Effect of Zirconia Morphology on Hydrodeoxygenation of Phenol over Pd/ZrO2

This work studies the effect of zirconia structure on the performance of Pd/ZrO2 catalysts for hydrodeoxygenation of phenol at 300 °C and 1 atm using a fixed bed reactor. Benzene was the major product over Pd/t-ZrO2, while significant formation of cyclohexanone was observed over Pd/m-ZrO2. On the other hand, Pd/m,t-ZrO2 exhibited intermediary behavior. DRIFTS of adsorbed pyridine, NH3-TPD, and the dehydration of the cyclohexanol reaction revealed that the Pd/t-ZrO2 catalyst exhibits a higher density of oxophilic sites than Pd/m-ZrO2 and Pd/m,t-ZrO2. This promoted the formation of deoxygenated products. However, a mechanism involving dehydration of cyclohexanol to cyclohexene, followed by dehydrogenation to benzene, may not be ruled out. Pd/ZrO2 catalysts significantly deactivated as a function of time on stream. Results of dehydrogenation of cyclohexane and dehydration of cyclohexanol indicate that the Pd particle size increased and the density of oxophilic sites decreased during the hydrodeoxygenation of...