Ammonia Desorption Peaks Can Be Assigned to Different Copper Sites in Cu/SSZ-13

Leistner, Kirsten; Xie, Kunpeng; Kumar, Ashok; Kamasamudram, Krishna; Olsson, Louise

doi:10.1007/s10562-017-2083-8

Cited by 70 publications

(50 citation statements)

References 19 publications

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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%

“…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%

“…An attempt to assign the peaks to specific Cu sites was made in Ref. [8] where the intermediate and high temperature peaks were attributed to Cu coordinated to the zeolite framework in 6-and 8-membered rings, respectively.…”

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: 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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“…The band Catalysts 2018, 8, 593 7 of 15 centered at 205 nm was assigned to the oxygen-to-metal charge transfer related to Cu 2+ ions [9,15]. The 300-600 nm region was attributed to transitions in Cu x O, such as charge transfer transitions in O-Cu-O and Cu-O-Cu [4,31]. In addition, the region between 600 and 800 nm was assigned to the electron d-d transitions of Cu 2+ in distorted octahedral surrounding by oxygen in CuO particles [9,15].…”

Section: Uv-vis Drs 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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“…After deconvoluting the profiles (Figure 6b), all zeolites show three desorption peaks centered at about2 00 (low temperature), 250 (mediumt emperature), and 340 8C( high temperature), respectively.T he last two peaks can be roughlya ttributed to NH 3 desorption at strong and weak Brønsted acid sites, and the low-temperature peak can probably be assigned to NH 3 desorption at Lewis acid sites. [34][35][36] Thus, the approximate B/L ratio can be calculated by integration of the desorption signals (Table1). The B/L ratios of H-beta-7 and H-beta-19 are higher than those of Hbeta-22 and H-beta-36.…”

Section: Aciditycharacterizationmentioning

confidence: 99%

Excellent Performances of Dealuminated H‐Beta Zeolites from Organotemplate‐Free Synthesis in Conversion of Biomass‐derived 2,5‐Dimethylfuran to Renewable p‐Xylene

Zhao

et al. 2018

ChemSusChem

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Direct synthesis of renewable p-xylene (PX) by cycloaddition of biomass-derived 2,5-dimethylfuran (2,5-DMF) and ethylene was achieved over Al-rich H-beta zeolites synthesized by an organotemplate-free approach and their dealuminated counterparts with different Si/Al ratios. Among them, H-beta zeolite with an Si/Al ratio of 22, obtained from an Al-rich parent by dealumination, was found to be an excellent catalyst for the synthesis of PX. A PX yield of 97 % and 2,5-DMF conversion of 99 % were obtained under optimized conditions. These results are even better than those of a commercial H-beta zeolite prepared using a organotemplate synthesis with a similar Si/Al ratio of 19. The excellent performance of the H-beta zeolite with Si/Al ratio of 22 is closely related to its acidity and porous structure. A moderate Brønsted/Lewis acid ratio can improve the conversion of 2,5-DMF to as high as 99 %. Furthermore, dealuminated H-beta zeolite has a secondary pore system that facilitates product diffusion, which increases the selectivity to PX. In addition, this catalyst shows better regeneration. After five successive regeneration cycles, the yield of PX was still as high as 85 % without obvious dealumination. This work provides a deeper understanding of the more general Diels-Alder cycloaddition of furan-based feedstocks and olefins and significantly improves the potential for the synthesis of chemicals from lignocellulosic biomass.

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Ammonia Desorption Peaks Can Be Assigned to Different Copper Sites in Cu/SSZ-13

Abstract: Graphical AbstractKeywords Copper loading · Cu/SSZ-13 · NH 3 adsorption · Chabazite · Six-membered rings · Large cages · Si/Al ratio

Cited by 70 publications

References 19 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

Excellent Performances of Dealuminated H‐Beta Zeolites from Organotemplate‐Free Synthesis in Conversion of Biomass‐derived 2,5‐Dimethylfuran to Renewable p‐Xylene

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