The catalytic effects of nickel and iron deposited on an FCC (fluidized catalytic cracking) catalyst via metal naphthenates were studied in a micro activity test (MAT) unit after both oxidative and reductive treatments of the catalyst samples. The dehydrogenation activity of nickel was found to be close to the clehydrogenation activity of vanadium - and not several times higher than that of vanadium as is often reported - when deposited on the commercial FCC catalyst used in this study followed by steam deactivation (oxidative treatment) at 760 degrees C. However, the dehydrogenation activity of nickel was significantly intensified after post-treatment with a CO/N-2 mixture at this temperature (reductive treatment). The results show that iron did not have a dehydrogenation activity after steaming, but had a significant dehydrogenation activity after steaming when followed by exposure to the CO/N-2 mixture at 760 degrees C. The results indicate that the presence of deposited iron was inducing an additional catalytic cracking activity for the FCC catalyst. It was observed that co-impregnation of equal loadings of nickel, iron and vanadium on the FCC catalyst led to a considerably higher dehydrogenation activity than could be expected from the catalytic behaviour of the separate elements. The dehydrogenation activity was however slightly reduced by the reductive treatment as the reduced dehydrogenation activity from the lower oxidation state of vanadium (V3+) more than compensated the increased dehydrogenation activity of iron and nickel. A slightly increased gasoline production after the reductive treatment of the co-impregnated sample was a result of the increased production of gasoline from the FCC catalyst itself, which more than compensated for the reduced gasoline production from nickel. (C) 2008 Elsevier B.V. All rights reserved.