Abstract:
This paper presents a detailed study of catalyst deactivation as a result of simultaneous sulfur poisoning and coke deposition during biogas dry reforming. Experiments are performed at 700 and 800 °C with 5 and 10 ppm of H2S in model biogas with CH4/CO2 = 1.5 and 2.0. To assess the relative effect of chemisorbed sulfur in deactivating the supported Ni catalyst as compared to that of coke deposition, the experiments are performed with and without H2S in the feed. The catalyst deactivation is found to be faster in the presence of H2S. The deactivation due to sulfur chemisorption is not reversible at 700 °C, while at 800 °C the catalytic activity of Ni starts to recover on removing H2S from the feed stream. The results show that the exit CO mole fraction goes up for the sulfur poisoned catalyst which suggests that the reverse water gas shift and coke gasification reactions are not suppressed to the same degree as the reforming reaction. The fresh and the spent catalysts are characterized using XRD, BET, EDS, and TEM. The characterization of the spent catalyst shows that dry reforming of model biogas, with and without the presence of H2S, leads to the formation of multiwalled carbon nanotubes for the chosen operating conditions.