Although　both　H-2　and　CO　can　be　thermodynamically　oxidized　by　O-2　over　TiO2　under　ultraviolet　light　(UV)　irradiation,　it　was　found　that　CO　not　H-2　could　be　oxidized　over　an　anatase　TiO2　in　this　work.　The　chemisorption　results　of　CO　and　H-2　at　TiO2　surface　under　UV　irradiation,　investigated　by　a　gas　sensing　testing,　showed　that　CO　adsorption　at　TiO2　would　cause　the　decrease　of　TiO2　surface　impedance,　where　as　H-2　adsorption　would　cause　its　increase.　It　is　proposed　that　the　CO　adsorbed　at　TiO2　donate　electrons　toTiO(2)　(as　a　process　of　CO　pre-oxidation),　resulting　in　its　oxidation.　In　contrast,　the　H-2　adsorbed　at　TiO2　accept　electrons　from　TiO2　(as　a　process　of　H-2　pre-reduction),　which　makes　it　difficult　to　be　oxidized.　This　result　indicates　that　the　photocatalytic　oxidation　of　a　reactant　over　TiO2　not　only　depends　on　the　formation　of　the　photo-generated　carriers　and　the　subsequent　activated　oxidizing　species,　but　may　be　also　depends　on　the　electron　transfer　behavior　at　the　interface　of　the　adsorbed　reactant　and　TiO2.　(C)　2015　Elsevier　B.V.　All　rights　reserved.