Stability of a Bifunctional Cu-Based Core@Zeolite Shell Catalyst for Dimethyl Ether Synthesis Under Redox Conditions Studied by Environmental Transmission Electron Microscopy andIn SituX-Ray Ptychography

Abstract

AbstractWhen 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/Al2O3@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) andin situhard X-ray ptychography with a specially designedin situcell. 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 andin situX-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 situX-ray ptychography indicated the occurrence of structural changes also on theµm 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 correlativein situmicroscopy techniques for hierarchically designed catalysts.