Understanding Rates and Regioselectivities for Epoxide Methanolysis within Zeolites: Mechanism and Roles of Covalent and Non-covalent Interactions

David S. Potts, Jessica K. Komar, Huston Locht, David W. Flaherty

Research output: Contribution to journalArticlepeer-review

Abstract

Rates and selectivities for liquid-phase reactions depend on the structure and acidity of active sites within zeolite catalysts and the solvent environment surrounding the active sites. Here, we demonstrate and explain the effects of these interactions on the ring-opening of 1,2-epoxybutane (C4H8O) with methanol (CH3OH) in acetonitrile (CH3CN) solvent over *BEA zeolites by varying the identity of the catalytically active element within the framework (Al, Sn, Ti, Zr) and composition of the fluid. Molecular interpretations of kinetics show that the nucleophilic attack to C4H8O determines product formation rates at sites saturated by C4H8O- or CH3OH-derived intermediates and favors the production of terminal ethers. Among Lewis acid catalysts, turnover rates increase with exponential dependence upon C4H8O adsorption enthalpies, measured by liquid-phase isothermal titration calorimetry, which reflects covalent and non-covalent interactions. The activation enthalpies for ring-opening and C4H8O adsorption enthalpies are least endothermic in CH3CN and become more endothermic with the addition of CH3OH. Greater concentrations of CH3OH increase regioselectivities toward the terminal alcohol due to the enrichment of CH3OH near active sites and preferential stabilization of transition states by non-covalent interactions (e.g., hydrogen bonding). These findings demonstrate opportunities to leverage cooperative inner- and outer-sphere interactions to control rates and regioselectivities of zeolite-catalyzed ring opening reactions and guide strategies to create desired products.

Original languageEnglish (US)
Pages (from-to)14928-14944
Number of pages17
JournalACS Catalysis
Volume13
Issue number22
DOIs
StatePublished - Nov 17 2023

Keywords

  • active metal
  • calorimetry
  • ring opening
  • solid−liquid interfaces
  • solvent structure
  • structure function relationship

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry

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