Hydrodeoxygenation of phenol over niobia supported Pd catalyst

This work investigates the performance of Pd supported on SiO2 and Nb2O5 for the HDO of phenol reaction at different temperatures using a fixed-bed reactor. The type of support significantly affects activity and product distribution. The reaction rate for HDO of phenol over Pd/Nb2O5 was 90-fold higher than that observed for silica supported catalyst. Cyclohexanone was the dominant product for Pd/SiO2, whereas benzene was mainly formed on Pd/Nb2O5. The high activity and selectivity to deoxygenated products of Pd/Nb2O5 for HDO of phenol is likely due to the strong interaction between the oxophilic sites represented by Nb5+/Nb4+ cations and the oxygen from the phenol molecule. This promotes hydrogenation of the carbonyl function, resulting in the formation of 2,4-cyclohexadienol, which is dehydrated to benzene. For Pd/SiO2 catalyst, the hydrogenation of the ring is the main reaction pathway observed. The reaction pathway was also affected by the reaction temperature, the hydrogenation of the carbonyl group being favored at high temperature.