The turnover frequencies of catalytic systems based on Ni(acac)(2)-AlEt3 or AIEt(2)(OEt) in the hydrogenation of benzene and its methyl-substituted homologs (toluene, three isomers of xylene, and 1,3,5-trimethylbenzene) have been determined at temperatures of 80-120 degrees C, initial P-H2 = 15 bar, and different ratios of Al/Ni. The size and nature of the nanoparticles forming in the systems based on Ni(acac)(2)-AlEt3 or AlEt2(OEt) under the benzene hydrogenation condition shave been resolved by high-resolution electron microscopy and X-ray microanalysis. This study included the performance of competitive hydrogenation reactions of benzene with toluene or three xylene isomers. The relative adsorption constants of toluene and three xylene isomers have been determined and the stereochemistry of the hydrogen addition to the arene ring has also been elucidated.