Characterization of CoCu- and CoMn-Based Catalysts for the Fischer–Tropsch Reaction Toward Chain-Lengthened Oxygenates

The need for a sustainable energy supply in the face of depleting oil reserves has reignited the importance of Fischer–Tropsch (FT) synthesis technology. Presently, the FT process is practiced at the industrial scale to predominately produce synthetic diesel-type fuels and lubricants. More recently, the possibility of hydrogenating CO toward oxygenates, and not just hydrocarbons, has been explored. We have developed a series of CoCuMn and CoMnK catalysts prepared via the oxalate co-precipitation route that are capable of forming oxygenates with desirable selectivity. Upon H₂-assisted thermal decomposition of the resultant mixed metal Co₁Cu₁Mn₁ oxalates, catalysts naturally exhibited a cobalt core–copper shell configuration with Mn₅O₈ dispersed throughout the catalyst nanoparticle as determined via Atom Probe Tomography (APT). We suggest structural changes are induced by the CO and H₂ reactants to form the catalytically active phase under real-time reaction conditions as demonstrated by corroborative Density Functional Theory calculations and experimental evidence. APT studies also show that a Co₄Mn₁K_0.1 catalyst post reaction contained a cobalt carbide phase as determined from a Co/C ratio of 2/1. Manganese and potassium were found only in the outermost part of the particle. Both catalysts were found to contain the presence of a Mn₅O₈ oxidic phase before and post reaction which we attribute to the high activity toward oxygenates of these two catalysts.