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.