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Cobalt-promoted palladium as a three-way catalyst

Cobalt-promoted palladium as a three-way catalyst

Authors :
Magnus Skoglundh
Kjell Jansson
Lars Löwendahl
Bernhard Hirschauer
Leif Dahl
Hanna Johansson
Source :
Scopus-Elsevier
Publication Year :
1996
Publisher :
Elsevier BV, 1996.

Abstract

Fifteen catalysts were prepared by intermittently impregnating alumina washcoats with water solutions containing La3+, Co2+ and PdCl42- ions/complex and calcining them at 550-820 degrees C. The catalysts were evaluated with respect to light-off performance, at stationary and transient feed gas stoichiometry, respectively, and redox characteristics, using NO/CO/C3H6/O-2/N-2 gas mixtures to simulate car exhaust. Alumina supported Pd exhibited three-way activity, i.e., simultaneous oxidation of CO and C3H6 and reduction of NO in a narrow interval around stoichiometric composition of the feed gas. Compared to Pd alone, addition of La or Co caused a widening of the interval under net reducing conditions. Addition of Co to Pd caused a significant increase in the activities for oxidation of CO and C3H6 under stoichiometric conditions. The conversions of CO and C3H6 started at about 100 degrees lower temperatures over Co-promoted Pd compared to unpromoted Pd. A marked increase in the activity for the reduction of NO at transient conditions was observed over Co-promoted Pd compared to unpromoted Pd. The catalysts were characterized by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy combined with energy-dispersive spectroscopy analysis, X-ray photoelectron spectroscopy (XPS), and specific surface area measurements. Only Co2+ could be detected by XPS in the surface layers of the Co-containing sample. A significant part of the cobalt is present in forms which can be oxidized and reduced under synthetic car exhaust conditions. These oxidizable/reducible cobalt sites are predominantly active for oxidation of CO and C3H6, hence promoting the reduction of NO over Pd by initiating these exothermic reactions in the catalyst.

Details

ISSN :
09263373
Volume :
7
Database :
OpenAIRE
Journal :
Applied Catalysis B: Environmental
Accession number :
edsair.doi.dedup.....2685e824f5e06ecdd902f60acf8f3c5b
Full Text :
https://doi.org/10.1016/0926-3373(95)00049-6