Higher tolerance to sulfur poisoning in CO2 methanation by the presence of CeO2

This study investigates the deactivation mechanism of CeO2-promoted catalyst for the CO2 methanation reaction. The catalytic performance was evaluated at high temperature (T = 500 degrees C, P = 5 barg) and under the presence of unfavourable H2S impurities (1-5 ppm). The thermal stability of the CeO2-promoted catalyst was excellent, while the non-promoted sample suffered from nickel sintering. In contrast, the presence of H S-2 was detrimental for both catalysts. The tolerance to H S-2 of CeO2-promoted sample was higher; keeping one third of the initial catalytic activity under continuous addition of H2S. The identification of crystallographic planes associated with Ce2O2S phase (HRSTEM) evidenced that the addition of CeO2 to nickel catalyst minimized the formation of non-active NiS sites. This finding was further confirmed through DRIFT spectroscopy since for the Ni-CeO2/gamma-Al2O3, methane formation derived from formate dissociation was followed by hydrogenation of the adsorbed CO on the remaining available active sites.