Carbon monoxide oxidation over copper and nitrogen modified titanium dioxide⋆

Copper-Titanium Dioxide (Cu-TiO2) catalysts have been widely used to catalyze small molecules through photo- and thermal-catalytic approaches. We report nitrogen doped titanium oxide (N-TiO2) improved catalytic performance of Cu-TiO2 in the carbon monoxide oxidation reaction. Anatase TiO2 and rutile TiO2 are chosen to investigate the effect of the TiO2 phase for nitrogen modification. XPS and DFT results showed both interstitial nitrogen and substitutional nitrogen exists over nitrogen doped anatase TiO2, N-TiO2 (A). Only substitutional nitrogen exists over nitrogen doped rutile TiO2, N-TiO2 (R). Compared with copper over titanium dioxide (Cu-TiO2) catalysts, copper over nitrogen doped titanium dioxide catalysts (Cu-N-TiO2) showed enhanced redox properties based on analysis of temperature programmed reactions including H2-TPR and CO-TPSR. IR studies using CO as a probe molecule as well as copper XPS results showed that surface copper concentration distributed differently with the addition of nitrogen. Therefore, correlation between the ratio of [Cu+]/[Osurf.] and the reaction rate is suggested, because this ratio represents contributions from both active and spectator species in the carbon monoxide oxidation reaction.