Preparation method and application of hollow multi-shell metal oxide catalyst

Abstract

The invention discloses a preparation method and application of a hollow multi-shell metal oxide catalyst, the catalyst is a Pd-CoOx-C spherical catalyst taking a carbon sphere carrier as a substrate, cobalt nitrate as a cobalt source and sodium tetrachloropalladate as a palladium source, and the catalyst is applied to catalytic oxidation of toluene and methyl ethyl ketone. The preparation method of the catalyst comprises the following steps: preparing the uniformly dispersed carbon sphere carrier by using a hydrothermal method; the Pd-CoOx-C spherical catalyst is prepared by taking the carbon sphere carrier as a substrate, cobalt nitrate as a cobalt source, sodium tetrachloropalladate as a palladium source and ethanol as a solvent through a hydrothermal method. Pd-CoOx-C ball solid powder obtained through centrifugation and drying is placed in a muffle furnace to be heated and roasted at different heating rates and subjected to heat preservation, and the hollow multi-shell metal oxide catalyst can be obtained. The hollow multi-shell Pd-Co3O4 catalyst has the characteristics of simple preparation process, low cost, high yield, regular and controllable catalyst morphology and the like. The hollow multi-shell Pd-Co3O4 catalyst prepared by the invention shows excellent catalytic performance on toluene and methyl ethyl ketone oxidation.

Description

Technical Field

[0001] The invention belongs to the field of functional material applications, and in particular relates to a preparation method and application of hollow multi-shell metal oxide catalysts. Background Art

[0002] With the continuous development of industry, the emission of volatile organic compounds (VOCs) is increasing day by day, especially in the coating industry. The emission of VOCs is complex and has a great impact on the environment and human health. Long-term exposure can cause bone marrow and genetic damage. Blood examination can find leukopenia, thrombocytopenia, pancytopenia and aplastic anemia, and even leukemia. The most common toluene and methyl ethyl ketone are the most serious, so they are urgently needed to be eliminated. The catalytic oxidation method can control the emission of volatile organic compounds by completely eliminating VOCs with its advantages of energy saving, environmental protection, simple equipment and low operating cost. The key is the preparation of efficient catalysts.

[0003] Factors that restrict the activity of catalysts generally include specific surface area, surface oxygen species, surface oxygen vacancies, etc. Previous studies have shown that spherical catalysts have higher specific surface area and higher electron transfer efficiency than general catalysts. By improving the preparation of spherical catalysts, it is expected to obtain catalyst samples with higher activity. Based on the factors that restrict the activity of the catalyst, carbon spheres are selected as the substrate, and nitrates or nitrates + precious metal salts are deposited on the surface. Through heat treatment and doping, the carbon spheres are burned off to expose more active sites, thereby improving the contact between toluene and methyl ethyl ketone and the active sites, thereby obtaining a hollow multi-shell catalyst that is more efficient in eliminating toluene and methyl ethyl ketone. Summary of the invention

[0004] In order to overcome the above shortcomings, the present invention provides a preparation method and application of a hollow multi-shell metal oxide catalyst, so as to better apply the hollow multi-shell catalyst to eliminate multi-component VOCs.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: Application of hollow multi-shell metal oxide catalyst, wherein the catalyst is Pd-CoO with carbon ball carrier as substrate, cobalt nitrate as cobalt source and sodium tetrachloropalladate as palladium source x -C spherical catalyst, the catalyst is applied to the catalytic oxidation of toluene.

[0006] The preparation method of the hollow multi-shell metal oxide catalyst is as follows: Step 1: preparing a uniformly dispersed carbon sphere carrier by a hydrothermal method; Step 2: Using carbon ball carrier as substrate, cobalt nitrate as cobalt source, sodium tetrachloropalladate as palladium source, and ethanol as solvent, Pd-CoO was obtained by hydrothermal method. x -C spherical catalyst; Step 3: Centrifuge and dry the Pd-CoO x -C ball solid powder is placed in a muffle furnace and heated to 450-550°C at different heating rates for calcination and kept warm for 5-7 hours to obtain a hollow multi-shell metal oxide catalyst.

