Hydrodeoxygenation of phenol over metal supported niobia catalysts

This work studied the performance of Rh, Pd and Ni supported on Nb2O5 catalysts for hydrodeoxygenation of phenol in the vapor phase. In general, an increase in reduction temperature favored benzene selectivity. For Ni/Nb2O5, this selectivity increased around 50%. The change in reduction temperature also affected the reaction rates. After reduction at 500 °C, there was a decline in these rates for all samples (a 75-fold decrease for Pd/Nb2O5). This behavior was related to structural modifications caused by strong metal-support interaction (SMSI). For Pd sample, the increase in benzene selectivity (around 30%) was related to a partial encapsulation of the metal by NbOx, which led to an electron enrichment of the Pd particles, as indicated by XPS analysis. This alteration caused an enhancement in the adsorption of phenol through its oxygen. For Rh/Nb2O5, the reduction temperature did not change the benzene selectivity. According to TPR-XANES results, Rh is fully reduced for both reduction conditions studied. On other hand, Ni sample was not fully reduced after H2 treatment at 300 °C, as observed in TPR-XANES at Ni K-edge. It was hypothesized that higher reduction temperatures favored the Ni-NbOx interface, which probably improved the oxophilicity of this sample and, consequently, the benzene selectivity.