Molecular-Level Insight into Selective Catalytic Reduction of NO_<i>x</i> with NH₃ to N₂ over a Highly Efficient Bifunctional V_<i>a</i>-MnO_<i>x</i> Catalyst at Low Temperature

Abstract

Selective catalytic reduction of NOx with ammonia (SCR) is not only an important model catalytic reaction but is also significant in terms of improving environmental air quality and human health. However, SCR catalysts suffer from low activity and selectivity to N2 at low temperature, which in part may be attributed to our limited understanding of the reaction mechanism. Here, an unambiguous molecular-level mechanism is presented for an improved low-temperature SCR activity using bifunctional catalysts composed of highly active oxides (Mn2O3) for NH3 activation and highly selective vanadates (Mn2V2O7) that promote N2 formation. NH3 is initially activated by Mn2O3 to form an NH2 intermediate. Transfer of NH2 to Mn2V2O7 then takes place, which facilitates the capture of gaseous NO leading to the formation of NH2NO over Mn2V2O7, whereafter NH2NO is efficiently converted to the preferred N2 rather than the undesired byproduct, N2O. The proximity of the two components achieved via sol–gel preparation plays a crucial role in the transfer of active intermediates.