CoOx and FeOx supported on ZrO2 for the simultaneous abatement of NO and N2O with C3H6

MeOx/ZrO2 (Me = Co and Fe) catalysts were studied for the simultaneous selective catalytic reduction of NO and N2O in the presence of O2 using C3H6 as reducing agent (SCRsim). To give a better insight in the simultaneous process we investigated the reactions related to SCRsim (SCRN2O, SCRNO, N2O decomposition and C3H6 combustion) as well as the abatements in the absence of O2 (CRsim, CRN2O, CRNO). Catalytic results showed that, in the presence of O2 excess, CoOx/ZrO2 and FeOx/ZrO2 catalysts were scarcely active and unselective for the separate NO and N2O abatements with C3H6 and are ineffective for their simultaneous abatement. Because C3H6 preferentially reacted with O2, NO was poorly reduced and N2O was abated, at a temperature above that of complete C3H6 conversion, via both SCRN2O and decomposition. Conversely, in the absence of O2 in the feed, on both catalysts NO and N2O were efficiently reduced by C3H6, but undesired by-products formed. The activity for SCRsim strongly depended on the C3H6/O2 feeding ratio. With suitable feeding mixture O2 was completely consumed and the residual propene efficiently and simultaneously reduced NO and N2O, with negligible formation of by-products. In hydrothermal conditions both catalysts were slightly and reversibly deactivated. Characterization by XRD, UV-vis DRS and FTIR after catalytic experiments showed that dispersed Co2+ and Fe3+ species were stable on zirconia surface and that no significant segregation phenomena occurred in hydrothermal conditions.