Al-MIL-53 metal-organic framework supported Ru catalyst for selective hydrodeoxygenation of lignin-derived phenols into cyclohexane

Catalytic hydrodeoxygenation (HDO) of guaiacol, as a bio-oil model compound, was investigated employing Ru/Al-MIL −53 Metal-Organic Framework and Ru/γ-Al₂O₃ catalysts under external molecular hydrogen. Notably, the HDO results attributed the remarkable potential of the Ru/Al-MIL −53 MOF toward the comparatively high conversion of guaiacol (70%) together with a high proportion of cyclohexanol (23%) at a catalyst/feed (C/F) ratio of 1:5. However, only a 30% conversion was found with only 3.5% cyclohexanol for Ru/γ-Al₂O₃ for the same C/F ratio. This was due to the high porosity and presence of numerous vacancies in the MOF, which directly affects the H₂-dissociation/ spillover that assists the transfer of produced H-radicals for further conversion of the adsorbed guaiacol molecules. Notably, the activity of Ru/Al-MIL −53 was remarkably increased by decreasing the amount of guaiacol. The maximum conversion was achieved (100%) for a C/F ratio of 1:1, with a higher (96.2%) selectivity for cyclohexane. The reusability test for the spent catalyst did not show any significant change in catalyst performance for up to five successive cycles.