Effect Of Loadings On Structure And Performance Of Ni₂P/SiO₂ Catalysts For Hydrodechlorination Of Chlorobenzene

The highly dispersed Ni₂P/SiO₂ catalysts with different nickel phosphide loadings were prepared by the combination of modified sol-gel, impregnation and the temperature-programmed reduction (TPR) methods. The physicochemical properties of the Ni₂P/SiO₂ were characterized by means of H₂-TPR, N₂ adsorption-desorption, XRD, TEM, XPS, H₂-TPD, NH3-TPD, ICP-AES. The catalyst activity in the hydrodechlorization (HDC) of chlorobenzene was tested in an atmospheric fixed-bed reactor.Combining modified sol-gel, impregnation and TPR methods, the prepared Ni₂P/SiO₂ gave highly dispersed nickel phosphide even at high Ni₂P loadings. The sizes of Ni₂P particles ranged from 4 to 7 nm. With the increase of the Ni₂P loadings, BET specific surface area and pore volume of the catalysts decreased and the Ni₂P crystallites become larger, leading to lower Ni₂P dispersion. In addtion, the active surface and the amounts of spillover hydrogen species and acid sites firstly increased and then dereased. The acidity of the Ni₂P/SiO₂ catalysts may be attributed to Ni sites bearing small positive charge and P-OH groups.During the HDC of chlorobenzene, the activities of Ni₂P/SiO₂ catalysts increased at first and then decreased. The Ni₂P catalysts conaining 14.2 and 19.4 wt.% Ni showed better activity and stability. This is attributed to their larger active surfaces, more spilt-hydrogen species and acid sites.