The influence of Si/Al ratio on the catalytic property and hydrothermal stability of Cu-SSZ-13 catalysts for NH3-SCR

Fan, Chi; Chen, Zhe; Pang, Lei; Ming, Shujun; Zhang, Xiaofeng; Albert, Kouadio Brou; Liu, Peng; Chen, Hanping; Li, Tao

doi:10.1016/j.apcata.2017.11.021

Cited by 121 publications

(78 citation statements)

References 47 publications

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“…In the literature, three peaks are generally present in the desorption profile of ammonia from Cu-CHA [8][9][10][11]. A low-temperature peak below 200 • C , an intermediate-temperature peak at 250−350 • C and a high-temperature peak at 400−500 • C .…”

Section: Resultsmentioning

confidence: 99%

“…In particular, copper-exchanged zeolites and zeotypes with the small-pore chabazite framework structure (Cu-CHA) is the state-of-the-art catalyst for NH 3 -SCR which combines a good performance in the temperature range 200−550 • C with a high hydrothermal stability [5][6][7]. The NH 3 -TPD profile of Cu-CHA is characterized by three desorption peaks [8][9][10][11][12][13][14][15][16][17]; a low-temperature peak below 200 • C , an intermediate-temperature peak at 250−350 • C and a high-temperature peak at 400−500 • C.…”

Section: Introductionmentioning

confidence: 99%

“…The low-temperature peak is generally assigned to NH 3 adsorbed to Lewis acid sites [8][9][10][11][12][13]17] whereas the peak at 400−500 • C has been attributed to NH 3 adsorbed on Brønsted acid sites. NH 3 adsorbed at Cu-sites has been suggested to give rise to the intermediate-temperature peak at 250−350 • C [8][9][10][11][12]. An attempt to assign the peaks to specific Cu sites was made in Ref.…”

Section: Introductionmentioning

confidence: 99%

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Interpretation of NH3-TPD Profiles from Cu-CHA Using First-Principles Calculations

Chen

Janssens²,

Skoglundh

et al. 2018

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Temperature-programmed desorption (TPD) with ammonia is widely used for zeolite characterization revealing information on acidity and adsorption sites. The interpretation of TPD measurements is, however, often challenging. One example is the NH 3 -TPD profile from Cu-chabazite (Cu-CHA) which generally is deconvoluted in three peaks with contributions from NH 3 on Lewis acid sites, copper sites and Brønsted acid sites. Here, we use density functional theory calculations combined with kinetic simulations to analyze this case. We find a large number of possible species, giving rise to overlapping features in the NH 3 -TPD. The experimental low-temperature peak (below 200 • C ) is assigned to NH 3 desorption from Lewis acid sites together with NH 3 desorption from a [Cu(II)(OH)(NH 3 ) 3 ] + complex. The intermediate-temperature peak ( 250−350 • C ) is attributed to decomposition of a linear [Cu(I)(NH 3 ) 2 ] + complex and a residual from [Cu(II)(OH)(NH 3 ) 3 ] + . The hightemperature peak is predicted to have contributions from Brønsted acid sites ( NH + 4 ), [Cu(I)NH 3 ] + and [Cu(II)(NH 3 ) 4 ] 2+. The present work shows that NH 3 -TPD from Cu-CHA can be reconciled with copper complexes as NH 3 storage sites.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Interpretation of NH3-TPD Profiles from Cu-CHA Using First-Principles Calculations

Chen

Janssens²,

Skoglundh

et al. 2018

Top Catal

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“…For the fresh sample, two peaks centered at ≈220 • C and ≈350 • C represent the reduction of [Cu(OH)] + in the CHA cages to Cu + and the reduction of Cu 2+ near 6 MR to Cu + , respectively [5,[26][27][28]. Another peak centered at 280-300 • C was present for the Na impregnated catalysts, which was assigned to the reduction of copper oxides species to Cu 0 [6,26]. Meanwhile, the reduction peak at ≈410 • C, which was attributed to the reduction of CuAlO x species, is shown for Na-Cu-1.5 [13,29,30].…”

Section: H 2 -Tpr Resultsmentioning

confidence: 98%

“…Cu/SSZ-13, one of the chabazite (CHA) zeolites with a simple topological structure, receives a lot of attention because it provides the opportunity to understand the SCR mechanism of zeolites [1]. Besides, compared with other commercial zeolites, such as ZSM-5 and BEA, Cu/SSZ-13 catalysts with outstanding NH 3 -SCR performance and hydrothermal stability are suitable for selection as a good candidate to meet the China VI emission regulation [2][3][4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

