Acidity and catalytic activity of cobalt-molybdena catalyst supported on alumina. The effect of incorporation sequence of sodium and fluoride ions Original Research Article

Two series of CoMo/Al2O3 catalysts containing F and Na ions were prepared. Acid properties of these catalysts were characterized using FT-IR spectroscopy of adsorbed pyridine and t-butyl cyanide. Their catalytic activities in cumene conversion as well as hydrodesulfurization of thiophene were also determined. In this study the catalysts were prepared in a one-step procedure (sample denotation CoMoX, where X=F− or Na+) and in a two-step procedure, with X were deposited either before (X/CoMo) or after (CoMo/X) Mo, Co and Al2O3 components. It was found that the ratio of Brönsted to Lewis acid sites decreases in the following sequence: F/CoMo>CoMo/F>CoMoF. In the same order total conversion of cumene decreases. However, cumene dealkylation decreases as follows: CoMo/F>F/CoMo>CoMoF. This order overlaps the decreasing sequence of Brönsted acid sites concentration. HDS activity of fluoride containing catalysts was the highest for the F/CoMo sample. A similar activity was shown by CoMoF catalysts, whereas the activity was the lowest for CoMo/F. The sodium-modified CoMosingle bondAl2O3 catalysts do not contain Brönsted acid sites while Lewis acid sites completely disappear after heating at 200°C, 10−5 Torr. These samples were inactive in cumene dehydrogenation. The samples containing fluoride show significantly higher HDS activity than their sodium analogues. For each series of catalysts the highest HDS activity is shown by samples prepared in the two-step procedure where F− and Na+ ions were introduced first.