The influence of the cobalt particle size and particle size distribution in determining Fischer-Tropsch (FT) performance for silica supported catalysts was investigated. Using a line broadening powder X-ray diffraction analysis, both the particle size and particle size distribution of cobalt were estimated and compared to the FT activity and stability at industrially relevant conditions (210 degrees C, H-2/CO = 2, 20 bar). It was shown that the apparent turnover frequency increased linearly with Co-0 particle size up to 9.8 nm, the largest size tested. For the first time, it has been shown that the breadth of the particle size distribution correlates directly to catalyst stability. Using these correlations, a highly active and stable catalyst was developed, showing a deactivation rate of -0.08% CO converted/day in a microchannel reactor with an activity of 0.25 mol(CO) g(Co)(-1) h(-1). (C) 2013 Elsevier B.V. All rights reserved.