Phase Separation of CuPd Alloy Nanocatalysts in CO Oxidation

Alloy nanocatalysts exhibit enhanced activity, selectivity, and stability mainly due to their versatile phases and atomic structures. However, nanocatalysts' "real" functional structures may vary from their as-synthesized status due to the structural and chemical changes during the activation and reaction conditions. Herein, we studied the activated CuPd/CeO₂ nanocatalysts under the CO oxidation reaction featuring an atomic-scale phase separation process, resulting in a notable "hysteresis" in catalyst performance. Through the "identical-location" transmission electron microscopy (TEM) characterization, we found that the CuPd nanoparticles (NPs) evolve to a Cu₂O/CuPd or CuPdO_<i>x</i> phase depending on different surface planes of CeO₂ supports under the reaction condition. The detailed dynamic information is obtained by <i>in situ</i> environmental TEM-<i>in situ</i> DRIFTS characterizations to further decouple the effect of pure CO and O₂ gas. The interfacial binding energies between alloy nanoparticles and CeO₂ supports are found to play a critical role in determining the phase separation behaviors. These atomic insights highlight the importance of both the phase separation of alloy nanocatalysts and <i>in situ</i> characterizations of "live" catalysts.