[0007] Further optimization, the step of a hydrothermal method is specifically: putting glucose and CTAB in a beaker, adding deionized water and ultrasonically dissolving them.

[0008] Further optimization, in step 1, the mass ratio of glucose to CTAB is 13-15:0.5-1.5.

[0009] Further optimization, in step 1, the hydrothermal temperature is 170-190° C., and the stirring time is 9-11 h.

[0010] Further optimization, the amount of cobalt nitrate added in step 2 is 1.00-1.92 g.

[0011] Further optimization, the amount of solvent ethanol added in step 2 is 10-30 mL.

[0012] Further optimization was performed, and the ultrasonic time in step 2 was 1.5 h.

[0013] Further optimization, the hydrothermal temperature in step 2 is 150-170°C.

[0014] Further optimization, the heating rate of the muffle furnace in step three is 1°C / min, 2°C / min, 10°C / min, and 15°C / min.

[0015] The beneficial effects of the present invention are: 1. Using carbon spheres as the matrix, a hollow multilayer spherical catalyst is constructed; 2. High-temperature calcination of carbon spheres to expose the porous hollow structure of the catalyst, increase the specific surface area of ​​the catalyst, regulate the electronic structure and chemical properties of the catalyst surface, and adjust the number of oxygen vacancies on the catalyst surface and the contact residence time between VOCs and active sites; 3. When the catalyst is calcined at different heating rates, the removal rate of the carbon balls is positively correlated with the shell formed by cobalt oxide on the catalyst surface, and finally a hollow multi-shell metal oxide catalyst is obtained.

[0016] In summary, the present invention has the characteristics of simple preparation process, cheap raw material price, high yield and regular and controllable catalyst morphology. The hollow multi-shell Pd-Co3O4 catalyst prepared by the present invention exhibits excellent catalytic performance for the oxidation of toluene and methyl ethyl ketone. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG1 is a wide-angle XRD spectrum of a sample obtained in Example; FIG2 is a TEM image of samples Co3O4-double shelled and Pd-Co3O4-quadruple shelled prepared in the embodiment; FIG3 is a catalytic activity curve diagram of the sample prepared in the embodiment; Figure 4 The catalytic activity curve of toluene in a mixture of toluene and methyl ethyl ketone of the sample prepared in the example; Figure 5 The catalytic activity curve of methyl ethyl ketone in a mixture of toluene and methyl ethyl ketone of the sample prepared in the example; Figure 6 This is a thermal stability curve of the sample HoMS-Pd-Co3O4 prepared in the example to toluene; Figure 7 This is the thermal stability curve of the sample HoMS-Pd-Co3O4 prepared in the example to methyl ethyl ketone. DETAILED DESCRIPTION

[0018] In order to more clearly understand the above-mentioned purposes, features and advantages of the present invention, the present invention is described in detail below in conjunction with specific embodiments. The following embodiments are implemented based on the technical solutions of the present invention, and detailed implementation methods and specific operating procedures are given. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the following embodiments.

[0019] Example 1 First, take 2.8g of glucose and 0.2g of CTAB in a 50mL beaker, add 30mL of deionized water and ultrasonically dissolve, then transfer the mixed solution to a 50mL autoclave and keep it in an oven at 180℃ for 10h. When the temperature drops to room temperature, wash it with distilled water and anhydrous alcohol by centrifugation, and dry the obtained solid in a vacuum oven at 60℃ for 12h to obtain brown carbon spheres.

