Molecular-Level Insight into Selective Catalytic Reduction of NO_x with NH₃ to N₂ over a Highly Efficient Bifunctional V_a-MnO_x Catalyst at Low Temperature

Abstract

Selective catalytic reduction of NOx with ammonia (SCR) is not only an important 17 model catalytic reaction, but also significant in terms of improving environmental air quality and 18 human health. However, SCR catalysts suffer from the low activity and selectivity to N2 at low 19 temperature, which in part may be attributed to our limited understanding of the reaction 20 mechanism. Here, an unambiguous molecular-level mechanism is presented for an improved 21 low-temperature SCR activity using the bifunctional catalysts composed of highly active oxides (Mn2O3) for NH3 activation and highly selective vanadates (Mn2V2O7) which promote N2 23 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 by-product, N2O. The proximity of the two components achieved via sol-gel preparation plays a crucial role in the transfer of active intermediates.

A Review of Low Temperature NH3-SCR for Removal of NOx

“…Particularly, Mn-based binary oxides are popular and proven to be effective catalysts for low-temperature NH 3 -SCR reaction [42,50,51]. Recently, Xin et al [52] designed bifunctional V a -MnO x (where a represents the molar ratios of V / (V + Mn)) catalysts composed of Mn 2 O 3 and Mn 2 V 2 O 7 phases that significantly improved both NO x conversion and N 2 selectivity in comparison with Mn 2 O 3 at low-temperature ( Figure 1). Although Mn 2 V 2 O 7 showed an excellent N 2 selectivity, the NO x conversion is much lower on it.…”

Fabrication and Characteristics of Mn@ Cu3(BTC)2 for Low-Temperature Catalytic Reduction of NOx with NH3

“…e Mn 2p 3/2 peak can be deconvoluted into two peaks centered at 641.0 eV and 644.2 eV, which indicate the presence of Mn 3+ and Mn 4+ ions [29][30][31]. Xin et al [32] has suggested that Mn 3+ could activate NH 3 into NH 2 intermediate that will readily react with NO to produce N 2 . Previous studies also confirmed that ample amount of Mn 4+ ions is one of the key factors enhancing NH 3 oxidation in the NH 3 -SCR process due to the strong oxidizing state of Mn (IV) [15,16].…”

Single-atom site catalysts for environmental catalysis

“…Among post-combustion technologies, selective catalytic reduction (SCR) is regarded as ideal for NOx removal due to its superior NOx removal efficiency, relatively simple installation equipment, and reasonable operation cost, etc. [82,[113][114][115][116][117]. PGMs have been proven efficient catalysts for SCR of NO in the presence of reducing agents, such as CO, H2, NH3, and HC.…”