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

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/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) 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.

Stability of Cobalt Particles In and Outside HZSM‐5 under CO Hydrogenation Conditions Studied by ex situ and in situ Electron Microscopy

“…Those methods are performed preferably as close as possible to typical operating conditions. However, the detailed molecular understanding remains a significant technical challenge [27–30] …”

“…However, the detailed molecular understanding remains a significant technical challenge. [27][28][29][30] One of the most attractive techniques for characterization on an atomic scale is transmission electron microscopy (TEM), as it provides spatially-resolved information on the cobalt nanoparticle size distribution and the morphology. [31] In particular, environmental TEM (ETEM) allows investigation of the catalyst evolution under controlled gas environment and elevated temperatures.…”

Correlative Laboratory Nano‐CT and 360° Electron Tomography of Macropore Structures in Hierarchical Zeolites

“…Lab Nano‐CT reaches almost the same spatial resolution as synchrotron Nano‐CT. However, the latter technique enables shorter acquisition times, which are beneficial for in situ and operando experiments like in situ X‐ray ptychography, [ 5d,40 ] operando Micro‐CT of Li‐ion battery materials, [ 16b,41 ] interrupted in situ Nano‐CT of mechanical testing, [ 42 ] in situ and operando Nano‐CT of fuel cell electrodes [ 43 ] or environmental in situ Nano‐CT of a fuel cell. [ 44 ] Similar experiments can also be realized on lab Nano‐CT instruments, albeit at lower temporal resolution or by interrupted in situ experiments, where before and after an experiment, e.g., mechanical testing [ 45 ] or in situ heating, [ 46 ] Nano‐CT datasets are collected.…”

Sorption enhanced dimethyl ether synthesis under industrially relevant conditions: experimental validation of pressure swing regeneration

“…This deactivation can be caused by the competing adsorption of water, dimers, trimers, or even larger alcohol-water clusters, but also the (reversible) formation of (surface) boehmite was shown. 27 Despite the large attention for more active low-temperature methanol dehydration catalysts, 4,6,59,69,71,73,74,[76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95] γ-Al 2 O 3 remains the catalyst of choice for industrial DME production, due to its low cost, high surface area, good thermal and mechanical stability, and high selectivity to DME because its relatively weak Lewis acid sites do not promote side reactions. 4,70,96,97 In contrast to direct DME synthesis, SEDMES offers two specific advantages for the (γ-Al 2 O 3 ) catalyst: the system is operated at low steam pressures and is periodically regenerated due to its adsorptive nature.…”