Catalytic performances of soluble Co, Co/Mn, Co/Mn/Br, and Co/Mn/Ce catalysts for m-xylene (MX) oxidation without acetic acid (HAc) solvent were studied, comparing with Co/HAc catalysts. In m-toluic acid (MTA) production, a Ce-salt promoter could effectively substitute for bromide salts and the recycle alcohol/aldehyde liquid mixture acts as a more efficient promotor than either peroxides or MTA itself. The Co/Mn/Ce system, free of acetic acid and Br-, was a superior catalyst in terms of activity and selectivity to MTA. Just as for p-xylene oxidation using Co/Mn/Br catalysts, both the MX reaction rate and the MTA selectivity increased with temperature when using Co/Mn/Ce catalysts. Unlike p-xylene oxidation however, MX oxidation resulted in more coupling products. For MX oxidation catalyzed by a supported Co-imide complex in supercritical CO2, the activity was lower by more than an order of magnitude, but the MTA selectivity was greater.