Hollow metal oxide particles

Inorganic substances Uke small metal clusters, metal oxides etc. may also be deposited on the surface of single or bundled carbon nanotubes. It is possible, for instance, to decorate multiwalled nanotubes with nanoparticulate oxides of zinc or magnesium. To this end, a surfactant-mediated dispersion of MWNT is solubilized in cyclohexane with Triton X-114 as a surface-active agent to obtain a water/ oil emulsion. Aqueous solutions of the respective metal acetates are added afterward and are then found in the aqueous portion of the emulsion. Subsequently increasing the pH value to about 9.5 causes a precipitation of the metal hydroxides that deposit on the nanotube surface in the shape of hollow spheres. Final calcination at 450 °C transforms these hollow particles into the crystalhne metal oxides. Particles measuring about 5 nm or 30-40 nm have been observed for ZnO or MgO, respectively (Figure 3.84b). 

Nanosize-Controlled Syntheses of Indium Metal Particles and Hollow Indium Oxide Particles via the Sputter Deposition Technique in Ionic Liquids, Chem. Mater. 22 3283-3287. 

For the special case of a model Pd4 cluster situated in pseudomorphic fashion on MgO(OOl), we considered two adsorption sites for CO, on-top and in the four-fold hollow. The interaction with the support reverses the order of stability of the sites, with CO being more stable on the hollow site of the free cluster (262 vs. 130 kJ/mol) and on the on-top site of the MgO supported cluster (192 vs. 159 kJ/mol). This very important result shows that relatively small perturbations due to the metal-oxide interface can suffice to change the order of stability of adsorption sites of a metal particle even when there is no large electron density transfer from or to the support. This implies that the catalytic activity and selectivity of a deposited metal particle can be modified compared to the free particle even by a relatively inert support. 

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