Effect of metal-organic compounds on thiophene hydrodesulphurization over sulphided forms of fluoride-containing CoMo/Al 2O 3 catalysts

Abstract

The effect of adding fluoride at various stages of preparation of CoMo/γ-Al 2O 3 catalysts was investigated with X-ray photoelectron spectroscopy (XPS) and with a pulse reactor method for activity in hydrodesulphurization (HDS) of thiophene and deactivation by nickel and vanadium naphthenate (NiN and VN). Activity is lowered by increasing fluoride content, except for initial activity at a fluoride-to-aluminium (F/Al) ratio of 0.1. It may be correlated with a decreased surface area and dispersion of the molybdenum sulphide phase. Deactivation in HDS of thiophene strongly increases with the fluoride concentration, probably due to an increased acidity induced by the fluoride anions. XPS data suggest that fluoride is highly dispersed except at the highest concentration, i.e. F/Al=0.2. Fluorination of the catalysts has an inhibiting effect on deactivation by NiN and VN and the highest initial and final activity is observed at F/Al=0.1. XPS intensity data suggest that the dispersion of deposited metals decreases with increasing fluoride concentration and that the deposition occurs to a higher extent at the exterior of the particles than the interior under the conditions applied. Both sulphidic and oxidic forms are detected. The order of adding fluoride and the salts of cobalt and molybdenum results in minor differences in activity, except when metal naphthenates are deposited.