A Pt / Si-WO3 catalyst for efficiently catalytically oxidizing toluene and a preparation method thereof

Abstract

A Pt / Si-WO3 catalyst for efficiently catalytically oxidizing toluene and a preparation method thereof belong to the fields of catalytic chemistry and environmental chemistry. First, P123 is dissolved in THF to form a uniform solution i, and another (1,5-cyclooctadiene) dichloroplatinum is dissolved in THF to form a uniform solution ii. Then, H4SiW 12 O 40 is dissolved in THF to form a uniform solution iii. The solutions ii and iii are simultaneously added to the solution i and stirred to obtain a transparent colloidal solution, which is cast onto a glass petri dish and slowly evaporated at room temperature for 12 h. Heat treatment is carried out. First, it is kept warm in an oven at 100 °C for 12 h to remove the excess THF, then it is kept warm in air at 350 °C for 2 h, and then it is subjected to gradient calcination to 500 °C and kept warm for 1 h under a nitrogen atmosphere. The catalyst of the present invention shows good catalytic activity for toluene oxidation and has good water resistance, and has good application prospects in the field of air pollution control.

Description

Technical Field

[0001] The present invention relates to a Pt / Si-WO3 catalyst for efficiently catalytically oxidizing toluene and a preparation method thereof. Specifically, Pt nanoparticles are loaded onto the surface of mesoporous Si-WO3 by a sol-gel method, and then an x wt% Pt / Si-WO3 catalyst is obtained through high-temperature calcination treatment. The supported catalyst exhibits good catalytic activity for toluene oxidation. It belongs to the fields of catalytic chemistry and environmental chemistry. Background Art

[0002] The rapid development of social economy has accelerated the pace of urban construction. The development of industrial production activities and the continuous operation of transportation in cities have led to an increasing amount of waste gas discharged into the atmosphere. The waste gas contains a large number of toxic and harmful pollutants, among which volatile organic compounds (VOCs) account for a large proportion. Their harm has a wide range and a deep degree, and has become one of the urgent problems that need to be solved in our country. VOCs mainly come from industries such as fuel combustion, industrial production, transportation, pharmaceuticals, and building materials. They have stable chemical properties, strong toxicity, are difficult to degrade, and are easily enriched in soil and organisms, having an adverse impact on the ecological environment and human health. Toluene, as a typical volatile organic compound, is widely used in the chemical manufacturing industries such as decorative materials, solvents, and paint coatings, making toluene one of the main pollutants in indoor air. Research has found that toluene is irritating to the skin and mucous membranes and has an anesthetic effect on the central nervous system. Therefore, removing toluene from the air is of great significance to human health and improving air quality. Currently, the main control technologies for toluene at home and abroad include physical methods, chemical methods, biological methods, and various coupling methods. The catalytic oxidation method has become an effective way to purify low and medium concentration toluene waste gas due to its advantages such as high efficiency, energy saving, environmental protection, and high removal rate. Supported noble metal catalysts (such as Au, Pd, and Pt, etc.) have been widely used due to their excellent catalytic activity for VOCs elimination at relatively low temperatures due to their own characteristics. Among them, Pt-based catalysts are considered to be effective and ideal catalysts for catalytic oxidation of toluene. Transition metal oxides with redox properties are often the first choice for the support of supported noble metal catalysts. In addition, doping metal oxides with heteroatoms (such as Si, N, P, S, etc.) will generate a large number of lattice defects and surface adsorbed oxygen species, which is beneficial to improving catalytic activity. Oxides with porous structures can efficiently disperse noble metal particles, and the large specific surface area and developed pore structure are beneficial to the adsorption and activation of VOCs molecules, which is the key to the high activity of this type of catalyst. Based on the above considerations, in the present invention, the heteroatom Si is doped into the redox WO3 to construct a mesoporous Si-WO3 support, and by controlling the loading amount of Pt, a series of x wt% Pt / Si-WO3 (x = 0, 0.19, 0.48, and 0.81) catalysts are successfully prepared. The prepared catalysts are successfully used for catalytic elimination of toluene and have excellent catalytic activity.

