(704h) Reaction Mechanisms for Aldol Condensation Determined By Topology of CeO2 Catalyst Facets
AIChE Annual Meeting
Tuesday, November 17, 2020 - 9:15am to 9:30am
Here, we explore the role of geometric and acid-base properties on the mechanism of the aldol condensation reaction catalyzed by CeO2 nanoshapes, combining experimental kinetics and DFT calculations. In the crucial CâC coupling step, the two carbonyl adsorbates are bound to two adjacent cations. On the CeO2 (110) plane, all atoms lie on the same layer, favoring the interaction between adsorbates and facilitating the bimolecular CâC coupling. Thus, the initial unimolecular deprotonation is rate limiting. By contrast, the (100) and (111) planes have open structures with O on the top layer and Ce on the layer below. The O layer interferes between adsorbates linked to Ce sites, making the CâC coupling rate limiting. As one of the major products, water helps overcoming this spatial hindrance by remote bond polarization via H-bonds. Therefore, water promotion is only observed on those planes for which the bimolecular step is rate limiting.