Effect of biomass-derived synthesis gas impurity elements on cobalt Fischer-Tropsch catalyst performance including in situ sulphur and nitrogen addition

The effect of 10 typical biomass-derived synthesis gas impurities on cobalt Fischer–Tropsch catalyst performance was investigated at industrially relevant conditions. Impurities (0–1000 ppmw) were introduced ex situ by incipient wetness impregnation to give 23 different compositions. The presence of alkali (Na, K) and alkaline earth elements (Ca, Mg) did not affect the ex situ-measured cobalt surface area but decreased the in situ activity, thereby decreasing the apparent turnover frequency. The C5+ selectivity increased and decreased upon addition of alkali and alkaline earth metals, respectively. Mn, Fe, and P had minor effects on catalyst performance. The presence of Cl decreased cobalt surface without affecting activity, thus increasing the turnover frequency. The changes in turnover frequency correlated with element electronegativity. In situ addition of H₂S and (CH3)2S (2.5–10 ppm) decreased activity at all concentrations. However, product selectivity was not affected. Addition of NH₃ (4 ppm) did not change catalytic performance.