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

Abstract

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 Pt8/TiO2(110) 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 473–623K and the classical redox pathway becomes dominant at temperatures above 673K. The improved activity of the TPB compared to the Pt(111) 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.