Properties of alumina supported Pd-Fe and Pt-Fe catalysts prepared using surface organometallic chemistry

The Pd-Fe. and Pt-Fe catalysts supported on alumina were prepared by a surf ace organometallic route using ferrocene. The materials were characterised using hydrogen chemisorption, TEM, EDX and EPR spectroscopy and evaluated f or the hydrogenation of 1,3-butadiene. Addition of iron suppresses the chem isorption of hydrogen for both the palladium and platinum catalysts. The ED X analysis of Pd-Fe/Al2O3 indicated that the palladium and iron exist toget her on the support and EPR studies for both the iron doped palladium and pl atinum catalysts showed a peak at g = 2.1 which can be interpreted as metal lic iron possibly in interaction with the noble metal, with another at g = 4.3 attributed to ferric iron. These results provide evidence for a selecti ve reaction between the ferrocene and surface of the reduced monometallic c atalyst to give iron in association with the platinum group metal. The cata lysts were believed to consist mainly of palladium or platinum in close ass ociation with the iron, as MFe0 and/or the metal with an overlayer of FeOx. In the hydrogenation of 1,3-butadiene, addition of iron appeared to suppre ss total hydrogenation, in particular of 1-butene. This was particularly ev ident for the platinum catalyst with a large decrease in n-butane formation for Pt-Fe/Al2O3 at the same activity compared to Pt/Al2O3. This enhancemen t in the selectivity for the Pt-Fe catalyst may be attributed to both geome tric and electronic effects. (C) 2001 Elsevier Science B.V All rights reser ved.