Correlation between donating or accepting electron behavior of the adsorbed CO or H2 and its oxidation over TiO2 under ultraviolet light irradiation

Although both H2 and CO can be thermodynamically oxidized by O2 over TiO2 under UV irradiation, only CO was oxidized by O2 over TiO2 due to its donating electrons to TiO2, while H2 was not oxidized by O2 under the same condition due to its accepting electrons from TiO2.