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Mechanistic origin of the different activity of Rh-ZSM-5 and Fe-ZSM-5 in N2O decomposition

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Abstract.
A temporal analysis of products (TAP) reactor was used to study relationships between the mechanism
of direct N2O decomposition over metal-loaded zeolites and their resulting activity. Rh-ZSM-5 (prepared
by incipient wetness) and Fe-ZSM-5 (prepared by liquid-ion exchange) were chosen as prototypic catalysts
displaying low (650 K) temperature activity, respectively. Transient studies at
the same contact time revealed the higher activity of Rh-ZSM-5 below 623 K and significantly stronger
N2O adsorption over Rh species than over Fe species in the zeolites. Several microkinetic models were
applied for simultaneous fitting the transient responses of N2O, N2, and O2 . Classical reaction schemes
failed to describe the experimental data. The preferred models of N2O decomposition over Rh-ZSM-5 and
Fe-ZSM-5 differ in the reaction pathways of O2 formation. For both catalysts, free active metal sites (*)
and those occupied by monoatomic oxygen species (*-O) from N2O participate in the decomposition of
gas-phase N2O. Gas-phase O2 is formed directly on N2O interaction with *-O over Rh-ZSM-5, whereas
the latter reaction over Fe-ZSM-5 leads to a surface bi-atomic oxygen species (O-*-O), followed by its
transformation to *-O2. The latter species desorbs as molecular oxygen. Comparison of ion-exchanged
and steam-activated Fe-ZSM-5 [J. Phys. Chem. B 110 (2006) 22586] revealed that the reaction mechanism
is independent of the iron constitution induced by the preparation and activation routes, despite
important differences in catalytic activity. Our quantitative microkinetic analysis demonstrated that both
the stronger reversible N2O adsorption and, most importantly, the faster desorption of O2 are distinctive
mechanistic features of Rh-ZSM-5, likely indicating its high de-N2O activity.

Keywords:
N2O decomposition
Metal zeolites
Rh-ZSM-5
Fe-ZSM-5
Oxygen formation
Mechanism
Kinetics
TAP reactor

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Informasi Detail

Judul Seri

Journal of Catalysis

No. Panggil

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Penerbit

London : Elsevier Inc.., 2008

Deskripsi Fisik

Journal of Catalysis 256 (2008) 248–258

Bahasa

English

ISBN/ISSN

00219517

Klasifikasi

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Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

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Subjek

KIMIA

Info Detail Spesifik

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Pernyataan Tanggungjawab

agus

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