Effect of metal loading in unpromoted and promoted CoMo/Al₂O₃–TiO₂ catalysts for the hydrodeoxygenation of phenol

This paper reports the effects of changes in the supported active phase concentration over titania containing mixed oxides catalysts for hydrodeoxygenation (HDO). Mo and CoMo supported on sol–gel Al₂ O₃ –TiO₂ (Al/Ti = 2) were synthetized and tested for the HDO of phenol in a batch reactor at 5.5 MPa, 593 K, and 100 ppm S. Characterization results showed that the increase in Mo loading led to an increase in the amount of oxide Mo species with octahedral coordination (Mo^Oh), which produced more active sites and augmented the catalytic activity. The study of the change of Co concentration allowed prototypes of the oxide species and their relationship with the CoMo/AT2 activity to be described. Catalysts were tested at four different Co/(Co + Mo) ratios. The results presented a correlation between the available fraction of Co^Oh and the catalytic performance. At low Co^Oh fractions (Co/(Co + Mo) = 0.1), Co could not promote all MoS₂ slabs and metallic sites from this latter phase performed the reaction. Also, at high Co/(Co + Mo) ratios (0.3 and 0.4), there was a loss of Co species. The Co/(Co + Mo) = 0.2 ratio presented an optimum amount of available Co^Oh and catalytic activity since the XPS results indicated a higher concentration of the CoMoS phase than at a higher ratio.