Development of alternative ways to produce clean fuels is a significant and strategically important challenge. One of the most effective approaches is the Fischer-Tropsch synthesis (FTS), which is realized over Coor Fe-based catalysts. In this work spark plasma sintering was applied for the synthesis of bulk core shell Co and Fe CNT-supported FTS catalysts. The effect of the sintering temperature on the structure, evolution, and catalytic performance of the samples was studied by combination of physicochemical methods. Catalysts showed high activities and TOFs without pre-reduction: 11.6 molCOg(Co)(-1) s(-1) and 0.1 s(-1) for Co and 20.3 mol(CO)g(Fe)(-1) s(-1) and similar to 0.9 s(-1) for Fe samples. The unusual dependence of C5+ selectivity on the Co particle size along with the presence of the amorphous carbide and amorphous carbon layers under graphitic shell in Fe catalysts point to the diffusion of reagents and products through shell defects and the catalytic reaction on the particle core surface. (c) 2020 Elsevier Inc. All rights reserved.