Method for low-temperature heat treatment of toluene by using composite material having ternary NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure

Abstract

A method for the low-temperature heat treatment of toluene by using a composite material having a ternary NiO nanosheet @ bimetallic CeCuO.sub.x microsheet core-shell structure. The composite material having the ternary NiO nanosheet @ bimetallic CeCuO.sub.x microsheet core-shell structure is placed in an environment containing toluene, and is heated at a low temperature to complete the treatment of toluene. The use of precious metal particles loading is avoided for the catalyst, and the costs of materials is thus greatly reduced. Moreover, nickel oxide grows on CeCuO.sub.x microsheet nanosheets. The preparation process is relatively simple, and the catalytic performance on toluene is excellent. Therefore, the method has high economical practicability and research value. The 3Ni/CeCuO.sub.x catalyst may completely catalyze toluene at 210 C., which has great research significance and certain application prospects for the actual solution of toluene polluted gas in the air environment.

Claims

1. A method for a low-temperature heat treatment of toluene by using a ternary NiO nanosheet @ bimetallic CeCuO.sub.X microsheet core-shell structure composite material, comprising the following steps: (1) mixing a cerium salt, a copper salt, an organic acid, and a solvent, performing a solvothermal reaction, and calcining a reaction product of the solvothermal reaction to obtain a CeCuO.sub.X microsheet; (2) performing a water bath reaction of a mixture of a nickel salt, urea, and the CeCuO.sub.x microsheet in an alcohol/water mixed solvent, and calcining a reaction product of the water bath reaction to obtain the ternary NiO nanosheet @ bimetallic CeCuO.sub.x microsheet core-shell structure composite material; and (3) placing the ternary NiO nanosheet @ bimetallic CeCuO.sub.x microsheet core-shell structure composite material into a toluene-containing environment, heating at a low temperature, and completing the low-temperature heat treatment of toluene, wherein a molar ratio of the cerium salt, the copper salt and the organic acid in step (1) is 2:(1.0-1.1):(4.0-4.1); the solvent is dimethylformamide (DMF); and the organic acid is terephthalic acid; and wherein the low-temperature heat treatment is conducted 200-220 C.

2. The method according to claim 1, wherein Ce(NO.sub.3).sub.3.Math.6H.sub.2O and Cu(NO.sub.3).sub.2.Math.3H.sub.2O are used as starting materials, and the CeCuO.sub.x microsheet is prepared in the presence of terephthalic acid.

3. The method according to claim 1, wherein in step (2), a molar ratio of the nickel salt to urea is 1:(5.0-5.1), and the nickel salt is Ni(NO.sub.3).sub.2.

4. The method for the low-temperature heat treatment of toluene by using a ternary NiO nanosheet @ bimetallic CeCuO.sub.X microsheet core-shell structure composite material according to claim 1, wherein in the ternary NiO nanosheet @ bimetallic CeCuO.sub.X microsheet core-shell structure composite material, a weight of NiO nanosheet is 1-5 times of a weight of bimetallic CeCuO.sub.X microsheet.

5. The method for the low-temperature heat treatment of toluene by using a ternary NiO nanosheet @ bimetallic CeCuO.sub.X microsheet core-shell structure composite material according to claim 1, wherein in step (1), a temperature of the solvothermal reaction is 80 C.-90 C., and a reaction time is 24-25 hours; and the calcination is performed in air, a calcination temperature is 350 C.-400 C., and a calcination time is 4-4.5 hours.

6. The method for the low-temperature heat treatment of toluene by using a ternary NiO nanosheet @ bimetallic CeCuO.sub.X microsheet core-shell structure composite material according to claim 1, wherein in step (2), a temperature of the water bath reaction is 80 C.-90 C., and a reaction time is 2-2.5 hours; the calcination is performed in air, a calcination temperature is 350 C.-400 C., and a calcination time is 4-4.5 hours.

7. The method for the low-temperature heat treatment of toluene by using a ternary NiO nanosheet @ bimetallic CeCuO.sub.X microsheet core-shell structure composite material according to claim 1, wherein the toluene-containing environment is a gas environment.

8. The method for the low-temperature heat treatment of toluene by using a ternary NiO nanosheet @ bimetallic CeCuO.sub.X microsheet core-shell structure composite material according to claim 7, wherein a toluene concentration is 10 ppm-100 ppm in the toluene-containing environment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a scanning electron microscope (SEM) image of a CeCuOx microsheet.