[0020] Example 2 First, take 1.46g of cobalt nitrate hexahydrate in a small beaker and add 20mL of ethanol to ultrasonically dissolve it. Then add 50mg of carbon microsphere template, transfer it to a 50mL autoclave after ultrasonication for 1.5h, and keep it in a 160℃ oven for 6h. After cooling to room temperature, collect the solid by centrifugation at 7000rpm and 10min with anhydrous ethanol, and dry it in a 60℃ vacuum oven for 12h to obtain a black semi-finished solid powder. The obtained black semi-finished solid powder is heated to 500℃ at a heating rate of 1℃ / min, 2℃ / min, 10℃ / min, and 15℃ / min, and kept warm for 6h to be calcined, and finally single-shell, double-shell, triple-shell and quadruple-shell hollow cobalt tetraoxide balls can be obtained respectively.

[0021] Example 3 First, take 1.46g of cobalt nitrate hexahydrate in a small beaker, add a certain amount of ruthenium trichloride according to the mass percentage of 1wt%, and add 20mL of ethanol to dissolve it by ultrasound. Then add 50mg of carbon microsphere template, transfer it to a 50mL self-pressure reactor after ultrasound for 1.5h, and keep it in a 160℃ oven for 6h. After cooling to room temperature, use anhydrous ethanol to collect the solid by centrifugation at 7000rpm and 10min, and dry it in a 60℃ vacuum oven for 12h to obtain a black semi-finished solid powder. The obtained black semi-finished solid powder is calcined at a heating rate of 15℃ / min for the calcination rate of the four-shell layer with the best activity, and finally obtains a four-shell hollow cobalt oxide ball doped with ruthenium.

[0022] Example 4 First, take 1.46g of cobalt nitrate hexahydrate in a small beaker, add a certain amount of sodium tetrachloropalladate according to the mass percentage of 1wt%, and add 20mL of ethanol to dissolve it by ultrasound. Then add 50 mg of carbon microsphere template, transfer it to a 50 mL autoclave after ultrasound for 1.5h, and keep it in a 160℃ oven for 6h. After cooling to room temperature, collect the solid by centrifugation at 7000 rpm and 10 min with anhydrous ethanol, and dry it in a vacuum oven at 60℃ for 12h to obtain a black semi-finished solid powder. The obtained black semi-finished solid powder is calcined at a heating rate of 15℃ / min for the calcination rate of the four-shell layer with the best activity, and finally obtain a four-shell hollow cobalt oxide ball doped with ruthenium.

[0023] like Figure 1 As shown in the figure, (a), (b), (c), (d), and (e) are the wide-angle XRD spectra of Co3O4-single shelled, Co3O4-double shelled, Co3O4-triple shelled, Co3O4-quadruple shelled, and Pd-Co3O4-quadrupleshelled, respectively. By comparing with the standard spectrum of Co3O4, it was found that the cobalt tetroxide catalyst sample was successfully prepared.

[0024] like Figure 2 As shown in the figure, (a) and (b) are TEM images of Co3O4-double shelled and Pd-Co3O4-quadrupleshelled respectively. The TEM results show that single-shell, double-shell, triple-shell, quadruple-shell and Pd-doped quadruple-shell catalyst samples were successfully prepared.

[0025] like Figure 3As shown, the catalytic activity of (a) Co3O4-single shelled, (b) Co3O4-double shelled, (c) Co3O4-triple shelled, (d) Co3O4-quadruple shelled, and (e) Pd-Co3O4-quadruple shelled catalysts in the presence of 1000 ppm toluene was tested. The test conditions were: 1000 ppm toluene + 20 vol% O2 + N2 (balance gas). The test results showed that the Pd-Co3O4-quadruple shelled catalyst had the lowest T 50 as well as T 90 , respectively: 240℃ and 255℃, which also means that the catalyst has the best catalytic performance.

[0026] like Figure 4 As shown, the catalytic activity of (a) Co3O4-singleshelled, (b) Co3O4-double shelled, (c) Co3O4-triple shelled, (d) Co3O4-quadruple shelled, and (e) Pd-Co3O4-quadruple shelled catalysts in the presence of 1000 ppm toluene and 1000 ppm methyl ethyl ketone was tested. The test conditions were: 1000 ppm toluene + 1000 ppm methyl ethyl ketone + 20 vol% O2 + N2 (balance gas). The test results show that the Pd-Co3O4-quadruple shelled catalyst has the lowest T 50 as well as T 90 It also means that the catalyst has the best catalytic performance.

