Recent advances in supported molecular sieve catalysts with wide temperature range for selective catalytic reduction of NO X with C3H6

Abstract

NO _X is a major atmospheric pollutant that is emanated by motor vehicles, thermal power plants, and industrial boilers. Therefore, the removal of NO _X is a research hotspot in the exhaust gas treatment field. Numerous methods have been used to eliminate NO _X : the selective catalytic reduction of NO _X using C₃H₆ as the reducing agent (C₃H₆-SCR) is an effective method to remove NO _X . The key issue in NO _X removal in C₃H₆-SCR is to obtain catalysts with low-temperature activity and wide operating temperatures. Till date, different supported wide-temperature-active molecular sieve catalysts have been prepared and used in C₃H₆-SCR reactions. Studies have shown that the catalytic performance of supported catalysts is related not only to the active component but also to the structural and textural parameters of the molecular sieve supports. This review summarizes the structural and textural characteristics, catalytic properties, and catalytic mechanism of molecular sieve catalysts with different pore structures for C₃H₆-SCR reactions. The design strategies of supported molecular sieve catalysts are suggested. The goal of this review is to highlight (1) the structural and textural characteristics and low-temperature catalytic performance of different supported molecular sieve catalysts; (2) the relationship between wide-temperature window and loaded active components, as well as carriers of the supported molecular sieve catalysts; and (3) design strategies and development prospects of supported molecular sieve catalysts with low-temperature activity and wide-temperature operating range for C₃H₆-SCR reactions.

Fig. 1. DRIFTS study of the adsorbed species formed on the surface of the Cu-ZSM-5 catalyst for NO reduction by propene under reaction conditions at 400 °C.

Fig. 2. TEM images of aged Cu-ZSM-5-ZrO₂ catalysts: (a) Cu-ZSM-5-ZrO₂ (0 wt%) and (b) Cu-ZSM-5-ZrO₂ (2 wt%).

Fig. 3. TPR of (a) Cu-ZSM-5 and (b) CeO₂–Cu-ZSM-5 as detected by the CuK edge in XANES.

Fig. 4. In situ FTIR spectra of the adsorbed species formed on La–Cu-ZSM-5/cordierite at 523 K.

Fig. 5. TPR profile of Fe-zeolite catalysts.

Fig. 6. SEM images of SAPO-34 zeolites with different Si/Al ratios.

Fig. 7. C₃H₆-TPD profiles of fresh and leached Cu-SSZ-13 catalysts.

Fig. 8. NO-TPD profiles of SBA-15 and 0.5% Pt-SBA-15.

Fig. 9. H₂-TPR profiles of Cu–Al-MCM-41 samples with Si/Al = 10: (a) Cu–Al-MCM-41-10-31, (b) Cu–Al-MCM-41-10-61, (c) Cu–Al-MCM-41-10-93, and (d) Cu–Al-MCM-41-10-120.

Fig. 10. XRD patterns of two different SnO₂–Al₂O₃ catalysts: (a) Sn⁵ (IM) and (b) Sn⁵ (SG).

Fig. 11. HC-SCR redox mechanism schematic.

Junqiang Xu

Honglin Wang

Fang Guo

Chuan Zhang

Jiaqing Xie