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

Abstract

Conspectus Heterogeneous 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...

Exploration and Insight of Dynamic Structure Evolution for Electrocatalysts

“…To advance the understating of electrocatalyst structure evolution, it is essential to combine electrochemical methods and in situ/operando spectroscopy technologies, such as X-ray absorption spectroscopy. This approach enables the observation of dynamic behavior of electrocatalyst evolution, including key details of the active states, and helps to clarify the internal mechanism . Electrochemistry can provide overall insights into the evolution behavior of electrochemical cells and their components, and by coupling it with element-specific spectroscopic techniques, it is possible to further correlate electrochemical performance with changes in the oxidation state of specific elements at the atomic scale, thus allowing us to reveal the evolution of these elements in a coordination environment.…”

“…This approach enables the observation of dynamic behavior of electrocatalyst evolution, including key details of the active states, and helps to clarify the internal mechanism. 57 Electrochemistry can provide overall insights into the evolution behavior of electrochemical cells and their components, and by coupling it with element-specific spectroscopic techniques, it is possible to further correlate electrochemical performance with changes in the oxidation state of specific elements at the atomic scale, thus allowing us to reveal the evolution of these elements in a coordination environment. Moreover, considering that electrochemistry and in situ spectroscopy measure macroscopic current and microscopic electron gain and loss of elements, respectively, their combination realizes fine tracking of electrons.…”

In Situ TEM Characterization and Modulation for Phase Engineering of Nanomaterials

“…With decades of technological advancement, so-called controlled atmosphere transmission electron microscopy (CATEM) or environmental transmission electron microscopy (ETEM) has been developed and utilized to investigate the interactions between nanomaterials and various environmental factors, including gas type, temperature, and pressure, in real time. There are two main types of ETEM methods proposed so far (Figure ): the aperture approach, which relies on a specially designed gaseous sample chamber of the TEM (also referred to as the ETEM method), and the window approach, which uses a customized TEM holder with a MEMS-based nanoreactor (also referred to as the gas holder method). ,, …”

“…There are two main types of ETEM methods proposed so far (Figure 33): the aperture approach, which relies on a specially designed gaseous sample chamber of the TEM (also referred to as the ETEM method), and the window approach, which uses a customized TEM holder with a MEMS-based nanoreactor (also referred to as the gas holder method). 200,395,396 The key feature of the aperture approach is the use of a pair of small pressure-limiting apertures located on both sides of the specimen, which restrict the leakage of gas molecules into the high vacuum TEM column (Figure 33a, left). The balance of the chamber gas pressure is controlled by the size of the small apertures and the connected differential pumping system.…”

Direct Operando Visualization of Metal Support Interactions Induced by Hydrogen Spillover During CO2 Hydrogenation

“…As a result, locating active sites within heterogeneous catalysts has been identified as a fundamental knowledge gap and the latest challenge shared by microscopy and catalysis communities. [23,24] Gas-phase electron microscopy studies represent the forefront of operando investigations, providing singleparticle and subnanometer resolutions necessary to distinguish between different surface sites (Figure 1d), and locate those sites sufficiently close to the supported NP to enable reagent interaction and contribute to the reaction. [16] Very recently, the impact of TiO 2 as a reducible support for CO 2 hydrogenation showed the evolution of strong MSI overlayers under reaction conditions using operando electron microscopy to identify the active catalyst -support dynamic and explain activity and selectivity trends.…”