Low methane selectivity using Co/MnO catalysts for the Fischer-Tropsch reaction: Effect of increasing pressure and Co-feeding ethene

CO hydrogenation using cobalt/ manganese oxide catalysts is described and discussed. These catalysts are known to give low methane selectivity with high selectivity to C₃ hydrocarbons at moderate reaction conditions (GHSV < 500 h^–1, < 600 kPa). In this study the effect of reaction conditions more appropriate to industrial operation are investigated. CO hydrogenation at 1–2 MPa using catalyst formulations with Co/Mn = 0.5 and 1.0 gives selectivities to methane that are comparable to those observed at lower pressures. At the higher pressure the catalyst rapidly deactivates, a feature that is not observed at lower pressures. However, prior to deactivation rates of CO + CO₂ conversion > 8 mol/1-catalyst h can be observed. Co-feeding ethene during CO hydrogenation is investigated by the reaction of¹³C0-¹²C₂H₄-H₂ mixtures and a significant decrease in methane selectivity is observed but the hydrogenation of ethene is also a dominant reaction. The results show that the co-fed ethene can be molecularly incorporated but in addition it can generate a C, species that can react further to form methane and higher hydrocarbons.