[0003] As far as we know, there is no literature and patent reporting the research on preparing x wt% Pt / Si-WO3 catalysts by loading Pt onto mesoporous Si-WO3 supports using the sol-gel method and using them for toluene catalytic oxidation. The present invention discloses a controllable preparation method of xwt% Pt / Si-WO3 catalysts. It is found that the x wt% Pt / Si-WO3 catalysts have excellent catalytic activity and water resistance for toluene oxidation. Summary of the Invention

[0004] The object of the present invention is to load Pt onto the surface of mesoporous Si-WO3 by the sol-gel method, and obtain an x wt% Pt / Si-WO3 supported catalyst through calcination for catalyzing the toluene oxidation reaction.

[0005] A catalyst for catalytic oxidation of toluene and its preparation method, which specifically includes the following steps:

[0006] (1) Preparation of mesoporous Si-WO3 support

[0007] Dissolve the triblock copolymer P123 in tetrahydrofuran (THF), stir to form a homogeneous solution, denoted as solution ⅰ; take another portion of THF, denoted as solution ⅱ; then dissolve H4SiW 12 O 40 in THF, stir to form a homogeneous solution, denoted as solution ⅲ; add solution ⅱ and solution ⅲ into solution ⅰ simultaneously, stir for 1 h to obtain a transparent colloidal solution, cast this solution onto a glass petri dish, and slowly evaporate THF at room temperature for 12 h; then perform heat treatment on the sample evaporated at room temperature for 12 h. First, keep it in an oven at 100 °C for 12 h to remove the excess THF solution, then keep it in air at 350 °C for 2 h, and then perform gradient calcination in a nitrogen atmosphere (that is, first heat up to 350 °C at a heating rate of 1 °C / min, and then heat up to 500 °C at a heating rate of 5 °C / min) to 500 °C and keep it for 1 h to obtain the mesoporous Si-WO3 support.

[0008] (2) Preparation of x wt% Pt / Si-WO3 catalyst

[0009] Dissolve P123 in 3 mL of THF, stir to form a homogeneous solution, denoted as solution ⅰ, take a certain amount of dichlorobis(1,5-cyclooctadiene)platinum and dissolve it in 1 mL of THF, stir to form a homogeneous solution, denoted as solution ⅱ, then dissolve H4SiW 12 O 40Dissolve it in THF and stir to form a homogeneous solution, denoted as Solution ⅲ. After the solid components in the above three groups of solutions are fully dissolved, add Solution ⅱ and Solution ⅲ to Solution ⅰ simultaneously, and stir magnetically for 1 h to obtain a transparent colloidal solution. Cast this solution onto a glass petri dish. The subsequent heat treatment method is the same as that for the preparation of the mesoporous Si-WO3 support in (1) above; during the calcination process, the structure-directing agent P123 is decomposed, and at the same time, silicotungstic acid is in-situ decomposed into Si-doped WO3, and (1,5-cyclooctadiene) platinum dichloride is pyrolytically reduced to Pt nanoparticles and dispersed on the surface of the Si-WO3 support, finally obtaining the target product x wt% Pt / Si-WO3 catalyst. The catalyst prepared by the present invention is used for the catalytic oxidation of toluene. x = 0.01 - 0.9, x = 0.19 - 0.81.

[0010] Furthermore, the mass ratio of the above P123 to H4SiW 12 O 40 is 0.2:2.5 - 2.80.

[0011] Catalyst performance evaluation:

[0012] In the toluene oxidation activity evaluation system, the reaction gas composition is 1000 ppm toluene + 20 vol% (volume percentage) O2 + N2 (balance gas), the space velocity (SV) is 20000 mL / (g·h), take 0.05 g of the catalyst with a particle size of 40 - 60 mesh. To prevent local overheating during the oxidation reaction, dilute the catalyst with quartz sand (the mass ratio of the catalyst to quartz sand is 1:5), and load it into a quartz fixed-bed micro-reactor (inner diameter = 6 mm). Evaluate the activity of the catalyst for its oxidation reaction with toluene as the reactant under atmospheric pressure. Use a gas chromatograph to on-line detect the reaction outlet gas, and analyze the data by the area normalization method. Use the reaction temperatures (T 50％ and T 90％ ) at which the toluene conversion rates are 50% and 90% respectively to evaluate the activity of the catalyst. The results show that on the 0.81 wt% Pt / Si-WO3 catalyst, T 50％ and T 90％ are 170 °C and 180 °C respectively, indicating that this catalyst has excellent catalytic activity.

