An infrared study of species from ethylene,hydrogen and carbon monoxide adsorbed on palladium/silica catalysts

Two different procedures, A and B, for preparing palladium on silica catalysts give different infrared spectra, and to a large measure different surface species, from the adsorption of ethylene, hydrogen or carbon monoxide. A π-species (I) from ethylene is found on both catalyst preparations. On preparation A the other dominant species is probably the σ-diadsorbed species (II). On preparation B additional strong bands are tentatively interpreted in terms of a doubly π - bonded non-associatively adsorbed species (III). Only preparation B gives absorptions in the accessible region above 1300 cm^?1 which can be attributed to adsorbed hydrogen.