Brookite-TiO<sub>2</sub>-Supported Pt Bilayers for the Low-Temperature Water–Gas Shift Reaction
Wenning Zhao, Junjun Wang, Xixiong Zhang, Guanghui Zhang, Yong Li, Zheng Jiang, Mingrun Li, Yan Zhou, Yuemin Wang, Wenjie Shen
Abstract
Highly dispersed Pt species, typically subnanometric clusters and single-atoms, feature catalysis that differed significantly from that of the faceted nanoparticles. However, the catalytic chemistry of these size-specified Pt entities is still a subject of debate. Here, we report that metallic Pt clusters in a bilayer geometry, dispersed on TiO 2, served as the active phase for the low-temperature water–gas shift reaction. The control of Pt dispersion was done by treating a Pt/TiO 2 sample, where 3 nm Pt particles dispersed over rod-shaped brookite-TiO 2, with oxidative and reductive gases at elevated temperatures (673–873 K). The oxidative treatment of the Pt/TiO 2 precursor yielded subnanometric PtO x clusters (<1 nm) at 773 K and cationic Pt single-atoms at 873 K. Combined microscopic and spectroscopic characterizations revealed that the PtO x clusters had a monolayer geometry, in which the Pt atoms were loosely connected via the Pt–O–Pt bond and chemically anchored on the surface of TiO 2 via the Pt–O–Ti bond. While the cationic Pt single-atoms not only located on the surface but also diffused into the subsurface/bulk of TiO 2, presenting in diverse coordination environments. Catalytic evaluations found that the subnanometric PtO x clusters were more active for the low-temperature water–gas shift reaction than the cationic Pt single-atoms. More interestingly, the H 2 -reduction of the PtO x clusters at 773 K resulted in metallic Pt clusters that adopted predominately a bilayer geometry at an appropriate Pt 0 /(Pt 0 + Pt 2+ ) ratio. The surficial metallic Pt atoms tuned the electronic structure of the positively charged Pt atoms at the Pt–TiO 2 interface and thus enhanced the catalytic activity dramatically.