The selective catalytic reduction of NOx with ethanol was investigated over a reference 3 Ag/γ-Al2O3 and compared to 3 Cu/γ-Al2O3 and 3 Fe/γ-Al2O3 as cost-efficient, non-noble metal catalysts. In particular, the evolution of by-products was studied using on-line Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS) analysis. For all catalysts, acetaldehyde was obtained through two different potential reaction pathways: (i) selective dehydrogenation and (ii) partial oxidation. The highest yields of acetaldehyde and NOx-species were found for the Ag-based catalyst. In the light of the highest yield of acetaldehyde formation, exclusively for the Ag-based catalyst, a third reaction pathway including dehydration of ethanol to ethene and the oxidation to ethene oxide is possible. The adsorption capacity of NOx and the activity for the oxidation of NO were investigated by NOx temperature-programmed desorption (TPD) experiments. This leads to the assumption that the formation of surface nitro species over the Ag-based catalyst is pronounced as confirmed by the evolution of products from the decomposition of either nitromethane or nitroethane such as CH4, CH3OH, CH2O and NH3. The formation of NH3 on the catalyst surface is an important reaction pathway in the EtOH-SCR. As shown by NH3-TPD, lattice oxygen on the Fe- and Cu-containing catalysts is active for NH3 oxidation. The resulting surface nitrates are important in the reaction mechanism of the EtOH-SCR. This was confirmed by catalytic experiments with different feed gas compositions comprising NO, NO2 or a NOx-free feed gas.
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