(677b) Solvation of Water and Alkanols Confined within Brønsted Acid Zeolites: Kinetic Effects of Protonated Clusters and Extended Networks
AIChE Annual Meeting
2020 Virtual AIChE Annual Meeting
Catalysis and Reaction Engineering Division
Fundamentals of Catalysis and Surface Science III: Solvent Effects in Microporous Materials
Thursday, November 19, 2020 - 8:15am to 8:30am
Turnover rates (373 K, per H+) of gas-phase ethanol dehydration to diethyl ether (DEE), adsorption isotherms, and infrared (IR) spectra, are measured on a suite of H-Al-Beta-F zeolites of varying Al content and silanol defect density. The structures of most-abundant (C2H5OH)(H+)(H2O)n clusters are corroborated by ab initio molecular dynamics simulations, and IR spectra show that extended hydrogen-bonded networks form as capillary condensation occurs (10â75 kPa H2O). Kinetic data and metadynamics simulations show that solvation of (C2H5OH)(H+)(H2O)n clusters and transition states by extended solvent networks causes strong inhibition (PH2O-3), which is described by non-ideal thermodynamic formalisms that account for the more extensive disruption of hydrogen bonds by DEE transition states relative to the relevant precursors. We also show how different micropore geometries influence the reorganization of such water networks.
Turnover rates (373 K, per H+) of gas-phase bimolecular dehydration of C2H5OH-CH3OH mixtures to form methyl ethyl ether (MEE) and dimethyl ether (DME) products on a CHA zeolite are measured under conditions where H+ are covered by (H+)(CH3OH)n clusters (n = 1â4). The dependence of DME and MEE formation rates on CH3OH pressure is consistent with kinetically relevant formation of DME through trimolecular pathways, whereas larger MEE transition states prefer bimolecular pathways. The speciation of protonated clusters that influence kinetics within alkanol-filled pores contrasts the preeminence of extended hydrogen-bonded networks and their reorganization within H2O-filled micropores.