Bifunctional ZnO-MgO/activated carbon adsorbents boost H2S room temperature adsorption and catalytic oxidation

Abstract

A series of bifunctional ZnO-MgO/activated carbon adsorbents (denoted as MgxZn1-x/AC) were synthesized. The molar ratio of Mg/(Mg + Zn) was optimized maintaining a 20 wt. % total content of oxides. The materials were characterized using adsorption of nitrogen, TEM-EDS, XPS, XRD, FT-IR, TG and CO2-TPD. On them an H2S breakthrough capacity was measured in moist and dry conditions in the absence of oxygen in a gas stream. The best adsorbent retained 113.4 mg/g at moist conditions and 96.5 mg/g at dry conditions. Besides a large surface area and pore volume, and a high dispersion of ZnO, the high H2S removal capacity was attributed to MgO, which, owing to its basicity and limited solubility in water, continuously promoted the formation of HS− important for reactive adsorption and then for catalytic oxidation. The detected surface reaction/catalytic oxidation products were ZnS, elemental sulfur and sulfates. Based on the results obtained, plausible desulfurization mechanisms were proposed.