Effect Of Preparation Conditions And Element Addition On The Catalytic Performance Of VO_x/TiO₂Catalyst

Chlorinated volatile organic compounds are toxic, can cause seriousdamage and pollution to the living beings and environment and the eliminationof it has become a hot topic in the research area of green chemistry. VO_x/TiO₂（V/Ti）catalyst has been widely used as its high catalytic performance. In thisthesis, a series of catalysts were prepared、characterized and evaluated in theircatalytic performance of chlorobenzene, the results as follows:1. The effect of the morphology of carrier、the preparation methods and thepreparation conditions of catalyst on the performance of the V/Ti catalyst wereinvestigated.Two kinds of TiO₂hollow spheres and TiO₂nanoparticles were preparedusing carbon templating and hydrothermal method, respectively, and three V/Ticatalysts were prepared by incipient-wetness impregnation method using thesethree kinds of TiO₂as support. The experimental results show that the particlesize of three carriers is in accord with the specific surface area of these threecatalysts, that is to say, the smaller the particle size, the larger the specificsurface area. And the V/Ti catalyst with TiO₂nanoparticle as carrier exhibitedthe highest activity in the catalytic combustion of chlorobenzene.A series of V/Ti catalysts with the same vanadium addition content wereprepared by drying mixing method、incipient-wetness impregnation method andwet impregnation method，respectively. According to the comparison of thethree catalysts, the catalyst prepared by incipient-wetness impregnation methodexhibited the highest activity for catalytic destruction of chlorobenzene owingto the well-dispersed VO_xactive phase at the surface of the support TiO₂,without the production of the microcrystlline and the strongest oxidation ability.It shows that the dispersion state of active component VO_xon the TiO₂supportplays an important role in the catalytic destruction of chlorobenzene over V/Ticatalysts prepared by different methods.The effect of the vanadium loading content、calcination temperature on the nature and catalytic performance of the V/Ti catalyst were studied, and a seriesof catalysts were prepared by incipient-wetness impregnation method. When themass ratio of V/V+TiO₂is0.055, the catalyst exhibited the highest activity forcatalytic destruction of chlorobenzene as the VO_xactive species almostcompletely dispersed at the surface of the support TiO₂. When the loadingcontent of vanadium go beyond a limit, the V₂O₅crystalline phase appeared inthe catalyst because of the lower dispersion state of vanadium at the surface ofsupport TiO₂. We can conclud that the decrease of the catalytic activity ofcatalyst is related to the emergence of V₂O₅phase. The V/Ti catalyst with500℃calcination temperature had the highest catalytic activity. As the rise of thecalcination temperature, in addition to the anatase of TiO₂, the rutile of TiO₂andthe V₂O₅crystalline phase appeared in succession in catalyst. It shows that theappearing of V₂O₅and TiO₂rutile phase is the main reason of significantlyworse catalytic activity of V/Ti catalyst.2. The effect of the addition of tungsten or lanthanon to the V/Ti catalyst onthe nature and catalytic performance of V/Ti catalyst were researched. A series ofcatalysts were prepared using incipient-wetness impregnation method.The addition of a certain amount of W to the V/Ti based catalyst caninhibit the transition of anatase to rutile TiO₂, promote the dispersion of activecomponent VO_xon the support TiO₂, improve the oxidation ability of catalystand then improve the catalytic activity. The oxidation ability and catalyticactivity of catalyst decreased when the addition of W was excessive, leading tothe formation of WO₃.The addition of a certain amount of La or Ce to the V/Ti catalyst couldimprove the distribution of the active component VO_xon the surface of thesupport, and the addition of Ce could also increase the oxidation ability of thecatalyst. Therefore the addition of a certain amount of La or Ce to the V/Ticatalyst could improve the catalytic activity of catalyst in the catalyticcombustion of chlorobenzene. The catalytic activity of catalyst decreased whichmight be attributed to the formation of crystal or complex oxide species whenthe addition of Ce or La was excessive.