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

Selective catalytic reduction of NO_<i>x</i> 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