(2) FIG. 2 is a transmission electron microscope (TEM) diagram of the CeCuOx microsheet.

(3) FIG. 3 is a scanning electron microscope (SEM) of the 3Ni/CeCuOx core-shell structure composite material.

(4) FIG. 4 is a transmission electron microscope (TEM) diagram of the 3Ni/CeCuOx core-shell structure composite material.

(5) FIG. 5 is a graph of the thermal catalytic effect of the NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure composite material on toluene gas.

DETAILED DESCRIPTION

(6) The preparation method of the NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure composite material disclosed by the invention includes the following steps: (1) dissolving a cerium salt, a copper salt and terephthalic acid (H.sub.2BDC) in a solvent, mixing, placing the mixture into a high-pressure reactor, carrying out a solvothermal reaction, and carrying out centrifugal washing, drying and calcining treatment to obtain a CeCuOx micro-sheet. (2) dissolving a nickel salt and urea in a mixed solution of ethanol and water, adding CeCuOx powder to conduct a reaction heating with a water bath, and then centrifugal washing, drying, and calcining to obtain the NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure composite material.

(7) The ternary NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure composite material is placed in a toluene-containing environment, heated at a low temperature to complete the treatment of toluene.

(8) The starting materials used in the present invention are conventional commercially available, and the preparation method and test method are conventional methods in the art, and the operation method for treating toluene is known in the art. The present invention creatively discloses that a new catalyst replaces the existing noble metal catalyst to realize low-cost and low-temperature catalytic toluene.

(9) Preparation Example: the preparation of CeCuOx including the following steps: dissolving Ce(NO.sub.3).sub.3.Math.6H.sub.2O (0.868 g, 2 mmol) and Cu(NO.sub.3).sub.2.Math.3H.sub.2O (0.242 g, 1 mmol) in DMF (40 mL) at room temperature, and stirring at 1000 rpm for 2 h; dissolving H.sub.2BDC (0.664 g, 4 mmol) in DMF (40 mL), and stirring at 1000 rpm for 2 h. The two solutions were then mixed with ultrapure water (20 mL) in a stainless steel autoclave, thermally reacted at 80 C. for 24 hours, washed several times with DMF and ethanol, then dried under vacuum at 65 C. for 6 h, and then calcined at 350 C. in air for 4 h, increasing the heating temperature from room temperature to 350 C. at a rate of 3 C./min to obtain the CeCuOx microsheet. FIG. 1 is an SEM image of a CeCuOx microsheet, and FIG. 2 is a TEM image of the CeCuOx microsheet; and it can be seen from figures that the microsheet has a two-dimensional layered structure, a regular parallelogram morphology.

(10) Preparing the ternary NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure composite material include the following specific steps: an amount of nickel oxide being 3 times of CeCuOx, dissolving Ni(NO.sub.3).sub.2 and urea in a molar ratio of 1:5 in a 100 mL water/alcohol of 1/1 volume ratio, adding 100 mg of prepared CeCuOx microsheet powder, and reacting the obtained solution at 80 C. for 2 hours under stirring. The reaction mixture was filtered and washed, then dried at 90 C. and calcined at 350 C. under an air atmosphere at a heating rate of 3 C./min for 4 h to obtain a ternary NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure composite material, named as 3Ni/CeCuOx (representing the weight ratio of NiO nanosheet to bimetallic CeCuOx microsheet of 3:1), and performance and characterization testing were performed. FIG. 4 is an SEM image of the 3 Ni/CeCuOx composite material, and FIG. 5 is a TEM image of the 3Ni/CeCuOx composite material. It can be seen from the figures that the nickel oxide successfully grows on the CeCuOx microsheet, and the distribution is uniform.

(11) The amount of Ni(NO.sub.3).sub.2 was changed to obtain materials with the weight ratio of NiO nanosheet to the bimetallic CeCuOx microsheet being 1:1, 5:1, named as NiCeCuOx, 5NiCeCuOx, respectively.

