Synthesis, Characterization and Surface Reaction Studies of Rhodium Nanoparticles on Selected Substrates

This thesis aims to achieve a fundamental understanding of catalysis and surface reaction chemistry by assembling structurally uniform supported metal clusters from organometallic precursors. In the course of this study rhodium dicarbonyl acetylacetonate (Rh(CO)2(acac)) and hexarhodiumhexadecylcarbonyl (Rh6(CO)16) were chosen as representative mononuclear and multinuclear organometallic species, respectively. First, the adsorption of Rh(CO)2(acac) on Al2O3/Ni3Al(111), and rutile TiO2(110) surfaces and the subsequent formation of Rh deposits has been examined using a combination of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. It was found that the organometallic molecule bind preferentially to specific sites associated with the surface structure. DFT calculations suggest that the parent molecule, however, must be at least partially deligated as its interaction with the Al2O3/Ni3Al(111), rutile TiO2(110) substrates is very weak. In addition, Rh6(CO)16 was deposited on TiO2(110) single crystal by chemical vapor deposition (CVD) of Rh6(CO)16 powder at 323 K and by surface synthesis of supported Rh(CO)2(acac) on TiO2(110) substrate at 373K with the presence of CO at 10-7 mbar. It was shown that the first method resulted in aggregated clusters with a wide size distribution range, while the second method resulted in intact, site isolated, and smaller Rh6(CO)16 particles with a narrow size distribution. Moreover, annealing the deposited clusters to 573K confirmed the high stability of assembled particles prepared by second method. This study demonstrates that synthesizing intact, site isolated Rh6(CO)16 clusters via Rh(CO)2(acac) is a key factor in preparing intact, site isolated Rh6 particles. Finally, Graphene sheets were prepared by means of thermal dissociation of ethylene (C2H4). The graphene preparation method used in this study resulted in large sheets which fully covered Cu(111) surface. Subsequently, Rh nanoclusters were prepared on the substrate by employing Rh(CO)2(acac) as a precursor. The STM obtained after Rh deposition confirmed that moiré pattern on graphene/Cu(111) is the preferential nucleation site.