Characterization and Activity of Supported Palladium Combustion Catalysts

The catalytic activity of Pd supported on γ-Al2O3, Ba-Al2O3, and La–Al2O3 has been examined in complete oxidation of methane when operating in excess of oxygen. Two different sizes of Pd particles have been considered. Foreign ions have a strong influence with respect to the stabilization of alumina when submitted to a temperature as high as 1000°C. In contrast, no specific effect can be detected when the samples are calcined at 500°C. Interaction with the supported palladium particles, observed during the combustion reaction, has been investigated by X-ray photoelectron spectroscopy and temperature-programmed oxidation. The difference in combustion activity is attributed to the difference in surface oxidation states of the Pd particles. The presence of foreign ions in the alumina structure results in surface PdO only. When supported on γ-Al2O3, small amounts of metallic Pd can be detected, resulting in a lower ignition temperature.