Mechanism of the selective catalytic reduction of NOx by C2H5OH over Ag/Al2O3

The mechanism of the selective catalytic reduction (SCR) of NOx by C2H5OH over silver catalyst (Ag/Al2O3) was investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Attention was focused on the formation and reactivity of novel enolic species on the Ag/Al2O3 surface. DRIFTS spectra show that the surface enolic species, which was derived from partial oxidation of C2H5OH over Ag/Al2O3 in the presence of excess oxygen, play a crucial role in the formation of isocynate species (NCO) by reaction with NO+O2 or NO3− absorbed on the surface of Ag/Al2O3. 2,3-dihydrofuran was used to an enolic model compound in our DRITFS study, and the results support our assignment. A novel mechanism of the SCR of NOx by C2H5OH is proposed based on the DRIFTS studies. The mechanistic differences between the SCR of NOx by C2H5OH and that by C3H6 are discussed. The high reactivity of the enolic species results in high surface concentration of NCO and high efficiency of NOx reduction using C2H5OH as a reductant. The results of density functional theory (DFT) calculations are in good agreement with the DRIFTS spectra, and support our suggestions about the surface enolic species.