Water dissociation on the low-coordinated sites of MgO nanopowders

The configurations associated with the dissociative adsorption of water on a variety of low-coordinated sites of MgO(100) surfaces, including corners, steps, MgO vacancies, and kinks on <010> steps, have been studied and assigned by combining infrared spectroscopy and ab initio calculations. Three kinds of MgO powders were examined: powders of very high specific surface area prepared by chemical vapor synthesis and well-defined cubic smoke particles obtained by combustion in either 20: 80 or 60: 40 O-2: Ar mixtures, the latter one involving less defects and smaller particles. It appears that an imperative requirement to obtain a precise characterization of the reactive behavior of defects is to keep the samples in ultra-high vacuum conditions and to control the water partial pressure finely.