Unveiling the Ni2+ coordination sites effect of Ni-Al spinel catalysts for phenanthrene hydrogenation saturation

Nickel–aluminum (Ni–Al) spinel catalysts with distinct Ni/Al molar ratios were synthesized to construct Ni 2+ coordination sites. Owing to the favorable distribution of Ni 2+ coordination sites and the presence of suitable concentration of Ni 2+ in octahedral sites, Ni/Al-0.725 catalyst achieved an 86.1 % average yield of perhydrophenanthrene, which was higher than that obtained with Ni/Al-0.25 (6.3 %). Characterization results indicated that Ni 2+ of the Ni/Al-0.725 catalyst was present in octahedral sites and ∼ 40.4 % Ni 2+ was reduced to Ni, whereas the active Ni metal of Ni/Al-0.25 catalyst mainly comprised Ni 2+ occupying tetrahedral sites as precursors. Furthermore, the Ni/Al-0.725 catalyst exhibited the smallest Ni particle size (2.82 nm) and the largest Ni available surface (19.62 m 2 /g sample ), which helped alleviate competitive adsorption among aromatic hydrocarbons. The Ni reduced by the spinel catalysts was in an electron-deficient state, which enhanced the adsorption of polycyclic aromatic hydrocarbons.