On the link between CO surface coverage and selectivity to CH4 during CO2 hydrogenation over supported cobalt catalysts

An operando IR study was carried out to investigate the loss of selectivity to higher hydrocarbons observed over cobalt-based Fischer-Tropsch catalysts when CO is replaced with CO2. Our data unambiguously show that the structure and oxidation state of the surface of metallic cobalt remains the same whether CO2 or CO are cofed with H2. The selectivity to CH4 appears to increase monotonously with decreasing surface coverage of adsorbed CO. The switch from Fischer-Tropsch synthesis to methanation using CO2-rich feeds over metallic cobalt can therefore be assigned to surface coverage effects only, assuming that most, if not all, hydrocarbons products are formed on metallic cobalt.