Surface Speciation\nin Microwave-Assisted CO Oxidation\nover PerovskitesThe Role of Water and Activation Pretreatment

As a model for the energy-efficient aftertreatment of\nexhaust gas\ncomponents, we studied microwave-assisted (MW) CO oxidation over a\n(La,Sr)CoO<sub>3‑δ</sub> (LSC) perovskite oxide catalyst\nunder dry and humidified conditions. We found that the use of a MW-based\nprocess can offer multiple advantages over traditional thermocatalysis\nin this scenario, as the nature of the MW-solid interaction offers\nquick, adaptive, and energy-efficient heating as well as improved\nyield and lower light-off temperatures. As found by combined CO and\nwater MW-desorption experiments, the presence of technically relevant\namounts of water leads to a competition for surface active sites and\nthus slows the reaction rate without indications for a fundamental\nchange in the mechanism. Remarkably, the performance loss related\nto the presence of water was less pronounced in the MW-assisted process.\nAdditionally, while we recorded a temperature-dependent degradation\nof the reaction rate in extended MW-catalysis experiments both in\ndry and humidified conditions, it quickly recovered after a short\nreactivation MW-treatment. Our study confirms that surface reaction\ncan be driven by the use of MW-radiation in a similar magnitude that\ncan be achieved by thermal activation at significantly higher temperatures.\nThe nature of the effect of the MW-treatment on the structural and\nelectronic surface properties of the LSC material was investigated\nby X-ray absorption (XAS) and X-ray photoelectron spectroscopy (XPS).\nWe found evidence of a significant structural, chemical, and electronic\nreorganization of the oxide surface, possibly consistent with the\noccurrence of overheated surfaces or “hotspots” during\nMW-exposure, which may explain the increased catalytic and heating\nproperties of the LSC after the MW-pretreatment. The good catalytic\nperformance, quick response to MW-heating, and long-term stability\nof the catalyst all indicate the promising potential of a MW-based\nprocess for the energy-efficient exhaust aftertreatment using noble-metal-free\noxide catalysts.