The combination of an alkali-promoted iron-based Fischer-Tropsch catalyst and an acidic co-catalyst (HZSM-5) for syngas conversion to hydrocarbons was studied in a Berty microreactor. It was found that a physical mixture of the two catalysts resulted in severe alkali migration from the iron catalyst to the zeolite, so that this mode of the bifunctional process does not seem viable. However, by separating the catalytic layers by means of a wire mesh inside the microreactor, it was confirmed that the addition of HZSM-5 to the Fischer-Tropsch process improved both the selectivity and the quality of the gasoline product fraction. The deactivation behaviour of the acidic co-catalyst is also reported. (C) 2004 Elsevier B.V. All rights reserved.