Origin of the unique activity of Pt/TiO2 catalysts for the water-gas shift reaction

Periodic density functional theory calculations and microkinetic modeling are used to illustrate the specific role of the three-phase boundary (TPB) in determining the activity and selectivity of TiO2-supported Pt catalysts for the water-gas shift (WGS) reaction. The Pt-8/TiO2(1 1 0) catalyst model identified from a systematic ab initio atomistic thermodynamics study is used to investigate the redox mechanism and associative pathway with redox regeneration of the WGS reaction. Analysis of a microkinetic model determined exclusively from first principles suggests that a CO-promoted redox pathway dominates in the low-temperature range of 473-623 K and the classical redox pathway becomes dominant at temperatures above 673 K. The improved activity of the TPB compared to the Pt(1 1 1) surface can be explained by a reduced CO adsorption strength on Pt sites at the TPB, an increased number of oxygen vacancy at the TPB, and a significantly facilitated water activation and dissociation. (C) 2013 Elsevier Inc. All rights reserved.