Studies of catalytic activity of a series of nickel-molybdenum catalysts supported on Al2O3 modified with berate ions were performed for the hydrotreating of coal Liquid. Decomposition of isopropyl alcohol, diacetone alcohol and ethylbenzene was performed for the characterization of acidity of the catalysts. Quinoline and carbazole hydrodenitrogenation (HDN) were used as test reactions. It was found that modification of the support with berate ions increases the acidity of nickel-molybdenum catalyst, in particular, the amount of acidity centers of intermediate strength. However, although the modification practically does not affect the hydrosulfurization activity of coal Liquid, it considerably affects its HDN activity. In the latter case, it leads to an increase in the resistance to coking of the modified catalysts. This particularly applies to the HDN process in which the above catalysts are still very active after a long period of run, and hence their dehydrogenation activity rises. The high HDN activity is connected to the increasing number of acid centers of intermediate strength. (C) 2000 Elsevier Science Ltd. All rights reserved.