Theoretical and experimental insights into CO2 formation on Co2C catalysts in syngas conversion to Value-Added chemicals

Cobalt carbide (Co 2 C) has been discovered as the promising active phase for Fischer–Tropsch to olefins (FTO) process and higher alcohols synthesis (HAS) from syngas, in the form of nanoprisms and nanospheres, respectively. However, CO 2 formation is inevitable on Co 2 C catalysts, especially in FTO process. So far, the mechanism of CO 2 formation on Co 2 C surfaces is less understood. This work provides fundamental insights into CO 2 formation on Co 2 C nanospheres and nanoprisms through computational and experimental study. DFT calculations demonstrate that: Co 2 C (1   0   1) and (0   2   0) surfaces exposed on Co 2 C nanoprisms are basically not active for water gas shift (WGS) reactions but the introduction of Na greatly promotes CO 2 formation. CO 2 is less favored on Co 2 C(1   1   1) surface which is dominant on Co 2 C nanospheres, however, the reverse WGS activities can be promoted with Na addition. The experimental results confirmed removing Na from Co 2 C can efficiently suppress WGS activity, thus reducing CO 2 selectivity while the selectivity of light olefins retained. Though previous studies focused on Na addition to promote the yield of light olefins, our work indicates that Na also promotes undesired CO2 formation. Our results suggest that Na is crucial for active phase formation but not necessarily beneficial during the CO hydrogenation reactions.