Preparation Of Pt-Loaded Micro/Mesoporous Silica Catalysts And Thrie Performance In Toluene Adsorption And Catalysis

Volatile organic compounds（VOCs）are important precursors to photochemical smog and air pollution.Mainly from industrial solvent use,with high vapor pressure,low water solubility,and high toxicity.The pollution control of low concentration,high air volume,intermittent VOCs-containing exhaust gases in industries such as auto repair and painting is difficult.Toluene is one of the more commonly used industrial organic solvents,which is strongly toxic,and long-term exposure to toluene can increase the risk of cancer.There are currently two mainstream treatment methods,adsorption and catalytic oxidation.The adsorption method is a simple and inexpensive process suitable for treating low concentrations of VOCs,but there are problems such as low adsorbent desorption efficiency and high desorption temperature.The catalytic oxidation method has high purification efficiency,but has the problem of high energy consumption for treating discontinuous low air volume VOCs.Therefore,the development of adsorptive/catalytic coupling materials,which can not only play the advantages of both,but also provide a stable adsorption-desorption cycle for non-stationary waste gases,is an important direction of current research.Silicon dioxide is favorable for toluene adsorption and its low temperature desorption due to its high specific surface area and adjustable pore size distribution.Noble metal catalysts have more excellent catalytic oxidation activity compared with transition metal catalysts.However,the noble metal loaded silica materials suffer from the problem that the adsorption capacity and catalytic activity are very easy to be reduced under water vapor conditions.In this thesis,micro/mesoporous silica loaded with different concentrations of Pt and its hydrophobic modification were carried out to investigate their adsorption/desorption performance,catalytic oxidation performance and their water vapor resistance to toluene.The main findings are as follows:（1）Pt/microporous silica catalyst preparation and its bifunctional performance for toluene adsorption and catalysis.The ordered microporous silica was synthesized by ionic liquid,and the noble metal Pt-loaded adsorption/catalytic bifunctional material was prepared by wet impregnation method,and the mass percentage of Pt/microporous silica（Pt/MS）was regulated from 1.0 wt.%to 3.5 wt.%to obtain the best toluene adsorption/catalytic performance.The specific surface areas of the catalysts were in the range of 650-750 m²/g,with pore diameters of 1.1-1.5 nm and pore volumes of 0.28-0.35 m²/g.The hydrophobic modification performance study of the synthesized Pt/MS catalysts by silane coupling agent species was further investigated with an optimum hydrophobic angle of 142.5°.The hydrophobic modified catalyst,2.0Pt/MS-H toluene saturation adsorption capacity reached56.09 mg/g,significantly higher than the pre-modified value of 25.3 mg/g,with an optimum desorption temperature of 60℃.The catalyst had superior adsorption and desorption cycle stability,maintaining about 95%of the adsorption capacity after five adsorption and desorption cycles.90%of the toluene catalytic decomposition temperature was optimum at T₉₀=149℃.This study shows that Pt/MS is a superior material for VOCs adsorption and catalytic integration.（2）Preparation of Pt/mesoporous silica catalysts and their bifunctional performance for toluene adsorption and catalysis.The ordered mesoporous silica with a specific surface area of 824m²/g and a pore size distribution concentrated at 3-4 nm was prepared by ionic liquid.different ratios of Pt were loaded by wet impregnation and further hydrophobically modified.The morphological structures of the catalytic materials were characterized by BET,contact angle,XRD,IR,SEM and TEM,and the catalytic adsorption at room temperature,desorption at low temperature and catalytic decomposition of toluene performance were evaluated by online chromatography,and the catalyst performance was further analyzed by H₂-TPR and XPS.The results showed that the adsorption capacity of Si O₂-350 was 28.3 mg/g and that of 3.0Pt/Si O₂ was 18.9 mg/g.The hydrophobically modified samples exhibited better toluene adsorption capacity of 53.1 mg/g compared with both,and the IR results suggested that this might be the effect of the hydrophobic modifier functional groups encapsulated on the material surface.Furthermore,compared to the very low optimum desorption temperatures of 44℃ and 37℃ for the Si O₂-350 and 3.0Pt/Si O₂ samples,the maximum desorption temperature of the hydrophobically modified sample increased to 52℃,which is slightly higher than the room temperature to facilitate the coupled VOCs adsorption/desorption-catalysis performance.90%toluene decomposition temperature of the3.0Pt/Si O₂-H material decreased to T₉₀=129℃ and exhibited superior resistance to water vapor and adsorption-desorption/decomposition of toluene.