Dynamical Observation and Detailed Description of Catalysts under Strong Metal-Support Interaction

Shuyi Zhang, Philipp N. Plessow, Joshua J. Willis, Sheng Dai, Mingjie Xu, George W. Graham, Matteo Cargnello, Frank Abild-Pedersen, and Xiaoqing Pan, 2016
crystalization of catalysts amorphous titania layer
Image courtesy of Nano Lett

Abstract

Understanding the structures of catalysts under realistic conditions with atomic precision is crucial to design better materials for challenging transformations. Under reducing conditions, certain reducible supports migrate onto supported metallic particles and create strong metal−support states that drastically change the reactivity of the systems. The details of this process are still unclear and preclude its thorough exploitation. Here, we report an atomic description of a palladium/titania (Pd/TiO2) system by combining state-of-the-art in situ transmission electron microscopy and density functional theory (DFT) calculations with structurally defined materials, in which we visualize the formation of the overlayers at the atomic scale under atmospheric pressure and high temperature. We show that an amorphous reduced titania layer is formed at low temperatures, and that crystallization of the layer into either mono- or bilayer structures is dictated by the reaction environment and predicted by theory. Furthermore, it occurs in combination with a dramatic reshaping of the metallic surface facets

Impact Statement

Catalytic behavior of TiO2 supported Pd nanoparticles is studied under sequential reducing and oxidizing environments. The experiments were carried out under 1atm pressure and at elevated temperatures of up to 500 °C. It was observed that TiO2 layer forms, first as a monolayer and then double layer, during the reducing step. Formation for of the double layer resulted in a round-to-faceted transformation of the Pd nanoparticles. High resolution HAADF and ABF STEM imaging, EELS and DFT calculations revealed unprecedented details toward understanding strong metal support interaction of catalysts.