Effect of SiO2 coating on the structure and naphthalene hydrogenation performance of Ni2P/Al 2O3 catalyst

The thermal stability of jet fuel could be significantly improved by hydrogenated aromatics or cycloal-kanes,which might be derived from the hydrogenation of naphthalene aromatics existing in coal tar.The key point for realizing this chemical process is to develop a kind of catalyst for aromatics hydrogenation with high selectivity.The commercial metal sulfide catalyst is generally used in this process,but it is hard to control the selectivity of aromatic hydrogenation.In recent year,Ni2P catalysts are found to present application potential in the field of catalytic hydrogenation due to their special crystal structure and electronic property.However,the unsupported Ni2P catalysts generally possess low specific surface area,poor dispersion of active components,less mechanical strength and poor heat dissipation,which result in low activity.Thus,a support is widely employed to disperse Ni2P particles,furthermore,different supports could greatly affect the formation,size distribution and activity of Ni2P.In this study,a series of Ni2P/Al2O3 catalysts with SiO2 coating on Al2O3 surface (Cat-xSi) was prepared using hypophosphite disproportionation method so as to adjust the interaction among Ni species in the precursors,Ni2P and the support,leading to the formation of more Ni2P and higher dispersion of Ni2P.Meanwhile,the influence of SiO2 coating on its structure and hydrogenation performance were investigated.When the naphthalene hydrogenation reaction was performed at 340 ℃,4 MPa,H2/oil volume ratio of 600,and a weight hourly space velocity (WHSV) of 20.8 h-1,all the Cat-xSi catalysts showed a better naphthalene conversion (higher than 65%) than that of Cat-0Si catalyst (56%),which highlights the importance of SiO2 coating.The coating of SiO2 over γ-Al2O3 not only promotes the formation of more Ni2P particles in the Cat-xSi catalyst,but also achieves the better dispersion of Ni2P sites.Furthermore,the SiO2 coating leads to the formation of small-sized Ni2P particles with the more exposed Ni(2) sites and appearance of higher-level electron deficiency of Niδ+ in Ni2P.The Cat-16.0Si catalyst contains more Ni2P particles with smaller size and the stable highest-level electron deficiency of Niδ+,which contribute to a better aromatic hydrogenation activity (72%) than that of the other catalysts in this study.