EFFECTS OF THE ADDITION OF LANTHANA ON THE THERMAL-STABILITY OF ALUMINA-SUPPORTED PALLADIUM

Promotional effects of lanthana on the catalytic property of Pd/Al2O3 toward methane combustion were examined. The results revealed that Pd/Al2O3 became active on raising the temperature above 767 K but its activity decayed considerably at high temperatures. Addition of La2O3 to the Pd/Al2O3 catalyst inhibited this activity decay. Hydrogen chemisorption and BET measurements revealed that the addition of La2O3 to Pd/Al2O3 not only enhanced the thermal stability of gamma-Al2O3 but also retarded the supported Pd from sintering upon calcinations at T>923 K. Temperature-programmed oxidation studies further demonstrated that the retardation in Pd sintering resulted from an increase in the bond strength of Pd-O. Therefore, the increase in the bond strength of Pd-O may account for the promotional effect of lanthana and the long lifetime of La-added Pd/Al2O3 catalyst in methane combustion.