Identification of active sites and reaction mechanism on low-temperature SCR activity over Cu-SSZ-13 catalysts prepared by different methods

Zhang, Tao; Qiu, Feng; Chang, Huazhen; Li, Xiang; Li, Junhua

doi:10.1039/c6cy00737f

Cited by 83 publications

(50 citation statements)

References 41 publications

(48 reference statements)

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“…The first H2 reduction peak at around 208 o C was ascribed to the reduction of the surface CuO particles to Cu 0 [17,32]. The peak at around 248 o C was attributed to the reduction of the isolated Cu 2+ to Cu + [12,28], and the peak at 316 o C was assigned to the reduction of the inner nanosized CuO [16,28,33]. In addition, the peak at high temperature range, i.e.…”

Section: Temperature-programmed Reduction By H2mentioning

confidence: 99%

The Cu migration of Cu-SAPO-34 catalyst for ammonia selective catalytic reduction of NOx during high temperature hydrothermal aging treatment

Zhao

et al. 2019

Catalysis Today

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Two kinds of Cu-SAPO-34 catalysts, prepared with a one-pot technique using Cutetraethylenepentamine as co-template and an ion-exchange method, were hydrothermally treated at 750 o C for at least 16 h. The migration of Cu species during hydrothermal treatment and the corresponding effect on the selective catalytic reduction (SCR) of NOx were examined and characterized. A certain amount of CuO exists outside and inner the crystallites in the as prepared ion-exchanged sample, whereas copper is mainly atomically dispersed in the one-pot sample existing as isolated Cu 2+ .After hydrothermal treatment for 16 h, the amount of the inner nanosized CuO in the ion-exchanged sample reduced and the copper disperses to form more isolated Cu 2+ . However, surface CuO particles increase at the sacrifice of isolated Cu 2+ with extending the hydrothermal treatment to 24 h. Aggregation of Cu 2+ species also happens during the aging treatment over the one-pot prepared sample where the initial Cu is atomically

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Section: Temperature-programmed Reduction By H2mentioning

confidence: 99%

The Cu migration of Cu-SAPO-34 catalyst for ammonia selective catalytic reduction of NOx during high temperature hydrothermal aging treatment

Zhao

et al. 2019

Catalysis Today

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“…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%

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

Chen

Janssens²,

Skoglundh

et al. 2018

Top Catal

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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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“…H 2 -TPR measurement is a common method to get the variation of all reducible copper species, thus the fresh and Na impregnated catalysts were measured and the results are shown in Figure 6a. 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].…”

Section: H 2 -Tpr Resultsmentioning

confidence: 98%

“…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: 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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Identification of active sites and reaction mechanism on low-temperature SCR activity over Cu-SSZ-13 catalysts prepared by different methods

Abstract: Cu-SSZ-13 catalysts with similar Si/Al and Cu/Al ratios were prepared by aqueous solution ion-exchange (Cu-SSZ-13-I) and one-pot synthesis (Cu-SSZ-13-O) methods.

Cited by 83 publications

References 41 publications

The Cu migration of Cu-SAPO-34 catalyst for ammonia selective catalytic reduction of NOx during high temperature hydrothermal aging treatment

The Cu migration of Cu-SAPO-34 catalyst for ammonia selective catalytic reduction of NOx during high temperature hydrothermal aging treatment

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

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