Effect of the fluorine-addition order on the hydrodesulfurization activityof fluorinated NiW/Al2O3 catalysts

Fluorinated NiW/Al2O3 catalysts with different orders of fluorine addition have been prepared, tested for hydrodesulfurization (HDS) of thiophene, and characterized using nitric oxide chemisorption and temperature programmed sulfidation. The catalyst surface area has been affected by fluorine additi on but not by the order of fluorination. The fluorine addition-order does n ot affect the amount of fluorine retained in the catalysts after the calcin ation and the reaction seeps, either. On the other hand, the order of fluor ine addition changes the dispersion of the nickel and the tungsten species, incorporation of nickel with the tungsten edge sites, and consequently the HDS activity of the catalysts. The catalyst fluorinated in the last step, i.e., after addition of both tungsten and nickel, shows the highest activit y in thiophene HDS, which is supported by other experimental results indica ting the most nitric oxide chemisorption and the largest incorporation of n ickel with the tungsten species. Accordingly, enhancement of the catalyst a ctivity by fluorination is due to the repartition of the metal species rath er than to partial solubilization of alumina in the fluorine-addition step.