Bimetallic cobalt-molybdenum oxide (CoMoOx) has been prepared and converted into CoMoNx, CoMoCx, and CoMoSx materials by temperature-programmed reactions with ammonia, ethane or hydrogen sulfide, respectively. These new bimetallic materials have been characterised using X-ray diffraction (XRD) and solid state NMR and tested for pyridine hydrodenitrogenation (HDN) at various temperatures. The initial HDN activity of the catalysts decreases in order CoMoCx similar to CoMoNx similar to CoMoOx > CoMoSx. The stability order of the first three of catalysts is CoMoCx > CoMoNx > CoMoOx, and their activities decrease with the time on stream. In contrast the pyridine conversion over CoMoSx is more stable and activity increases with the time on stream, from 30 to over 50%, this is accompanied by the formation of CoMoSCx material. The high catalytic activity of the CoMoCx catalyst may reflect the ability to hydrocrack pyridine to yield methane. The CoMoSx catalyst system has the highest selectivity to the products cyclopentane (35%) and pentane (27%). (C) 2004 Elsevier B.V. All rights reserved.