Rare-earth ion exchanged Cu-SSZ-13 zeolite from organotemplate-free synthesis with enhanced hydrothermal stability in NH₃-SCR of NO_x

Abstract

Rare-earth Y exchanged Al-rich Cu-CHA shows significantly improved hydrothermal stability in NH3-SCR reaction.

Effect of Ion-Exchange Sequences on Catalytic Performance of Cerium-Modified Cu-SSZ-13 Catalysts for NH3-SCR

“…Usui et al [5] demonstrated that introduction of a small amount of Ce by wet and solid-state ion-exchange routes could improve SCR activities over a broad temperature range, because it enabled abundant Brønsted acidity sites and stabilized the framework of SSZ-13. The results of Zhao et al [6] also confirmed that rare earth ions (Ce 3+ , La 3+ , Sm 3+ , Y 3+ , Yb 3+ ) that modified Al-rich Cu-SSZ-13 catalysts had no significant impact on low-temperature NO conversions in the fresh catalyst but displayed enhancement of low temperature activity after hydrothermal aging when compared with Cu-SSZ-13. Similarly, Wang et al [7] reported that Ce or Sm could be introduced into Cu-SSZ-13 by ion exchanged preparation procedures, and the counterparts were investigated in detail.…”

Recent progress in the improvement of hydrothermal stability of zeolites

“…The stabilization effect of the introduction of rare earth cations into small pore zeolites has been less explored probably because of the limited diffusion of the relatively large hydrated rare earth ions through the 8R windows. The incorporation of Ce, La, Sm, Y and Yb into the Cu-SSZ-13 zeolites has been reported to enhance the framework stability aer hydrothermal aging at 800 C. 161,163,167,168 163 reported the incorporation of Ce 3+ cations to stabilize the Al in framework positions in the zeolite Cu-SSZ-13 aer hydrothermal treatment at 800 C for 20 h; moreover, the H 2 -TPR results suggested that the Cu 2+ cations in the aged Ce-containing samples are mainly located in the 6R, suggesting that the presence of Ce prevents the migration of Cu 2+ during the steaming treatment.…”

“…Zhao et al 168 studied the effect of incorporation of several rare earth cations (Ce, La, Sm, Y, and Yb), finding that Y 3+ cations led an enhancement of the hydrothermal stability and catalytic performance of Cu–CHA in the NH 3 –SCR reaction. However, an excess of Y 3+ causes difficulties in the incorporation and diffusion of Cu 2+ cations and reduces the activity of the catalyst at low temperatures in the SCR reaction.…”

“…Despite the increasing number of studies, the explanation for the stability enhancement is still not clear. While some authors concluded that the presence of RE mainly stabilizes the zeolite framework 167 and limits the dealumination process, 168 some others claim that the presence of RE inhibits the agglomeration of Cu 2+ into CuO x clusters. 161 According to a previous study, the formation of CuO x clusters is the main contribution of the structural collapse of the catalysts during hydrothermal aging.…”

A Green CeO2−WO3/TiO2 Medium‐Low Temperature de‐NOx Catalyst for Selective Catalytic Reduction of NOx with NH3

“…Catalysts were the core part of SCR reaction, various catalysts have been developed, such as manganese-based catalyst, [5][6][7][8] vanadium-based catalyst, [9][10][11][12] rare earth-based catalyst, [13,14] carbon-based catalyst, [15][16][17] etc. Among them, cerium-based catalysts have gradually become a research hotspot because of the great performance and wide temperature windows.…”