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.