Abatement of Nitrogen Oxides via Selective Catalytic Reduction over Ce₁–W₁ Atom-Pair Sites

Abstract

Environmentally benign CeO2–WO3/TiO2 catalysts are promising alternatives to commercial toxic V2O5–WO3/TiO2 for controlling NOx emission via selective catalytic reduction (SCR), but the insufficient catalytic activity of CeO2–WO3/TiO2 catalysts is one of the obstacles in their applications because of a lack of an in-depth understanding of the CeO2–WO3 interactions. Herein, we design a Ce1–W1/TiO2 model catalyst by anchoring Ce1–W1 atom pairs on anatase TiO2(001) to investigate the synergy between Ce and W in SCR. A series of characterizations combined with density functional theory calculations and in situ diffuse-reflectance infrared Fourier-transform experiments reveal that there exists a strong electronic interaction within Ce1–W1 atom pairs, leading to a much better SCR performance of Ce1–W1/TiO2 compared with that of Ce1/TiO2 and W1/TiO2. The Ce1–W1 synergy not only shifts down the lowest unoccupied states of Ce1 near the Fermi level, thus enhancing the abilities in adsorbing and oxidizing NH3 but also makes the frontier orbital electrons of W1 delocalized, thus accelerating the activation of O2. The deep insight of the Ce–W synergy may assist in the design and development of efficient catalysts with an SCR activity as high as or even higher than V2O5–WO3/TiO2.

Improved N2 Selectivity of MnOx Catalysts for NOx Reduction by Engineering Bridged Mn3+ Sites

“…The valence state of Ti and Zr is also analyzed, both of which remain in the positive tetravalent (Figures S30, S31). , However, the binding energy of Ti 2p over Mn/ZrTi-A is higher than Mn/ZrTi-C and Mn/Ti. Mn/ZrTi-A is also the highest for the binding energy of Zr 2p, which means that the transfer of electrons from Ti/Zr to Mn is attributed to the formation of the unique Mn 3+ bridged on both Ti 4+ and Zr 4+ sites through oxygen.…”

NO Selective Catalytic Reduction over Atom-Pair Active Sites Accelerated via In Situ NO Oxidation

“…Single W atoms (marked by red circles) on the TiO 2 (001) surface are clearly observed in Figures 2c and S5, and the W atoms are exactly anchored on the fourfold hollow sites of the (001) surface. 34 Due to the close atomic mass of V and Ti atoms, it is difficult to directly observe the distribution of V atoms on TiO 2 via STEM imaging. Energy dispersive X-ray (EDX) spectroscopy was further performed, and the mapping image shows the uniform distribution of V and W on TiO 2 (Figure 2d).…”

“…It is obvious that the V and W anchoring on TiO 2 (001) does not change the nanosheet morphology of TiO 2 , as further evidenced by the similar specific surface area of V 1 –W 1 /TiO 2 (∼49 m 2 g –1 ) and TiO 2 (∼55 m 2 g –1 , Table S1). Single W atoms (marked by red circles) on the TiO 2 (001) surface are clearly observed in Figures c and S5, and the W atoms are exactly anchored on the fourfold hollow sites of the (001) surface . Due to the close atomic mass of V and Ti atoms, it is difficult to directly observe the distribution of V atoms on TiO 2 via STEM imaging.…”

Insight into the Promotion Effect of Trace Pd Doping on the Catalytic Performance of Ag/Al2O3 for C3H6-SCR of NOx

“…The emission of nitrogen oxides (NO x ) from heavy-duty diesel vehicles has attracted much attention. Selective catalytic reduction of NO x with ammonia (NH 3 -SCR) is a leading technology for NO x removal and has been commercially applied on heavy-duty diesel vehicles for exhaust purification. − Typical NH 3 -SCR catalysts such as Cu-SSZ-13 and V 2 O 5 –WO 3 (MoO 3 )/TiO 2 possess excellent deNO x performance, , but their tolerance toward hydrocarbon compounds (HCs) is still not good enough. − The NH 3 -SCR converter on a heavy-duty diesel vehicle is usually located after the diesel oxidation catalyst (DOC) and diesel particle filter (DPF) to avoid the negative effect of HCs, etc . However, in the promising new strategies SCRF (SCR catalyst coated directly on the DPF) and cc-SCR (close-coupled SCR catalyst), the SCR catalyst is exposed to HC-containing conditions. ,,, In these situations, the development of efficient HC-SCR catalysts may be an important supplement to traditional NH 3 -SCR.…”