Quo Vadis Micro-Electro-Mechanical Systems for the Study of Heterogeneous Catalysts Inside the Electron Microscope?
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REVIEW
Quo Vadis Micro‑Electro‑Mechanical Systems for the Study of Heterogeneous Catalysts Inside the Electron Microscope? Maxime Boniface1,2 · Milivoj Plodinec1 · Robert Schlögl1,2 · Thomas Lunkenbein1 Accepted: 4 November 2020 / Published online: 17 November 2020 © The Author(s) 2020
Abstract During the last decade, modern micro-electro-mechanical systems (MEMS) technology has been used to create cells that can act as catalytic nanoreactors and fit into the sample holders of transmission electron microscopes. These nanoreactors can maintain atmospheric or higher pressures inside the cells as they seal gases or liquids from the vacuum of the TEM column and can reach temperatures exceeding 1000 °C. This has led to a paradigm shift in electron microscopy, which facilitates the local characterization of structural and morphological changes of solid catalysts under working conditions. In this review, we outline the development of state-of-the-art nanoreactor setups that are commercially available and are currently applied to study catalytic reactions in situ or operando in gaseous or liquid environments. We also discuss challenges that are associated with the use of environmental cells. In catalysis studies, one of the major challenge is the interpretation of the results while considering the discrepancies in kinetics between MEMS based gas cells and fixed bed reactors, the interactions of the electron beam with the sample, as well as support effects. Finally, we critically analyze the general role of MEMS based nanoreactors in electron microscopy and catalysis communities and present possible future directions. Keywords MEMS · TEM · In situ · Operando · Characterization · Catalysis
1 Introduction Micro-electro-mechanical systems (MEMS) refer to devices that have characteristic dimensions in the micrometer regime. They combine electrical and mechanical components on a single chip and are fabricated by integrated circuit batch-processing technologies. In recent years the level of miniaturization and integration of MEMS technology has been used to scale down laboratory systems such as sensors or heaters to length-scales that are compatible with electron microscopes and allows for their integration. This has enabled a new era of in situ (scanning) transmission electron Dedicated to Prof. Dr. Norbert Kruse on the occasion of his 70th birthday. * Thomas Lunkenbein lunkenbein@fhi‑berlin.mpg.de 1
Department of Inorganic Chemistry, Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany
Department of Heterogeneous Reactions, Max Planck Institute for Chemical Energy Conversion, 45413 Mülheim a.d. Ruhr, Germany
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microscopy ((S)TEM), which is a reference technique for the spatially-resolved structural and chemical analysis of solids [1–4]. These novel lab-on-a-chip systems enable live imaging of structural and morphological changes of solids from the microscale down to the atomic scale under various external stimuli, such as heat, mechanical stress or electrical bias, which can be also combined with
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