Applied Catalysis B: Environmental 31 (2001) 27–38 NO x release from a noble metal/BaO catalyst: dependence on gas composition Annika Amberntsson a,b,∗ , Hans Persson a,b , Per Engström a,b , Bengt Kasemo a,b a Competence Centre for Catalysis, Chalmers University of Technology, SE-41296 Gothenburg, Sweden b Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg, Sweden Received 2 April 2000; received in revised form 29 October 2000; accepted 29 October 2000 Abstract Automotive lean-NO x has become one of the major issues in catalysis research, due to increased environmental concerns. In the present study the NO x storage/release concept has been investigated with respect to the NO x release kinetics. The importance of the gas composition during NO x release, including the λ-value, humidity, O 2 , and CO 2 concentration, was studied in flow reactor experiments performed with a commercial, noble metal BaO type catalyst. The main conclusions are that CO 2 has a promoting and O 2 a blocking effect on the NO x release. © 2001 Elsevier Science B.V. All rights reserved. Keywords: NO x storage; Lean-burn; NO x reduction; Barium oxide; NO x release 1. Introduction The fuel consumption by gasoline engines is of increasing importance, primarily due to its suspected cause of a greenhouse effect through carbon dioxide (CO 2 ) emissions [1]. With a better fuel efficiency, the CO 2 emissions and their contribution to the global warming would be significantly reduced. However, even without a CO 2 -related greenhouse effect, an improved fuel economy is desired, to reduce the consumption of (finite) fossil fuels, and to improve household and corporate economies. One way to improve the fuel economy, is to run the engine at oxygen excess, so-called lean-burn opera- tion. This reduces the fuel consumption (by 20–30% [2]) and thus, the amounts of CO 2 , carbon monoxide ∗ Corresponding author. Tel.: +46-31-772-29-59; fax: +46-31-772-29-67. E-mail address: ambernt@fy.chalmers.se (A. Amberntsson). (CO) and hydrocarbons (HC) emitted during driving. The latter two are reduced due to a more complete internal combustion process. However, running the engine lean increases the production of nitrogen oxides (NO x ) during the com- bustion [2–3], and obstructs the “normal” function of a three-way catalyst (TWC) for NO x reduction. NO x emissions are a major environmental and health is- sue, since they are suspected to cause acidification of ground and lake water and eutrofication. NO x together with HC also produces smog and earth level ozone [4]. Since the traditional TWC does not work for lean exhausts one must find new ways to reduce the NO x emissions under oxidising conditions. Several solutions to this problem have been suggested, but currently two major approaches have reached the pro- duction stage. One solution is selective catalytic re- duction, where, ammonia or hydrocarbons are added to the exhaust to selectively reduce NO x . Another ap- proach is the NO x storage concept, which can further 0926-3373/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0926-3373(00)00266-6