Structured bimetallic Pd-Pt/gamma-Al2O3 catalysts on FeCrAlloy fibers for total combustion of methane

Bimetallic Pd-Pt/Al2O3 catalysts were deposited by dip coating on FeCrAlloy-type fibers. The influence of different gaseous pretreatments (under O-2/H-2 or H-2 flows) on the physico-chemical properties and the catalytic activity in the total combustion of methane were investigated. Dispersion of Pd and Pt appeared to be a crucial parameter for the catalytic performances. All directly calcined catalysts displayed better catalytic behaviour than the pretreated ones. Long duration tests demonstrated that a bimetallic Pd-Pt catalyst has a better catalytic behaviour than a Pd-based one, which undergoes through sintering as evidenced by the formation of larger agglomerates. After the long duration test, palladium is in a fully oxidized state (PdO) (as well as platinum (PtO)). It is suggested that the better catalytic behaviour of the Pt-Pd catalyst could be due to an active cooperation between PtO, formed during the early stages of the catalytic reaction, and PdO. Two hypotheses can be put forward; in the first case, NO could supply oxygen atoms to PdO, which actually would play the active role in the catalytic reaction. In the second case, CH4 would be adsorbed and dissociated on Pt atoms, and PdO would supply oxygen atoms leading to the formation Of CO2. (c) 2007 Elsevier B.V. All rights reserved.