Skeletal rearrangement of hydrocarbons on the rare earth mixed valence intermetallic compound CePd3

Abstract The skeletal rearrangements (isomerization, hydrogenolysis, dehydrocyclization) of methylcyclopentane, 2-methylpentane, and 3-methylhexane have been studied on the intermetallic compound CePd 3 and compared with results obtained on classical supported palladium catalysts prepared by impregnation. CePd 3 exhibited a very low activity; the reaction mechanisms involved were quite different from what is known of palladium catalysts and they were attributed instead to cerium atoms present in an oxidized form. However, an activation with air at room temperature or at 120 °C dramatically increased the catalytic activity and the reactions involved were characteristic of palladium atoms, with a surprising selectivity toward aromatization and 1–5 ring closure. This enhancement was interpreted as due to a complete rearrangement of the surface, yielding active palladium sites on the surface. This phenomenon was related to the specific properties of cerium atoms which can undergo fast fluctuations of valence as revealed by photoelectron spectroscopy.