Catalytic Oxidaiton Of Toluene And Dichloromethane Over Supported Metal Oxides

Enviromental problems have become more serious with the development of human seociety,in particularly,the abatement of air pollution has turned to emergency.Volatile organic compounds?VOCs?are the main air pollutants,which have harmful effects on the environment and human being.These compounds can destroy the ozone layer by forming photo-chemical fog,and bring bad influence on human health.Therefore,considerable efforts have been made for the elimination of VOCs.In general,VOCs can be removed by using different technologies,such as adsorption and catalytic oxidation.Physical adsorption method is an effective way for removing VOCs.However,it still has some drawbacks or limitations,like competitive adsorption,difficulty in regeneration.Currently,catalytic oxidation has been regarded as one of the most efficient methods to completely destroy the VOCs pollutants,while many kinds of supported noble metal compounds and metal oxides have already been tested as active catalysts for the catalytic oxidation of various VOCs.Although significant progresses have been made during the past decades,it is still an attractive subject to develop more efficient and low-cost VOCs oxidation catalysts.In this work,a series of supported transition-metal oxides catalysts have been prepared,and characterized by different means,including N2-adsorption/desorption measurements,X-ray diffraction?XRD?,scanning electron microscopy?SEM?,hydrogen temperature-programmed reduction?H2-TPR?and ammonia temperature-programmed desorption?NH3-TPD?.Their catalytic performances were investigated by the aerobic oxidation of toluene and dichloromethane,two representative VOCs.The main research contents and results are as follows:A series of Al₂O₃ supported transition-metal oxides catalysts were prepared by wet-impregnation method and deposition-precipitation method.It was found that supported binary-metal oxides showed much higher catalytic activity for the complete oxidation of toluene and dichloromethane compared with the corresponding single component metal oxide.As proved by H2-TPR and other characterization results,the addition of the second component could influence the reducibility of the supported metal oxides,and increase the dispersion degree of active components on the surface of Al₂O₃ support.Therefore,it can be concluded that the redox properties of the supported metal oxides could be adjusted by introducing suitable components and adopting effective preparation methods,thus resulting in the formation of active catalysts for VOCs oxidation.By using a novel material of nickel foam?NF?as support,a few transition-metal oxides supported catalysts were prepared via citric acid-mediated sol-gel route.It was found that the NF supported Cu-Mn-Ce catalyst?Cu: Mn: Ce = 1: 1: 1?,which was calcined at 500 ?,showed very high catalytic activity for the oxidation of toluene.A 98% conversion of toluene could be achieved at the reaction temperature of 260 ? for the aerobic oxidation of low-concentration of toluene?1000 ppm?.The main features of NF support,such as special three-dimensional network,high porosity and large specific surface area,are beneficial to the high dispersion of active components,thus fabricating highly active NF supported Cu-Mn-Ce oxides catalyst for the catalytic oxidation of VOCs.