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Detailed kinetic modeling of NOx storage and reduction with hydrogen as the reducing agent and in the presence of CO2 and H2O over a Pt/Ba/Al catalyst

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Abstract.
A detailed kinetic model of NOx storage and reduction, in the presence of H2O and CO2, with hydrogen
as the reducing agent was developed and validated in this study. The mechanism was derived from
flow reactor experiments conducted at 200–400 ◦C over a Pt/Ba/Al monolith sample. The detailed kinetic
model is divided into four sub-models: (i) NO oxidation over Pt, (ii) NOx storage, (iii) NOx reduction
over Pt, and (iv) NOx regeneration. The sub-model for NOx storage is based on our earlier work and
is further developed in this study to include high concentrations of CO2 and H2O in the feed and
also low temperature storage. In the model NOx is allowed to be stored on two different types of
storage sites: BaCO3 and a second storage site denoted S3. Based on experimental results many studies
suggests multiple storage sites one these catalysts, and there are different explanations (i) alumina and
barium sites (ii) bulk and surface barium, (iii) barium close and far from the noble metal, etc. The
disproportionation route, where NO2 is stored over BaCO3, is included in the NOx storage model. To
account for the storage occurring at lower temperatures NO can be stored over both BaCO3 and S3
in the presence of O2. NO adsorbed over S3 can be further oxidized to NO2 by reacting with oxygen
on neighboring Pt sites. The second storage site (S3) is important in order to explain NOx storage
at low temperatures and the disproportionation reaction is essential to describe the storage at high
temperatures. The NOx reduction sub-model used here was developed earlier over Pt/Si. Additional to
the reduction of NOx into N2, it describes the formation of NH3 over Pt. In the sub-model describing the
regeneration of NOx, adsorbed NOx species react with hydrogen adsorbed on Pt sites. Ammonia oxidation
over Pt and reactions between surface species of barium and NH3 according to ammonia selective
catalytic reduction (SCR) chemistry are also incorporated in the regeneration sub-model. The full model
can describe the complete uptake of NOx in the beginning of the lean period, the NOx breakthrough,
and the slow NOx storage in the end of the lean period very well as well as the following release and
reduction. It can also predict the gradual decrease in the storage capacity occurring in lean/rich cycling
experiments. Furthermore, the ammonia formation predicted by the model fits well with experimental
data. The model was validated with short lean (60 s) and rich (15 s) cycles which were not included in
the model development. The model could predict these experiments well for all three temperatures (200,
300 and 400 ◦C).

Keywords:
Detailed kinetic modeling
NOx storage and reduction
Pt/Ba/Al
H2
NH3 formation
H2O
CO2

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Ketersediaan

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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 258 (2008) 273–288

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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