(610c) SCR of NO with CO: A Mechanistic Investigation

Although the main reducing agent used in the selective catalytic reduction (SCR) of NO is NH3, renewed interest has been devoted towards CO recently due to the socio-economic concerns associated with the former reductant. In the present investigation, a series of transition metal oxides promoted titania catalysts (MOx/TiO2; M = Cr, Mn, Fe, Ni, Cu) were prepared and evaluated for NO reduction with CO at low temperatures (175-200 °C) and industrially relevant conditions. Finally, we are proposing a reaction mechanism for this reaction with MnOx/TiO2 catalyst. In-situ FT-IR experiments of NO adsorption on the catalyst revealed monodentate (peaks at 1248, 1291 and 1495 cm-1) and bidentate (peaks at 1584 and 1612 cm-1) nitrate formation. CO adsorption on the catalyst leads to the formation of carbonate species in addition to CO2 formation (~2350 cm-1). Peaks in the 1313-1442 cm-1 frequency region are observed due to monodentate carbonates whereas peaks at 1551 and 1626 cm-1 indicate bidentate carbonate formation. Interestingly, in the case of NO and CO coadsorption over MnOx/TiO2, the formation of CO2 is inhibited. The formation of N2O as an intermediate can be observed from the occurrence of small peaks at 1289 and 2220 cm-1. Remarkably, isocyanate (-NCO) species are not observed (neat peak at 2178 cm-1) in our FT-IR spectra. This indicates that the reaction mechanism in the present case follows a different pathway from that of the metal based catalysts. The role of lattice oxygen in the reaction mechanism is substantiated by transient analysis studies. More details about the mechanistic pathway will be discussed in the presentation.