Improved Automotive NO x Aftertreatment System: Metal Ammine Complexes as NH 3 Source for SCR Using Fe-Containing Zeolit
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Improved Automotive NOx Aftertreatment System: Metal Ammine Complexes as NH3 Source for SCR Using Fe-Containing Zeolite Catalysts Tue Johannessen Æ Henning Schmidt Æ Anne Mette Frey Æ Claus Hviid Christensen
Received: 10 November 2008 / Accepted: 25 November 2008 / Published online: 9 January 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Ammonia storage is a challenge in the selective catalytic reduction of NOx in vehicles. We propose a new system, based on metal ammines as the ammonia source. In combination with iron containing zeolites as the SCR catalyst it should be possible to obtain a low temperature system for NOx removal. Keywords SCR NO Metal ammines Ammonia storage Fe-containing zeolites
1 Introduction It has become increasingly important to reduce the emission of nitrogen oxides from both stationary and mobile combustion technologies in order to protect the environment from high level of NOx pollution. High levels of NOx can lead to problems such as acid rain, oxygen depletion, as well as forest and crops damage. Thus, it can be considered extremely harmful to the environment. Furthermore, the compounds are toxic for humans at inhalation. Nitrogen oxides are emitted with the exhaust gasses during the combustion of both fossil fuels and biofuels. This means that it is necessary to clean the exhaust gas in both stationary and automotive application [1]. Approximately 20% of all NOx emissions originate from vehicles [2]. In vehicles, the problem with high exhaust T. Johannessen H. Schmidt Amminex A/S, Gladsaxevej 363, 2860 Søborg, Denmark A. M. Frey C. H. Christensen (&) Center for Sustainable and Green Chemistry, Department of Chemistry NanoDTU, Technical University of Denmark, 2800 Lyngby, Denmark e-mail: [email protected]
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levels of NOx is especially seen for lean-burn vehicles (diesel and lean-burn gasoline). In a lean-burn engine, the ratio between air and fuel is higher than the stoichiometric ratio resulting in excess oxygen in the exhaust gas. For modern gasoline cars, the commercially used three-way catalyst only functions properly when the ratio is very close to stoichiometric fuel mixture. In a lean-burn vehicle, the oxidation of CO and hydrocarbons can still take place efficiently but the excess of oxygen simply prevents the reduction of nitrogen oxides. Lean-burn engine operation can be used in gasoline-driven cars to improve the fuel economy. Furthermore lean-burn combustion methods are used in diesel cars. Since the number of diesel cars is currently increasing significantly, it would be of major importance to develop a way to efficiently eliminate this source of NOx pollution [3, 4]. The environmental concerns have resulted in a continually decrease in the allowed NOx concentrations in countries such as Japan, Europe and US controlled by legislation. Therefore, the catalytic removal of NO using selective catalytic reduction (SCR) appears to become crucial for reducing the emissions from diesel cars and lean-burn cars as it appears to be the only viable technology to
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