A role of components in Pt-ZrO2/Al2O3 as a sorbent for removal of NO and NO2

Oxide sorbents for NOx based on Pt-ZrO2/Al2O3 have been investigated. To clarify the role of each component, the sorption of NO and NO2 was compared using the samples composed of one or two components among Pt, ZrO2, and Al2O3. The sorption of NO and NO2 proceeded also on ZrO2, Al2O3, and ZrO2/Al2O3 without a Pt catalyst, but the rate of NO., removal was too slow to use any of them as sorbents. The NO2 removal was always higher than the NO removal on these oxides. These results indicate that the promotion of catalytic oxidation of NO to NO2 and successively to nitrate ions is an important role for the Pt catalyst. Although both alumina and zirconia demonstrated the NOx storage action, combination of the two components gave rise to the maximum capacity. The ZrO2 surface was more effective than the Al2O3 surface when NOx uptakes were compared per surface area basis. The FT-IR spectra after sorption of NO and NO2 demonstrated a strong band attributed to stored nitrate ions. (C) 2002 Elsevier Science B.V. All rights reserved.