Tailoring the Electronic Structure of Single Ag Atoms in Ag/WO₃ for Efficient NO Reduction by CO in the Presence of O₂

Abstract

Developing efficient catalysts for the selective catalytic reduction of NO x by CO (CO-SCR) is the key challenge for commercializing this technology. Ag-based catalysts with relatively low costs are promising but widely believed to be not efficient enough for this reaction. Here, we demonstrate that atomically dispersed Ag supported on ordered mesoporous WO 3 (m-WO 3 ) can serve as a highly active catalyst for CO-SCR under O 2 -containing conditions. By altering the amount of the Ag precursor, the local environment of the Ag atom coordinated with the O atom can be tailored. Furthermore, at 250 °C and an O 2 /CO ratio of 2.5:1, 0.3Ag/m-WO 3 (0.3 wt % Ag) with six-coordinated Ag−O exhibited much better catalytic performance than 5 Ag/m-WO 3 (5 wt % Ag) with twocoordinated Ag−O (e.g., 0.43 vs 0.02 mol NO g Ag −1 h −1 in the reaction rate) and previously reported Ag-based catalysts in the literature. The theoretical calculations confirm that the six-coordinated Ag atoms in 0.3Ag/m-WO 3 possess a more positive oxidation state and a higher d-band center than the two-coordinated Ag atoms in 5Ag/m-WO 3 , promoting its bonding strength with coadsorption of the critical intermediates of N 2 O* and CO*. This work provides a feasible route for regulating the local environment of a Ag single atomic catalyst to enhance its catalytic property for CO-SCR.

Triangle Cl−Ag1−Cl Sites for Superior Photocatalytic Molecular Oxygen Activation and NO Oxidation of BiOCl

“…The atoms dispersion and coordination environment of Ag were further checked by X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Figure 1e displayed the absorption threshold of Ag 1 /BiOCl was between that of Ag foil, Ag 2 O and AgCl, [16] suggesting the oxidation state of Ag δ + (0 < δ < 1) in Ag 1 /BiOCl. The main peak at 2.15 Å in the Fouriertransformed k 2 -weighted EXAFS (Figure 1f) image corresponded to the first coordination shell of AgÀ Cl.…”

IrSn Bimetallic Clusters Confined in MFI Zeolites for CO Selective Catalytic Reduction of NOx in the Presence of Excess O2

“…Nitrogen oxides (NO x ) emitted from vehicle exhaust and stationary sources are harmful to human health. − Ammonia selective catalytic reduction (NH 3 –SCR) of NO x shows high NO x removal efficiency − but has limitations, for example, the periodic addition of reducing agents and easy contamination by other components in the exhaust gas. − Most vehicle exhaust and special stationary sources (sintering flue gas, coke oven flue gas, and waste incineration flue gas) contain nitrogen oxides (NO x ) and carbon monoxide (CO) simultaneously, both of these two harmful gases needs to be treated before emission. − CO selective catalytic reduction (CO-SCR) technology is a promising technology which could simultaneous removal of NO x and CO in the flue gas without adding extra reducing agents. − …”

Performance of Mn-Ce-Fe/FA Catalysts on Selective Catalytic Reduction of NOX with CO under Different Atmospheres

“…However, NH 3 -SCR has many limitations, such as the addition of ammonia, the high requirements on gas pipe materials, the secondary pollution caused by ammonia leakage, etc [11]. Therefore, it is a better choice to replace ammonia with CO which exists in the exhaust gas produced by combustion reaction [12], which is more economical and environmentally friendly [13,14]. Scholars Tauster and Murrell [15,16] proposed the research area of SCR of NO by CO in the experiment, and have found that precious metals such as Ir-Pt-Pd have better denitrification performance than normal metals [17].…”