Revealing Phase-Dependent Catalytic Behavior of Ru Nanoparticles via Operando TEM.

The crystal phase of metal nanocatalysts plays a critical role in determining their catalytic performance, yet the atomic-scale mechanisms underlying their phase-dependent reactivity remain poorly understood. Here, using operando gas-cell transmission electron microscopy (TEM), we directly correlate the crystal structures of Ru nanoparticles (NPs) with their catalytic behavior during CO oxidation. We find that face-centered cubic (fcc) Ru exhibits high catalytic activity and structural stability, whereas hexagonal close-packed (hcp) Ru deactivates rapidly because of its pronounced susceptibility to oxidation. Furthermore, the transformation of fcc Ru NPs to hcp phase results in a marked loss of catalytic activity, underscoring the detrimental impact of phase instability under reaction conditions. These findings highlight the importance of direct observation of catalysts in reactive environments and provide mechanistic insights crucial for the rational design of phase-engineered nanocatalysts.