Nickel-based alumina supported catalysts for dry reforming of biogas in the absence and the presence of H2S: Effect of manganese incorporation

In this study, the effects of manganese incorporation on the activity of nickel-based sol-gel alumina-supported catalysts in the dry reforming of biogas were investigated in the absence and the presence of H2S. This article presents new information on reactions using gas mixtures of H2S, CO2, and CH4. Characterization studies were performed to explain catalyst performance during activity tests using XRD, N2 adsorption/desorption, XPS, DRIFTS, TGA/DTA, and SEM/EDX techniques. N2 adsorption/desorption and XRD studies showed that synthesized catalysts have a mesoporous structure with metallic nickel and gamma-Al2O3 phases. Activity tests of the catalysts were performed in a tubular reactor at 750 degrees C and 1 atm in the absence and the presence of H2S (2 ppm and 50 ppm). Alumina-supported Ni, and Ni-Mn catalysts showed stable activity during dry reforming of biogas reaction in the absence of H2S. Mn incorporation decreased the activity of Ni-based catalysts in terms of CH4 conversion; however, it increased its activity in terms of CO2 conversion due to enhancement of reverse water gas shift reaction. In the catalytic activity tests performed in the presence of 2 ppm H2S, the activity of mono and bimetallic catalysts decreased slightly with reaction time. In order to explain the effect of H2S in the feed stream on the catalytic activity for dry reforming, reaction tests were performed with different gas mixtures, namely: H2S + He, H2S + CO2 + He, and H2S + CO2 + CH4 + He. In that case, the reactor exit stream was analyzed by an online FTIR spectrometer. In reaction tests, different sulfur components, such as H2S, COS, S, SO2, and H2O were observed by FTIR analyses. In the case of the presence of H2S in the feed stream, the formation of COS and H2O were predominantly observed. Mn incorporation did not enhance the sulfur resistance of Ni catalyst due to the formation of sulfate on the catalyst surface.