Effect of Co doping on structure and phenanthrene hydrogenation saturation of Ni/NiAlO_x catalyst

Coal tar is rich in dense cyclic aromatic hydrocarbons phenanthrene, and perhydrophenanthrene is an ideal component for high energy density fuels used in aerospace because of its high energy, high density and high stability. The key is to design efficient hydrogenation catalysts. Noble metal catalysts have the characteristics of high hydrogenation capacity, but have the disadvantage of high cost. Traditional nickel-molybdenum-sulfur catalysts have weak hydrogenation capacity, and nickel based catalysts are widely used in the aromatics hydrogenation saturation field due to their low price and high hydrogenation saturation capacity. The Ni/NiAlO_x catalysts are used by the strong interaction between the active nickel metal and the support nickel aluminum spinel, which makes the active component nickel show the “electron deficient” state and promote the adsorption and activation of aromatics. This catalyst has high perhydrophenanthrene selectivity, but perhydrophenanthrene selectivity decreases gradually as the reaction proceeding, mainly due to the change of nickel's electron density during the reaction. Considering that cobalt has a similar structure to nickel, it is easy to dissolve into the nickel lattice and directly modulate nickel's electronic structure. The catalysts with different cobalt contents were prepared by the sol-gel method followed by impregnation method, and then the effect of cobalt doping on the structure and the performance of Ni/NiAlO_x catalysts with phenanthrene hydrosaturation was investigated. The catalysts were evaluated at a reaction temperature of 300 ℃, pressure of 5.0 MPa, reaction feed: 1% phenanthrene/decahydronaphthalene solvent, feed rate: 6 mL/h, hydrogen flow rate: 60 mL/min, and weight hourly space velocity: 52 h^-1. The catalyst with cobalt doping of 2% had a perhydrophenanthrene selectivity of 53.6% at the 6th of the reaction, which was higher than that of the Ni/NiAlO_x catalyst. This is due to the fact that the appropriate content of cobalt doping promotes the reduction of active metal, reduces the catalyst particle size, stabilizes the “electron deficiency” of the active component Ni, promotes the adsorption of aromatics, and finally improves the catalyst stability.