MnOx supported on Fe–Ti spinel: A novel Mn based low temperature SCR catalyst with a high N2 selectivity

Abstract

In this work, a novel 10% Mn/Fe–Ti spinel catalyst with an excellent N2 selectivity was developed for the selective catalytic reduction (SCR) of NO with NH3 at low temperatures. The mechanism of NO reduction and N2O formation over Fe–Ti spinel, 10% Mn/Fe–Ti spinel and 5% Mn–10% Fe/TiO2 was investigated using in situ DRIFT study and the transient reaction study. Meanwhile, the reaction kinetic constant of the SCR reaction (i.e., N2 formation) through the Eley–Rideal mechanism, the reaction kinetic constant of the SCR reaction through the Langmuir–Hinshelwood mechanism and the reaction kinetic constant of the non selective catalytic reduction (NSCR) reaction (i.e., N2O formation) were obtained according to the steady state kinetic study. They all indicate that the NSCR reaction over 10% Mn/Fe–Ti spinel through the Eley–Rideal mechanism was cut off. NH2 adsorbed on 10% Mn/Fe–Ti spinel can be hardly oxidized to NH as NH2 mainly adsorbed on the support (i.e., Fe–Ti spinel) of 10% Mn/Fe–Ti spinel, which was far away from Mn4+ cations on 10% Mn/Fe–Ti spinel. Therefore, the NSCR reaction over 10% Mn/Fe–Ti spinel through the Eley–Rideal mechanism was suppressed. However, the regeneration of Fe3+ on Fe–Ti spinel was accelerated due to the rapid electron transfer between Mn4+ and Fe2+ on 10% Mn/Fe–Ti spinel resulting in a remarkable promotion on NH3 activation although NH3 adsorbed on 10% Mn/Fe–Ti spinel cannot be directly activated by Mn4+ on 10% Mn/Fe–Ti spinel. Therefore, the SCR reaction over Fe–Ti spinel was promoted remarkably after the load of MnOx. As a result, 10% Mn/Fe–Ti spinel showed an excellent SCR performance especially N2 selectivity at low temperatures, which was much better than 5% Mn-10% Fe/TiO2 with the same chemical composition.