Stabilization of Alkanol-Alkanone Heteroclusters in Medium-Pore Zeolites Drives Orders-of-Magnitude Rate Enhancements in Proton-Catalyzed Dehydration Reactions

Modern catalytic approaches to manipulating reactivities predominantly rely on (post-)synthetic methods that engineer active sites and their local environments from a materials perspective, while the dynamic creation and disruption of reactive and spectator species through co-adsorbate interactions is much less explored and understood. Herein, C₃─C₆ aliphatic alkanones have been identified as potent promotors for Brønsted acid-catalyzed alkanol dehydration within the subnanometric zeolite pores, with the MFI topology being the most efficacious (up to two orders of magnitude rate enhancement and > 99.8% olefin) and featuring a remarkable stability (> 140 h on stream) at both kinetically limited and practically relevant conversions. Rigorous kinetic descriptions are combined with density functional theory methods to assess the structures, stabilities and reactivities of all plausible intermediates derived from the reactant and cofeed during 2-propanol (IPA) dehydration in MFI pores. Stoichiometric clustering of alkanones with IPA-derived monomers and dimers, driven by strong H-bonds and stabilized by pore confinement, induces the formation of protonated bi- and termolecular species with distinct reactivities for intra- and intermolecular dehydration, which depends on the alkanone identity. These mechanistic underpinnings reward us with an ability to predict reactivity and selectivity trends and rationally design optimal solvent systems or cofeeding schemes for alkanol dehydration.