Strong chemical interaction between PdO and SnO2 and the influence on catalytic combustion of methane

Several palladium-tin oxide (PdO-SnO2) catalysts were prepared by the impregnation (PdO/SnO2) and co-precipitation (PdO-SnO2) methods. Among the catalysts tested, the SnO2-supported 11 wt.% PdO catalyst prepared by the impregnation method showed the highest conversion at low temperatures. The reduction and adsorption properties of PdO/SnO2 were quite different from those of PdO/Al2O3 and PdO/ZrO2. X-ray diffraction (XRD) of these catalysts revealed that 10 nm PdO particles were supported on SnO2 for the impregnated catalysts, while the co-precipitated catalysts were composed of uniform PdO-SnO2 mixed oxide particles. Even at room temperature, the PdO particles in PdO/SnO2 were easily reduced to metallic Pd and absorbed H-2 with the H-2/Pd weight ratio of 0.3%. In both PdO/SnO2 and PdO-SnO2 samples, adsorption of CO was significantly suppressed because of the interaction between Pd and SnO2; the metal surface area was difficult to estimate by the CO pulse technique. (C) 2003 Elsevier B.V. All rights reserved.