AVS 49th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoA

Invited Paper SS1-MoA5
Fundamental Studies of Function and Deactivation of NOx Storage Catalysts

Monday, November 4, 2002, 3:20 pm, Room C-108

Session: Surface Reactions: CO and NO
Presenter: E. Fridell, Chalmers University of Technology, Sweden
Authors: E. Fridell, Chalmers University of Technology, Sweden
A. Amberntsson, Chalmers University of Technology, Sweden
P. Broqvist, Chalmers University of Technology, Sweden
J. Dawody, Chalmers University of Technology, Sweden
A.W. Grant, Chalmers University of Technology, Sweden
L. Olsson, Chalmers University of Technology, Sweden
M. Skoglundh, Chalmers University of Technology, Sweden
Correspondent: Click to Email
We have investigated the function of the different components in so called NOx storage catalysts regarding both the storage/reduction of NOx and deactivation by sulphur. These types of catalysts are used in lean burn applications for trapping NOx as nitrates, which in turn are reduced during lean conditions We have investigated model samples containing Ba compounds for storage of NOx and Pt and Rh as catalysts for oxidation and reduction reactions. We find that NO2 plays an important role in the storage mechanism as an oxidising agent. Two different mechanisms for this are discussed: The formation of surface peroxides and the oxidation of nitrites to nitrates. FTIR studies show that NOx is stored as surface nitrates. The stability of these species is also confirmed by first principle calculations. The sulphur deactivation is found to be more severe when SO2 is added during the rich phase than when SO2 is added during the lean period. This observation is found to be connected to the interaction between Pt and SO2. FTIR shows the formation of bulk sulphates both under lean and rich conditions. The influence of the choice of noble metals for the deactivation and regeneration was also investigated. It is found that Rh plays an important role for the regeneration after sulphur deactivation. Further, XPS studies show that the formation of platinum oxides is significant in the presence of NO2, especially for the Ba-containing samples. This has strong implications for the reactions.