Efficient low temperature lean NO sub(x) reduction over Ag/Al sub(2)O sub(3) - A system approach

• Published in: Applied catalysis. B, Environmental Environmental, 2011-04, Vol.104 (1-2), p.74-83
• Main Authors: Kannisto, H, Karatzas, X, Edvardsson, J, Pettersson, L J, Ingelsten, H H
• Format: Article
• Language: English
• Subjects: Byproducts; Carbon monoxide; Catalysis; Catalysts; Fuels; Gas composition; Reduction; Reforming
• ISSN: 0926-3373
• DOI: 10.1016/j.apcatb.2011.02.026

This study focuses on lean NO sub(x) reduction (LNR) by n-octane using silver-alumina based catalysts, with the addition of hydrogen. The work takes a system approach, where parameters such as temperature, reformate gas composition, fuel penalty and realistic monolith samples are considered. The LNR catalyst samples were prepared by impregnation and sol-gel methods and the NO sub(x) reduction performance was characterized by flow-reactor experiments, where realistic engine-out gas compositions were used. The hydrogen feed over the LNR catalyst samples was determined via data achieved by autothermal reforming experiments over a rhodium based catalyst, using real diesel as feedstock. The LNR catalyst samples generally show an enhanced NO sub(x) reduction when hydrogen is added to the gas feed. In particular, a 2 wt% silver-alumina sample with the addition of minute amounts of platinum, shows a high increase in NO sub(x) reduction when hydrogen is added to the feed. The addition of CO, a potential poison in the reaction and a by-product from the reforming, did not show any significant effect on the LNR catalyst performance at the conditions used. This is beneficial, since it renders a CO clean-up step in the reformer system unneeded. Ammonia formation is discussed in terms of a possible dual-SCR system. Finally, the fuel penalty for hydrogen production and hydrocarbon addition is taken into consideration. It is found that an addition of 1000 ppm H sub(2) leads to unacceptable fuel penalties.