Electronic structure changes introduced by nitrogen on the N-doped VOx/TiO2 system: Consequences on partial oxidation catalysis

Abstract

The catalytic activity for ethanol partial oxidation of supported vanadium oxide catalysts prepared on N doped TiO2 (VOx/N-TiO2) was correlated to the electronic structure of the vanadium clusters present in the catalyst surface. In situ Raman and UV–vis spectra together with ethanol temperature programmed desorption (TPD) profiles indicate that in all materials studied the average VOx cluster size is very similar, irrespective of the presence of nitrogen. However, the distribution of active sites and the reducibility of the VOx species are significantly affected by the presence of nitrogen in the support. The electronic structure of these materials was investigated using periodic density functional theoretical calculations. It was found that, compared to the nitrogen free materials, the electronic structure of reduced VOx is affected by the presence of N, as well as nitrogen position on the TiO2 supports (interstitial vs. substitutional). Our analysis revealed that after vanadia reduction during ethanol oxidation, reduced VOx sites (V+4) form, accompanied by the simultaneous reduction of adjacent Ti cations (Ti+3). Calculated optical absorption spectra are also provided and matched with experimental spectroscopic results, confirming these observations.