Redox chemistry of : Detection of cuprous ions by FTi.r.

Sárkány, János; Sachtler, Wolfgang M.H.

doi:10.1016/0144-2449(94)90047-7

Cited by 90 publications

(51 citation statements)

References 22 publications

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“…The amplitude of that band is as much as twofold smaller for Cu-ZSM-5 than for HZSM-5. The similar findings were reported earlier [35], claiming the existence of a reverse proportionality in intensity of the protonic OH ± band at 3610 cm ±1 and copper concentration in the zeolite. Obviously, copper has a negative influence on the population of Brùnsted acid centers of HZSM-5.…”

Section: Resultssupporting

confidence: 78%

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Acid Sites in HZSM-5 Upon Copper Exchange by FTIR and DSC Using Ammonia

Bošković¹,

Vulic

Kis

et al. 2001

Chem. Eng. Technol.

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The acidity of the parent HZSM‐5 zeolite and Cu‐HZSM‐5 catalyst has been examined by FTIR and DSC using ammonia desorption. Sites of different strength were found in HZSM‐5, desorbing ammonia at a relative temperature difference of about 100 °C. Upon copper exchange a fraction of Brønsted sites were transformed to Lewis sites, but the acid strength of the remaining Brønsted sites was increased. Aside from Lewis sites originating from copper exchange, there might be some additional sites formed from precipitated copper. This could explain the quantity of adsorbed NH3 on Cu‐ZSM‐5 which is higher than theoretically expected. While changing their nature, acid sites of higher strength keep their location, which is manifested by some diffusion effect towards ammonia.

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Section: Resultssupporting

confidence: 78%

“…1 ± right). The theoretical adsorption capacity for NH 3 could be even lower by taking into account the possibility of Cu 2+ reduction in the procedure of FTIR vacuum pretreatment [35,36]. The attempt to explain this extra ammonia as physically adsorbed fails, since it is obvious from Fig.…”

Section: Resultsmentioning

confidence: 99%

Acid Sites in HZSM-5 Upon Copper Exchange by FTIR and DSC Using Ammonia

Bošković¹,

Vulic

Kis

et al. 2001

Chem. Eng. Technol.

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“…This reflects the adsorption of CO on Cu + , as previously detected by infrared spectroscopy. 18,40 During H 2 -TPR, CO desorbs at $700 K (see insert in Fig. 9), immediately before the second H 2 consumption peak.…”

Section: Reduction Of Cumentioning

confidence: 99%

Spectroscopic and chemical characterization of active and inactive Cu species in NO decomposition catalysts based on Cu-ZSM5

Costa

Modén

Meitzner

et al. 2002

Phys. Chem. Chem. Phys.

152

145

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The number and type of Cu 2+ species present on O 2 -treated Cu-ZSM5 catalysts (Si/Al ¼ 13.1-14.6) with varying Cu/Al ratios (0.12-0.60) were measured using temperature-programmed reduction in H 2 or CO and desorption of O 2 with He as the carrier. The effluent stream was monitored using mass spectrometry and the structure and oxidation state was determined in parallel by X-ray absorption spectroscopy. Isolated Cu 2+ monomers and oxygen-bridged Cu 2+ dimers interacting with Al-Al next nearest neighbor pairs were the predominant Cu species on these catalysts. The fraction of Cu present as dimers increased from 0.46 to 0.78 as Cu/Al ratios increased from 0.12 to 0.60, as expected from the decreasing average Cu-Cu distance with increasing Cu content. In contrast, monomers reached a plateau of $0.15 Cu 2+ /Al, suggesting that only some Al-Al pairs can interact with small Cu 2+ monomer structures, while a much larger fraction can bind with larger oxygen-bridged Cu 2+ dimers. The measured distribution of Cu dimers and monomers is consistent with the number and bond distances of Al-Al pairs for the Si/Al ratio in these ZSM5 samples. The distributions of Cu species obtained from the amount of CO 2 formed (from CO), the amount of H 2 O formed (from H 2 ), and the amount of CO adsorbed after reduction in CO are in excellent agreement. The number of oxygen atoms removed as O 2 was significantly smaller than that removed with H 2 or CO, suggesting that only proximate Cu dimers autoreduce via recombinative desorption steps. NO decomposition turnover rates (normalized per Cu dimer) were nearly independent of Cu content, except at the lowest Cu/Al ratio, consistent with the involvement of Cu dimers as the active Cu species in NO decomposition redox cycles on Cu-ZSM5. Multiple O 2 and CO 2 peaks during desorption and reduction in CO suggest the presence of Cu dimers with varying oxygen binding energy and reactivity. The Cu dimers initially formed at low Cu/Al contents during exchange are less reducible, consistent with their lower NO decomposition turnover rates.

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“…According to Sarkany [31][32][33][34] the red shift of the perturbed T-O-T band results from the interaction of bare metal ions with the negatively charged zeolite framework. Fig.…”

Section: Drift Study Of Ln-mordenitesmentioning

confidence: 99%

“…9. There is an evident difference in the wavenumber ν TOT position of asymmetric stretching vibration band, known as the T-O-T band [31], for particular elements. This band is responsible for vibration in Al-O-Si structural subunits and is very sensitive to metal ions present in the zeolite structure.…”

Section: Drift Study Of Ln-mordenitesmentioning

confidence: 99%