Insight into the Mechanism of Selective Catalytic Reduction of NO_<i>x</i> by Propene over the Cu/Ti_0.7Zr_0.3O₂ Catalyst by Fourier Transform Infrared Spectroscopy and Density Functional Theory Calculations

Abstract

The mechanism of selective catalytic reduction of NO_<i>x</i> by propene (C₃H₆-SCR) over the Cu/Ti_0.7Zr_0.3O₂ catalyst was studied by <i>in situ</i> Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. Especially, the formation and transformation of cyanide (−CN species) during the reaction was discussed. According to FTIR results, the excellent performance of the Cu/Ti_0.7Zr_0.3O₂ catalyst in C₃H₆-SCR was attributed to the coexistence of two parallel pathways to produce N₂ by the isocyanate (−NCO species) and −CN species intermediates. Besides the hydrolysis of the −NCO species, the reaction between the −CN species and nitrates and/or NO₂ was also a crucial pathway for the NO reduction. On the basis of the DFT calculations on the energy of possible intermediates and transition states at the B3LYP/6-311 G (d, p) level of theory, the reaction channel of −CN species in the SCR reaction was identified and the role of −CN species as a crucial intermediate to generate N₂ was also confirmed from the thermodynamics view. In combination of the FTIR and DFT results, a modified mechanism with two parallel pathways to produce N₂ by the reaction of −NCO and −CN species over the Cu/Ti_0.7Zr_0.3O₂ catalyst was proposed