Effect of fluoride promoter on the catalytic activity of NiWF/γ-Al₂O₃ for hydrodenitrogenation and hydrodesulfurization of coal tar

A series of NiWF (x)/γ-Al₂O₃ catalysts were prepared by adding different amounts of ammonium fluoride, and the effects of fluoride amount on the structure and physicochemical properties were investigated with X-ray diffraction, X-ray photoelectron spectroscopy, NH₃-TPD and high resolution transmission electron mcroscopy (HRTEM) techniques and N₂ sorption experiment. Their hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) catalytic performances were evaluated in a fix-bed reactor with low and middle-temperature coal tar obtained from Inner Mongolia as feedstock. Although fluoride amount has little effect on the pore diameter and pore volume of the catalysts, increase of the fluoride amount decreases the specific surface area. In addition, the sulfidation degree of the catalyst decreases with the fluoride amount when it is sulfided at 643 K for 6 h. Also, the numbers of strong acid sites and total amount acid sites change with increasing fluoride amount. They slightly increase at first, but then obviously decrease. HRTEM shows that WS₂ slabs have a typical layered structure. The catalytic activity of NiWF (x)/γ-Al₂O₃ for HDN and HDS of coal tar shows a volcanic trend with the fluoride amount.