An integrated reaction model of guaiacol hydrodeoxygenation using activated carbon supports: effects of support properties, metals, and solvents†

The hydrodeoxygenation (HDO) of guaiacol, a model compound for lignin-derived pyrolysis oils, was investigated using Ru and Ni catalysts supported on activated carbons derived from both commercial and renewable (food waste) sources. Comprehensive characterization of support properties including porosity, surface area, hydrophobicity, and morphology revealed their significant influence on catalyst performance. Liquid-phase HDO reactions were conducted in both aqueous and organic (decane) environments to evaluate solvent effects on reaction pathways and product distributions. Ru-based catalysts demonstrated superior activity compared to Ni-based catalysts, while supports with higher mesoporosity facilitated better metal dispersion and enhanced catalytic performance. Notably, food waste-derived activated carbon supports performed comparably or better than commercial activated carbon when combined with Ru, indicating their potential as sustainable catalyst supports. Mathematical optimization techniques were employed to estimate kinetic parameters and elucidate reaction pathways, revealing notable differences between aqueous and organic media. Specifically, methoxycyclohexanone dominated in organic medium, while cyclohexanol prevailed in aqueous medium. The optimization study identified that cyclohexanol was not an intermediate for cyclohexane production, contrary to conventional understanding. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis provided insights into adsorption phenomena, explaining carbon balance discrepancies observed particularly in aqueous-phase reactions. This integrated experimental and computational approach advances the understanding of guaiacol HDO reaction mechanisms and provides guidance for the rational design of efficient catalysts for bio-oil upgrading.