Effects of Mn promotion on the structure and catalytic performance of Co2C-based catalysts for the Fischer–Tropsch to olefin reaction†

Abstract

An investigation into the effect of an Mn promoter on the structure and catalytic performance of Co₃O₄ catalysts for the Fischer–Tropsch to olefin (FTO) reaction was conducted. It was found that the introduction of the Mn promoter into Co₃O₄ precursors altered the morphology of the catalytic active phase from Co₂C nanospheres to Co₂C nanoprisms with specifically exposed facets of (101) and (020), which exhibited enhanced activity and C⁼_2–4 selectivity compared to those of Mn-free Co₂C nanospheres. Further studies suggested that the Mn promoter could interact with Co to form Co_xMn_1−xO intermediates, which were readily involved in the formation of Co₂C nanoprisms rather than Co₂C nanospheres. Additionally, Mn-doping improved CO adsorption capacity, creating a C-rich and H-poor micro-environment around Co₂C active sites. As a result, the as-prepared 10Mn/Co₃O₄ catalyst exhibited the highest activity (25.8 C%) and C⁼_2–4 selectivity (54.1 C%) together with a relatively lower CH₄ selectivity (8.5 C%). Moreover, product distribution significantly deviated from classical Anderson–Schulz–Flory (ASF) distribution. However, excessive Mn addition would cover the Co₂C active sites, leading to decreased catalytic activity and olefin selectivity.