Bimodal mesoporous TiO2 supported Pt, Pd and Ru catalysts and their catalytic performance and deactivation mechanism for catalytic combustion of Dichloromethane (CH2Cl2)

Pt-, Pd-, and Ru-doped bimodal mesoporous TiO2 catalysts were prepared by wet impregnation and applied to the catalytic combustion of dichloromethane (DCM). The Pd/TiO2 and Ru/TiO2 catalysts exhibited excellent catalytic activity. Total oxidation of DCM was obtained at 335 degrees C with less undesired CO and byproducts (CxHyClz) A certain decrease in the selectivity of the Pd/TiO2 catalyst was observed in a long-term stability test, whereas RuiTiO(2) displayed appreciable stability. Pt/TiO2 was easily deactivated and showed the poorest performance for DCM decomposition. Deactivation of the catalysts was related to the deposition of carbon species and chlorine poisoning, whereby the active sites for DCM decomposition were occluded. Furthermore, the adsorption of chlorine species could change the chemical states of the Pd or Pt species and generate inactive species. Deactivation of the Ru/TiO2 catalyst was inhibited to some extent as carbon and chlorine species could be removed by RuO2. Moreover, the larger pore-size distribution of RucTiO(2) was favorable for the desorption of by-products during DCM oxidation.