Methane combustion activity of unsupported PdO–ZrO2 binary oxides

Methane combustion activity of unsupported PdO–nZrO2 binary oxides (0 ⩽ n ⩽ 2) was studied in connection with the reduction/reoxidation behavior of Pd. The addition of small amount of ZrO2 (n = 0.1) significantly improved the catalyst light-off characteristics by accelerating the reoxidation step in the redox cycles of Pd species. The effect would be associated with the formation of highly oxidized Pd species on the PdO/ZrO2 interface, which may increase the rate of oxygen exchange between gas and solid phases.