Copper-Promoted ZnO/SiO2 Regenerable Sorbents for the Room Temperature Removal of H2S from Reformate Gas Streams

The Cu-ZnO/SiO2 sorbent for ultradeep adsorptive removal of H2S from the reformate streams at room temperature was prepared and tested, and characterization of the active sites was performed. The Cu dopant significantly enhances desulfurization capacity of ZnO/SiO2 sorbent at room temperature (up to 92% utilization of ZnO), and the sorbent maintains a high sulfur uptake capacity upon multiple cycles (up to 10) of regeneration by a simple thermal oxidation in air. The "as-prepared" ("calcined") sorbent contains Cu in the Cu2+ form, O, Si, and Zn as ZnO, while the "spent" ("sulfided") sorbent contains Cu, O, Si, S, and Zn as the ZnS form, as found by XPS. XRD suggests that both zinc and copper compounds of the Cu-ZnO/SiO2 sorbent are nanodispersed. ESR spectroscopy found that the "calcined" and "sulfided" Cu-ZnO/SiO2 sorbents contain Cu2+ in the single dispersion and coordination state. During H2S adsorption, partial reduction of Cu2+ to Cu+ occurs: the higher Cu concentration in the sorbent, the lower the reduction yield of Cu2+ to Cu+, thus correlating with sulfur uptake capacity. The "deactivated" sorbent (10-11 adsorption/regeneration cycles) is enriched with a different chemical form of Cu2+, compared to the "as-prepared" sorbent.