Naphthalene Hydrogenation over Silica Supported Nickel Phosphide in the Absence and Presence of N-Containing Compounds

Silica supported nickel phosphide catalysts with initial Ni/P molar ratios from 0.5 to 2.0 and the sum of NiO and P2O5 loadings from 10 to 40 wt % in their precursors have been prepared by the temperature-programmed reduction method and characterized by means of X-ray diffraction, N2 physisorption, CO chemisorption, and pyridine adsorption with in situ Fourier transform-infrared (FT-IR) spectroscopy. Naphthalene hydrogenation was carried out at 340 °C and 4.0 MPa over the as-prepared Ni2P/SiO2 catalysts. Mutual influences of naphthalene hydrogenation and quinoline hydrodenitrogenation were investigated under similar conditions. The catalyst with Ni/P = 1.25 and 30 wt % loading showed the complete naphthalene conversion as well as 92.1% of selectivity to decalin. It was observed that cis-decalin converted partly into trans-decalin under the studied conditions. Addition of quinoline into naphthalene hydrogenation obviously decreased naphthalene conversion and selectivity to decalin over the Ni2P/SiO2 catalysts due to the strong adsorption of quinoline on active sites. The similar effects of the quinoline hydrogenated compounds on naphthalene hydrogenation were also observed over the Ni2P/SiO2 catalysts. The addition of naphthalene had no effect on quinoline hydrogenation to tetrahydroquinoline but inhibited tetrahydroquinoline hydrogenation to decahydroquinoline. Naphthalene conversion over the Ni2P/SiO2 catalyst in the presence of quinoline and dibenzothiophene decreased with the increase of their contents. It is noteworthy that naphthalene conversion could be recovered after the removal of quinoline while the hydrogenation activity could not in the case of dibenzothiophene.