The Effect of CeO2 on the Hydrodenitrogenation Performance of Bulk Ni2P

Bulk Ni2P and CeO2-containing bulk Ni2P (Ce-Ni2P(x), where x represents the Ce/Ni atomic ratio) were prepared by a co-precipitation method followed by an in situ H-2 temperature-programmed reduction procedure. The catalysts were characterized by XRD, CO chemisorption, TEM, N-2 adsorption-desorption, XPS and X-ray absorption spectroscopy (XAS). Their hydrodenitrogenation performances were studied using quinoline (Q) and decahydroquinoline as the model compounds. Both the hydrogenation and C-N bond cleavage activities of Ni2P were improved by the introduction of CeO2. CeO2 mainly accelerated the denitrogenation of Q to propylcyclohexane rather than to propylbenzene. XRD and XPS measurements revealed that the Ce species in Ce-Ni2P(x) were mainly in the oxide form and both Ce4+ and Ce3+ species coexisted on the surface of the catalysts. Addition of CeO2 significantly decreased the particle size of Ni2P, resulting in increased specific surface areas and CO uptakes, possibly due to the strong interaction between the Ce species and Ni2P. At a Ce/Ni atomic ratio higher than 0.25, segregation of CeO2 took place. XAS results of the passivated catalysts showed that CeO2 not only affected the oxidability of Ni2P but also led to the formation of metallic Ni. The promoting effect of CeO2 was discussed by considering the electronic interactions between Ce species and Ni2P as well as the presence of the amorphous Ni and low valence Ce3+ species.