A study of CO hydrogenation on MCM-41 and SiO2-supported Ru-promoted Co catalysts has been performed using both global rate measurements and steady-state isotopic transient kinetic analysis (SSITKA). A significant increase in CO hydrogenation was observed when MCM-41 was used as the support in the order M1 > M2 > SiO2 at methanation conditions, where M1 and M2 are small pore (d(p) = 3 nm) and larger pore (d(p) = 7 nm) MCM-41, respectively. TOFH based on H-2 chemisorption can be misleading since any suppression of hydrogen chemisorption, as probably occurred for CoRu/M1, results in larger values of TOFH being calculated. SSITKA results, on the other hand, provide a measure of the "true" intrinsic CO hydrogenation activity of the Co sites. SSITKA studies indicated that the higher CO hydrogenation rates for MCM-41-supported catalysts are due to their greater number of active sites, not to a change in the intrinsic site activity. N-2 physisorption and XRD results reveal that the structure of MCM-41 became less ordered and the surface area decreased after standard reduction and 24 h of FTS, probably due to an effect of water vapor produced during metal reduction and reaction. However, the Co surface was still accessible since there was no significant loss of activity with TOS. The extent of deactivation during the initial reaction period was similar for MCM-41- and SiO2-supported CoRu catalysts. By providing high activity and unrestricted diffusion of FT reactants and products, CoRu/MCM-41 may be potentially useful for FTS as well as for other catalytic applications, although modified forms of MCM-41 will probably be required in order to increase its hydrothermal stability.