Kinetics of PdO formation and CO reduction on Pd(110)

Recent studies have identified the ‘subsurface’ oxygen on Pd(110) as a nucleation of an oxide phase. This species has been postulated as responsible for oscillations in the catalytic CO oxidation on this surface. We have investigated the kinetics of this oxide formation and its reduction by CO on Pd(110) at temperatures and pressures where oscillations occur, using temperature-programmed desorption and X-ray photoelectron spectroscopy. The rate of oxide reduction measured was found to agree approximately with previously measured values for chemisorbed oxygen, indicating that the oxide species are weakly bound or unstable. However, we find significant qualitative and quantitative differences in the kinetics of oxide formation and other mechanisms assumed in previous studies.