Formation of Mo and MoSx nanoparticles on Au(111) from Mo(CO)6 and S2 precursors:: electronic and chemical properties

Mo(CO)(6) can be useful as a precursor for the preparation of Mo and MoSx nanoparticles on a Au(1 1 1) substrate. On this surface the carbonyl adsorbs intact at 100 K and desorbs at temperatures lower than 300 K. Under these conditions, the dissociation of the Mo(CO)(6) molecule is negligible and a desorption channel clearly dominates. An efficient dissociation channel was found after dosing Mo(CO)(6) at high temperatures (> 400 K). The decomposition of Mo(CO)(6) yields the small coverages of pure Mo that are necessary for the formation of Mo nanoclusters on the Au(1 1 1) substrate. At large coverages of Mo (>0.15 ML), the dissociation of Mo(CO)(6) produces also C and O ad-atoms. Mo nanoclusters bonded to Au(1 1 1) exhibit a surprising low reactivity towards CO. Mo/Au(1 1 1) surfaces with Mo coverages below 0.1 ML adsorb the CO molecule weakly (desorption temperature < 400 K) and do not induce C-O bond cleavage. These systems, however, are able to induce the dissociation of thiophene at temperatures below 300 K and react with sulfur probably to form MoSx nanoparticles. The formed MoSx species are more reactive towards thiophene than extended MoS2(0 0 0 2) surfaces, MoSx films or MoSX/Al2O3 catalysts. This could be a consequence of special adsorption sites and/or distinctive electronic properties that favor bonding interactions with sulfur-containing molecules. (C) 2001 Elsevier Science B.V. All rights reserved.