Study of the Catalytic Activity–Semiconductive Properties Relationship For BaTiO3 and PbTiO3 Perovskites, Catalysts for Methane Combustion
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The electrical conductivity of barium and lead perovskites used as catalysts for the total oxidation of methane, has been measured under nitrogen, methane–nitrogen mixture, air and methane–air mixture (reaction mixture) at the catalytic reaction temperature. The two compounds appeared to be p-type semiconductors under air with positive holes as the main charge carriers but became n-type when contacted with methane–nitrogen mixture. Their conductivities differ by 1.5 orders of magnitude as n-type semiconductors and by three orders of magnitude when being p-type semiconductors. These results explained the difference in the catalytic activity encountered on the two solids. The alkane activation was proposed to be related in both cases to the p-type semiconducting properties of the solids, likely through hydrogen abstraction by a surface O− species, forming a CH 3 • radical. The overall reaction mechanism on both perovskites can be assimilated to a Mars and van Krevelen mechanism.
KeywordsElectrical conductivity Ba–Ti perovskite Pb–Ti perovskite Catalytic total oxidation Methane
The authors are grateful to Dr. Éva Makó from the University of Pannonia for her XRD expertise and for unit cell parameters calculation. The Romanian National Authority for Scientific Research (ANCS) is acknowledged for the financial support of this work under the contract PN II nr. 105/15.09.2008.