Abstract
Direct conversion of methane to value-added oxygenate products is of considerable importance for effective valorization of methane, but remains a grand challenge in heterogeneous catalysis due to the high energy barrier required for the first CH bond activation and facile overoxidation of products. Generally, there exists a scaling relationship in direct conversion of methane that is a lower activation energy for methane dissociation always accompanies with undesired lower activation energy for overoxidation. In this study, by combining theoretical calculations and experiments, we systematically investigated the CO-assisted low-temperature selective oxidation of methane using H2O2 under aqueous conditions over atomically dispersed Rh/ZrO2. The results reveal that the introduction of CO on Rh/ZrO2 breaks the scaling relationship, which not only facilitates methane activation and conversion benefiting from the Rh-CO coordination, leading to a substantial enhancement of oxygenate products yield, but also prevents the overoxidation of CH3 species, achieving the improvement of methane activation and suppression of overoxidation concurrently. The dynamic metal-intermediate coordination-induced reactivity modulation mechanism was unveiled, in which electronic state and catalytic property of Rh-O active center dynamically changes along with the change of Rh-intermediate coordination during the reaction, giving rise to the dynamic shift of reactivity descriptors towards more optimal values and consequently enabling the facilitation of the initial CH bond activation while suppression of the following overoxidation. This study opens up new perspectives to tune the catalytic performance and offers a comprehensive picture of the dynamics of atomically dispersed Rh-based catalysts in the field of selective oxidation of methane.
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