ToF-SIMS studies of the TiO_2-ZrO_2 supported palladium as trace level used in the total oxidation of TCE in humid air (Conference Paper)

摘要

New pre-reduced titanium-zirconium (x/1-x) oxide(s) supported palladium samples 0.5w% Pd/Ti_xZr_(1-x) (x = 0; 0.2; 0.3; 0.5; 0.7; 0.8; 1) have been shown to be efficient catalysts for the total oxidation of trichloroethylene (solvent widely used in dry cleaning and degreasing processes) in humid air (1mol%). A challenging task which must be addressed regarding that type of reaction is the chlorine location on the used catalyst surface in order to better understand the catalyst functioning. In spite of a few studies, time-of-flight secondary ion mass spectroscopy (ToF-SIMS) has been elsewhere proved to be a highly relevant tool to resolve such a problem. Hence, in this study, Tof-SIMS measurements have been performed on as-prepared and selected used Pd/Ti_xZr_(1-x) catalysts (x = 0; 0.2; 0.5; 1). On fresh catalysts, the Pd-based ions detected in both polarities are Pd~+, PdO~- and PdO_2 ~-. In addition, detection of Ti_2ZrO_5 ~+ and TiZr_2O_5 ~+ cluster ions provides for the first time a direct proof of titanium-zirconium mixed oxides (x≠ 0; 1). The negative ion-mass spectrum of the related used samples exhibit relevant signals attributed to PdCl_2 ~-, ZrO_2Cl~- and TiO_2Cl~- cluster ions. The chlorinated PdCl_2 ~- ion provides direct spectroscopic clue that some Cl atoms are still bound to Pd. By opposition, the quasi non-observance of MCl~- (M = Zr; Ti) indicates that chlorine deposit on the support does not directly affect the titanium and zirconium atoms.