Effect of H2S on the Catalytic Conversion of Biogas to Syngas

Abstract

The dry reforming of biogas provides a promising route for generating syngas sustainably by concurrently converting CH₄ and CO₂. However, the presence of trace H₂S in biogas streams can significantly influence catalyst stability and performance. In this study, Ni-based catalysts promoted with M (M = K, Mg, Ba, Y, Ce, La) and supported on commercial or sol-gel alumina were synthesized via wet impregnation. The physical and chemical characteristics of the catalysts were analyzed using XRD, N₂ adsorption–desorption, DRIFTS, TGA, Raman, XPS, SEM, TPR and ICP-OES techniques. All samples exhibited mesoporous structures, while DRIFTS results indicated that promoter addition reduced the surface acidity of Ni-based commercial alumina-supported catalyst in the following order: K > Mg > Y > Ce > Ba > La. In H₂-TPR profile of sol-gel alumina supported Ni-La catalyst, a broad reduction peak spanning from 700 °C to 900 °C were observed, indicating the reduction of nickel aluminate spinel (NiAl₂O₄) phases, which are associated with strong interactions between Ni species and the alumina support. XRD analysis showed that La incorporation increased the nickel crystal size, which may have enhanced the reducibility of nickel species in Ni-based alumina catalyst, particularly in commercial alumina-supported catalyst. Catalytic activity was tested at 750 °C under atmospheric conditions in the presence of 50 ppm H₂S. The incorporation of La decreased CH₄ conversion from 77% to 62% and significantly suppressed coke formation from 9% to 1.2% for the sol-gel alumina-supported catalyst. The results demonstrated that the effect of La strongly depended on the support type. For the commercial alumina-supported catalyst (CAL), La enhanced Ni reducibility and improved sulfur tolerance, whereas for the sol-gel alumina- supported catalyst (SGA), La decreased catalyst acidity, contributing to a substantial reduction in carbon deposition. These findings highlight the critical balance between promoter effects, catalytic activity, sulfur tolerance, and coke suppression in Ni-based systems.