In situ XANES characterization of the Cu oxidation state in Cu-ZSM-5 during NO decomposition catalysis

Liu, Di-Jia; Robota, Heinz J.

doi:10.1007/bf00769481

Cited by 135 publications

(84 citation statements)

References 17 publications

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“…As was discussed in the Introduction, it is known that the Cu(I) concentration correlates with the NO decomposition rate [32]. Finally, the fact that the retardation of the O 2 release step causes a retardation of the reaction cycle strongly indicates that O 2 release of the bis(µ-oxo)dicopper core with regeneration of the Cu + · · ·Cu + pair (step 3) is rate limiting in the NO decomposition.…”

Section: O 2 Release From Bis(µ-oxo)dicoppermentioning

confidence: 93%

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An operando optical fiber UV–vis spectroscopic study of the catalytic decomposition of NO and N2O over Cu-ZSM-5

Groothaert

Lievens

Leeman

et al. 2003

Journal of Catalysis

138

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The role of the bis(µ-oxo)dicopper core, i.e., [Cu 2 (µ-O) 2 ] 2+ , in the decomposition of NO and N 2 O by the Cu-ZSM-5 zeolite has been studied with combined operando UV-vis monitoring of the catalyst and on-line GC analysis. An optical fiber was mounted on the outer surface of the quartz wall of the plug-flow reactor and collected the UV-vis diffuse reflectance spectra under true catalytic conditions.

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Section: O 2 Release From Bis(µ-oxo)dicoppermentioning

confidence: 93%

“…Now, a growing consensus is found that monovalent copper participates in the NO decomposition reaction [27][28][29][30][31][32][33]. A number of experimental and computational studies propose a redox process cycling between Cu(I) and Cu(II)-ELO species (ELO, extralattice oxygen) [27][28][29][30][33][34][35][36][37][38].…”

Section: Introductionmentioning

confidence: 99%

An operando optical fiber UV–vis spectroscopic study of the catalytic decomposition of NO and N2O over Cu-ZSM-5

Groothaert

Lievens

Leeman

et al. 2003

Journal of Catalysis

138

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“…The near-edge spectral region is sensitive to the Cu oxidation state. [9][10][11][34][35][36][37][38] Fig. 4a and 4b shows near-edge spectra for Cu(0.38) during reduction in H 2 at increasing temperatures.…”

Section: Reduction Of Cumentioning

confidence: 99%

“…9 The parallel increase in the concentration of Cu + species detected by XAS and in the rate of NO decomposition was used as evidence for Cu + as a reaction intermediate. 10,11 A mechanism involving NO coordination to Cu 2+ without the involvement of reduction-oxidation cycles has also been suggested 12 but it has not been supported by experimental evidence. N-N formation has been proposed to occur via adsorption of two NO molecules on a single Cu + site to form dinitrosyl complexes {Cu + (NO) 2 4,[18][19][20] This step resolves the charge balance concerns and it is consistent with the observed increase in NO decomposition turnover rates as the Cu/Al ratio increases and oxygen-bridged dimers become more prevalent.…”

Section: Introductionmentioning

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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“…These results indicate that Cu catalyzes the recombination of O atoms in a LH reaction. The catalytic action of Cu is well known and is believed to result from its ability to change between the +1 and +2 oxidation states [52][53][54][55]. Fe is known to behave similarly, cycling between Fe 2+ and Fe 3+ [56].…”

Section: Determination Of Recombination Coefficients Using the Spinnimentioning

confidence: 99%

Experimental and modeling study of O and Cl atoms surface recombination reactions in O2 and Cl2 plasmas

Stafford

Guha

Khare

et al. 2010

Pure and Applied Chemistry

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Abstract:In low-pressure plasmas commonly used in materials processing, plasma-wall inter actions play a crucial role in the evolution of the plasma properties both over time and across large-area wafers. We have recently studied the heterogeneous recombination of O and Cl atoms on reactor walls in O 2 and Cl 2 plasmas through both experiments and modeling. The Langmuir-Hinshelwood (i.e., delayed) recombination was investigated using a "spinning-wall" technique in which a portion of the substrate surface is periodically exposed to an inductively coupled plasma and to a differentially pumped chamber where either Auger electron spectroscopy (AES) or line-of-sight mass spectrometry (MS) is used to detect surface and desorbing species. In this paper, a review of the various effects driving the O and Cl atoms recombination dynamics on anodized aluminum (AA) and stainless steel (SS) surfaces is presented. It is shown that recombination probabilities, γ, can vary following plasma exposure due to surface conditioning. In Cl 2 plasmas, γ was also found to depend on the Cl-toCl 2 number density ratio, a mechanism ascribed to a competition for adsorption sites between Cl and Cl 2 . We have also determined the recombination rates of Cl atoms in Cl 2 high-density plasmas sustained by electromagnetic surface waves by comparing the measured degrees of dissociation of Cl 2 to those predicted by an isothermal fluid model. For a reactor with large SS and quartz surfaces exposed to the plasma, γ values and their dependence on the Cl-toCl 2 number density ratio were consistent with those obtained from the rotating substrate technique. Similar values were obtained for plasmas sustained in a quartz discharge tube. It is expected that for plasmas sustained in or adjacent to a silica tube or plate, the Cl atoms recombination coefficient becomes independent of chamber wall material due to reactor seasoning, producing a silicon-oxychloride layer.

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In situ XANES characterization of the Cu oxidation state in Cu-ZSM-5 during NO decomposition catalysis

Cited by 135 publications

References 17 publications

An operando optical fiber UV–vis spectroscopic study of the catalytic decomposition of NO and N2O over Cu-ZSM-5

An operando optical fiber UV–vis spectroscopic study of the catalytic decomposition of NO and N2O over Cu-ZSM-5

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

Experimental and modeling study of O and Cl atoms surface recombination reactions in O2 and Cl2 plasmas

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