The decomposition of methanol catalyzed with Rh nanoclusters supported on an ordered thin film of Al2O3/NiAl­(100) became enhanced on decreasing the size of the clusters. The decomposition of methanol (and methanol-d 4) proceeded through dehydrogenation; the formation thereby of CO became evident above 200 K, depending little on the cluster size. In contrast, the production of CO and hydrogen (deuterium) from the reaction varied notably with the cluster size. The quantity of either CO or hydrogen produced per Rh surface site was unaltered on clusters of diameter >1.5 nm and height >0.6 nm, corresponding to about 65% of methanol undergoing decomposition on adsorption in a monolayer on the clusters. For clusters of diameter <1.5 nm and height <0.6 nm, the production per Rh surface site increased with decreasing size, up to 4 times that on the large clusters or Rh(100) single-crystal surface. The reactivity was enhanced largely because, with decreasing cluster size, the activation energy for the scission of the O–H bond in the initial dehydrogenation became smaller than the activation energy for the competing desorption. The property was associated with the edge Rh atoms at the surface of small clusters.

The decomposition of methanol on Pt nanoclusters grown from vapor deposition onto an ordered Al 2 O 3 / NiAl(100) thin film was investigated under ultrahigh vacuum conditions with various surface probe techniques. The Pt clusters had mean diameter near 2.3 nm and height 0.4 nm before their coalescence; consisting of phase fcc, the clusters grew with their facets either ( 111) or ( 001) parallel to the θ-Al 2 O 3 (100) surface, depending on the temperature of growth. More than half the adsorbed monolayer of methanol on the Pt clusters decomposed via two channels: dehydrogenation to CO and C−O bond scission. The dehydrogenation was dominant and induced first at low-coordinated Pt sites, at 150 K on Pt(001) clusters and 200 K on Pt(111) clusters, whereas both lowcoordinated and some terrace Pt sites exhibited reactivity, despite the cluster size. On average, one CO was produced per surface Pt site, for a monolayer of methanol on either Pt(111) or Pt(001) clusters. In the other reaction, scission of the C−O bond occurred primarily in methanol itself and began about 250 K; the intermediate methyl preferentially formed methane on combining with atomic H from dehydrogenated methanol. No preferential reaction site for the C−O bond scission is indicated, but this process showed a remarkable dependence on the size and lattice parameter of the clusters: the probability of C−O bond scission decreased when the size increased and the lattice parameter decreased.

Self-organized patterning of supported nanoclusters by virtue of low cost and readiness for mass production is considered as one of the most promising methods; however, this approach is challenging, since the capability of controlling the patterns relies on a suitable combination of clusters and templates. In this paper we demonstrate that Co nanoclusters grown from vapour deposition over Al2O3 thin films on NiAl(100) substrate make a perfect combination for self-organized patterning. Uniform and sizeable Co nanoclusters are formed only on crystalline Al2O3 films and they are highly aligned by protrusion structures of the crystalline Al2O3. Through simple thermal treatments we can pattern the crystalline Al2O3 films and consequently the grown Co nanoclusters. The patterns are robust as they are sustained even when the Co nanoclusters are flashed to 750 K, exposed to atmosphere or the coverage is increased to coalescence. Moreover, the patterns can be further refined by using STM tips. The results imply potential applications in both fundamental and applied researches for electronic and magnetic nanodevices as well as catalysis.

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The temperature-dependent oxidation of Pt nanoclusters on a thin film of Al2O3 on NiAl(100), in the absence of a gaseous oxidizing agent, was investigated with various surface probe techniques. The Pt clusters (of mean diameter 2.2 nm and height 0.4 nm) grown from vapor deposition on the thin film of Al2O3 on NiAl(100) at 300 K became partially oxidized, as charge transfer from the Pt clusters to the oxide was indicated by a significant negative shift (0.4−0.5 eV) of binding energy (BE) of Alox 2p and O 1s states from Al2O3. The oxidation of the cluster proceeded to a further level when the sample was annealed above 450 K; the Pt 4f7/2 core level moved positively from BE 72.0 eV with increasing annealing temperature and eventually attained 72.6 eV above 650 K, which indicates a state of Pt2+. Accompanying this further oxidation, signals of both Alox 2p and O 1s shifted back to greater BE. The valence spectra indicate that the Pt−Al2O3 interaction was sustained whereas a new Pt−O bond was formed. Formation of a Pt x Al y O z complex is proposed to explain the observations. The new Pt oxide binding was substantially stronger than the initial one, as was evident from the oxidized clusters being resistant to sintering induced in electrochemical processes. The oxidation was associated also with a migration of oxide materials onto the Pt clusters, as both Al2O3(100) and NiAl(001) facets roughened after the annealing, and a probe of methanol adsorption showed no bare Pt clusters exposed but alumina-like structures on the surface.

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