Probing Biomass Mimic Guaiacol Confinement and Interactions in ZSM-5 Zeolite

Abstract

The catalytic upgrading of biomass-derived compounds in zeolites such as ZSM-5 remains poorly understood at a molecular level, particularly with respect to adsorption and confinement of trapped species. Guaiacol, a key product of catalytic fast pyrolysis of lignocellulosic biomass, exhibits complex behaviour in ZSM-5, yet direct experimental evidence of zeolite-guaiacol host-guest interactions has been lacking. Here, we directly identify distinct in-pore and ex-pore guaiacol species in adsorbed ZSM-5 and trapped unreacted species following catalytic upgrading. These species are distinguished using ¹H and ¹³C magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy differentiating through characteristic differences in chemical shifts, linewidths and relaxation data observables, and are complemented by thermogravimetric analysis coupled with mass spectrometry (TGA-MS) to reveal differences in their desorption profiles. Furthermore, ¹⁷O isotopic enrichment of the ZSM-5 framework enables two-dimensional ¹H-¹⁷O dipolar heteronuclear multiple-quantum coherence (D-HMQC) NMR experiments, providing molecular-level insight into the through-space interactions between guaiacol and framework oxygen atoms. Together, these results suggest the location, confinement and reactivity of guaiacol within ZSM-5 pores, offering atomic-scale observations for the rational design of future zeolite catalysts for sustainable fuel production.