The combination of an iron-based Fischer-Tropsch catalyst and an HZSM-5 co-catalyst was studied in a Berty micro reactor at two temperatures, namely 330 and 350 degrees C. The higher operating temperature adversely affected the performance of the iron catalyst, as it caused a shift in the Fischer-Tropsch product spectrum towards lighter hydrocarbons at the expense of the desired product (gasoline). The synthesis performance of the HZSM-5 co-catalysts over the course of the bifunctional process experiments, the distribution of the xylene isomers during these runs, and subsequent thermogravimetrical analysis of the spent zeolite samples were all largely in agreement with respect to the amount and location of the coke formed on the different zeolitic co-catalysts during synthesis. It was found that the increased synthesis temperature had little effect on the performance of an HZSM-5 zeolite with a high aluminium content, but substantially improved the performance and useful lifetime of an HZSM-5 zeolite with a low aluminium content. Published by Elsevier B.V.