CN101703932B - Method for preparing Pd and Pt loaded mesoporous manganese oxide for catalytically eliminating VOCs - Google Patents

Abstract

The preparation method of Pd and Pt loaded mesoporous manganese oxide used for catalytic elimination of VOCs belongs to the field of catalysts. The invention provides a preparation method of a mesoporous manganese oxide carrier and a catalyst loaded with precious metals Pt and Pd, which are used for low-temperature catalytic elimination of VOCs gas. The mesoporous manganese oxide support was prepared by the sol-gel (sol-gel) method, and the noble metals Pt and Pd were supported by the improved wet impregnation method. The prepared catalyst has high catalytic combustion activity for benzene and CO at lower temperature. The invention has the advantages of low energy consumption, simple and convenient operation, mild reaction conditions, can reduce secondary pollution, and can work continuously.

Description

Preparation method of Pd and Pt supported mesoporous manganese oxide for catalytic elimination of VOCs

technical field

The invention relates to the preparation of a cheap and simple mesoporous manganese oxide carrier, and the preparation method of the noble metal Pt and Pd catalyst loaded therein, and is used for low-temperature catalytic elimination of VOCs gas.

Background technique

Mesoporous oxide materials are the most common type of mesoporous materials and also the most widely used type of materials. After years of research, mesoporous oxide materials have gradually been understood by people for their unique characteristics and superior performance. Their applications are not limited to traditional catalysis, adsorption, etc. Multifunctional materials in bioengineering, medicine and other fields.

Volatile organic compounds (VOCs) are the main pollutants in the urban atmosphere, mainly from vehicle exhaust emissions, industrial production and energy use. Most of VOCs are toxic and can induce disease, carcinogenesis, and even teratogenicity. VOCs pollution has been listed as one of the five major factors that endanger human health internationally. The formation of ozone-based photochemical smog is mainly a chemical reaction process dominated by VOCs. Therefore, the control and governance of atmospheric VOCs is a key issue in environmental protection.

Benzene is the most difficult substance to convert among all VOCs gases, and it is one of the most widely distributed substances indoors and outdoors. Therefore, the present invention uses benzene as a probe to study the catalytic elimination of VOCs. At present, there are few studies on the catalytic elimination of benzene at home and abroad, and the reaction temperature for complete catalytic elimination of benzene is relatively high. For example: In the paper "The effect of mass transfer on the catalyticcombustion of benzene and methane over palladium catalysts supported on porous materials" (Catal. Today, 83(2003) 131-139) published by the Gon SeoO research group in South Korea, the airspeed is 60,000h-1, when the concentration of benzene is 10,000ppm (space velocity is lower than 80,000h-1 of the present invention, benzene concentration is higher than 1000ppm of the present invention), use FAU zeolite, MCM-41 and KIT-1 supported Pd catalyst to Benzene undergoes catalytic combustion reaction, and the temperature for complete catalytic elimination of benzene is mostly above 300°C.

The implementation of this project is funded by the National Natural Science Foundation of China (No. 20777005), the Beijing Natural Science Foundation of China (No. 8082008) and the Excellent Talent Fund of the Beijing Organization Department (No. 20071D0501500210), and is the research content of these projects.

Contents of the invention

The object of the invention is to provide a preparation method for Pd and Pt loaded mesoporous manganese oxide to catalyze and eliminate VOCs gas at low temperature.

The catalyst of the present invention has high low-temperature catalytic elimination activity for low-concentration benzene (1000ppm) at high space velocity (80,000h ^-1 ): 1) Pt-loaded mesoporous manganese oxide catalyst can completely decompose benzene at 190-200°C Oxidize to CO ₂ and H ₂ O, fully oxidize CO to CO ₂ at 80-90°C; 2) Pd supported mesoporous manganese oxide catalyst, completely oxidize benzene to CO ₂ and H ₂ O at 290°C, at 57 CO is completely oxidized to CO ₂ at -70°C.

The preparation of the mesoporous manganese oxide provided by the invention is used as a catalyst carrier, and Pt and Pd are prepared by supporting the carrier. Using maleic acid and potassium permanganate as raw materials, the mesoporous manganese oxide carrier was prepared by the sol-gel (sol-gel) method, and the Pt and Pd catalysts were supported by the wet impregnation method. The specific preparation is realized through the following technical scheme:

The preparation method of above-mentioned catalyst provided by the present invention, comprises the steps:

(1) Preparation of mesoporous manganese oxide

Make a solution of _KMnO4 and maleic acid with a molar ratio of 1 to 4:1, add KOH to adjust the pH to 7 to 10, keep the temperature at 30°C to 60°C, stir for 10 to 30 minutes, and then let it stand for 15 to 10 minutes. 30 hours. Pour off the supernatant, suction filter at room temperature, and wash with ethanol to obtain a black-brown gel, and then vacuum-dry the gel at 80°C-120°C for 15-24 hours to obtain a black solid. The solid is soaked in ethanol solution for 15-24 hours, filtered with suction, washed with distilled water, and dried under vacuum at 80°C-120°C to obtain a black powdery solid. In an air flow of 20-40ml/min, the powdery solid is calcined at 200°C-400°C for 2-5 hours to obtain the mesoporous manganese oxide.

