Elucidating the Role of Support Oxygen in the Water–Gas Shift Reaction over Ceria-Supported Gold Catalysts Using Operando Spectroscopy

Abstract

Supported-metal (Au, Pt) ceria-based catalysts are considered as promising candidates for the water–gas shift (WGS) reaction at low temperatures. Two main mechanisms have been proposed in the literature, the redox and associative mechanisms. A key step in both mechanisms has been considered to be the cleavage of O–H bonds. In this mechanistic study, the role of surface and bulk oxygen species involved in the WGS reaction over ceria-supported gold catalysts (Au/CeO2) was elucidated directly using operando Raman spectroscopy combined with isotope labeling and supported by DFT+U calculations. Exposure of Au/CeO2 to pure H218O results in a complete replacement of surface 16O ions by 18O ions as rationalized by dissociative adsorption of H218O in the presence of a surface oxygen vacancy and a subsequent backward reaction restoring lattice oxygen as 18O and releasing H216O. This reaction pathway is accessible even in the absence of CO. Exposure to reaction conditions leads to (i) a complete disappearance of the...