A RAIRS investigation of desorption and dissociation of water on NiO thin films probed by NO and CO titration

Abstract

CO and NO adsorption onto a thin film of NiO grown on a single crystal Ni{110} substrate has been studied with high resolution RAIRS in order to characterise the oxidation states of the Ni adsorption sites on the surface. Adsorption onto Ni 2+ sites on ordered NiO crystallites and Ni 2+ sites at structural defects, such as steps and kinks, can be distinguished, and the frequencies observed are in good agreement with those identified on NiO powders. A small number of metallic Ni 0 sites are also identified. Water adsorbs molecularly on the regular oxide terraces at 130 K. Dissociation of water to form OH ads occurs only at defect sites. Gentle annealing causes diffusion of water, forming a uniform monolayer prior to desorption in the range 175–250 K.