Chiang Mai Journal of Science

     Carbon dioxide hydrogenation is an attractive route for converting greenhouse gases into valuable fuels and chemicals. In this work, the effect of manganese (Mn) promoter loading on Co/SiO₂ catalysts was systematically investigated for CO₂ hydrogenation under mild reaction conditions. Catalysts with different Mn loadings (1–7 wt%) were synthesized using the incipient wetness impregnation method and characterized by XRD, BET, TEM, H2-TPR, and CO₂-TPD techniques. The introduction of Mn significantly influenced the physicochemical properties of the catalysts, including metal dispersion, surface basicity, and reducibility. The BET analysis revealed a gradual decrease in surface area with increasing Mn loading due to partial pore blocking, while H₂-TPR results indicated enhanced reducibility associated with Co–Mn interactions. CO₂-TPD results demonstrated that Mn addition increased the strength of basic sites, which facilitates CO₂ adsorption and activation. Catalytic testing at 230 °C and atmospheric pressure showed that the 20CS5Mn catalyst exhibited the lowest methane selectivity and favors to produce C₅⁺ selectivity. The reaction pathway is proposed to proceed through a reverse water–gas shift (RWGS) reaction followed by Fischer–Tropsch-like hydrogenation of CO intermediates on cobalt active sites. Although the selectivity toward C₅⁺ hydrocarbons remained relatively low, Mn promotion was found to slightly enhance hydrocarbon chain growth compared with the unpromoted catalyst.