Bifunctional catalysts of nickel sulphide supported on zeolites NaY, USY and ZSM-5 have been tested in simultaneous thiophene hydrodesulphurisation (HDS) and 1-pentene hydroisomerisation (HYD/ISO). The catalysts were prepared by ion-exchange and studied in their oxidic and sulphided forms using several physico-chemical techniques such as chemical analysis, X-ray diffraction (XRD), IR of the framework vibration, N-2 adsorption-desorption isotherms, ammonia temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) of adsorbed NO. The best balance of the HDS and HYD functions was achieved over the Ni(6.6)USY sample, which showed an HDS/HYD ratio about three-fold larger than a commercial CoMo/Al2O3 catalyst as well as some skeletal isomerisation of 1-pentene (selectivity 2.7%). On the basis of the catalyst structure-activity relationship, it can be inferred that the catalytic response of Ni(6.6)USY catalyst is linked to a homogeneous distribution of nickel species within the zeolite pores and also to the greater acidity of the USY zeolite. NaY-supported and Ni(2.7)USY catalysts showed almost exclusively double bond isomerisation whereas both double bond and skeletal isomerisation were observed for the ZSM-5 and its nickel-loaded counterparts. Factors minimizing 1-pentene hydrogenation during the simultaneous HDS of thiophene and 1-pentene hydroisomerisation over sulphided Ni/NaY, NWUSY and Ni/ZSM-5 catalysts are discussed. (C) 2003 Elsevier B.V. All rights reserved.