Modulated experiments (MES-PSD) by diffuse reflectance infrared (DRIFT) spectroscopy allowed identification of carboxyl species as a key intermediate during WGS reaction over Au/CeO2 catalyst.
ChemCatChem homepage for more articles in the collection. The mechanism of the low-temperature water gas shift reaction (LTWGS) on an Au/CeO2 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 Ce4+ can be reduced to Ce3+ and that formate (HCOO) species cannot be directly related to the CO2 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 H2O 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 Ce3+. Conversely, signals in-phase with the conversion of CO to CO2 are observed and assigned to carboxyl [C(O)OH] and carboxylate (CO2
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.Zum Volltext