Cooperative Effects between Hydrophilic Pores and Solvents: Catalytic Consequences of Hydrogen Bonding on Alkene Epoxidation in Zeolites

• DOI: 10.1021/jacs.8b12861
• Publication Date: 2019-01-16T21:01:36Z
• Authors: Daniel T. Bregante; Alayna M. Johnson; Ami Y. Patel; E. Zeynep Ayla; Michael J. Cordon; Brandon C. Bukowski; Jeffrey Greeley; Rajamani Gounder; David W. Flaherty
• Keywords: Alkene

Hydrophobic voids within titanium silicates have long been considered necessary to achieve high rates and selectivities for alkene epoxidations with H2O2. The catalytic consequences of silanol groups their stabilization hydrogen-bonded networks water (H2O), however, not demonstrated in ways that lead a clear understanding importance. We compare turnover 1-octene epoxidation H2O2 decomposition over series Ti-substituted zeolite *BEA (Ti-BEA) encompasses wide range densities nests ((SiOH)4). most hydrophilic Ti-BEA gives are 100 times larger than those defect-free Ti-BEA, yet similar all (SiOH)4 densities. These differences cause the also give highest selectivities, which defies conventional wisdom. Spectroscopic, thermodynamic, kinetic evidence indicate these due changes electronic affinity active site, structure Ti–OOH intermediates, or mechanism epoxidation. Comparisons apparent activation enthalpies entropies show reflect favorable entropy gains produced when transition states disrupt H2O clusters anchored near sites. Transition hydrogen bond reactive species, such becomes insensitive presence (SiOH)4. Collectively, findings clarify how molecular interactions between solvent networks, polar surfaces can influence (and other reactions) catalysts.