Hydrothermal aging alleviates the inhibition effects of NO2 on Cu-SSZ-13 for NH3-SCR

Shan, Yulong; Sun, Yangyang; Du, Junjie; Zhang, Yan; Shi, Xun; Yu, Yunbo; Shan, Wenpo

doi:10.1016/j.apcatb.2020.119105

Cited by 77 publications

(64 citation statements)

References 53 publications

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“…Three peaks can be observed under 500 • C for Cu-SSZ-13. Peak A was assigned to the reduction of Cu(OH) + species in CHA cages; peak B was attributed to the reduction of CuO x species; and peak C represented the consumption of H 2 by Cu 2+ species near d6r [33,34]. It is worth mentioning that no peak corresponding to CuO x species was observed in the XRD patterns, indicating that these CuO x species were highly dispersed.…”

Section: Characterization Of Catalystsmentioning

confidence: 99%

Promoting Effect of Mn on In Situ Synthesized Cu-SSZ-13 for NH3-SCR

Wang

Shi

et al. 2020

Catalysts

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The effect of Mn impregnation on the NH3-SCR (selective catalytic reduction of NOx by NH3) activity of in situ synthesized Cu-SSZ-13 was investigated in this work. It was found that Mn addition could efficiently improve the low-temperature activity of Cu-SSZ-13. The optimal amount of Mn was 5 wt.%, and NOx conversion was improved by more than 20% over a temperature range of 120 °C to 150 °C. SEM (scanning electron microscopy), XRD (X-ray diffraction), N2 adsorption-desorption, H2-TPR (temperature programmed reduction of H2), NH3-TPD (temperature programmed desorption of NH3) and in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) experiments were conducted to investigate the changes in the zeolite structure, active sites, acid sites and reaction mechanism. The impregnated MnOx species caused a decline in the crystallinity of Cu-SSZ-13 but markedly improved the redox ability. Nitrate and nitrite species were observed in the Mn-modified Cu-SSZ-13, and the formation of these species was thought to cause the observed increase in low-temperature NH3-SCR activity. The results show that the addition of Mn is a promising method for promoting the low-temperature catalytic activity of Cu-SSZ-13.

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Section: Characterization Of Catalystsmentioning

confidence: 99%

Promoting Effect of Mn on In Situ Synthesized Cu-SSZ-13 for NH3-SCR

Wang

Shi

et al. 2020

Catalysts

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“…Monomeric copper cations in the ion-exchange positions of the zeolitic framework are reported to be catalytically active in low-temperature NH 3 -SCR [11][12][13]. Shan et al [11] reported that monomeric Cu 2+ cations in Cu-SSZ-13 zeolites are catalytically active in the oxidation of NO to NO 2 , which is necessary for fast-SCR (2NH 3 + NO + NO 2 → 2N 2 + 3H 2 O), important for low-temperature NH 3 -SCR. On the other hand, it was reported that aggregated CuO species are significantly less active in the NO 2 formation [11].…”

Section: Introductionmentioning

confidence: 99%

“…Shan et al [11] reported that monomeric Cu 2+ cations in Cu-SSZ-13 zeolites are catalytically active in the oxidation of NO to NO 2 , which is necessary for fast-SCR (2NH 3 + NO + NO 2 → 2N 2 + 3H 2 O), important for low-temperature NH 3 -SCR. On the other hand, it was reported that aggregated CuO species are significantly less active in the NO 2 formation [11]. Clark et al [12] reported that stable solvated Cu + cations are responsible for the limitation of low-temperature NH 3 -SCR efficiency, while at higher temperature, the reduction of Cu 2+ to Cu + is the rate limiting step in the case of Cu-exchanged small-pore SSZ-13 zeolites.…”

Section: Introductionmentioning

confidence: 99%

Ferrierite and Its Delaminated and Silica-Intercalated Forms Modified with Copper as Effective Catalysts for NH3-SCR Process

et al. 2020

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The main goal of the study was the development of effective catalysts for the low-temperature selective catalytic reduction of NO with ammonia (NH3-SCR), based on ferrierite (FER) and its delaminated (ITQ-6) and silica-intercalated (ITQ-36) forms modified with copper. The copper exchange zeolitic samples, with the intended framework Si/Al ratio of 30 and 50, were synthetized and characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (low-temperature N2 adsorption), form and aggregation of deposited copper species (UV-vis-DRS), surface acidity (NH3-TPD) and reducibility (H2-TPR). The samples of the Cu-ITQ-6 and Cu-ITQ-36 series were found to be significantly more active NH3-SCR catalysts compared to Cu-FER. The activity of these catalysts in low-temperature NH3-SCR was assigned to the significant contribution of highly dispersed copper species (monomeric cations and small oligomeric species) catalytically active in the oxidation of NO to NO2, which is necessary for fast-SCR. The zeolitic catalysts, with the higher framework alumina content, were more effective in high-temperature NH3-SCR due to their limited catalytic activity in the side reaction of ammonia oxidation.

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“…21 In our recent study, we found that the inhibiting effect of NO 2 was closely related to Brønsted acid sites (BASs) and can be alleviated by hydrothermal aging due to the decrease in the number of BASs in Cu-SSZ-13. 22 Therefore, we speculated that NO 2 reduction probably occurs at BASs. Also, we previously observed the reaction between NO and NH 4 NO 3 occurring at BASs over the H-SSZ-13 catalyst.…”

Section: Introductionmentioning

confidence: 97%

Strikingly Distinctive NH3-SCR Behavior over Cu-SSZ-13 in the Presence of NO2

Shan

et al. 2021

Preprint

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Commercial Cu-exchanged small-pore SSZ-13 (Cu-SSZ-13) zeolite catalysts are highly active for the selective catalytic reduction (SCR) of NOx with NH3, but distinct from other catalyst systems, their activity is unexpectedly inhibited in the presence of NO2. Here, we combined kinetic experiments, in-situ/operando X-ray absorption spectroscopy, and density functional theory (DFT) calculations to obtain direct evidence that under reaction conditions, strong oxidation by NO2 forces Cu ions to exist mainly as fixed framework Cu2+ species (fw-Cu2+), which impede the formation of dynamic binuclear Cu+ species that serve as the main active sites for the standard SCR (SSCR) reaction. As a result, the SSCR reaction is significantly inhibited by NO2 in the zeolite system, and the NO2-involved SCR reaction occurs with an energy barrier higher than that of the SSCR reaction on dynamic binuclear sites. Moreover, the NO2-involved SCR reaction tends to occur at the Brønsted acid sites (BAS) rather than the fw-Cu2+ sites. This work clearly explains the strikingly distinctive selective catalytic behavior in the zeolite system.

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Hydrothermal aging alleviates the inhibition effects of NO2 on Cu-SSZ-13 for NH3-SCR

Cited by 77 publications

References 53 publications

Promoting Effect of Mn on In Situ Synthesized Cu-SSZ-13 for NH3-SCR

Promoting Effect of Mn on In Situ Synthesized Cu-SSZ-13 for NH3-SCR

Ferrierite and Its Delaminated and Silica-Intercalated Forms Modified with Copper as Effective Catalysts for NH3-SCR Process

Strikingly Distinctive NH3-SCR Behavior over Cu-SSZ-13 in the Presence of NO2

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