Phosphotungstate organic–inorganic hybrid materials [CH2COOHmim]H2PW12O40, [(CH2)3COOHmim]H2PW12O40 and [Bmim]H2PW12O40 with dual catalytic oxidation active centers, including carboxylic acid group and phosphotungstate anion, were synthesized from bisulfate acidic ionic liquid in a one-step method, and well characterized by XRD, 1H NMR, 13C NMR, 31P NMR, FT-IR, and UV–vis. Then, these obtained hybrids were employed as catalysts for the selective oxidation of N-methylmorpholine (NMM) into N-methylmorpholine-N-oxide (NMMO) using H2O2 as an oxidant. As expected, the –COOH functionalized hybrids showed much better activity than the conventional hybrid [Bmim]H2PW12O40, and even much better than the mixture of corresponding ionic liquid and H3PW12O40, suggesting the existence of dual active species and synergistic effect between the cation and phosphotungstate in hybrids. The best catalyst [(CH2)3COOHmim]H2PW12O40 gave an NMM conversion of 98.7% and selectivity to NMMO of 98.8%. The structural characterization by 31P NMR, UV–vis, Raman and 13C NMR analysis of the catalyst before and after oxidation demonstrated the existence of the catalytic active species PW12O403− and peroxy carboxylic acid. Finally, a possible catalytic mechanism has been proposed. [ABSTRACT FROM AUTHOR]