NOx control by catalytic oxidation combined with wet absorption has been a promising technology for the flue gas treatment of industrial boiler and furnace. LaMnO3+delta perovskites were investigated as catalysts for NO oxidation. The comparison between metal substitution of La and Mn cations was researched. The activity results indicated that La site substitution was more favorable for NO oxidation than Mn site substitution. LaCoMnO exhibited the highest activity in NO oxidation with maximum value of 83.74% at 250 degrees C. That value further increased to 89.96% after acid etching (LaCoMnO-A), and closely, such high value of 89.78% was achieved at 220 degrees C. The surface area was significantly improved by acid etching, i.e., from 47.0 m(2)/g to 212.0 m(2)/g, Tremendous changes in crystalline structure and morphology were taken place, i.e., perovskites phase disappeared and MnO2 was detected instead; compact amorphous particle morphology was replaced by multiple layer structure. Even more, Mn4+ ions and oxygen vacancies accumulated on the surface were improved. Deservedly, the redox property was enhanced enormously, especially at low temperature. Subsequently, SO2 poisoning tests were conducted at 250 degrees C under 20 ppm SO2. Interestingly, no decrease was observed for LaCoMnO-A within 480-min SO2 poisoning test, which was totally contrasted with the nearly complete deactivation results of LaCoMnO. In-situ DRIFTS measurements validated nitrate disappeared and replaced by sulfate formation on the catalyst surface. Merely, under low-concentration SO2 atmosphere, the monodentate nitrate and bidentate nitrate were destroyed, while the free nitrates exhibited higher resistance. Overall, the acid etching improved the catalyst resistance to SO2, which may have the potential to apply in the flue gas treatment of low-sulfur and sulfur-free fuel fired boiler and furnace.