Importance of re-oxidation of palladium by interaction with lanthana for propane combustion over Pd/Al2O3 catalyst

Lanthana-modified Pd/Al2O3 catalyst was prepared using an incipient wet impregnation method followed by aging in a steam-containing air at 1050 °C for 5 h. The loading of lanthana inhibited the phase transformation of gamma alumina and the sintering of palladium during the thermal aging, resulting in a higher dispersion of palladium on the aged catalyst. The C3H8 oxidation activities of the catalysts were measured by temperature-programmed reaction after the oxidative, reductive and inert pre-treatments. The catalytic activity of the catalyst was found to be determined mainly by the oxidation state of Pd. The lanthana-modified catalyst exhibited a superior activity in respect to the lanthana-free catalyst after the reducing and inert pre-treatments, while both the pre-oxidized catalysts show similar propane oxidation activities. Oxidized palladium was more active than metallic species for propane combustion. A higher Pd2+/Pd ratio was detected on the aged Pd/La/Al2O3 catalyst by XPS. The CO-IR and TGA results proved that the metallic palladium species can be more quickly re-oxidized by interaction with lanthana at low temperatures.