Molecular-Level Insight into Selective Catalytic Reduction of NOx with NH₃ to N₂ over a Highly Efficient Bifunctional Va-MnOx Catalyst at Low Temperature

Selective catalytic reduction of NO x 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 N 2 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 (Mn 2 O 3 ) for NH 3 activation and highly selective vanadates (Mn 2 V 2 O 7 ) that promote N 2 formation. NH 3 is initially activated by Mn 2 O 3 to form an NH 2 intermediate. Transfer of NH 2 to Mn 2 V 2 O 7 then takes place, which facilitates the capture of gaseous NO leading to the formation of NH 2 NO over Mn 2 V 2 O 7, whereafter NH 2 NO is efficiently converted to the preferred N 2 rather than the undesired byproduct, N 2 O. The proximity of the two components achieved via sol–gel preparation plays a crucial role in the transfer of active intermediates.