Modifying the acid sites (number and strength) of H-ZSM-5 zeolite via doping with 3.0 wt.% HCl or HF for being used as catalysts for the hydroconversion of cyclohexene (CHE) in a flow-type fixed-bed reactor operated atmospherically in H-2 carrier gas at temperatures of 50-400 degrees C. The acid sites strength distribution in these zeolite forms was evaluated using temperature programmed desorption (TPD) of presorbed ammonia in a differential scanning calorimeter (DSC). Either HCl or HF incorporation has increased both acid sites number and strength in the zeolite to varying extents. Hydrochlorination enhanced the acid sites number in the zeolite to a larger extent than hydrofluorination, whereas, the latter enhanced the acid sites strength to a larger extent than hydrochlorination. Nevertheless, not only the acid catalysed reactions; i.e., isomerisation of the six-membered-ring of CHE to the five-membered ring compounds (methylcyclopentenes (MCPEs) plus methylcyclopentane (MCPA)) and hydrocracking reactions to lower molecular weight components, were enhanced via both hydrohalogenation treatments of the zeolite, but also hydrogenation of CHE to cyclohexane and MCPEs to MCPA and dehydrogenation of CHE to cyclohexadienes (CHDEs) plus benzene were also enhanced. (c) 2005 Elsevier B.V. All rights reserved.