Manganese promotion of a cobalt Fischer-Tropsch catalyst to improve operation at high conversion

The addition of manganese to cobalt-based Fischer-Tropsch catalysts increases activity and significantly improves liquid fuel yield by decreasing CO2 CH4 selectivity. These effects are particularly noticeable at high CO conversions where the catalyst is exposed H2O, low H2, partial pressures. Under these conditions, manganese-promotion causes a shift in maximum from 61 C-% 79 (at CO-conversion levels 78% 91%, respectively), thus enabling once-through operation. Our CO-TPD DFT studies show that promotion cannot be linked enhanced adsorption nor C-O bond cleavage (both typically postulated mechanisms). Rather, our DFT-calculations indicate modelled as oxide cluster on Co(1 1 1) associated with improved oxygen removal catalytically active surface, explaining reduced selectivity towards conversion and, thus, methane yield.