Ignition in alkane oxidation on noble-metal catalysts
Catalysis Today, 47 (1-4):
219-228 (1999)Abstract
The ignition behavior in the oxidation of four simple alkanes (methane,
ethane, propane and isobutane) with air on a platinum-foil catalyst,
as well as that of ethane/air mixtures on four noble-metal foil catalysts
(Pt, Pd, Rh, and Ir) was studied at atmospheric pressure over the
entire range of fuel-to-air ratios. While, Pd showed the widest range
of surface flammability, ignition temperatures for ethane/air mixtures
were lowest on Pt. Both, Rh and Ir deactivated rapidly under fuel-lean
conditions and ignited considerably higher than Pd and Pt. The surface
ignition temperatures were found to correlate well with the C-H bond
energy of the hydrocarbon and the metal-oxygen bond energy of the
noble metal. A very simple analytical model was able to reproduce
the dependence of surface ignition temperatures on fuel-to-air ratios,
yielding apparent activation energies for the surface reactions and
indicating an oxygen-covered surface before catalytic ignition due
to strong site competition between the hydrocarbon and oxygen on
the catalyst surface.