Transient Studies of Oxygen Removal Pathways and Catalytic Redox Cycles during NO Decomposition on Cu−ZSM5

Modén, Björn; Costa, Patrick Da; Lee, Deuk Ki; Iglesia, Enrique

doi:10.1021/jp020731g

Cited by 44 publications

(29 citation statements)

References 40 publications

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“…Thus, the difference in contact between soot and the catalyst resulting from the different mixing of the solids is substantially attenuated since the NO/NO 2 couple acts as an oxygen carrier. Such a role of NO 2 as an oxygen carrier has also been reported in the case of deNO x reactions over metalozeolites [53].…”

Section: Catalytic Activitysupporting

confidence: 65%

Strong Enhancement of deSoot Activity of Transition Metal Oxides by Alkali Doping: Additive Effects of Potassium and Nitric Oxide

et al. 2016

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A series of potassium-promoted spinels (Mn, Fe, Co) were prepared with various K ? promoter locations: on the surface (surface promotion) or in the bulk (formation of new layered and tunneled nanostructures via solid state reaction). All prepared samples were characterized by means of X-ray diffraction, Raman spectroscopy, X-ray fluorescence and N 2 -BET specific surface area analysis. Catalytic activity in soot combustion in different reaction conditions was investigated (tight contact, loose contact, loose contact with NO addition). It was shown that in all cases the nanostructuration is more effective than the surface promotion, with the layered structures of KCo 4 O 8 , KMn 4 O 8 being the most catalytically active phases, lowering the soot combustion down to 250°C. The difference in activity between tight and loose contacts can be bridged in the presence of NO due to its transformation into NO 2 , which acts as the oxygen carrier from the catalyst surface into soot particles, eliminating the soot-catalyst contact difference.

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Section: Catalytic Activitysupporting

confidence: 65%

Strong Enhancement of deSoot Activity of Transition Metal Oxides by Alkali Doping: Additive Effects of Potassium and Nitric Oxide

et al. 2016

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“…Such sites would also be unable to participate in redox cycles requiring recombinative desorption steps. Our recent results 22,23 have shown, however, that oxygen removal steps involving NO 2 formation and decomposition of NO 2 and the use of NO as an oxygen carrier among distant redox sites allow all dimers to participate in NO decomposition redox cycles, irrespective of their relative proximity. …”

Section: Distributions Of Al-al Pairsmentioning

confidence: 90%

“…22,23 In this study, the NO decomposition rate data are correlated with the amounts of different Cu species in order to determine which Cu species are active for NO decomposition. Steadystate NO decomposition rates (N 2 + N 2 O formed per total Cu atom) are shown in Fig.…”

Section: Dependence Of Catalytic No Decomposition Rates On the Numbermentioning

confidence: 99%

“…22,23 Here, we report chemical and spectroscopic characterization data for a series of Cu-ZSM5 samples with varying Cu/Al ratio using X-ray absorption spectra during oxygen removal by treatment with H 2 , CO, or He, along with mass spectrometric analysis of the amount of oxygen removed during these thermal treatments (as H 2 O, CO 2 , or O 2 ). These combined methods have led to a quantitative assessment of the number of Cu 2+ and {Cu 2+ -O…”

Section: Introductionmentioning

confidence: 99%

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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.

Self Cite

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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“…Recent computational contributions of Goodman et al [38,42] stressed the eventual role of double-O-bridged copper pairs, i.e., [CuO 2 Cu] 2+ . Based on this knowledge, [CuO 2 Cu] 2+ has been included in some recent NO decomposition cycles [43][44][45] and is proposed to play a role in O 2 formation, either directly via the release of O 2 or indirectly via recombinative desorption requiring vicinal oxocations or NOmediated oxygen removal. However, in the latter studies, none of the double-O-bridged copper pairs that are proposed in the theoretical contribution of Goodman et al [38] were identified spectroscopically.…”

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 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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Transient Studies of Oxygen Removal Pathways and Catalytic Redox Cycles during NO Decomposition on Cu−ZSM5

Cited by 44 publications

References 40 publications

Strong Enhancement of deSoot Activity of Transition Metal Oxides by Alkali Doping: Additive Effects of Potassium and Nitric Oxide

Strong Enhancement of deSoot Activity of Transition Metal Oxides by Alkali Doping: Additive Effects of Potassium and Nitric Oxide

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

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

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