Diffuse reflectance FTIR has been used to elucidate the mechanism of the reaction of H2S with high surface area ZnO prepared from hydrozincite and, hence, containing some residual CO2. Hydrogen sulfide is converted into ZnS by successive proton transfers to chemisorbed hydroxyls on the Zn- and O-polar hexagonal faces : Much product molecular water remains adsorbed on the prism faces or combined with residual carbonate as hydrozincite. Counterdiffusion of Zn2+ and H+ is proposed as the transport mechanism in the reaction of bulk solid ZnO.