Microsc. Microanal. 23, 501–512, 2017 doi:10.1017/S1431927617000332 © MICROSCOPY SOCIETY OF AMERICA 2017 Stability of a Bifunctional Cu-Based Core@Zeolite Shell Catalyst for Dimethyl Ether Synthesis Under Redox Conditions Studied by Environmental Transmission Electron Microscopy and In Situ X-Ray Ptychography Sina Baier, 1 Christian D. Damsgaard, 2,3 Michael Klumpp, 4 Juliane Reinhardt, 5 Thomas Sheppard, 1,6 Zoltan Balogh, 2 Takeshi Kasama, 2 Federico Benzi, 1 Jakob B. Wagner, 2 Wilhelm Schwieger, 4 Christian G. Schroer, 5,7 and Jan-Dierk Grunwaldt 1,6, * 1 Institute for Chemical Technology and Polymer Chemistry, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany 2 Center for Electron Nanoscopy, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark 3 Department of Physics, Center for Individual Nanoparticle Functionality, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark 4 Institute of Chemical Reaction Engineering, Friedrich-Alexander University Erlangen-Nürnberg (FAU), 91058 Erlangen, Germany 5 Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607 Hamburg, Germany 6 Institute of Catalysis Research and Technology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany 7 Department Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany Abstract: When using bifunctional core@shell catalysts, the stability of both the shell and core–shell interface is crucial for catalytic applications. In the present study, we elucidate the stability of a CuO/ZnO/Al 2 O 3 @ZSM-5 core@shell material, used for one-stage synthesis of dimethyl ether from synthesis gas. The catalyst stability was studied in a hierarchical manner by complementary environmental transmission electron microscopy (ETEM), scanning electron microscopy (SEM) and in situ hard X-ray ptychography with a specially designed in situ cell. Both reductive activation and reoxidation were applied. The core–shell interface was found to be stable during reducing and oxidizing treatment at 250°C as observed by ETEM and in situ X-ray ptychography, although strong changes occurred in the core on a 10 nm scale due to the reduction of copper oxide to metallic copper particles. At 350°C, in situ X-ray ptychography indicated the occurrence of structural changes also on the μm scale, i.e. the core material and parts of the shell undergo restructuring. Nevertheless, the crucial core–shell interface required for full bifunctionality appeared to remain stable. This study demonstrates the potential of these correlative in situ microscopy techniques for hierarchically designed catalysts. Key words: core–shell catalyst, dimethyl ether, correlative imaging, ETEM, X-ray microscopy I NTRODUCTION In recent years, core@shell materials with hierarchical structures spanning different length scales have attracted a lot of attention in heterogeneous catalysis, as their unique structure has been shown to result in enhanced catalytic behavior (Zhong & Maye, 2001; Sankar et al., 2012; Zaera, 2013; Schwieger et al., 2016). These materials require characterization on different length scales, where micro- scopic studies are one of the key techniques available (Weckhuysen, 2009; Basile et al., 2010; Grunwaldt & Schroer, 2010; Andrews & Weckhuysen, 2013; Grunwaldt et al., 2013). In general, core@shell-type catalysts can be divided into three groups based on the specific function of the core and the shell: (i) Bimetallic core@shell nanoparticles (Zhong & Maye, 2001; Huang et al., 2010; Sankar et al., 2012; Zaera, 2013) in which the catalytic activity of the surface is improved by the core@shell design (length scale: 2–50 nm). (ii) Catalyst core@porous inert shell (Lee et al., 2011; Xu et al., 2013) in which the catalyst lifetime can be improved by encapsulation of the catalytically active core in a porous, protective shell or inside pores (usually in the length scale: 5–200 nm). This can prevent catalyst deactivation through sintering or coking for example. (iii) Catalyst core@porous catalyst shell structures for consecutive, e.g. two-step reactions (Yang et al., 2007, 2010, 2012, 2013; Bao et al., 2011; Lee et al., 2011; Li et al., 2012, 2015a; Nie et al., 2012; Pinkaew et al., 2013; Wang et al., 2013, 2014; Ding et al., 2015; Garcia-Trenco & Martinez, 2015; Phienluphon et al., 2015), in which the hierarchical combination of two catalytically active materials in a core@shell arrange- ment enables two reaction steps in one single process stage [length scale: 500 nm to millimeters, called product design (Ng et al. 2007)]. *Corresponding author. grunwaldt@kit.edu Received July 1, 2016; accepted February 11, 2017 . https://doi.org/10.1017/S1431927617000332 Downloaded from https://www.cambridge.org/core. IP address: 52.71.253.68, on 27 Jul 2021 at 09:52:34, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms