The present work is focused on the modification of ZnO based sorbents by promoting with varied molar ratios of transition metals for enhancing their H₂S removal capacity at low temperatures. Silica supported sorbents with formulation M_xZnO_1-x/SiO₂, (M = Mn, Fe, Co, Ni, Cu) were prepared by incipient wetness method and tested in 1 vol% flowing H₂S/H₂ in packed bed reactor in both dry and moist conditions. Cu_0.05ZnO_0.95/SiO₂ showed the highest capacity of 77 mg S/g sorbent and almost 90% theoretical metal utilization followed by Fe > Co > Ni = Mn at same doping levels. The structural modification of ZnO surface with Cu-promoter (5 mol%) showed up to 30% increase in saturation capacity over the un-promoted ZnO/SiO₂ and 58% increase over commercial ZnO sorbent, examined under identical conditions. The experimental results on the effect of varying Cu concentration level in Cu_xZnO_1-x/SiO₂, where 0≤x≤1, revealed that Cu_0.2ZnO_0.8/SiO₂ showed the highest capacity of 106 mg S/g sorbent. The bulk and surface properties of the sorbents before and after promotional modification were characterized by X-ray diffraction and N₂ adsorption-desorption isotherms. The sulfided sorbents were thermally regenerated under airflow for repeated use in multiple adsorption- desorption cycles. To investigate the influence of the structural modification on the regenerability of Cu_xZnO_1-x/SiO₂, the sorbents promoted with distinct Cu-contents were tested at wide temperature range for multiple cycles.

Furthermore, to develop novel microfibrous entrapped sorbents and enhance the H₂S removal efficiency for fuel cell application, composite bed design in which glass fiber entrapped sorbent (particle size – 150-250 μm) is used as the polishing layer at the downstream of a packed bed, was comparatively examined. This new and pioneer design resulted a dual advantage of lower pressure drop and enhancement in sulfur adsorption capacity at the same time.