On the Importance of Metal-Oxide Interface Sites for the Water-Gas Shift Reaction Over Pt/CeO2 Catalysts

The objective of this work is to understand the unique catalysis and importance of the three-phase boundary (TPB) of CeO₂ supported Pt catalysts for the water-gas shift (WGS) reaction.  The mechanism of the WGS at the Pt/CeO₂ interface has been investigated using plane wave DFT calculations by considering the following pathways: (i) redox pathway, (ii) associative carboxyl pathway, and (iii) associative carboxyl pathway with redox regeneration. Analysis of a microkinetic model containing all these pathways indicates that the CO promoted carboxyl pathway with redox regeneration is the most favorable pathway with the lowest activation barrier and highest rate. The calculated apparent activation barrier and reaction orders for this pathway are in excellent agreement with experimental values from three independent research groups. In general, this study reveals that the Pt sites away from the TPB likely act primarily as a CO reservoir and the oxide support plays an essential role in O-H bond breaking and H-atom transfer to the metal surface. Overall, catalysis seems to be dominated by interface sites.