Hydrogenation of polycyclic aromatic hydrocarbons in coal tar to cycloalkanes can significantly enhance the utilization efficiency of coal resource. Though hydrogenation saturation of polycyclic aromatic hydrocarbons is thermodynamically feasible, the hydrogenation rate is still limited by competitive adsorption and increasing steric hindrance, resulting in low selectivity of fully saturated products. Phenanthrene, a typical polycyclic aromatic hydrocarbon, was served as the model compound to investigate the hydrogenation mechanism and develop highly active catalysts. In this work, a series of Ni/NiAlO catalysts (Ni/Al molar ratio of 1.45:2) calcinated at different temperatures were synthesized by a sol-gel method modified with citric acid. When the hydrogenation saturation reaction was performed at 300 °C, 5 MPa, a H2/oil volume ratio of 600, and a weight hourly space velocity (WHSV) of 52 h-1, a higher initial activity of 94% selectivity to perhydrophenanthrene was achieved over the catalyst calcinated at 650°C. By adjusting the calcination temperature, the existing forms of nickel could be regulated, which resulted in different metal support interactions and Ni dispersions. It was indicated that under the same Ni/Al molar ratio, most of nickel entered into octahedral sites at 650°C, leaving little free NiO and less nickel occupying in tetrahedral sites. This structure presented a higher dispersion of Ni, contributing to a remarkable obvious reaction rate (1.53×10-3 mol kg-1 s-1). However, the selectivity of perhydrophenanthrene decreased gradually during the hydrogenation process, which can be attributed to the variation in the electron-deficient structure of surface metals. As a result, improving the stability of the metallic electronic structure during the reaction can further improve the hydrogenation activity.

Synthesis of Ni/NiAlO catalyst and its application in deep hydrogenation of phenanthrene

ACS Spring Meeting 2021

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