(2) Preparation of Pd and Pt supported mesoporous manganese oxide by wet impregnation method

Add the above-mentioned mesoporous manganese oxide into the prepared 0.1-0.4M Pd(NO ₃ ) ₂ solution to form a suspension, wherein the molar ratio of Mn:Pd is 15-40:1, and add nitric acid to the above-mentioned suspension Adjust the pH to 6-9, stir at room temperature for 10-24 hours, then add 0.2-0.7M NaBH ₄ solution and continue stirring for 4-7 hours, and ultrasonically treat for 15-30 minutes. The above solution was rotary evaporated at room temperature for 8-16 hours to obtain a black solid. The solid is washed several times with distilled water and ethanol respectively, and then vacuum-dried at 80-120 DEG C for 18-24 hours, and the Pd-loaded mesoporous manganese oxide catalyst is obtained after drying.

Add the above-mentioned mesoporous manganese oxide into the prepared 0.1-0.5M H ₂ PtCl ₆ solution to form a suspension, wherein the molar ratio of Mn:Pt element is 15-40:1, and add nitric acid to adjust the pH to 6-9, stir at room temperature for 10-24 hours, then add 0.2-0.7M NaBH ₄ solution and continue stirring for 4-7 hours, and ultrasonically treat for 15-30 minutes. The above solution was rotary evaporated at room temperature for 8-16 hours to obtain a black solid. The solid was washed several times with distilled water and acetone, and it was enough to detect the absence of ^Cl- ions with AgNO ₃ solution. Vacuum at 80-120 DEG C for 18-24 hours, and after drying, the Pt-loaded mesoporous manganese oxide catalyst is prepared.

The invention does not need to add any fuel, directly uses _O2 in the air as an oxidant, has the advantages of low energy consumption, simple operation, mild reaction conditions, can reduce secondary pollution, and can work continuously.

Description of drawings

Fig. 1 is the XRD pattern of the Pd-supported mesoporous manganese oxide catalyst prepared by Examples 1 and 2 of the present invention

Fig. 2 is the XRD pattern of the Pt-supported mesoporous manganese oxide catalyst prepared by Examples 3 and 4 of the present invention

Fig. 3 is the _N adsorption/desorption isotherm graph of the Pd and Pt supported mesoporous manganese oxide catalysts prepared in Examples 1 to 4 of the present invention

Fig. 4 is the pore size distribution diagram of the Pd and Pt loaded mesoporous manganese oxide catalysts prepared in Examples 1 to 4 of the present invention

Fig. 5 is the benzene catalytic oxidation curve diagram of the Pd and Pt supported mesoporous manganese oxide catalysts prepared in Examples 1 to 4 of the present invention

Fig. 6 is the CO catalytic oxidation curve graph of the Pd and Pt supported mesoporous manganese oxide catalysts prepared in Examples 1 to 4 of the present invention

Detailed ways

Potassium permanganate, maleic acid, sodium borohydride and sodium hydroxide used in the preparation of the catalyst were produced by Beijing Chemical Plant and were analytically pure. Pd(NO ₃ ) ₂ ·2H ₂ O and H ₂ PtCl ₆ ·6H ₂ O were produced by Shanghai Xingao Chemical Reagent Co., Ltd., analytically pure.

The present invention will be further described below by embodiment:

Example 1

(1) Prepare a solution of _KMnO4 and maleic acid with a molar ratio of 1:1, add KOH to adjust the pH to 7, keep the temperature at 30°C, stir for 10 minutes, and then let stand for 15 hours. Pour off the supernatant, suction filter at room temperature, wash with ethanol to obtain a dark brown gel, and then vacuum-dry the gel at 80° C. for 15 hours to obtain a black solid. The solid was soaked in ethanol solution for 15 hours, filtered with suction, washed with distilled water, and vacuum-dried at 80° C. to obtain a black powdery solid. In an air flow of 20ml/min, the powdery solid was calcined at 200°C for 2 hours to obtain mesoporous manganese oxide.

Put the above mesoporous manganese oxide into the prepared H ₂ PtCl ₆ solution (according to Mn:Pt molar ratio 40:1), stir the suspension at room temperature for 10 hours, adjust the pH to 6 with nitric acid, and then add 0.2M NaBH ₄ solution Stirring was continued for 10 hours; ultrasonic treatment was performed for 15 minutes, and the above solution was rotary evaporated at room temperature for 8 hours to obtain a black solid. The solid was washed several times with distilled water and acetone, until no ^Cl- ions were detected by AgNO ₃ solution, and dried in vacuum at 80°C for 18 hours to obtain a Pt-loaded mesoporous manganese oxide catalyst.

