(419g) Liquid Water-Tolerant Solid Bronsted Acid Catalysts Based on Sulfonic Acid-Functionalized Zeolite Beta

Water is a byproduct of many emerging reactions in green chemistry (e.g., as an environmentally friendly leaving group), a desirable solvent, and a major constituent of biomass feedstocks. As a result, designing solid Bronsted acid catalysts that are stable and active around liquid water is critical for these various applications driven by sustainable chemistry agendas. In this work, strong acidity, hydrophobicity, and confinement were integrated into a solid material by functionalizing the intrapore voids of the siliceous Beta-framework molecular sieve with phenethyl-sulfonic acid sites (PE-Betas). These PE-Betas were evaluated as catalysts in the hydroxyalkylation/alkylation reaction of 2-methylfuran with acetone as a representative biomass upgrading reaction that generates a stoichiometric amount of liquid water. Compared to conventional aluminosilicate Betas, phenethyl-sulfonic acid-functionalized mesoporous SiO2 gel, and commercial sulfonic acid catalysts, the PE-Betas showed superior turnover numbers (TON) due to the combination of high acid site strength and hydrophobicity that arises from the confined PE groups. Further, the hydrophobicity and TON over PE-Betas were invariant with acid site density, showing that these materials effectively decouple the active site density−hydrophilicity relationship that is a fundamental limitation of conventional zeolites. These sulfonic acid-functionalized molecular sieves represent a distinct class of water-tolerant, strong Bronsted acid catalysts that may be well suited for a wide range of reactions that occur in or near liquid water. Looking ahead, achieving such tailored, multifunctional catalytic materials for diverse chemical processes in practice will require the development of advanced synthetic techniques, which is a core aim of ongoing efforts in our research.