The structure and reactivity of TiO2(110) supported palladium and rhodium

Palladium and rhodium overlayers on TiO2(110) deposited by metal vapour deposition (MVD) are characterised using a combination of XPS, LEED and FT-RAIRS of adsorbed CO. The RAIRS is sensitive to the local dielectric response in the neighbourhood of the CO probe molecule, and together with its fingerprint properties allows a characterisation of the size and morphology of the metal phases, particularly when combined with the other complimentary techniques. Palladium and rhodium overlayers deposited by MVD exhibit quite different structural behaviour on TiO2(110). A range of small to larger particles in registry with the substrate are produced in the case of palladium, while rhodium produces exclusively a large particle size with no apparent registry. High dispersion of rhodium is only possible using techniques of metal organic chemical vapour deposition (MOCVD), and this is illustrated with studies using rhodium carbonyl chloride as a precursor. The thermal stability and re-generation of the highly dispersed TiO2(110) supported rhodium gem-dicarbonyl is described, together with its reactivity with hydrogen.