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 surface organometallic route using ferrocene. The materials were characterised using hydrogen chemisorption, TEM, EDX and EPR spectroscopy and evaluated for the hydrogenation of 1,3-butadiene. Addition of iron suppresses the chemisorption of hydrogen for both the palladium and platinum catalysts. The EDX analysis of Pd-Fe/Al2O3 indicated that the palladium and iron exist together on the support and EPR studies for both the iron doped palladium and platinum catalysts showed a peak at g=2.1 which can be interpreted as metallic iron possibly in interaction with the noble metal, with another at g=4.3 attributed to ferric iron. These results provide evidence for a selective reaction between the ferrocene and surface of the reduced monometallic catalyst to give iron in association with the platinum group metal. The catalysts were believed to consist mainly of palladium or platinum in close association 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 suppress total hydrogenation, in particular of 1-butene. This was particularly evident 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 enhancement in the selectivity for the Pt-Fe catalyst may be attributed to both geometric and electronic effects.