Combined DFT and Operando Spectroscopic Study of the Water-Gas Shift Reaction over Ceria-Based Catalysts: The Role of the Noble Metal and Ceria Faceting

Abstract

Ceria loaded with noble metals (Cu, Au) is a highly active material for the lowtemperature water-gas shift reaction (LT-WGSR), but nevertheless details of the metal-support interaction as well as the role of the ceria surface termination and the metal loading are still unclear. Using operando Raman and UV/Vis spectroscopy combined with theoretical DFT calculations, we aim at a molecular-level understanding of LT-WGSR catalysts. In particular, by using this combined approach, we are able to draw conclusions about the reducibility state of the ceria support during reaction conditions. Our results show that the defect formation energy of the support does not play a major role for the WGSR, but rather other reaction steps like the dissociation of water or the desorption of CO2.

Approaching C1 Reaction Mechanisms Using Combined Operando and Transient Analysis: A Case Study on Cu/CeO2 Catalysts during the LT-Water–Gas Shift Reaction

“…Interestingly, the activities are very different from those of Cu/CeO 2 catalysts prepared by IWI, which is expected to result in lower copper dispersions than the DP method. According to Figure , polyhedra- and sheet-based catalysts gave by far the highest conversions, while for the catalysts in ref prepared by IWI, the cubes were more active than the polyhedra, which is consistent with literature results on 5 wt % Cu/CeO 2 catalysts prepared by the DP method . It needs to be mentioned, however, that for the catalysts used in this study, the copper loading was about 10 times smaller and thus on average smaller copper clusters are expected to be present on the surface .…”

“…Under these conditions, the bare ceria samples show no significant WGS activity. Interestingly, the activities are very different from those of Cu/CeO 2 catalysts prepared by IWI, 59 which is expected to result in lower copper dispersions than the DP method. According to Figure 1, polyhedra-and sheet-based catalysts gave by far the highest conversions, while for the catalysts in ref 59 prepared by IWI, the cubes were more active than the polyhedra, which is consistent with literature results on 5 wt % Cu/CeO 2 catalysts prepared by the DP method.…”

On the Utility of Ce3+ Spin−Orbit Transitions in the Interpretation of Rate Data in Ceria Catalysis: Theory, Validation, and Application

“…Cerium oxidethe most abundant rare-earth oxide in the earth’s crustis a common component in catalytic applications, examples of which include its use as an oxygen storage material in automotive exhaust emissions catalysis, − as a catalyst for water splitting and water–gas shift reactions, − as an electrolyte in solid oxide fuel cells and oxygen membranes, , and as a catalyst support or promoter for a broad range of organic transformations. ,, Especially important is its use in expanding the operating window for three-way catalysts , an application enabled by its propensity to act as a reversible oxygen sponge through the creation and healing of oxygen vacancies during rich and lean cycles, respectively. − …”