Preparation of Bimetallic Catalysts by Surface Organometallic Chemistry

Marshall, Robert (1999). Preparation of Bimetallic Catalysts by Surface Organometallic Chemistry. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00010216

Abstract

Surface organometallic chemistry (SOMC) has been used to prepare a range of bimetallic catalysts. This work reports, for the first time, the preparation of alumina supported palladium iron and platinum iron catalysts by reaction of ferrocene with a reduced monometalhc catalyst. In addition, alumina supported and carbon supported platinum tin and alumina supported palladium tin catalysts were prepared using this technique using tetrabutyl tin. The catalysts were characterised using a range of techniques to determine the extent of the interaction between the two metals. Hydrogen chemisorption, TEM, EDX and cyclic voltammetry provide evidence of such an interaction and indicate that the catalysts consist of bimetallic particles. This provides evidence for a selective reaction between the organometallic precursor and the parent metal. Mossbauer, EPR and EXAFS spectroscopies have been used to examine the effect of different reducing and oxidising environments on the structure of a PdFe catalyst. These suggest, that in air, the particles exist as palladium with an overlayer of FeO_x. The alumina supported catalysts were tested for the gas phase catalytic hydrogenation of 1,3-butadiene and crotonaldehyde. The results show, that the addition of the second metal, can modify the activity and selectivity of the parent catalyst towards these reactions, in particular PtFe which shows an enhanced activity for both. Comparison of the range of carbon supported platinum tin catalysts with different loadings towards the electrooxidation of carbon monoxide has shown a significant effect on the addition of a quarter of a monolayer coverage of tin. On further addition of tin, there is little further change in the electrochemical properties or indeed the number of exposed platinum sites. Comparison of a catalyst prepared using SOMC and another, of similar loading, prepared using hydrolysis/precipitation suggests that the SOMC exhibits a greater level of control over the electrocatalytic properties.