The addition of BaO, LaO3 and ZrO2 to the SiO2 support of a 12 wt.% Co/SiO2 catalyst modifies the reduction behavior of Co species and leads to changes in metal dispersion. These changes are due to a modified metal-support interaction (MSI) between cobalt species and the MexOy/SiO2 (MexOy: BaO, ZrO2 and La2O3) support. Catalyst characterization by temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) have been used to determine the relative strength of the MSI and the results suggest an increasing MSI in the order Co/SiO2 approximate to Co/BaO/SiO2 < Co/La2O3/SiO2 < Co/ZrO2/SiO2. The rate of catalyst deactivation during methane decomposition (CH4 double left right arrow C + 2H(2)) is shown to increase with increasing MSI. Analysis of the used catalysts also shows that an increasing rate of deactivation correlates with an increasing amount of graphitic carbon versus carbidic carbon on the used catalyst. It is suggested that an increase in graphitic carbon is a consequence of a strong MSI that limits carbon removal from the metal surface by filament formation. Consequently, graphitic, encapsulating carbon is formed from the carbon deposited during methane decomposition, leading to deactivation of the catalyst. (C) 2004 Elsevier B.V. All rights reserved.