Ignition in alkane oxidation on noble-metal catalysts

The ignition behavior in the oxidation of four simple alkanes (methane, eth ane, propane and isobutane) with air on a platinum-foil catalyst, as well a s that of ethane/air mixtures on four noble-metal foil catalysts (Pt, Pd, P h, and Ir) was studied at atmospheric pressure over the entire range of fue l-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 considera bly 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-ox ygen bond energy of the noble metal. A very simple analytical model was abl e to reproduce the dependence of surface ignition temperatures on fuel-to-a ir ratios, yielding apparent activation energies for the surface reactions and indicating an oxygen-covered surface before catalytic ignition due to s trong site competition between the hydrocarbon and oxygen on the catalyst s urface. (C) 1999 Elsevier Science B.V. All rights reserved.