[0027] like Figure 5 As shown in the figure, the thermal stability of the Pd-Co3O4-quadruple shelled catalyst is tested under the conditions of 1000ppm toluene (or 1000ppm methyl ethyl ketone) + 20vol% O2+ N2 (balance gas). The test results show that the Pd-Co3O4-quadruple shelled catalyst has excellent thermal stability for the catalytic oxidation of toluene and methyl ethyl ketone.

[0028] Co3O4-single shelled, Co3O4-double shelled, Co3O4-triple shelled, Co3O4-quadruple shelled, and Pd-Co3O4-quadruple shelled catalysts for oxidation of toluene and methyl ethyl ketone T 50 and mixed oxidation of toluene and methyl ethyl ketone T 50 The results show that the Pd-Co3O4-quadruple shelled catalyst has excellent catalytic activity for toluene and methyl ethyl ketone, and has the lowest apparent activation energy. When testing the catalytic oxidation of a mixture of toluene and methyl ethyl ketone, it was found that low temperature promoted methyl ethyl ketone, while high temperature promoted toluene.

[0029] The above shows and describes the main features, methods of use, basic principles and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements according to actual conditions, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. Application of hollow multi-shell metal oxide catalyst, characterized in that: The catalyst is a Pd-CoO catalyst with a carbon ball carrier as a substrate, cobalt nitrate as a cobalt source, and sodium tetrachloropalladate as a palladium source. x -C spherical catalyst, the catalyst is used for catalytic oxidation of toluene and methyl ethyl ketone.

2. The method for preparing the hollow multi-shell metal oxide catalyst according to claim 1, characterized in that: The specific steps of the preparation method are: Step 1: preparing a uniformly dispersed carbon sphere carrier by a hydrothermal method; Step 2: Using carbon ball carrier as substrate, cobalt nitrate as cobalt source, sodium tetrachloropalladate as palladium source, and ethanol as solvent, Pd-CoO was obtained by hydrothermal method. x -C spherical catalyst; Step 3: Centrifuge and dry the Pd-CoO x -C ball solid powder is placed in a muffle furnace and heated to 450-550°C at different heating rates for calcination and kept warm for 5-7 hours to obtain a hollow multi-shell metal oxide catalyst.

3. The method for preparing the hollow multi-shell metal oxide catalyst according to claim 2, characterized in that: The step of a hydrothermal method is specifically as follows: glucose and CTAB are placed in a beaker, and deionized water is added and ultrasonically dissolved.

4. The method for preparing the hollow multi-shell metal oxide catalyst according to claim 3, characterized in that: In the step 1, the mass ratio of glucose to CTAB is 13-15:0.5-1.

5.

5. The method for preparing the hollow multi-shell metal oxide catalyst according to claim 2, characterized in that: In the step 1, the hydrothermal temperature is 170-190° C., and the stirring time is 9-11 h.

6. The method for preparing the hollow multi-shell metal oxide catalyst according to claim 2, characterized in that: The amount of cobalt nitrate added in step 2 is 1.00-1.92 g.

7. The method for preparing the hollow multi-shell metal oxide catalyst according to claim 2, characterized in that: The amount of ethanol solvent added in step 2 is 10-30 mL.

8. The method for preparing the hollow multi-shell metal oxide catalyst according to claim 2, characterized in that: The ultrasonic time in step 2 is 1.5 h.

9. The method for preparing the hollow multi-shell metal oxide catalyst according to claim 2, characterized in that: The hydrothermal temperature in step 2 is 150-170°C.

10. The method for preparing the hollow multi-shell metal oxide catalyst according to claim 2, characterized in that: The heating rates of the muffle furnace in step 3 are 1°C / min, 2°C / min, 10°C / min, and 15°C / min.

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