A modular plug-and-play reaction platform for operando SEM investigations under fixed-bed conditions.

Fixed-bed reactors are widely employed in heterogeneous catalysis, providing controlled gas flow, efficient gas-solid contact, homogeneous heating and quantitative analysis of catalytic performance. Here, we present a modular platform for operando scanning electron microscopy (OSEM) inspired by these key design principles of fixed-bed reactors, while remaining compatible with the constraints of SEM operation. We demonstrate the system's capabilities using copper oxide reduction and the technologically relevant CO₂ hydrogenation over a zincian malachite catalyst as benchmark reactions. We further explore how pressure influences product distribution during CO₂ hydrogenation over a spinel catalyst. By combining the imaging ability of electron microscopy with quantitative performance analysis in the proposed configuration, the platform unlocks catalytic insights during activation, reaction and deactivation that were previously inaccessible to conventional SEM approaches.