Mechanistic insight into the selective catalytic reduction of NOx with propene on the Ce0.875Zr0.125O2 (110) surface

Abstract

Selective catalytic reduction of NO_x with hydrocarbons (HC-SCR) is a promising technology for the abatement of NO_x from vehicles. The reaction mechanism is mainly investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments, but the detailed reaction scheme is not yet clear, especially the complex interactions between catalyst interfaces and gas molecules. In this study, by using the periodic density functional theory (DFT) method, we propose a SCR-C₃H₆ scheme on the Ce_0.875Zr_0.125O₂ (110) surface. Firstly, C₃H₆ is partially oxidized by lattice or adsorbed oxygen to the acyl group following the Mars–van Krevelen (MVK) mechanism; then, the acyl group combines with nitrate to generate an RCOO–NO₂ intermediate, followed by decarboxylation and O-shift reactions to produce R–NO₂, R′CH–ONO, –NCO, and –CN species, which are finally converted into CO₂ and N₂. The simulation results are in good agreement with experimental values. In addition, some catalytic characteristics are found: (1) NO₃ can adsorb steadily on brid₁, brid₂, biden, and monoden sites of the Ce_0.875Zr_0.125O₂ (110) surface; (2) the activity sequence of C₃H₆ by lattice O is C_sp3–H bond > C_sp2–H bond > CC bond; (3) –NCO is formed more easily than –CN on the Ce_0.875Zr_0.125O₂ (110) surface due to the admirable activity of surface lattice oxygen.