(44g) Tuning Nanozeolite Hydrophobicity to Create Highly Active Catalysts for Alcohol Ring Opening of Epoxides

Catalytic activity can be significantly impacted by molecular interactions beyond the catalytic site in the outer sphere (e.g., solvation). The key challenge is to identify synthetic methods to control this catalytic reaction environment. In this work, we investigate how the molecular interactions between the catalyst and the substrates impact catalytic activity. These molecular interactions are tuned through controlling the hydrophobicity of the material through healing defects in the material. We synthesize a hydrophilic Lewis acid nanozeolite to produce nano-Sn-Beta. We have previously shown that nano-Sn-Beta can overcome diffusion limitations commonly observed with conventional Sn-Beta. Whereas conventional Sn-Beta is synthesized using fluoride ions to produce a material with few silanol defects, nano-Sn-Beta uses hydroxide ions as the mineralizing agent, leading to a hydrophilic material containing many silanols. We treat nano-Sn-Beta with tetraethyl ammonium fluoride to heal defects and reduce silanol content, as characterized through ²⁹Si NMR, TGA, and FTIR. The hydrophobic catalyst exhibits a significant increase in catalytic performance (90% increase in TOF₀) over the untreated material for the Lewis acid catalyzed epoxide ring opening with alcohols. Lewis base site quantification experiments confirm there is no change in the number of catalytic sites. ³¹P NMR with trimethylphosphine oxide, DRIFTS with deuterated acetonitrile, analysis of residual fluorine, and similar E_app suggest that there is little change in the nature of the active Sn site, and that the increased catalytic activity is attributed to beneficial entropic effects from the increased hydrophobic environment. Overall, this work will demonstrate the facile post-synthetic modification of nano-Sn-Beta to produce a hydrophobic zeolite framework and the effect of hydrophobicity on catalytic activity and selectivity.