A theoretical explanation of solvent effects in zeolite catalysis

摘要: In a previous study of solid acid catalysis (Nature (1998) 389, 832) we showed that the catalytic activity zeolites could be increased by coadsorption “solvent” molecules, such as nitromethane. These coadsorbates do not participate directly in reaction, but alter environment within zeolite reactivity is increased. this work provide further theoretical explanation observed upon coadsorption. We first use density functional theory (DFT) to proton affinity acetone, and complexes acetone with propane, bromomethane, nitromethane, nitroethane, nitropropane, acetonitrile. find much higher than for alone. Optimizations frequency calculations at B3LYP/6–311++G** level predict increases range from 0.9 kcal/mol acetone/propane complex 12.8 acetone/acetonitrile complex. The increase due coadsorbed molecules one causes experimentally. also used DFT (B3LYP/DZVP2) optimize geometry acetone–nitromethane contact cluster model HZSM-5. There greater transfer when nitromethane present, reflected shorter distance between acidic carbonyl carbon acetone. Predictions 1H 13C NMR isotropic chemical shifts indicate presence This demonstrates how promote reactivity.