Methane combustion over PdO-alumina catalysts: The effect of palladium precursors

The role of palladium precursors and the preparation route in the catalytic properties of PdO/Al2O3 catalysts toward methane oxidation was investigated in this paper. The catalysts were prepared using palladium chloride, nitrate and acetylacetonate as precursors and the preparation routes employed were impregnation of alumina with solutions of these precursors and the polyol method, in which palladium deposition is carried in a liquid polyol, e.g. ethylene glycol. All catalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), surface area measurements and temperature programmed desorption of O2 (TPD). Unsteady-state methane oxidation was carried out by temperature-programmed surface reaction (TPSR). The results obtained suggested that the use of different palladium precursors and preparation routes played an important role on the properties of the catalysts, as palladium particle size, thermal stability of PdO and catalytic properties toward methane combustion. The use of palladium acetylacetonate as precursor by the impregnation method generated well-dispersed PdO particles on alumina. Regarding the PdO thermal stability and the activity toward methane combustion, this catalyst also presented the highest thermal stability and catalytic activity.