Reversible transformation between terrace and step sites of Pt nanoparticles on titanium under CO and O2 environments

Abstract

Understanding the dynamic evolution of active sites of supported metal catalysts during catalysis is fundamentally important for improving its performance, which attracts tremendous research interests in the past decades. There are two main surficial structures for metal catalysts: terrace sites and step sites, which exhibit catalytic activity discrepancy during catalysis. Herein, by using in situ transmission electron microscopy and in situ Fourier transform infrared spectroscopy (FTIR), the transformation between surface terrace and step sites of Pt-TiO2 catalysts was studied under CO and O2 environments. We found that the {111} step sites tend to form at {111} terrace under O2 environment, while these step sites prefer to transform into terrace under CO environment at elevated temperature. Meanwhile, quantitative ratios of terrace/step sites were obtained by in situ FTIR. It was found that this transformation between terrace sites and step sites was reversible during gas treatment cycling of CO and O2. The selective adsorption of O2 and CO species at different sites, which stabilized the step/terrace sites, was found to serve as the driving force for active sites transition by density functional theory calculations. Inspired by the in situ results, an enhanced catalytic activity of Pt-TiO2 catalysts was successfully achieved through tuning surface-active sites by gas treatments.