Controlling the Fe2O3–SiO2 interaction: The effect on the H2S selective catalytic oxidation and catalyst deactivation

Abstract

Biogas utilization is one of the most promising options for reducing the consumption of fossil fuels for energy production, but the presence of H2S represents a serious industrial and environmental problem. In this work, two different synthesis methods (sol-gel and incipient wetness impregnation) were used to synthesize iron oxide supported on silica catalysts (Fe2O3/SiO2) with metal loadings ranging from 0.5 to 10 %wt. The catalysts were tested for the selective oxidation of H2S, changing the operating conditions like O2/H2S (0.5–2.5), temperature (170–250°C), and water content (0–50%). The optimum condition was O2/H2S = 0.5 and no water at 230 °C with the conversion of approximately 100%, the selectivity of 97%, and the deactivation of 0.6%. A detailed characterization of the fresh and spent catalysts’ surface revealed the presence of four deactivation mechanisms: metal surface reduction, oxygen vacancy loss, pore plugging, and sintering. Among the observed deactivation mechanisms, the sintering showed the highest impact on catalytic activity and deactivation. The sol-gel catalysts (SG) showed the highest metal-oxide/support interaction, which reduced the metal-oxide nanoparticles sintering compared with the incipient wetness impregnation method (IWI), reporting a lower sintering, higher activity, and selectivity, lower deactivation rates and lower sensitivity to the operating conditions. A catalytic cycle representing the possible surface intermediate states of the catalyst is proposed based on the performance and characterization results obtained.