Highly effective hydrodeoxygenation of guaiacol on Pt/TiO₂: Promoter effects

This work investigated Mg and Mo effect on the hydrodeoxygenation (HDO) of guaiacol over Pt/TiO₂ catalyst. The Pt-based catalysts were prepared by the incipient wetness impregnation technique, and tested at 285 °C and 4 MPa in a fixed bed reactor system. The properties of the catalysts were characterized by CO pulse chemisorption, H₂-TPD, NH₃-TPD, and XRD. The characterization results reveal that Mg or Mo species on Pt/TiO₂ increase Pt dispersion, and reduce the surface acidity of Pt/TiO₂. Moreover, Mg species lower the hydrogenolysis activity of Pt/TiO₂, while Mo species, on the contrary, activate more hydrogen in the reaction. Both Mg and Mo modified Pt/TiO₂ catalyst increase guaiacol conversion from 70% to 94% without catalyst deactivation. Mg does not improve the cyclohexane yield. Instead, more carbonaceous species deposit and even graphitic coke are observed on the catalyst after reactivity test. On the contrary, Mo increases the cyclohexane yield from 23.5% to 57.7% with only more active carbon formation on the catalyst after reactivity test, which indicates the active hydrogen species from metal sites and metal-support interface may play a critical role for deep HDO. For the possible reaction pathways, Mg inhibits dehydration and hydrogenolysis pathway from phenol to cyclohexane. However, Mo species favor hydrogenolysis while suppress dehydration to cyclohexane. Thus, Pt-Mo/TiO₂ is a promising catalytic system for HDO, and further optimization of its properties may lead to an effective catalyst for the HDO of real and complex pyrolysis bio-oils.