Regenerable Fe–Mn–ZnO/SiO2 sorbents for room temperature removal of H2S from fuel reformates: performance, active sites, Operando studies

Abstract

Fe- and Mn-promoted H₂S sorbents Fe_x–Mn_y–Zn_1−x−yO/SiO₂ (x, y = 0, 0.025) for desulfurization of model fuel reformates at room temperature were prepared, tested and characterized. Sulfur uptake capacity at 25 °C significantly exceeds that of both commercial unsupported ZnO sorbents and un-promoted supported ZnO/SiO₂ sorbents. Sulfur capacity and breakthrough characteristics remain satisfactory after multiple (∼10) cycles of adsorption/regeneration, with regeneration performed by a simple and robust heating in air. XRD shows that both “calcined” and “spent” sorbents contain nano-dispersed ZnO, and XPS confirms conversion of ZnO to ZnS. “Calcined” sorbent contains Fe³⁺ and Mn³⁺ that are reduced to Mn²⁺ upon reaction with H₂S, but not with H₂. Operando ESR is used for the first time to study dynamics of reduction of Mn³⁺ promoter sites simultaneously with measuring sulfidation dynamics of the Fe_x–Mn_y–Zn_1−x−yO/SiO₂ sorbent. Fe cations are believed to occupy the surface of supported ZnO nanocrystallites, while Mn cations are distributed within ZnO.