Role of H2O and O2 during the reactive adsorption of H2S on CuO-ZnO/activated carbon at low temperature

The reactive adsorption of H2S on CuO-ZnO dispersed onto activated carbon was investigated in different gas streams, containing either O2, H2O or O2/H2O, at room temperature and in a lab-scale fixed-bed reactor. Sorbents performances were analyzed in terms of H2S capture rate and capacity, and results correlated with the sulphur species formed upon adsorption under different experimental conditions. Temperature Programmed Desorption (TPD), porosimetric and XPS analyses were performed in order to support the adsorption dynamic tests. The co-presence of O2 and H2O caused a remarkable increase in H2S adsorption capacity, in particular for Cu-containing sorbents, favouring the formation of various sulphur species such as sulphides, sulphates and, above all, elemental sulphur. The analysis of the experimental data set showed the occurrence of two main H2S oxidation mechanisms with different rates: the first one quickly formed metal sulphates utilizing lattice oxygen from metal oxide clusters or superficial oxygen species; the second process was slower and required moisture and molecular oxygen in the feed gas to catalytically form elemental sulphur chains that progressively filled-up the sorbent microporosity.