Room-temperature metallo-organic chemical vapour deposition (MOCVD) of Rh(acac) 2(CO) 2 [(acac)=(CH 3CO) 2CH] to the TiO 2{110} surface leads to the formation of a molecular adlayer. Thermal desorption (TPD) and XPS indicate that the geminal dicarbonyl species derived from the Rh(acac)(CO) 2 species is the most thermally labile component of the adsorbed layer and is comparable in stability to that derived from [Rh(CO) 2Cl] 2 adsorption. The (acac) ligand undergoes a complex decomposition in the temperature region 500–775 K, and the carbon left behind appears to perturb the subsequent clustering Rh. The Rh 3d 5/2 binding energy (BE) is approximately constant at ∼307.4–307.2 eV in this temperature region, whereas in the [Rh(CO) 2Cl] 2-derived system, a BE of ∼307 eV (corresponding to Rh 0) is attained by 600 K. A Rh 3d 5/2 BE of 307 eV is only attained at T>775 K, and the remaining C residues are reacted away as CO by substrate oxygen. Ti 2p difference spectra show the formation of two distinct features during thermal treatment. One appears at high temperature with a BE shifted by ∼−2.0 eV from the bulk Ti 4+ photoelectron line and is associated with substrate reduction to Ti 3+ and the oxidation of surface bound carbon residues. The second appears at ∼−1.5 eV from the Ti 4+ line. This feature appears in concert with the decomposition of the Rh organometallics and is shown to be precursor-dependent both in magnitude and the temperature range in which it persists. Exposure of the thermally decomposed (600 K, Rh 3d 5/2 BE ∼307.3 eV) Rh(acac)(CO) 2/TiO 2 {110} to CO provides evidence for two stages in Rh redispersion. At room temperature, a species (C 1s BE∼286.6 eV: Rh 3d 5/2 BE ∼307.5) indicative of CO adsorption upon small Rh particles is observed. Further exposure to CO at a slightly elevated temperature leads to both linear CO species (BE 286 eV) and regeneration of around 25% of a geminal dicarbonyl species (BE 287.7 eV); this occurs in the absence of Cl and despite a surface C/Rh stoichiometry of ∼2–3. The latter observation indicates a mixture of CO-induced Rh redispersion and agglomeration.
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