Insight into the Mechanism of Selective Catalytic Reduction of NOx by Propene over the Cu/Ti0.7Zr0.3O2 Catalyst by Fourier Transform Infrared Spectroscopy and Density Functional Theory Calculations

Abstract

The mechanism of selective catalytic reduction of NOx by propene (C3H6-SCR) over the Cu/Ti0.7Zr0.3O2 catalyst was studied by in situ 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/Ti0.7Zr0.3O2 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/Ti0.7Zr0.3O2 catalyst was proposed.