The relationship between chemical state of Pd species and catalytic activity of methane combustion on Pd/CeO2

摘要: Three Pd/CeO2 catalysts are synthesized by reduction-deposition and an impregnation method (IMP) to clarify how the chemical state of Pd influences the catalytic performance for CH4 combustion. The results show that Pd/CeO2 (HHA), using hydrazine hydrate as a reductant, shows much higher catalytic activity and stability for CH4 combustion than Pd/CeO2 (FA), using formaldehyde as a reductant, and Pd/CeO2 (IMP). The results of our comprehensive characterization reveal that there are two different chemical states of Pd species on Pd/CeO2: Pd2+ in the form of PdO particles and Pdδ+ (2 < δ ≤ 4) in the form of PdxCe1−xO2, and the latter is mainly induced by the Pd species entering the lattice of CeO2, which acts as a transfer channel of active oxygen species from the CeO2 lattice to active Pd species. The activity of Pd/CeO2 directly correlates to the surface concentrations of PdO and adsorbed oxygen. An …