Mechanistic insights into the promotion of low-temperature NH3-SCR catalysis by copper auto-reduction in Cu-zeolites

Revealing the Formation and Reactivity of Cage-Confined Cu Pairs in Catalytic NOx Reduction over Cu-SSZ-13 Zeolites by In Situ UV–Vis Spectroscopy and Time-Dependent DFT Calculation

“…DFT interrogations revealed a lower energy of the O 2 -bridged Cu dimer than the cage-confined Cu I (NH 3 ) 2 pair (Figure S17), suggesting that the reaction between O 2 and the Cu I (NH 3 ) 2 pair is thermodynamically favorable. However, based on our previous work, samples treated with reducing gases such as NH 3 + NO or autoreduction under high-temperature N 2 exhibited enhanced activity in NH 3 -SCR due to the formation of Cu I ···NO + pairs . Moreover, according to the work of Paolucci et al, even when exposed to oxygen-containing atmospheres, some Cu I species in the catalyst will remain unoxidized. , …”

“…This N 2 generation pathway is governed by the rate of O 2 dissociation, , leading to similar initial N 2 generation rates over Ar- and O 2 -purged Cu-SSZ-13 after H 2 reduction. Meanwhile, the cage-confined Cu I (NH 3 ) 2 pairs could also activate NO to form NO + , which further combine with NH 3 to form nitrosamines (H 2 NNO). , The decomposition of H 2 NNO, however, requires the involvement of a H + or NH 4 + . , During Cu II → Cu I reduction, an intermediate H + is generated on the neighboring Brønsted site and transformed to intermediate NH 4 + after NH 3 adsorption. , Such intermediate NH 4 + in close intimacy with the Cu site could react with H 2 NNO (Path II in Figure S20), leading to a second N 2 generation peak over H 2 -reduced, Ar-purged Cu-SSZ-13. This assumption was confirmed by in situ DRIFTS, which revealed a less pronounced formation ( i.e.…”

Effect of the preparation method on the catalytic properties of copper-containing zeolite Y applied for NH3-SCR-DeNOx

“…This result remains in contrast to the data obtained before for Cu-containing SAPO-34, SSZ-13 and ZSM-5 where a higher NO conversion was achieved over Ar-activated samples. 43…”

“…This result remains in contrast to the data obtained before for Cu-containing SAPO-34, SSZ-13 and ZSM-5 where a higher NO conversion was achieved over Ar-activated samples. 43 The effect of different zeolite particle sizes on the catalytic activity in NH 3 -SCR-DeNO x was broadly investigated in the case of Cu-CHA. For instance, Gao et al 44 synthesized three types of Cu-SSZ-13 catalysts with different particle sizes (i.e., 0.26 μm, 0.45 μm and 1.3 μm), however, the activities in NH 3 -SCR-DeNO x over these three catalysts were quite similar to each other.…”

Cold-Start NOx Mitigation by Passive Adsorption Using Pd-Exchanged Zeolites: From Material Design to Mechanism Understanding and System Integration

“…Apart from Pd species, the spare BASs of zeolites also contribute to the storage capacity by adsorbing NO as NO + , which easily desorbs at 100–200 °C. − It has to be noted that the above-mentioned NO storage processes occur in the absence of H 2 O. With H 2 O vapor in the feed gas, NO adsorption on reducible Pd species (eqs and ) and BASs will be significantly restrained. , On account of the renewability of PNA, Pd sites need to be recovered after NO desorption.…”