Size and support effects for CO oxidation on supported Pd catalysts

Supporting Pd catalysts characterized significant different size distribution were obtained using PdCl2, [Pd(NH3)(4)](NO3)(2) and Pd(acac)(2) as precursors. High-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), in-situ Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were used to examine the dispersion of Pd. Catalytic performance measurements show that the activities for CO oxidation increase as the Pd particle size decreases and the O-2/CO ratio increases. The activities under oxygen rich conditions are significantly higher than those at near the stoichiometric conditions. Pd on TiO2 prepared by the Pd(acac)(2) precursor is highly dispersed, leading to a considerable activity for CO oxidation at near room temperature. CO oxidation on the 1 wt% Pd/TiO2 and under an O-2/CO ratio of 1 characterized an apparent activation energy of 36.7 kJ/mol, which is closed to those reported for CO oxidation on the supported Au catalysts. The present work demonstrates a high catalytic activity of highly dispersed noble metals, and suggests a promising approach of using noble metals as catalysts with exceeding high efficiency.