The Role of Impregnated Sodium Ions in Cu/SSZ-13 NH3-SCR Catalysts

Wang

et al. 2018

Catalysts

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To reveal the role of impregnated sodium (Na) ions in Cu/SSZ-13 catalysts, Cu/SSZ-13 catalysts with four Na-loading contents were prepared using an incipient wetness impregnation method and hydrothermally treated at 600 • C for 16 h. The physicochemical property and selective catalytic reduction (SCR) activity of these catalysts were studied to probe the deactivation mechanism. The impregnated Na exists as Na + on catalysts and results in the loss of both Brönsted acid sites and Cu 2+ ions. Moreover, the high loading of Na ions destroy the framework structure of Cu/SSZ-13 and forms new phases (SiO 2 /NaSiO 3 and amorphous species) when Na loading was higher than 1.0 mmol/g. The decreased Cu 2+ ions finally transformed into Cu x O, CuO, and CuAlO x species. The inferior SCR activity of Na impregnated catalysts was mainly due to the reduced contents of Cu 2+ ions at kinetic temperature region. The reduction in the amount of acid sites and Cu 2+ ions, as well as copper oxide species (Cu x O and CuO) formation, led to low SCR performance at high temperature. Our study also revealed that the existing problem of the Na ions' effect should be well-considered, especially at high hydrothermal aging when diesel particulate filter (DPF) is applied in upstream of the SCR applications.Catalysts 2018, 8, 593 2 of 15 (>0.5%) mainly due to the decreased amount of isolated Cu 2+ formed CuO x clusters. Wang et al. [10] further found that alkali decreased the number of Brönsted acid sites and NH 3 coverage, and would decrease the SCR reaction rate. In our previous study [11], the different contents of Na impact on Cu/SAPO-34 were also studied. Except for the decrease of active sites and acidity, the results also showed the framework of Cu/SAPO-34 damaged and CuAlO x species formed at a high content of sodium (>0.8%), and all these factors hindered the SCR activity.In recent years, some studies have also considered the Na ions' effect on Cu/SSZ-13 catalysts, but most of them focused on co-cation Na ions. Gao et al. [12] investigated the effects of co-cation Na on Cu/SSZ-13 catalyst. They found ≈1.78% Na promoted SCR performance at low temperatures and helped to improve the hydrothermal stability of Cu/SSZ-13 because Na ions modified the redox of active sites and protected the framework of CHA structure. Zhao et al. [13] found a high amount of co-cation Na ions decreased the hydrothermal stability of Al-rich Cu/SSZ-13 at 750 • C for 5 h because the excess amount of Na ions weakened the interaction between Cu ions and the zeolitic framework and formed Cu x O species. Xie et al. [14] found one-pot-synthesized Cu/SSZ-13 with higher co-cation Na contents showed poorer hydrothermal stability at 750 • C for 16 h, which was attributed to Cu species with poor stability and CHA structure deterioration. Even though some achievements have been made on co-cation Na, the conclusion could not be applied in real-world applications because co-cation Na ions have already existed before Cu exchange and could not represent the deposition of Na in the ...

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Charge Shielding Effect of Sodium Ions in Improving The Hydrophobicity and Performance of Co/Na‐SSZ‐13 Zeolite for Passive NO_x Adsorber

Chen,

Tao,

Yang

et al. 2024

Adv Funct Materials

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With increasingly stringent regulations, the reduction of NOx emissions during vehicle cold start is a major challenge. Pd‐modified zeolites are considered as the most promising passive NOx adsorber (PNA) for cold start NOx control. Nevertheless, the scarcity and the high cost of Pd limit its practical application. Herein, a non‐precious metal modified Co/Na‐SSZ‐13 zeolite for low‐temperature NOx adsorption is reported. This one‐pot synthesized Co/Na‐SSZ‐13 exhibits an extraordinary NOx storage capacity (212 µmol gcat−1) under humid conditions (3% H2O v/v), which is more than double that of conventional Co or Pd‐modified SSZ‐13. This is attributed to the absence of the inert cobalt phyllosilicate commonly found in conventional Co‐SSZ‐13, as well as the highly dispersed Co and Na ions as the effective NOx adsorption sites in Co/Na‐SSZ‐13. Moreover, the presence of Na ions shields the negative charge generated by the Al center and weakens the local electric field strength of the Al and Co centers. This lowers the H2O adsorption energy and improves the zeolite hydrophobicity, which enhances the NO storage capacity of the Co/Na‐SSZ‐13 under humid conditions. This work highlights the Co/Na‐SSZ‐13, synthesize via a simple and high‐efficiency method, as a promising substitute for noble metal PNA materials.

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The influence of Si/Al ratio on the catalytic property and hydrothermal stability of Cu-SSZ-13 catalysts for NH3-SCR

Cited by 121 publications

References 47 publications

Interpretation of NH3-TPD Profiles from Cu-CHA Using First-Principles Calculations

Interpretation of NH3-TPD Profiles from Cu-CHA Using First-Principles Calculations

The Role of Impregnated Sodium Ions in Cu/SSZ-13 NH3-SCR Catalysts

Charge Shielding Effect of Sodium Ions in Improving The Hydrophobicity and Performance of Co/Na‐SSZ‐13 Zeolite for Passive NO_x Adsorber

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The influence of Si/Al ratio on the catalytic property and hydrothermal stability of Cu-SSZ-13 catalysts for NH3-SCR

Cited by 121 publications

References 47 publications

Interpretation of NH3-TPD Profiles from Cu-CHA Using First-Principles Calculations

Interpretation of NH3-TPD Profiles from Cu-CHA Using First-Principles Calculations

The Role of Impregnated Sodium Ions in Cu/SSZ-13 NH3-SCR Catalysts

Charge Shielding Effect of Sodium Ions in Improving The Hydrophobicity and Performance of Co/Na‐SSZ‐13 Zeolite for Passive NOx Adsorber

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Charge Shielding Effect of Sodium Ions in Improving The Hydrophobicity and Performance of Co/Na‐SSZ‐13 Zeolite for Passive NO_x Adsorber