Catalytic Performance of Palladium Supported on Sheaf-Like Ceria in the Lean Methane Combustion

Sheaf-like CeO2 (CeO2-S) in microscale was prepared by the hydrothermal method, and then etched with KOH aiming to obtain an imperfect fluorite structure (CeO2-SK) with high content of oxygen vacancies and oxygen mobility. With CeO2-S and CeO2-SK as supports respectively, a modified colloidal deposition method was employed to obtain Pd/CeO2 catalysts for being used in lean methane combustion. According to the inductively coupled plasma (ICP), N2 physisorption and scanning electron microscopy (SEM) results, the Pd supported catalysts are very similar in their Pd loading, surface area and morphologies. SEM and transmission electron microscopy (TEM) results revealed various nanorods exposed CeO2 (110) and (100) facets on Pd/CeO2-SK surface after KOH etching. Raman spectra and H2-temperature programmed reduction (H2-TPR) results indicated that Pd/CeO2-SK catalyst has a much higher content of catalytic active PdO species than Pd/CeO2-S catalyst. It was also found that the catalytic performance of Pd/CeO2 in lean methane combustion depends greatly upon the exposing crystal planes and oxygen vacancies content of sheaf-like CeO2, and Pd/CeO2-SK exhibits higher activity than Pd/CeO2-S. The larger amount of CeO2 (110) and (100) planes on Pd/CeO2-SK surface can enhance the formation of oxygen vacancies, active Pd species and migration of lattice oxygen, which all evidently improve the redox ability and catalytic activity of the Pd/CeO2-SK catalysts in lean methane combustion.