Morphology and crystal–plane dependence of CeO2–TiO2 catalysts: Activity and mechanism for the selective catalytic reduction of NOx with NH3

Abstract

CeO2–TiO2 catalysts with four different morphologies were successfully synthesized by a hydrothermal method and tested for selective catalytic reduction of NOx with NH3 (NH3–SCR). For the four catalysts, CeO2–TiO2 nanocubes (CT–NC) and nanorods (CT–NR) preferentially exposed {100} and {110} facets, respectively; furthermore, nanosheets (CT–NS) and nanospheres (CT–NH) mainly exposed {111} facet. Interestingly, CT–NH catalyst showed the best NH3–SCR performance and the NOx conversion exceeded 97% at 325 °C. Through a series of characteristic methods manifested that the short–range ordered structure of Ce–O–Ti in CT–NH catalyst provided stronger surface acidic sites to promote the high–temperature activity. Moreover, the abundant Ce3+ species and appropriate reduction ability on {111} facet of CT–NH catalyst also caused outstanding deNOx activity. Reaction mechanism study showed that the Langmuir–Hinshelwood (L–H) mechanism and Eley–Rideal (E–R) mechanism existed simultaneously on all catalysts in NH3–SCR reaction. Meaningfully, two types of E–R mechanism were present on CT–NH catalyst, while L–H mechanism was dominant.