(670b) Impact of Extra Framework Al Species in Zeolites’ Catalytic Activities during Acylation of 2-Methylfuran with Acetic Acid

Zeolites, particularly MFI, have recently emerged as highly promising catalysts for direct Friedel-Crafts acylation reactions employing renewable carboxylic acids, yielding a versatile range of high-value fuels and essential commodity chemicals. The acylation of furanic compounds using carboxylic acids presents a particularly attractive avenue for the synthesis of sustainable surfactants.^1,2 However, the role of extra-framework alumina (EFAL) on catalyst reaction rates in zeolites has not been explored for this chemistry. In this study, we undertake a comprehensive investigation into the acylation of 2-methylfuran (2-MF) using acetic acid (AA) over EFAL-incorporating MFI (Si/Al=40) and BEA (Si/Al=150) zeolites, then contrasting their behaviors after EFAL removal via ammonium hexafluorosilicate (AHFS) washing. EFAL concentrations were measured via solid-state ²⁷Al-NMR analysis. Acylation under mild conditions, specifically within the 160-180°C range, remarkably uncovers higher activity over zeolites possessing EFAL, whereas reaction rates are reduced post-AHFS treatment. Interestingly, the removal of EFAL leads to a twofold increase in measured activation barriers, aligning them with those observed for all-framework aluminum MFI (Si/Al=140) zeolites. DFT calculations are presented that agree with the experimental activation energies, highlighting modifications to adsorbed intermediates and stabilization of kinetically relevant transition states due to the presence of extra lattice Al species. Understanding this complex interplay between extra-lattice alumina and Brønsted acid sites is significant for comprehending the underlying factors that govern the kinetics of the reaction and holds key implications for optimizing catalytic performance. This study substantially contributes to understanding of zeolite-catalyzed acylation, offering a pivotal framework to enhance catalytic efficiency within the territory of renewable chemical synthesis.

1) Gumidyala, A., et al. (2016). Science advances, 2(9), e1601072.

2) Alalq, I., et al. (2023). Journal of Catalysis, 426, 222-233.