Dissociation of CO and H2O during water–gas shift reaction on carburized Mo/Al2O3 catalyst

The dissociation of CO and H2O during the water–gas shift reaction (WGSR) on the 973 K-carburized 4.8 and 8.5 wt% Mo/Al2O3 catalysts at 423 K was studied by in situ mass and infrared spectroscopies. It was found that both CO and H2O were dissociated on the basis of the formation of H2, 13C18O, 13C18O2 and 13C18O16O after the injection of H218O into the 13C16O stream. Regarding the 12C- and 16O-labeled atoms, 12C16O2, 12C16O18O and 12C18O2 were not formed, but H216O, 12C16O, 12C18O and 13C16O2 were formed. The H216O, 12C16O and 13C16O2 were formed by the reaction of the dissociated 16O of 13C16O with the surface carbon or the lattice carbon atom of the Mo oxycarbide. The infrared spectroscopy results for the injection of H2O into the C18O flow showed that C18O had no effect on forming the formate group. The formate and carbonate which were probably formed during the CO2 hydrogenation were observed when using the 973 K-carburized Mo/Al2O3 catalyst and alumina in a stream of CO. The WGSR on the Mo oxycarbide of the carburized Mo/Al2O3 catalyst followed the redox route together with the dissociation-association mechanism.

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► The dissociation of CO and H2O and the mechanism for the water–gas shift reaction.
► 13C16O and H218O were dissociated to form 13C18O, 13C18O16O, 13C18O2 and H216O.
► The formate was formed through the carbonate species from the formed CO2 hydrogenation.
► The reaction on the carburized Mo/Al2O3 followed mainly the redox route.