photocatalyst with catalytic properties.
[0047] Using the zirconium and yttrium-doped titanium dioxide photocatalyst prepared in the above examples, an experiment was conducted to produce formic acid via carbon dioxide hydrogenation. The CO2 inlet rate was 30 ml / min, the H2 inlet rate was 30 ml / min, the reaction temperature was 250°C, and the reaction pressure was 3 MPa. The CO2 conversion rate was measured to be 20%, and the formic acid selectivity was 35%. Compared with Example 1, it was found that the zirconium and yttrium-doped titanium dioxide photocatalyst obtained by drying at room temperature and pressure had lower catalytic performance, mainly reflected in the low CO2 conversion rate. This is because drying at room temperature and pressure causes the aerogel cavities to collapse, the structure to be destroyed, resulting in a lower specific surface area and a significant decrease in catalytic performance.
[0048] Example 4
[0049] In this embodiment, the molar ratio of indium:scandium:silicon is 1:1:1. 1.215 g of indium nitrate pentahydrate and 1.284 g of scandium nitrate hexahydrate were added to 5 ml of anhydrous ethanol, along with 2.5 ml of tetraethyl silicate. The mixture was stirred until homogeneous to obtain mixed solution A. 0.3 ml of glacial acetic acid was added to 5 ml of anhydrous ethanol, along with 1 ml of 5% (w / w) polyvinyl alcohol aqueous solution. The mixture was stirred until homogeneous to obtain mixed solution B. Mixed solution B was slowly added to mixed solution A. After stirring until homogeneous, 1.5 ml of formamide solution was added. The mixture was allowed to stand for 20 minutes before hydrolyzing the gel.
[0050] The obtained gel was subjected to high-temperature aging in an oven at 70°C for 6 hours. After aging, the gel was placed in a 40% (v / v) tert-butanol aqueous solution, and the solution was replaced every 12 hours for a total of three times. After replacement, the resulting gel was freeze-dried in a vacuum freeze dryer for 12 hours to obtain silica aerogel. The silica aerogel was then heat-treated in a high-temperature tube furnace at 800°C for 8 hours to obtain an indium and scandium-doped silica photocatalyst with catalytic properties.
[0051] Using the indium and scandium-doped silica photocatalyst prepared in the above examples, an experiment was conducted to produce methane from carbon dioxide hydrogenation. The CO2 inlet rate was 10 ml / min, the H2 inlet rate was 40 ml / min, the reaction temperature was 200 °C, and the reaction pressure was 3 MPa. The CO2 conversion rate was found to be 80%, and the methane selectivity was 90%.
[0052] Example 5
[0053] In this embodiment, the molar ratio of copper:cerium:titanium is 2:3:5. 1.066g of copper sulfate and 1.277g of cerium sulfate were mixed together, and 2.5g of titanium dioxide aerogel was added. The mixture was thoroughly ground in a ball mill, and then dried at room temperature and pressure for 6 hours. The resulting metal-doped oxide was then heat-treated in a muffle furnace at 600°C for 3 hours to obtain a copper and cerium-doped titanium dioxide photocatalyst with catalytic properties.
[0054] Using the copper and cerium-doped titanium dioxide photocatalyst prepared in the above examples, an experiment was conducted to produce methanol from carbon dioxide hydrogenation. The CO2 inlet rate was 20 ml / min, the H2 inlet rate was 60 ml / min, the reaction temperature was 300℃, and the reaction pressure was 5 MPa. The CO2 conversion rate was 40%, and the methanol selectivity was 30%.
[0055] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make many modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experimentation on the basis of the prior art should be within the scope of protection defined by the claims.
Claims
1. A method for preparing a non-precious metal and rare earth metal composite doped oxide photocatalyst, characterized in that, The preparation method is either a liquid-phase method or a solid-phase method. The liquid phase method includes the following steps: Step 1) Mixing and Dissolving: Completely dissolve the non-precious metal source and rare earth metal source in anhydrous ethanol, and add the titanium source or silicon source, stir evenly to obtain mixed solution A; add the pH adjuster to anhydrous ethanol, and add a 1%-5% (w / w) polyvinyl alcohol aqueous solution, stir evenly to obtain mixed solution B. The molar ratio of non-precious metal element to titanium or silicon element in mixed solution A is 1:1-10, and the molar ratio of rare earth metal element to titanium or silicon element is 1:1-10. The pH of mixed solution B is adjusted to 4-5, and the molar ratio of rare earth metal to titanium or silicon is 1:1-10. The pH of mixed solution B is adjusted to 4-5. Step 2) Hydrolysis of gel: Slowly add the mixed solution B obtained in step 1) to the mixed solution A, stir evenly, add a weak base solution, and let stand to hydrolyze to obtain a gel; Step 3) High-temperature aging: Place the gel obtained in step 2) into an oven and age it at 60-80°C for at least 6 hours. Step 4) Solution replacement: After aging, the gel is placed in the prepared replacement solution and soaked for a period of time. The replacement solution is a 40% volume fraction aqueous solution of tert-butanol or a 50% volume fraction aqueous solution of ethanol. Step 5) Drying: The gel treated in step 4) is dried by freeze drying for 20-24 hours or by supercritical drying for 7-10 hours to obtain a non-precious metal and rare earth metal composite doped oxide aerogel. Step 6) High-temperature heat treatment: The oxide aerogel obtained in step 5) is placed in a high-temperature tube furnace for heat treatment. The temperature of the high-temperature heat treatment is 200℃~800℃ and the holding time is 2h~6h to obtain a non-precious metal and rare earth metal composite doped oxide photocatalyst with catalytic performance. Wherein, the non-precious metal source is one or more of copper, zinc, aluminum, zirconium, or indium; the rare earth metal source is one of cerium, scandium, yttrium, or lanthanum; the titanium source is at least one of tetrabutyl titanate, titanium tetrachloride, tetraisopropyl titanate, or titanium isopropoxide; the silicon source is tetraethyl silicate or silane; the pH adjuster is glacial acetic acid; and the weak alkaline solution is formamide or ammonia. The solid-state method includes the following steps: Step a: Mixing: Mix the non-precious metal source and the rare earth metal source together, then add silica aerogel or titanium dioxide aerogel, and mix them evenly in a mortar or ball mill. Step b: Drying: The mixture obtained in step a is dried to obtain an oxide that is composite doped with non-precious metals and rare earth metals. Step c: High-temperature heat treatment: The oxide obtained in step b is placed in a high-temperature tube furnace for heat treatment to obtain a non-precious metal and rare earth metal composite doped oxide photocatalyst with catalytic properties.
2. The preparation method of the non-noble metal and rare earth metal composite doped oxide photocatalyst according to claim 1, characterized in that, The copper source is at least one of copper nitrate, copper sulfate, and copper chloride; the zinc source is at least one of zinc nitrate, zinc sulfate, and zinc chloride; the aluminum source is at least one of aluminum nitrate, aluminum sulfate, and aluminum chloride; the zirconium source is at least one of zirconium nitrate, zirconium sulfate, and zirconium chloride; the indium source is at least one of indium nitrate, indium sulfate, and indium chloride; the cerium source is cerium nitrate or cerium sulfate; the lanthanum source is lanthanum nitrate or lanthanum sulfate; the scandium source is scandium nitrate or scandium sulfate; and the yttrium source is yttrium nitrate or yttrium sulfate.