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<p>Biorefinery technologies that convert lignin into platform chemicals are essential to reduce our future dependence on fossil resources. In these technologies, a key process is the acid-catalysed <i>O</i>-demethylation of guaiacol derivatives in hot-pressurized water using Brønsted mineral acids or microporous zeolites. The fundamental understanding of how hydronium ions behave in a confined environment versus bulk is still limited. Here we investigate the <i>O</i>-demethylation of guaiacol in hot-pressurized water with HCl or H-BEA zeolite catalysts to elucidate the impact of zeolite microporosity on reaction mechanisms and rates. Operando molecular simulations combined with experimental kinetic studies reveal that, regardless of the catalyst type, <i>O</i>-demethylation follows a concerted O-activated S<sub>N</sub>2 mechanism. The reaction rate is higher in the zeolite due to more active, under-coordinated hydronium ions. Additionally, the molecular organization of solvent and reactants around the confined active site plays a crucial role in modulating the association of the reacting species and the reaction kinetics.</p><p></p>

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Confined hot-pressurized water in Brønsted-acidic beta zeolite speeds up the O-demethylation of guaiacol

  • 期刊论文

  • 发表日期：

    2025年1月9日

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  • Massimo Bocus,
  • Elias Van Den Broeck,
  • Xian Wu,
  • Mathias Bal,
  • Jeroen Bomon,
  • Louis Vanduyfhuys,
  • Bert F. Sels,
  • Bert U. W. Maes,
  • Veronique Van Speybroeck

摘要

Biorefinery technologies that convert lignin into platform chemicals are essential to reduce our future dependence on fossil resources. In these technologies, a key process is the acid-catalysed O-demethylation of guaiacol derivatives in hot-pressurized water using Brønsted mineral acids or microporous zeolites. The fundamental understanding of how hydronium ions behave in a confined environment versus bulk is still limited. Here we investigate the O-demethylation of guaiacol in hot-pressurized water with HCl or H-BEA zeolite catalysts to elucidate the impact of zeolite microporosity on reaction mechanisms and rates. Operando molecular simulations combined with experimental kinetic studies reveal that, regardless of the catalyst type, O-demethylation follows a concerted O-activated SN2 mechanism. The reaction rate is higher in the zeolite due to more active, under-coordinated hydronium ions. Additionally, the molecular organization of solvent and reactants around the confined active site plays a crucial role in modulating the association of the reacting species and the reaction kinetics.