The effect of boron (as H3BO3) on the CO hydrogenation ability of Co/TiO2 catalysts was investigated using XRD, LRS, TGA, DRIFTS and a fixed bed flow reactor. The introduction of boron (0.02-1.5%) into a 10 wt% Co/TiO2 catalyst decreased the Co3O4 crystallite size (26-16 nm) in the oxidic catalysts (calcined at 300 degrees C) and decreased the hydrogen uptake (0.35-0.9 ml/g cat) in the reduced catalyst. Reduction of the Co/TiO2 catalyst was made more difficult by the presence of boron. The CO conversion and overall hydrogenation rate decreased with decreasing ease of reducibility and decreasing cobalt dispersion caused by boron. Turnover frequency (ca. 20 x 10(-3) s(-1)), however, remained constant throughout and was independent of the extent of reduction and dispersion of the catalysts. This provides further evidence of the structure-insensitivity of supported Co Fischer-Tropsch catalysts. Addition of small amounts of B (<0.1%) do, however, result in an increase in alpha, less CH4 production and an increase in the olefin/paraffin ratio. This suggests an increase in the monomer propagation to termination ratio. At higher B loadings, product selectivity shifted to the lower molecular weight hydrocarbons and CO2 selectivity increased (0-2.5%).