PdGa Alloy Dynamics under CO2 Hydrogenation from Surface Organometallic Chemistry on a Chip and Operando Transmission Electron Microscopy.

Industrial processes rely on the use of promoter elements to improve the performance of catalysts. Despite considerable efforts, the fundamental understanding of the origin of promotion remains elusive, partly due to the inherent complexity of catalytic systems. In this work, we develop a surface organometallic chemistry approach on an in situ MEMS chip for the preparation of tailored PdGa nanoparticles enabling to monitor the dynamic response of their structure and reactivity under a range of conditions ─ including CO2 hydrogenation ─ via operando (scanning) transmission electron microscopy. Upon air exposure, the PdGa nanoparticles exhibit a core-shell structure, which vanishes after reduction in H2, forming alloyed PdGa nanoparticles exhibiting structural defects. Notably, under CO2 hydrogenation conditions (3:1 H2:CO2, 230 °C) at 1 bar, PdGa-GaOx interfaces are dynamically formed, while methanol is concomitantly detected. This study reveals the highly dynamic nature of PdGa catalysts and points out the promotional role of Ga in driving methanol synthesis under CO2 hydrogenation via the formation of MGa-GaOx interfaces.