Quasi in‐situ catalytic studies using a TEM grid microreactor

Abstract

Conventionally, catalysts are analyzed in the transmission electron microscope (TEM) under static conditions in the vacuum. However, catalysts surfaces dynamically response to the reaction conditions. In addition, comparing TEM images before and after the catalytic reaction may give conclusions that are difficult to verify, because of the inhomogeneous conditions along the catalyst in normal fixed bed reactors [1]. For obtaining relevant information it is advisable to study the material under catalytic relevant conditions (gas composition, pressure, temperature) which also includes the monitoring of conversion. Therefore, in‐situ TEM approaches, such as environmental TEM (ETEM) or microelectromechanical systems (MEMS)‐based gas cell TEM holders, were developed. They allow the direct observation of the dynamic changes of a catalyst during the prevailing time of a reaction [2]. However, drawbacks regarding the reaction pressure and fast dynamics give rise to pressure gaps and may limit the resolution, respectively. To overcome these limitations we have developed a TEM grid microreactor that allows a decoupling of the catalytic reaction and the imaging process. This quasi in‐situ method combines relevant and well‐controlled conditions for all catalyst particles at ambient pressure with high resolution imaging of exactly the same particles. In order to avoid the exposure to ambient air, a secure transfer of the catalyst to and from the TEM can be guaranteed via the glovebox and vacuum transfer holders. Furthermore, the catalytic conversion can be followed by using an ultra‐sensitive proton‐transfer reaction mass spectrometer (PTR‐MS). Here, we present the utilization of this microreactor in the CO oxidation over metal catalysts. For instance, identical location imaging of active Pt nanoparticles (proven by PTR‐MS measurements) reveals structural changes, which are induced by the catalytic process (Figure 1). In conclusion, the microreactor complements the state of the art in‐situ imaging, where one can study the structural dynamics, by delivering catalytic relevant kinetic information, which can be coupled to changes on the atomic scale.