(2) Catalyst activity evaluation. The concentration of benzene is 1000ppm, and the space velocity is 80,000h ^-1 . Gas chromatography TCD detects _CO2 and CO in the reaction tail gas, and FID detects the content of benzene and other organic species. The temperature for the catalyst prepared in Example 1 of the present invention to completely catalyze the elimination of benzene is 190°C. When the temperature is in the range of 150°C to 190°C, the conversion rate of benzene rises linearly until it reaches 100%. In the catalytic elimination reaction of benzene, Benzene is completely converted to _CO2 and _H2O ; the temperature at which 50% of CO is converted to _CO2 is 60 °C, and the temperature at which CO is completely converted to _CO2 is 80 °C.

Example 2

(1) Prepare a solution of _KMnO4 and maleic acid with a molar ratio of 4:1, add KOH to adjust the pH to 10, keep the temperature at 60°C, stir for 30 minutes, and then let stand for 30 hours. Pour off the supernatant, suction filter at room temperature, and wash with ethanol to obtain a dark brown gel, which is then vacuum-dried at 120° C. for 24 hours to obtain a black solid. The solid was soaked in ethanol solution for 24 hours, filtered with suction, washed with distilled water, and vacuum-dried at 120° C. to obtain a black powdery solid. In an air flow of 40ml/min, the powdery solid was calcined at 400°C for 5 hours to obtain mesoporous manganese oxide.

Put the above-mentioned mesoporous manganese oxide into the prepared H ₂ PtCl ₆ solution (according to the Mn:Pt molar ratio of 15:1), and stir the suspension at room temperature for 24 hours, adjust the pH to 9 with nitric acid, and then add 0.7M NaBH ₄ solution Stirring was continued for 7 hours; ultrasonic treatment was performed for 30 minutes, and the above solution was rotary evaporated at room temperature for 16 hours to obtain a black solid. The solid was washed several times with distilled water and acetone, until no Cl ^- ions were detected by AgNO ₃ solution, and dried in vacuum at 120°C for 24 hours to prepare a Pt-loaded mesoporous manganese oxide catalyst.

(2) Catalyst activity evaluation. The concentration of benzene is 1000ppm, and the space velocity is 80,000h ^-1 . Gas chromatography TCD detects _CO2 and CO in the reaction tail gas, and FID detects the content of benzene and other organic species. The temperature for the catalyst prepared in Example 2 of the present invention to completely catalyze the elimination of benzene is 200°C. When the temperature is in the range of 150°C to 200°C, the conversion rate of benzene rises linearly until it reaches 100%. In the catalytic elimination reaction of benzene, Benzene is completely converted to _CO2 and _H2O ; the temperature for 50% conversion of CO to _CO2 is 63°C, and the temperature for complete conversion of CO to _CO2 is 90°C.

Example 3

(1) Prepare a solution of _KMnO4 and maleic acid with a molar ratio of 1:1, add KOH to adjust the pH to 7, keep the temperature at 30°C, stir for 10 minutes, and then let stand for 15 hours. Pour off the supernatant, suction filter at room temperature, wash with ethanol to obtain a dark brown gel, and then vacuum-dry the gel at 80° C. for 15 hours to obtain a black solid. The solid was soaked in ethanol solution for 15 hours, filtered with suction, washed with distilled water, and vacuum-dried at 80° C. to obtain a black powdery solid. In an air flow of 20ml/min, the powdery solid was calcined at 200°C for 2 hours to obtain mesoporous manganese oxide.

Put the above-mentioned mesoporous manganese oxide into the prepared Pd(NO ₃ ) ₂ solution (according to the Mn:Pd molar ratio of 40:1), and stir the suspension at room temperature for 10 hours, adjust the pH to 6 with nitric acid, and then add 0.2M NaBH ₄ The solution was stirred for an additional 4 hours and sonicated for 15 minutes. The above solution was rotary evaporated at room temperature for 8 hours to obtain a black solid. The solid was washed several times with distilled water and ethanol respectively, and then vacuum-dried at 80° C. for 18 hours, and the Pd-loaded mesoporous manganese oxide catalyst was prepared after drying.

(2) Catalyst activity evaluation. The concentration of benzene is 1000ppm, and the space velocity is 80,000h ^-1 . Gas chromatography TCD detects _CO2 and CO in the reaction tail gas, and FID detects the content of benzene and other organic species. The catalyst prepared in Example 3 of the present invention can catalyze and eliminate 50% of benzene at a temperature of 216° C., and the temperature at which benzene can be completely catalyzed and eliminated is 290° C. In the catalytic elimination reaction of benzene, benzene is completely converted into CO ₂ and H ₂ O; CO50 The temperature for % conversion to _CO2 is room temperature 25°C, and the temperature for complete conversion of CO to _CO2 is 57°C.

