Fischer-Tropsch Synthesis over Cobalt-loaded Oxidized Diamond Catalyst -Effect of Addition of Mn on Catalyst Performance

In a series of studies of powdered diamond (O-Dia)-supported catalyst, performance of Mn co-loaded Co/O-Dia for Fischer-Tropsch synthesis was examined. The addition of Mn to Co/O-Dia greatly increased CO conversion with a slight decrease in the selectivity to higher hydrocarbons (C-5 +). The fraction of olefin in the C-5 + liquid product largely increased. The higher activity of Co-Mn/O-Dia catalyst is ascribed to the higher dispersion of active Co particles on O-Dia with the addition of Mn. The optimal ratio of Mn to Co is in the range of 0.05 to 0.1 at a Co loading of 5 wt%. At a reaction temperature of 230 degrees C, CO conversion of 85 % with a chain propagation probability of 0.81 at SV of 4500 mL.h(-1).g-cat(-1) were obtained. On O-Dia Mn-co-loaded catalyst precursor CoOx could easily be reduced under moderate H-2 pretreatment conditions to give well-dispersed metallic Co particles ranging from 3 to 11 nm in diameter (average size 7.1 nm). In contrast, without Mn, the particle size distribution of Co was broad, ranging from 4 to 30 nm (average 14.9 nm) at a Co loading of 5 wt%. The role of Mn is to prevent sintering of Co during H-2 reduction.