(564e) Enhancing Hydrophobicity and Catalytic Activity of Nano-Sn-Beta for Alcohol Ring Opening of Epoxides through Post-Synthetic Treatment with Fluoride

Elucidation of structure-function relationships can enhance the performance of catalytic materials used for many reactions. Indeed, it has become increasingly evident that molecular interactions beyond the catalytic site in the outer sphere (e.g., solvation) significantly impact catalytic activity. The key challenge is to control this catalytic reaction environment. In this work, a highly active catalyst is achieved by tuning the molecular interactions between the catalyst and the substrates through post-synthetically modifying the hydrophobicity of the material. First, a hydrophilic Lewis acid nanozeolite is synthesized using a hydrothermal conditions 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 as the mineralizing agent, leading to more hydrophilic materials containing silanols. Building on the few examples that modify the hydrophobicity of MFI, we treat nano-Sn-Beta with tetraethyl ammonium fluoride to heal defects and reduce silanol content throughout the crystal, thereby increasing its hydrophobicity, as characterized through ²⁹Si NMR, TGA, and FTIR. The treated 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.