The design of supported Co-based Fischer-Tropsch (F-T) catalysts with suitable reducibility, dispersion, loading, and nanoparticle structure is necessary so that high catalytic activity and selectivity for C5+ hydrocarbons can be achieved. Herein, we report that pyrolyzing a Co-metal-organic framework-71 precursor can provide porous carbon-supported Co catalysts with completely reduced, well-dispersed face-centered cubic (FCC) Co nanoparticles (approximate to 10 nm in average size). The catalysts can be further tailored dimensionally by doping with Si species, and the FCC Co nanoparticles can be partially transformed into hexagonal close-packed Co via a Co2C intermediate. All the as-prepared catalysts had extremely high Co site density (>3.5 x 10(-4) mol/g-cat.) because they had a high number of Co active sites and low mass. Aside from having high F-T activity and C5+ selectivity, with diesel fuels being the main constituents, they showed unprecedentedly high C5+ space time yields (up to 1.45 g/(g-cat. h)) as compared to conventional Co catalysts. (c) 2017 American Institute of Chemical Engineers AIChE J, 63: 2935-2944, 2017