A study on the role of Ni atoms in the HDN activity of NiMoS2/Al2O3 catalyst

A monometallic catalyst MoS2/Al2O3 and a Ni-promoting catalyst NiMoS2/Al2O3 were prepared through using nano-sized MoS3 particles as the precursor. XPS analysis combined with a DST probe test indicate that, compared with the conventional catalyst Ref-MoS2/Al2O3 derived from nano-sized MoO3 particles, the MoS3-derived catalyst MoS2/Al2O3 not only contains nearly fully-sulfided Mo species, but also holds much more coordination unsaturated sites (CUS) on its MoS2 nanoslabs, thus resulting in the successful preparation of a bimetallic catalyst NiMoS2/Al2O3 with much weaker Mo-Al2O3 interaction and higher decoration degree of Ni atoms onto MoS2 nanoslabs as compared with the conventional counterpart. These significant structural advantages of the bimetallic catalysts not only avoid the strong interference of gamma-Al2O3 to the active phase, but also bring potential excellent Ni-promoting effects on the catalytic activity. Then, using quinolone (Q) as the reactant, the Ni-promoting effect on the hydrodenitrogenation (HDN) activity was discussed. It was found when MoS2 nanoslabs were decorated by Ni atoms, the HDN activity attains an essential improvement. Moreover, this Ni-promoting effect is much more beneficial to the Path II (Q -> 14THQ/58THQ -> DHQ -> PCHA -> PCHE + PCH) than Path I (Q -> 14THQ -> OPA -> PB). The origin of Ni-promoting effects on HDN activity was finally suggested: Ni atoms one hand activate H-2 to produce activated hydrogen which afterwards react with Mo-S2- species to form Mo-SH species, and on the other hand increase the basicity of the neighboring Mo-S2-, which together promote the cracking of C-N bonds and thereby remarkably enhance the HDN activity.