Phase Separation\nof CuPd Alloy Nanocatalysts in CO\nOxidation

Alloy nanocatalysts exhibit enhanced activity, selectivity,\nand\nstability mainly due to their versatile phases and atomic structures.\nHowever, nanocatalysts’ “real” functional structures\nmay vary from their as-synthesized status due to the structural and\nchemical changes during the activation and reaction conditions. Herein,\nwe studied the activated CuPd/CeO<sub>2</sub> nanocatalysts under\nthe CO oxidation reaction featuring an atomic-scale phase separation\nprocess, resulting in a notable “hysteresis” in catalyst\nperformance. Through the “identical-location” transmission\nelectron microscopy (TEM) characterization, we found that the CuPd\nnanoparticles (NPs) evolve to a Cu<sub>2</sub>O/CuPd or CuPdO<sub><i>x</i></sub> phase depending on different surface planes\nof CeO<sub>2</sub> supports under the reaction condition. The detailed\ndynamic information is obtained by <i>in situ</i> environmental\nTEM–<i>in situ</i> DRIFTS characterizations to further\ndecouple the effect of pure CO and O<sub>2</sub> gas. The interfacial\nbinding energies between alloy nanoparticles and CeO<sub>2</sub> supports\nare found to play a critical role in determining the phase separation\nbehaviors. These atomic insights highlight the importance of both\nthe phase separation of alloy nanocatalysts and <i>in situ</i> characterizations of “live” catalysts.