Highlights on Key Roles of Y on the Hydrothermal Stability at 900 °C of Cu/SSZ-39 for NH₃-SCR

Abstract

The continuously updated after-treatment system of diesel engines drives the selective catalytic reduction of ammonia (NH 3 -SCR) catalysts to withstand hydrothermal stability at higher temperatures (>800 °C). To meet the tightened emission of nitrogen oxides (NO x ), yttrium ions (Y 3+ ) were employed to improve the hydrothermal stability of the Cu/SSZ-39 catalyst at 900 °C. X-ray diffraction, solid nuclear magnetic resonance, H 2 temperature-programmed reduction, NH 3 temperature-programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectra verified the key role of Y 3+ on the stability of the structure of SSZ-39 zeolite and the isolated copper species. In detail, the optimized structural stability at 900 °C of the Y-modified Cu/SSZ-39 catalyst is achieved as a result of the spatial and electronic effects of Y 3+ at ion-exchanged sites. Furthermore, Y 3+ ions in the cages of SSZ-39 zeolite induce more isolated copper species in the double six-member rings of SSZ-39 zeolite. The modified catalyst by 1 wt % Y (Cu/Y 1.0 -SSZ-39) shows the best deNO x performance after hydrothermal aging at 900 °C for 10 h, including higher than 70% NO x conversion at 200−550 °C and the maximum NO x conversion of 94% at 300 °C, which is remarkably higher than the maximum NO x conversion of 38% over Cu/SSZ-39 after same hydrothermal aging. This work provides a vital research strategy for fabricating the extraordinary hydrothermally stabilized Cu-based zeolite catalysts for NH 3 -SCR reaction, which would meet the "near-zero" emission after hydrothermal aging at 900 °C in the future.

Enhanced Low-Temperature Activity and Hydrothermal Stability of Ce-Mn Oxide-Modified Cu-SSZ-39 Catalysts for NH3-SCR of NOx

“…Furthermore, CeMnO x /Cu-SSZ-39-A maintained the highest amount of Cu 2+ ions among the oxide-modified catalysts after hydrothermal aging (Table 2), which revealed its superior SCR activity (Figure 3b). This also indicated CeMnO x could effectively stabilize Cu-SSZ-39 zeolite and interact with the generated CuO species, contributing to its excellent hydrothermal resistance [27]. Figure 4(b1,b2) shows the O 1s XPS spectra of the catalysts.…”

“…Transition and rare-earth metals with variable oxidation states are commonly employed to modify Cu-SSZ-39 catalysts due to their outstanding redox properties and reactivity. For instance, Y 3+ ions were introduced to induce more Cu 2+ ions to locate in the stable ion-exchange (d6r) sites of SSZ-39 zeolite, thus inhibiting the deactivation of Cu-SSZ-39 catalysts even during hydrothermal aging at 900 • C [27]. Furthermore, Y 3+ ions could serve as a sacrificial agent for SO 2 poisoning to protect active Cu 2+ ions from inactivation in harsh conditions [28].…”

Revealing the Roles of Rh in Inhibiting “NOx Puff” on the Cu/Ba-CeO2 Catalyst during the Process of Lean NOx Trap

“…The different mass percentages ( x = 0.25, 0.5, 0.75, and 1) of Rh from the Rh­(NO 3 ) 3 and the 5 wt % Cu were coimpregnated on the Ba5Ce powder and followed the same dried and calcined process as CuxBa5Ce. The detailed preparation process of the monolithic catalysts refers to our previous studies , and Supporting Information (S1).…”

NOx reduction against sulfur poisoning by using Ce-modified Cu-SAPO-34 catalysts

“…S5, ESI †) suggest that Ce has the effect of mitigating the collapse of the zeolite framework due to the influence of sulfur, and other reports in the literature have similar roles regarding the protection of the zeolite framework by rare earth element. 37 3.2.2 The N 2 adsorption-desorption and ICP-OES. Table S1 (ESI †) shows that the BET surface area of Cu-F was the…”