Example 4

(1) Prepare a solution of _KMnO4 and maleic acid with a molar ratio of 4:1, add KOH to adjust the pH to 10, keep the temperature at 60°C, stir for 30 minutes, and then let stand for 30 hours. Pour off the supernatant, suction filter at room temperature, and wash with ethanol to obtain a dark brown gel, which is then vacuum-dried at 120° C. for 24 hours to obtain a black solid. The solid was soaked in ethanol solution for 24 hours, filtered with suction, washed with distilled water, and vacuum-dried at 120° C. to obtain a black powdery solid. In an air flow of 40ml/min, the powdery solid was calcined at 400°C for 5 hours to obtain mesoporous manganese oxide.

Put the above-mentioned mesoporous manganese oxide into the prepared Pd(NO ₃ ) ₂ solution (according to the Mn:Pd molar ratio of 15:1), and stir the suspension at room temperature for 24 hours, adjust the pH to 9 with nitric acid, and then add 0.7M NaBH ₄ The solution was stirred for 7 hours and sonicated for 30 minutes. The above solution was rotary evaporated at room temperature for 16 hours to obtain a black solid. The solid was washed several times with distilled water and ethanol, and then vacuum-dried at 120° C. for 24 hours. After drying, the Pd-loaded mesoporous manganese oxide catalyst was prepared.

(2) Catalyst activity evaluation. The concentration of benzene is 1000ppm, and the space velocity is 80,000h ^-1 . Gas chromatography TCD detects _CO2 and CO in the reaction tail gas, and FID detects the content of benzene and other organic species. The catalyst prepared in Example 4 of the present invention can catalyze and eliminate 50% of benzene at a temperature of 245° C., and the temperature at which benzene can be completely catalyzed and eliminated is 290° C. In the catalytic elimination reaction of benzene, benzene is completely converted into CO ₂ and H ₂ O; CO50 The temperature for % conversion to _CO2 is room temperature 35°C, and the temperature for complete conversion of CO to _CO2 is 70°C.

Claims (1)

1. the preparation method of the Pd and Pt loaded mesoporous manganese oxide that is used to catalyze and eliminate VOCs, it is characterized in that, preparation step is: (1) Preparation of mesoporous manganese oxide Make a solution of _KMnO4 and maleic acid with a molar ratio of 1 to 4:1, add KOH to adjust the pH to 7 to 10, keep the temperature at 30°C to 60°C, stir for 10 to 30 minutes, and then let it stand for 15 to 10 minutes. 30 hours; pour off the supernatant, suction filter at room temperature, and wash with ethanol to obtain a black-brown gel, and then vacuum-dry the gel at 80°C-120°C for 15-24 hours to obtain a black solid; Soak the solid in ethanol solution for 15 to 24 hours, filter it with suction, wash with distilled water, and vacuum-dry it at 80°C to 120°C to obtain a black powdery solid; ℃～400℃ roasting for 2～5 hours to obtain mesoporous manganese oxide; (2) Preparation of Pd and Pt supported mesoporous manganese oxide by wet impregnation method Take the above-mentioned mesoporous manganese oxide and add it to the prepared 0.1-0.4M Pd(NO ₃ ) ₂ solution to form a suspension, wherein the molar ratio of Mn:Pd is 15-40:1, and stir in the above-mentioned suspension at room temperature After 10-24 hours, add nitric acid to adjust the pH to 6-9; then add 0.2-0.7M NaBH ₄ solution and continue stirring for 4-7 hours, and ultrasonic treatment for 15-30 minutes; rotate the above solution at room temperature for 8-16 hours to obtain black Solid; the solid is washed several times with distilled water and ethanol, and then vacuum-dried at 80-120° C. for 18-24 hours, and the Pd-supported mesoporous manganese oxide catalyst is obtained after drying; Or take the above-mentioned mesoporous manganese oxide and add it to the prepared 0.1-0.5M H ₂ PtCl ₆ solution to form a suspension, wherein the molar ratio of Mn:Pt is 15-40:1. In the above-mentioned suspension, stir at room temperature for 10- After 24 hours, add nitric acid to adjust the pH to 6-9; then add 0.2-0.7M _NaBH4 solution to continue stirring for 4-7 hours, and ultrasonically treat for 15-30 minutes; rotate the above solution at room temperature for 8-16 hours to obtain a black solid; The solid is washed several times with distilled water and acetone, and it is enough to detect the absence of ^Cl- ions with AgNO ₃ solution; it is dried in vacuum at 80-120° C. for 18-24 hours, and the Pt-loaded mesoporous manganese oxide catalyst is obtained after drying.

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