Mechanism and Enhancement of the Low-Temperature Selective Catalytic Reduction of NOx with NH₃ by Bifunctional Catalytic Mixtures

Abstract

Enhancement of the low-temperature (LT) performance of selective catalytic reduction (SCR) of NOx with NH3 has been a spotlight in environmental catalysis. Here, we use a bifunctional catalytic system mixing V–W/Ti with an oxidative component, i.e., MnOx/CeO2, to achieve both improved LT-SCR activity and N2 selectivity. An integrated approach of steady-state kinetic measurements, chemical trapping techniques, time-resolved in situ FTIR spectroscopy, and density functional theory (DFT) calculations reveals that such a synergistic enhancement is at a short distance and is significant when V–W/Ti and MnOx/CeO2 are in intimate contact. These findings further suggest a bifunctional LT-SCR pathway mediated by a short-lived, mobile nitrite-precursor intermediate, which is facilely generated on the oxidative component and then communicates with the adjacent SCR phase through reacting with the abundant NH3 adsorbates there. Assembling such a mechanism with commercial SCR catalysts, accordingly, acts as a promising way to enhance the LT-SCR performance.

Simultaneous Catalytic Removal of VOCs and NOx with the Dual-layered Catalyst of CoCeOx and V2O5/TiO2

“…In our previous work, we found that improvement of SCR reactivity could be realized by utilizing the oxidizing properties of cobalt-cerium oxide (denoted as CoCeOx) catalyst and the acidity of the V2O5/TiO2. Moreover, we also revealed that oxidation ability was the dominant property to enhance the degradation performance for VOCs (Hu et al, 2021). Therefore, we propose a dual-layered structure to achieve an effective collocation with different functional areas, enhancing its total activity for NOx and VOCs removal.…”

Hydrotalcite-Modified Clinoptilolite as the Catalyst for Selective Catalytic Reduction of NO with Ammonia (NH3-SCR)

“…One of the possible applications of LDHs-derived materials is the selective catalytic reduction of nitrogen oxides with ammonia (NH 3 -SCR). The process aims to eliminate NO x produced by stationary and mobile sources of emissions to produce the mixture of N 2 and H 2 O [9]. In fact, the commercial catalysts of NH 3 -SCR, V 2 O 5 -MoO 3 (or WO 3 )-TiO 2 , exhibit relatively good catalytic activity; however, their performance is likewise limited, mainly due to a narrow temperature window, sensitivity to SO 2 and alkali metals, or the emission of cancerogenic vanadium [10].…”