The separate and simultaneous (with hydrodesulfurization-HDS) hydrodenitrogenation (HDN) reactions of refractory model compound was performed over NiB bulk alloy. The model compound was carbazole. The catalysts were characterized by X-ray diffraction (XRD) before and after reactions, also by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The surface properties and texture of sample was determined by N-2 BET specific surface area and chemisorption of CO. For the alone HDN of carbazole this catalyst was very active in the whole range of applied contact times. For simultaneous HDN/HDS reactions activity of catalyst depressed due to competition reaction of HDS and partially sulfidation of catalyst. The main product of the HDN reaction (alone) was bicyclohexyl (BCH). It was also observed the consecutive reaction of isomerisation of the main product of the HDN reaction, BCH transformed mainly into ethylbicyclo[4,4,0]decane (EBC[4.4.0]decane) and also to hexylcyclohexane (C6CH). During alone HDN reaction observed decompositions of NIB on metallic Ni and well dispersed boron. The alone reaction of HDN took place on metallic phase-Ni. Opposite for HDN reaction with HDS the consecutive reaction of isomerisation of the main product of the HDN was dominant - BCH transformed first of all into EBC[4.4.0]decane. During the HDN/HDS reaction observed partially formed Ni3S2, metallic Ni and Ni3B. The activity was attributed first of all by presence of Ni phase. (C) 2014 Elsevier B.V. All rights reserved.