The model. molybdenum-promoted nickel catalysts were investigated in hydrogenolysis of n-butane. For a certain amount of promoter, a maximum of activity and selectivity was observed. The XPS investigations showed that molybdenum exists on the surface at various oxidation states even in the reduced catalysts. The existence of Mo6+, Mox+ and Moo was affirmed, in a non-stoichiometric MoOx phase present in the outer shell of the catalyst grains was affirmed. The activity of the catalysts increases with increase of Mo6+ concentration. Additional experiments showed that the results of our investigations do not confirm any simple correlations between activities of the catalysts steam reforming of methane and the hydrogenolysis of n-butane. (C) 2003 Elsevier Science B.V. All rights reserved.