Conversion of long-chain normal paraffins found in Fischer-Tropsch products to high-quality transportation fuels, especially middle range products, was investigated using model hydrocarbons (n-C-24 and n-C-36) and a Fischer-Tropsch wax over modified zirconia catalysts. Most work was carried out using n-C-24 as a representative reactant. With Pt-promoted tungstated zirconia (Pt/WO3/ZrO2, 0.5 wt.% Pt and 12.5 wt.% W) used as a base, addition of sulfated zirconia (SO4/ZrO2), tungstated zirconia (WO3/ZrO2) or certain zeolites increased its reactivity and selectivity at 200 degreesC to middle range products such as kerosene and diesel fuel. The effect of improving the performance of Pt/WO3/ZrO2 by adding the zeolite, mordenite, was studied in detail; an optimal mixing ratio exists for maximum conversion of n-C-24 under certain reaction conditions. The hybrid catalysts are physical mixtures of compounds with different functions. Hybrid catalysts based on Pt/WO3/ZrO2 provide a promising way to obtain higher catalytic activity and higher selectivity for desired transportation fuels from Fischer-Tropsch products. (C) 2003 Elsevier Science B.V. All rights reserved.