This paper focuses on improving photocatalytic activity of N-doped TiO2 photocatalyst for efficiently utilizing solar energy. A simple H-2 reduction is found to remarkably enhance the photocatalytic activity of N-doped TiO2 for ethylene oxidation under visible light or simulated solar light irradiation. Ultraviolet/visible diffuse reflectance spectra (UV/vis DRS), X-ray photoelectron spectra (XPS) and electron paramagnetic resonance (EPR) spectra were employed to characterize the surface properties and chemical states of nitrogen dopants in H-2-reduced N-doped TiO2. The results reveal that H-2 reduction facilitates the creation of oxygen vacancies and Ti3+ species in N-doped TiO2 but without removal of nitrogen species from catalyst surface. The formed oxygen vacancies and Ti3+ species seriously influence electron excitation from doped nitrogen species and subsequently tune the generation of active oxygen species O-2(center dot-) radicals on N-doped TiO2. The synergistic effect of oxygen vacancies and doped nitrogen species contributes to the enhancement of photocatalytic activity of N-doped TiO2 samples, but the formed Ti3+ ions largely suppress the photocatalytic activity. (C) 2012 Elsevier B.V. All rights reserved.