Time‐resolved DRIFT Spectroscopy Study of Carbonaceous Intermediates during the Water Gas Shift Reaction over Au/Ceria Catalyst

Abstract ChemCatChem homepage for more articles in the collection. The mechanism of the low‐temperature water gas shift reaction (LTWGS) on an Au/CeO 2 catalyst was investigated by means of in situ diffuse reflectance infrared (DRIFT) spectroscopy. Under steady‐state LTWGS reaction (373–623 K), the catalyst is partially reduced, and signals from carbonate/formate dominates the infrared spectra. Time‐resolved pulse of CO experiment under a constant partial pressure of water at 423 K indicates that Ce 4+ can be reduced to Ce 3+ and that formate (HCOO) species cannot be directly related to the CO 2 production. Further information was obtained by performing modulation excitation spectroscopy (MES) experiments coupled with a phase‐sensitive detection (PSD) method. Under periodic modulation of the CO partial pressure while keeping the H 2 O concentration constant, most of the intense bands of carbonate and formate remained constant, indicating that these species are only spectators. The same is observed for the concentration of Ce 3+ . Conversely, signals in‐phase with the conversion of CO to CO 2 are observed and assigned to carboxyl [C(O)OH] and carboxylate (CO 2 δ− ) species, while some monodentate formate (m‐HCOO) also changes but at a lower rate. A plausible associative reaction mechanism where carboxyl/carboxylate are key intermediates is postulated.