Kinetics and Mechanism of the Reduction of NO by n-Octane over Pt/Al 2 O 3 under Lean-Burn Conditions

Author: Burch R.   Fornasiero P.   Watling T.C.  

Publisher: Academic Press

ISSN: 0021-9517

Source: Journal of Catalysis, Vol.176, Iss.1, 1998-05, pp. : 204-214

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Abstract

The effect of temperature, contact time, and reactant concentration on the reduction of NO by n-C 8 H 18 over Pt/Al 2 O 3 under oxidising conditions was investigated. The oxidation of n-C 8 H 18 appears to be delicately balanced between two kinetic regimes. At low [C 8 H 18 ]/[O 2 ] the coverage of oxygen on the Pt surface is high, while that of carbonaceous species is negligible, resulting in hydrocarbon oxidation being inhibited by oxygen and in the oxidation of NO to NO 2 . At higher [C 8 H 18 ]/[O 2 ] the surface is saturated with carbonaceous species, while the coverage of oxygen is negligible, resulting in hydrocarbon oxidation being zero order in hydrocarbon concentration and in no NO 2 formation being observed. The state of the Pt surface affects the mechanism of NO x reduction. Thus, NO x reduction via dissociation of NO on the Pt surface is favoured by a high coverage of carbonaceous species, while a high coverage of oxygen favours NO x reduction by reaction between n-C 8 H 18 -derived species and spilt-over NO 2 on the Al 2 O 3 support and/or metal-support interface. Separate kinetic models capable of fitting the data in these two regions have been developed. Copyright 1998 Academic Press.