Transition state stabilization depends on solvent identity, pore size, and hydrophilicity for epoxidations in zeolites

Ti-silicates activate H2O2 to form Ti-hydroperoxo and Ti-peroxo intermediates that can react with alkenes epoxide products. Comparisons of kinetics for 1-octene epoxidation on Ti-BEA Ti-MFI catalysts different hydrophilicities in methanol (CH3OH) or acetonitrile (CH3CN) solvents show the significance solvent stabilizing catalytically-relevant species complex interdependencies between solvent, catalyst topology, hydrophilicity. Epoxidation turnover rates are higher CH3CN than CH3OH Ti-BEA, but opposite trend is observed Ti-MFI. greater silanol densities, however, give their hydrophobic counterparts both solvents. Kinetic, spectroscopic, thermodynamic analyses differences mainly arise from changes stabilization reactive surface by mediated interactions, because mechanism reaction stability fluid-phase reactants remain similar CH3OH. Specifically, apparent activation free energy values (?GApp‡) indicate responsible alkene stabilized a extent Hydrophilic present lower ?GApp‡ regardless identity, which suggests these correspond number hydrogen-bonding molecules found near bound Ti active sites. Taken together, findings demonstrate role allowing recognize properties sites beyond length-scale covalent bonds, carry implications also other reactions within solvent-filled pores microporous materials.