[0013] The catalyst preparation process of the present invention is simple, shows good catalytic activity for the oxidation of toluene, and has good water resistance, and has good application prospects in the field of air pollution control. Description of the drawings

[0014] Figure 1XRD patterns of the as-prepared catalysts. (a) Si-WO3, (b) 0.19 wt% Pt / Si-WO3, (c) 0.48 wt% Pt / Si-WO3, (d) 0.81 wt% Pt / Si-WO3.

[0015] Figure 2 TEM images of the as-prepared catalysts. (a) and (b): Si-WO3, (c) and (d): 0.19 wt% Pt / Si-WO3, (e) and (f): 0.48 wt% Pt / Si-WO3, (g) and (i): 0.81 wt% Pt / Si-WO3.

[0016] Figure 3 (a) HAADF-STEM image and (b)-(f) elemental mapping patterns of Pt, Si, W, and O of the as-prepared 0.81 wt% Pt / Si-WO3 catalyst.

[0017] Figure 4 Activity curves of toluene catalytic oxidation over the as-prepared x wt% Pt / Si-WO3 catalysts and mesoporous Si-WO3 support. Reaction conditions: 1000 ppm toluene + 20 vol% O2 + N2 (balance gas), space velocity (SV) = 20000 mL / (g·h).

[0018] Figure 5 Water tolerance test results of the as-prepared 0.81 wt% Pt / Si-WO3 catalyst. Reaction conditions: 1000 ppm toluene + 20 vol% O2 + N2 (balance gas), space velocity (SV) = 20000 mL / (g·h), temperature = 175 °C, water vapor concentration = 3 vol%. Detailed Description of the Invention

[0019] To further illustrate the present invention, the following provides detailed descriptions with examples and presents the catalysts obtained by the present invention with the attached drawings.

[0020] Example 1

[0021] (1) Preparation of mesoporous Si-WO3 support

[0022] Dissolve 0.2 g of P123 in 3 mL of THF, stir to form a homogeneous solution, denoted as solution i. Take another 1 mL of THF, denoted as solution ii. Then add 2.64 g of H4SiW 12 O 40Dissolve it in 2.5 mL of THF and stir to form a homogeneous solution, denoted as Solution ⅲ. After the solid components in the above three groups of solutions are fully dissolved, add Solution ⅱ and Solution ⅲ to Solution ⅰ simultaneously, and stir magnetically for 1 h to obtain a transparent colloidal solution. Cast this solution onto a glass watch glass and slowly evaporate it in THF at room temperature for 12 h. Then heat-treat the sample evaporated at room temperature for 12 h. First, keep it in an oven at 100 °C for 12 h to remove the excess THF solution, then keep it in air at 350 °C for 2 h, and then carry out gradient calcination under a nitrogen atmosphere (using a heating rate of 1 °C / min when the temperature is lower than 350 °C and a heating rate of 5 °C / min when the temperature is higher than 350 °C) to 500 °C and keep it for 1 h to obtain the mesoporous Si-WO3 support.