Example 1

(12) The thermal catalytic condition of the p-toluene gas by the ternary NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure composite material was that the toluene concentration is 50 ppm (air is used as a filling gas, purchased from Messer Air Liquide Co. Ltd.), the amount of the catalyst was 50 mg, the catalyst was fixed on a fixed bed reactor through a U-shaped pipe according to a conventional method, the catalytic effect of the composite material on toluene gas under the heating condition was analyzed through gas chromatography, and the test condition was 36000 ml (h.Math.g).

(13) FIG. 5 is a graph of the thermal catalytic effect of the ternary NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure composite material on toluene gas. As shown in FIG. 5, the present invention can be applied to conversion of toluene at lower temperatures. Toluene pollution in air is mainly derived from building materials, indoor decorative materials, living and office supplies, outdoor industrial waste gas, automobile exhaust, photochemical smoke and the like, and the toluene specific catalytic effect is analyzed by gas chromatography, and the toluene conversion rate calculation method is shown in equation (1):

(14) $=\frac{C_0-C}{C_0}100\%$

(15) C.sub.0 and C are the initial concentration and test concentration of toluene in the experiment, respectively (tested once every 15 minutes).

(16) As shown in the comparative results of FIG. 5, the catalytic performance of the bimetallic CeCuOx sample with large sheet morphology is obviously superior to that of a single metal CeO.sub.2 and CuO sample, and the advantages of the bimetallic sample morphology structure are proved. In addition, nickel oxide is grown on the CeCuOx microsheet, so that the concentration of oxygen vacancies is further improved, the catalytic performance is obviously improved, the uniform growth of nickel oxide also greatly improves the catalytic performance of the nickel oxide, and the use of noble metals is avoided. Therefore, the 3Ni/CeCuOx composite catalyst is relatively economical and efficient.

(17) Comparative Example: performing the solvothermal synthesis at 80 C. in the preparation example C for 24 hours was changed to performing the solvothermal synthesis at 80 C. for 48 hours, and the remaining conditions were unchanged. CeCuOx was obtained. Microsheet was prepared according to the method of Example 2. 3Ni/CeCuOx was prepared. The same toluene conversion test was performed. Toluene gas cannot be completely catalyzed at 210 C., i.e., the conversion rate is less than 100%.

(18) The heating rate of 3 C./min in the preparation of the preparation example was changed to 10 C./min. The remaining conditions were unchanged. CeCuOx microsheet was prepared according to the method of Example 2. 3Ni/CeCuOx was prepared. The same toluene conversion test was performed. The conversion rate was less than 95% at 210 C.

(19) In the preparation of the composite material of the preparation example ternary NiO nanosheet @ bimetal, the core-shell structure composite material, the temperature 350 C. was changed to 400 C. The remaining conditions were unchanged. 3Ni/CeCuOx was prepared. The same toluene conversion test was performed. The conversion rate was less than 92% at 210 C.

(20) Comparative Example: dissolving Ni(NO.sub.3).sub.2 and urea in a molar ratio of 1:5 in a 100 mL solution having a water/alcohol volume ratio of 1/1, then placing the obtained solution under conventional stirring at 80 C. for 2 reaction hours, drying at 90 C., calcining at 350 C. in an air atmosphere at a heating rate of 3 C./min to obtain a solid material, performing the same toluene conversion test, and converting being less than 30% at 210 C.

(21) By analyzing the above experiments, it is indicated that the nickel oxide nanosheet using the technical solution of the present invention can successfully grow to the CeCuOx microsheet to form a core-shell structure composite material. The process is simple and feasible, the growth of nickel oxide is very uniform, and the composite material in a certain proportion has a relatively good catalytic activity for toluene. The NiO nanosheet @ bimetallic CeCuOx microsheet core-shell structure composite material has a relatively large specific surface area, a uniform pore size and a controllable structure; the growth of nickel oxide increases the oxygen vacancy and contact area of the carrier, which significantly improves the catalytic performance of the carrier catalyst; and the nanosheet grows uniformly on the bimetallic CeCuOx microsheet to form a core-shell structure. The large specific surface area can promote the catalytic performance, increase the reaction active site, and be a good multi-element transition metal-type catalyst material. Meanwhile, the loading of noble metal particles is avoided, the cost of the material is greatly reduced, the experimental process is relatively simple, and the catalytic performance on toluene is excellent, so that the catalyst provided by the invention further realizes the purpose of economic practicability.