The effect of CO on CO2 methanation over Ru/Al2O3 catalysts: a combined steady-state reactivity and transient DRIFT spectroscopy study

Abstract The reactivity of Ru/Al 2 O 3 catalysts in the hydrogenation of CO/CO 2 gas stream is investigated in this work to assess the possibility of carrying out CO 2 methanation even in the presence of CO in the feed stream. Such a goal is pursued by conducting reactivity studies at process conditions of industrial interest (i.e., at high CO x per-pass conversion and with concentrated CO x /H 2 streams) and by monitoring the surface species on the catalyst through transient DRIFTS-MS analysis. The catalyst shows gradual deactivation when the methanation is carried out in the presence of CO in the gas feed at low temperatures (200–300 °C). However, stable performance is observed at higher temperatures, showing CH 4 yields even higher than those observed during methanation of a pure CO 2 feed. DRIFTS-MS experiments agree with a CO 2 methanation pathway where CO 2 is adsorbed as bicarbonate on Al 2 O 3 and successively hydrogenated to methane on Ru, passing through formate and carbonyl intermediates. In the presence of CO at low temperature, the catalyst shows a higher CO coverage of the Ru sites, a larger formate coverage of the alumina sites and the presence of adsorbed carbonaceous species, identified as carboxylate and hydrocarbon species. By carrying out the CO 2 hydrogenation on the deactivated catalyst, carboxylates remain on the surface, effectively blocking CO 2 adsorption sites. However, the catalyst deactivation at low temperature is reversible as thermal treatment (>350 °C) is able to restore the catalytic activity. Notably, working above the carboxylate decomposition temperature ensures a clean catalyst surface without high CO coverage, resulting in stable and high performance in CO/CO 2 methanation.