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Promoted ZnO Sorbents for Low Temperature H2s Removal in PEM Fuel Cell

Priyanka Dhage, Vivekanand Gaur, Hongyun Yang, and Bruce Tatarchuk. Department of Chemical Engineering, Auburn University, Center for Microfibrous Materials Manufacturing, Auburn, AL 36849

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 MxZnO1-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. Cu0.05ZnO0.95/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 CuxZnO1-x/SiO2, where 0≤x≤1, revealed that Cu0.2ZnO0.8/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 CuxZnO1-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.