Promotional effect and mechanism study of nonmetal-doped Cr/CexTi1−xO2 for NO oxidation: tuning O2 activation and NO adsorption simultaneously

Abstract

Nonmetal-doped Cr/Ce_xTi_1−xO₂ catalysts were evaluated for selective catalytic oxidation (SCO) of NO, and these were synthesized by using cyanamide as a nonmetal source. The aim of this paper was to elucidate the detailed composition–structure–property relationships. The characterization results demonstrated that the optimized performance was correlated with the formation of superoxide radicals, which was derived from the nonmetal doping and confirmed by EPR studies. H₂-TPR and O₂-TPD experiments indicated that the addition of cyanamide was beneficial to tune O₂ activation and improve NO adsorption strength simultaneously. XPS results suggested that N species were successfully incorporated into the lattice of a cerium–titanium solid solution and substituted for oxygen. Additionally, the designed FTIR and Raman measurements were applied to identify the doping sites, that is, N species were inclined to substitute the O atoms around cerium to form the Ce–N–Ti and Ce–N–Ce bonds. Finally, the catalytic mechanism was tentatively proposed based on the analysis of in situ DRIFTS results.