Minimizing CoxMn1-xO content in a Co2C catalyst for low CO2 selectivity in Fischer-Tropsch synthesis to olefins

• CO 2 selectivity on a high Co 2 C content catalyst for FTO is as low as 3.86%. • High WGSR activity originates from Co x Mn 1-x O rather than Co 2 C. • Na promotion enhances WGSR on Co x Mn 1-x O, leading to high CO 2 selectivity. • CO 2 selectivity remains low in Co 2 C-rich catalysts, even with Na increased to 0.8%. The Co 2 C-based catalyst is a promising candidate for the Fischer-Tropsch to olefins reaction. However, it consistently exhibits high CO 2 selectivity (∼40 %), and the origin of the high activity in the water–gas-shift reaction is not well-understood. In this study, Co 2 C catalysts constructed with the same elemental compositions but using the melting and co-precipitation methods resulted in drastic differences in CO 2 selectivity − one at 3.8 % and the other at 35.3 %. A detailed structural study revealed that the presence of Co x Mn 1-x O instead of Co 2 C is responsible for the elevated CO 2 selectivity. Interestingly, Co x Mn 1-x O alone demonstrates limited CO 2 selectivity, but when promoted with Na, its WGSR activity is greatly enhanced. Conversely, the catalysts maintained consistently low CO 2 selectivity even with improved Na content, as long as a high fraction of Co 2 C is present. This finding is important for designing Co 2 C-based catalysts that can achieve high olefin selectivity while minimizing undesirable CO 2 emissions.