[0023] (2) Preparation of x wt% Pt / Si-WO3 catalyst

[0024] Dissolve 0.2 g of P123 in 3 mL of THF and stir to form a homogeneous solution, denoted as Solution ⅰ. Separately, dissolve 50 mg of (1,5-cyclooctadiene) platinum dichloride in 1 mL of THF and stir to form a homogeneous solution, denoted as Solution ⅱ. Then dissolve 2.64 g of H4SiW 12 O 40 in 2.5 mL of THF and stir to form a homogeneous solution, denoted as Solution ⅲ. After the solid components in the above three groups of solutions are fully dissolved, add Solution ⅱ and Solution ⅲ to Solution ⅰ simultaneously, and stir magnetically for 1 h to obtain a transparent colloidal solution. Cast this solution onto a glass watch glass. The subsequent heat-treatment method is the same as that for the preparation of the mesoporous Si-WO3 support in (1) above. During the calcination process, the structure-directing agent P123 is decomposed, and at the same time, silicotungstic acid is in-situ decomposed into Si-doped WO3, and (1,5-cyclooctadiene) platinum dichloride is pyrolytically reduced to Pt nanoparticles and dispersed on the surface of the mesoporous Si-WO3 support, finally obtaining the target product x wt% Pt / Si-WO3 catalyst, that is, the corresponding products are 0.19 wt% Pt / Si-WO3, 0.48 wt% Pt / Si-WO3, and 0.81 wt% Pt / Si-WO3. The catalyst obtained in the present invention is used for the catalytic oxidation of toluene.

[0025] (3) The x wt% Pt / Si-WO3 catalyst was used for the catalytic oxidation of toluene. The reaction gas composition was 1000 ppm toluene + 20 vol% O2 + N2 (balance gas), the total gas flow rate was 16.7 mL / min, the SV was 20000 mL / (g·h), 0.05 g of the catalyst with a particle size of 40 - 60 mesh was taken. To prevent local overheating during the oxidation reaction, quartz sand was used to dilute the catalyst (the mass ratio of the catalyst to quartz sand was 1:5), and it was loaded into a quartz fixed-bed micro-reactor (inner diameter = 6 mm). The activity of the catalyst for the oxidation reaction of toluene was evaluated under atmospheric pressure with toluene as the reactant. The T 50％ and T 90％ were 170 °C and 180 °C, respectively.

Claims

1. Application of an x wt% Pt / Si-WO3 catalyst in the catalytic oxidation of toluene, characterized in that, The preparation method of the catalyst comprises the following steps: Dissolve P123 in THF and stir to form a homogeneous solution, denoted as solution ⅰ. Separately, dissolve a certain amount of dichlorobis(1,5-cyclooctadiene)platinum in THF and stir to form a homogeneous solution, denoted as solution ⅱ. Then, dissolve H4SiW 12 O 40 in THF and stir to form a homogeneous solution, denoted as solution ⅲ. After the solid components in the above three groups of solutions are fully dissolved, add solution ⅱ and solution ⅲ to solution ⅰ simultaneously and stir magnetically for 1 h to obtain a transparent colloidal solution. Cast this solution onto a glass petri dish and slowly evaporate THF at room temperature for 12 h. Then, perform heat treatment on the sample evaporated at room temperature for 12 h. First, keep it in an oven at 100 °C for 12 h to remove the excess THF solution. Then, keep it in air at 350 °C for 2 h. Immediately afterwards, perform gradient calcination under a nitrogen atmosphere, that is, first heat it to 350 °C at a heating rate of 1 °C / min, and then heat it to 500 °C at a heating rate of 5 °C / min and keep it for 1 h. During the calcination process, the structure-directing agent P123 is decomposed, and at the same time, silicotungstic acid is in-situ decomposed into Si-doped WO3. Dichlorobis(1,5-cyclooctadiene)platinum is pyrolytically reduced to Pt nanoparticles and dispersed on the surface of the Si-WO3 support, and finally the target product xwt% Pt / Si-WO3 catalyst is obtained; x = 0.01 - 0.

9.

2. The application according to claim 1, characterized in that, x=0.19-0.81。 3. The application according to claim 2, characterized in that, The catalysts are 0.19 wt% Pt / Si-WO3, 0.48 wt% Pt / Si-WO3, and 0.81 wt% Pt / Si-WO3.

4. The application according to claim 1, wherein The mass ratio of the above P123 to H4SiW 12 O 40 is 0.2:2.5 - 2.

80.

5. The application according to claim 1, characterized in that, The catalyst has water resistance and is used for catalytic oxidation of toluene under conditions containing water vapor.

6. The application according to claim 5, characterized in that, 0.81 wt% Pt / Si-WO3 catalyst, T 50% and T 90% are 170 °C and 180 °C respectively.

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