The effect of solvent on the hydrogen-deuterium isotopic homomolecular exchange over a traditional Fischer-Tropsch cobalt catalyst (25% Co/Al2O3) was investigated using a plug flow reactor at two different reaction temperatures (room temperature (26 degrees C) and -20 degrees C) and at atmospheric pressure. In this study, three different solvents were tested, including n-pentane, n-hexadecane, and C-30 oil. The consumption of H-2 and D-2 is the same, and the concentration of the HD produced is twice the consumption of H-2 or D-2 at dry (without solvent) conditions. At room temperature and at -20 degrees C, conditions without solvent exhibited 100mol% exchange with the formation of H-2:HD:D-2 having a 1:2:1 ratio. For n-pentane solvent, the exchange rates were approximate to 97 and approximate to 80mol% at 26 and -20 degrees C, respectively. For the n-hexadecane and C-30 oil solvents, the initial exchange rate was approximate to 50mol%, with the exchange rate decreasing over time. The lower exchange rate with the n-hexadecane and C-30 oil solvents, and also n-pentane at -20 degrees C, is likely due primarily to the limited mobility of reactant molecules in the liquid-filled pores of the catalyst. Blocking or covering of the pores of the catalyst depends on the molecular mass and density of the solvent. No isotopic partitioning preference was observed at two different temperatures and various solvents for the active cobalt catalyst.