Revealing the ZrO2 crystal effect of Pd/ZrO2 catalyst for toluene combustion: A combined DRIFTS and DFT study.

The effect of ZrO 2 crystalline phases on Pd/ZrO 2 for catalytic combustion of toluene was investigated. It was found that Pd/t-ZrO 2 showed superior activity when the toluene concentration was lower than 2000 ppm, while Pd/m-ZrO 2 performed better with toluene concentration higher than 3000 ppm. Kinetic studies showed that the reaction order of toluene on Pd/t-ZrO 2 and Pd/m-ZrO 2 is 0 and 2, respectively. The catalytic activity was controlled by combined effect of PdO activity and quantity, which was correlated with the interaction between palladium and zirconia. The t-ZrO 2 increased PdO species activity, while m-ZrO 2 could enhance the amount of PdO. DFT results showed that the p-band center of the O of PdO on t-ZrO 2 was higher, suggesting that PdO was more active. In situ -DRIFTS revealed that the reaction pathway of catalytic oxidation of toluene on Pd/ZrO 2 was as follows: toluene was oxidized stepwise to benzyl alcohol, benzaldehyde, benzoic acid, CO 2 and H 2 O. [Display omitted] • Effect of Pd/ZrO 2 with different ZrO 2 crystal types for toluene combustion. • Catalytic activity was controlled by the comprehensive effect between PdO activity and PdO quantity. • The reaction order of toluene on Pd/t-ZrO 2 and Pd/m-ZrO 2 is 0 and 2, respectively. • Desorption energies of O atoms in O-Pd/m-ZrO 2 and O-P/t-ZrO 2. • The reaction pathway of catalytic combustion of toluene on Pd/ZrO 2 catalysts. [ABSTRACT FROM AUTHOR]