NO catalytic oxidation using 15% Mn/TiO2, 15% Co/TiO2, and 15% Mn Co(2:1)/TiO2 with a low molar ratio of O-3/NO was investigated. 03 improved NO catalytic oxidation performance, including the tolerance to H2O and SO2. Synergism occurred more clearly between 15% Mn Co(2:1)/TiO2 and 03 (O3/NO = 0.5) than between the other two catalysts and 03, below 250 degrees C. In situ diffuse reflectance infrared Fourier-transform spectroscopy indicated that O-3 accelerated the mass production of monodentate nitrates on 15% Mn Co(2:1)/TiO2 compared with 15% Mn/TiO2. Catalyst characterization results illustrated that cobalt-loading created lots of oxygen vacancies on 15% Mn Co(2:1)/TiO2, promoting redox capability and enhancing NO catalytic oxidation. In addition, 15% Mn Co(2:1)/TiO2 contained more Mn2O3, Mn3+, Mn4+, and chemisorbed oxygen on its surface than 15% Mn/TiO2 and 15% Co/TiO2, which could promote the synergistic effect of the catalyst. This study could reduce the consumption of ozone and reduce the harm of ozone leakage in NO oxidation, which could guarantee a high efficiency of NO oxidation in a wide temperature range (50-400 C).