The conversion of synthesis gas to hydrocarbon fuels by Co catalysts through the Fischer-Tropsch process has received renewed attention particularly with regard to the role of promoters. In this letter, we utilize scanning transmission electron microscopy imaging and electron energy-loss spectroscopy to elucidate the interaction between the Mn promoter, the Co nano-catalysts, and the TiO2 support. In-situ heating experiments show the diffusion of Mn and Ti-support onto the Co particle under reducing conditions.