Adsorption and decomposition of NO on Pd surfaces

The adsorption, dissociation and desorption of NO on Pd(1 1 1), (1 0 0) and (3 1 1) have been studied using infrared reflection absorption spectroscopy and temperature programmed desorption techniques. At 320 K, NO molecularly adsorbs on the threefold hollow site and the twofold bridge site for Pd(1 1 1) and Pd(1 0 0), respectively. As for Pd(3 1 1), NO adsorbs on the twofold bridge site of the (1 0 0) step. NO molecularly desorbs from both Pd(1 1 1) and Pd(1 0 0) near 550 K, while N2 and N2O are observed to desorb at 550 K for Pd(3 1 1). This result indicates that the stepped Pd(3 1 1) surface is active for the thermal dissociation of NO. On the Pd(3 1 1) surface, oxygen produced from the NO dissociation is incorporated into the bulk and oxidizes the surface Pd atoms, while oxygen produced from the O2 dissociation desorbs from the surface around 800 K. The adsorption of NO is significantly inhibited by the oxygen produced from the NO dissociation.