Insight into the Nature of Nickel Active Sites on the NiAl₂O₄ Catalyst for Phenanthrene Hydrogenation Saturation

Hydrogenation saturation of phenanthrene (a typical component of coal tar) could not only improve the combustion performance of fuel oil, but also obtain the raw material for preparing high-energy-density fuel. Nickel-based catalysts have been considered promising catalysts for the hydrogenation saturation of phenanthrene due to their appealing capacity to activate phenanthrene molecules. However, the Ni derivation precursor greatly affects its hydrogenation activity. In this work, the NiAl₂O₄ catalyst was obtained by the sol-gel method. Under the experimental conditions of temperature 300 °C, pressure 5 MPa, and WHSV 0.52 h^-1, the phenanthrene conversion over NiAl₂O₄ catalysts can be up to 99.7 and 93.9% for perhydrophenanthrene yield, while those of the traditional Ni/Al₂O₃ catalysts are just up to 96.8 and 77.3%, respectively. Moreover, the TOF of phenanthrene hydrogenation of the NiAl₂O₄ catalyst (3.01 × 10^-3 s^-1) surpasses that of the traditional Ni/Al₂O₃ catalyst (2.46 × 10^-3 s^-1), which indicates that Ni derived from NiAl₂O₄ has stronger phenanthrene hydrogenation activity. According to relevant characterizations, the superior hydrogenation performance of the NiAl₂O₄ catalyst derives from the stronger H₂ adsorption and dissociation ability and the formation of an electron-deficient structure of active metal Ni, which contributes to the improved adsorption and activation of the polycyclic aromatic hydrocarbons.