Toward In Situ Atomistic Design of Catalytic Active Sites via Controlled Atmosphere Transmission Electron Microscopy

ConspectusHeterogeneous catalysts are widely used in a variety of industrial fields, including environmental protection, energy conversion, and chemical production. Their performance during reactions is usually determined by a small fraction of sites at the catalyst surfaces/interfaces, namely, the active sites. Actually, since the concept of the "active sites" was proposed by Hugh Taylor in the 1920s, determining the active site at the atomic level and understanding the molecular processes that happened at the active site have become the top priority in catalysis research. Researchers tried different methods to acquire various information related to the surface/interface active sites, pursuing their rational design at the atomic level. Although great achievements have been made in catalyst surface study, in situ atomistic design of active sites remains challenging, due to the lack of direct information and effective manipulation means concerning the active sites. Specifically, many critical issues regarding the active sites under reaction conditions remain to be solved: (1) precisely identifying the active sites, which is the foundation for understanding the catalytical mechanism and rational design of the catalyst; (2) accurately manipulating the surface/interface active sites at the atomic scale, which is the basis for realizing the desired performance; (3) maintaining these designed active sites operating in a long-term with high efficiency without deactivation, which is extremely important to the practical applications of the catalysts. All these aspects rely on the fundamental understanding of the interactions between different surface/interface configurations of the catalyst and external environments (gas, pressure, temperature, etc.).In this Account, we present the recent progress in our group on the studies of surface/interface active sites via controlled atmosphere transmission electron microscopy (CATEM). We first briefly introduce the advances in CATEM technologies, including the window (closed) approach and aperture (open) approaches. Then, the challenge of identifying active sites is discussed, and our efforts in this target by determining surface atomic structures, tracking the active components, visualizing reacting molecules, and in situ evaluating catalytic performance are demonstrated. The next section focuses on the in situ manipulating active sites by controlling external environmental factors (e.g., gas, temperature, and pressure), including tailoring the catalyst shape, surface components, and interface with atomic precision. The fourth section discusses the strategies for the long-term stable operation of the active sites based on our in situ studies in understanding the deactivation mechanisms. In the end, we provide our perspectives on the future opportunities and some scientific and technical challenges in this booming area. This Account highlights the in situ atomic level design of the active sites based on the CATEM route, which provides an applicable strategy for deep understanding and the rational design of the catalyst active sites.