Hydrodeoxygenation of guaiacol over molybdenum-based catalysts: The effect of support and the nature of the active site

The hydrodeoxygenation (HDO) of guaiacol has been chosen as a model process for the upgrading of lignin-derived bio-oils. Tests were carried out in a batch reactor at 350 °C, 4000 kPa of H2, in the presence of several Mo-based catalysts prepared by impregnation of ammonium molybdate on SiO2, Al2O3, NaY zeolite, MgO, activated carbon, and graphite. These materials have been characterized by means of: N2 physisorption, XRD, FESEM/EDS, XPS, TPR-H2, and TPD-NH3, with the aim of correlating the physical and chemical properties of the prepared samples with the resulting features in the HDO reaction. Mo on activated carbon showed the best performances towards guaiacol demethoxylation, exhibiting complete conversion, 72 % of selectivity to phenol, and 19 % to p- and o-cresol. The high surface area and low acidity of activated carbon allow good dispersion of MoOx which exhibits characteristic fragments with a lamellar shape, able to provide a large active surface with localized acidity.