This paper presents a two-dimensional model of a preferential oxidation (PROX) reactor to be used in a beta 5 kWe hydrogen generator (HYGen II). to integrate with Polymer Electrolyte Fuel Cells (PEFCs). PROX reactors require Careful temperature control systems, in order to enhance optimization and control of the unit. The model concerns chemical kinetics and heat/mass transfer phenomena occurring in the reactor. Aim of the model is to investigate the effects of the molar ratio O-2/CO, the gas hourly space velocity (GHSV) and the inlet temperature on process performance of the reactor, in order to obtain high CO conversion and high selectivity with respect to the undesired H-2 oxidation. The model plays a key role in overcoming the issues of system design, by evaluating the temperature and the gas concentration profiles in the reactor. Simulation results showed the strong dependence of the overall performance upon the operating conditions examined. (c) 2008 Elsevier B.V. All rights reserved.