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Kinetic Studies of NOx Storage and Reduction Catalysts - Flow Reactor Experiments and Microkinetic Modeling

Anna Lindholm (Institutionen för kemi- och bioteknik, Kemisk reaktionsteknik ; Kompetenscentrum katalys (KCK))
Göteborg : Chalmers University of Technology, 2009. ISBN: 978-91-7385-344-6.- 146 s.
[Doktorsavhandling]

The NOx storage and reduction (NSR) technology is a promising technique to reduce NOx during oxygen excess e.g. in lean burn engine exhaust. A typical NSR catalyst consists of the following components: precious metals, such as platinum, palladium or rhodium, a storage component, usually barium, and a high surface area support, such as γ-alumina. By this method, NOx is stored in the catalyst for a relatively long lean period of time (minutes). To regenerate the catalyst, the engine operates in rich mode for a shorter time interval (seconds), during which the NOx stored is released and reduced to N2. The main objective of this work is to investigate the mechanism of storage and reduction of NOx over platinum, barium, and alumina based catalysts. This is accomplished through both flow reactor experiments and microkinetic modeling. In particular, the storage and reduction process when hydrogen is used as the reducing agent is examined. Additionally, the individual effect of the components in NSR catalysts and interactions between them are thoroughly investigated by studying Pt/Ba/Al, Pt/Al, and Pt/Si catalysts. Barium is the primary storage component in Pt/Ba/Al catalysts. However, it is shown that alumina contributes to the overall storage capacity. Thus, it is concluded that the storage of NOx occur on multiple storage sites. The storage capacity is influenced by the presence of H2O and CO2 in the feed. This work shows that byproducts such as N2O and NH3 can be formed when NOx is reduced with H2 and that the product selectivity is influenced by the temperature and the hydrogen concentration. Moreover, the performance of NSR catalysts is affected by the preparation procedure of the catalyst. The order of the impregnation steps influences the dispersion of barium, which impacts the utilization of storage components and the proximity between platinum and barium. Both the storage and regeneration processes are thereby affected by the preparation process. The reduction of NOx with H2 over platinum is investigated separately and a detailed kinetic model describing the process is developed in this work. This model is in turn used in a more comprehensive detailed model describing the complete NOx storage and reduction process in the presence of H2O and CO2, over a Pt/Ba/Al catalyst. The models are based on the results from the experimental investigations and can well describe the observed phenomena. Since the formation of significant amounts of NH3 is observed over Pt/Ba/Al catalysts the NOx reduction of a combined NSR and SCR system is investigated in this work. By placing an SCR catalyst downstream a Pt/Ba/Al catalyst the NOx reduction is improved and a decrease of the NH3 slip is achieved.

Nyckelord: NSR catalyst, NOx storage, NOx reduction, Pt/Ba/Al, microkinetic modeling, flow reactor experiments, combined NSR and SCR system


Även en opublicerad artikel är med i avhandlingen: Reduction of NOx over a combined NSR and SCR system Författare: Anna Lindholm, Kemisk reaktionsteknik Louise Olsson, Kemisk reaktionsteknik



Denna post skapades 2009-11-16. Senast ändrad 2013-09-25.
CPL Pubid: 101706

 

Institutioner (Chalmers)

Institutionen för kemi- och bioteknik, Kemisk reaktionsteknik (2005-2014)
Kompetenscentrum katalys (KCK)

Ämnesområden

Kemiteknik

Chalmers infrastruktur

Relaterade publikationer

Inkluderade delarbeten:


NOx storage and reduction over Pt based catalysts with hydrogen as the reducing agent Influence of H2O and CO2


A kinetic study of NOx reduction over Pt/SiO2 model catalysts with hydrogen as the reducing agent


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


The influence of the preparation procedure on the storage ande regeneration behavior of Pt and Ba based NOx storage and reduction catalysts


Examination

Datum: 2009-12-10
Tid: 10:00
Lokal: KB-salen, Kemigården 4, Chalmers Tekniska Högskola
Opponent: Professor Milos Marek, The Academy of Sciences of the Czech Republic, Tjeckien

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Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie 3025