Low-temperature catalytic combustion of methane over Pd/CeO2 prepared by deposition-precipitation method

Ceria supported 2 wt% Pd catalysts for low-temperature methane combustion were prepared by the impregnation (IM) and deposition-precipitation (DP) methods, which are denoted as Pd-IM and Pd-DP, respectively. DP was found to be an available method for achieving high activity and stability of the Pd/CeO2 catalyst. The temperatures for methane ignition (T-10%) and total conversion (T-100%) over Pd DP are 224 and 300 degrees C at GHSV of 50,000 h(-1), which are 83 and 110 degrees C lower than the corresponding temperatures of Pd/ Al2O3, X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) analyses show that palladium species in PdDP is highly dispersed, positively charged and difficultly reduced. Raman spectra disclosed that the largest concentration of defects and/or oxygen vacancies was formed in Pd-DP catalyst. A kind of cationic PdO delta+ sites with higher binding energies than PdO are in close vicinity to the oxygen vacancies in the CeO2 support and might act as the active centers for methane oxidation. Furthermore, the deactivation and steam aging tests for Pd-DP showed that the performance of this type of palladium was very stable and could be repeatedly recovered after several long time aging tests. (c) 2005 Elsevier B.V. All rights reserved.