Catalytic Oxidation of Carbon Monoxide on Monodispersed Platinum Clusters:  Each Atom Counts

Abstract

Nanoclusters open fascinating opportunities for quantum engineering because quantum-size effects become dominant in determining catalytic, − optical, electronic, and magnetic6 properties. We succeeded in the controlled production of low-energy and high-flux monodispersed cluster beams, which allow for a systematic study of their reactivity after deposition onto a chemically inert substrate. We investigated the catalytic reaction that is the oxidation of CO on platinum and observed a distinct atom by atom size dependency for monodispersed platinum clusters on thin MgO(100) films. These results clearly show that the efficiency of a heterogeneous catalytic reaction can be tuned by the judicious choice of particle size.

A Small Paramagnetic Platinum Cluster in an NaY Zeolite: Characterization and Hydrogen Adsorption and Desorption

“…Our theoretical calculations suggest that the Pt-Pt bond length is about 7-8% shorter for the naked Pt 13 cluster than for the fully hydrogen-covered Pt 13 H 30 cluster. This is consistent with the reported EXAFS experimental results by Koningsberger et al 21a The adsorbed hydrogen alters the electronic properties of the Pt atoms, decreasing the electron density between the atoms, which in turn leads to the increase of the Pt-Pt bond length.…”

“…Pt 13 is one of the smallest magic clusters, and for icosahedral symmetry, it has 12 equivalent Pt atoms surrounding another atom in the center. Despite the fact that only 12 equivalent nuclei were detected by EPR, the observed cluster is suggested to be icosahedral Pt 13 , with no significant spin density populating the 13th atom in the center so that it is invisible. Pt nanoparticles with an average diameter of 1 nm were also reported by Weckhuysen et al 15 Since they were prepared on NaY by a similar procedure and characterized by high-resolution transmission electron microscopy (HRTEM) and extended X-ray absorption fine structure (EXAFS), this supports the present observations and implies that the EPR silent clusters are of approximately the same size.…”

“…The fact that the spectra do depend to some extent on the zeolite structure (see Table 1) demonstrates that there is some interaction between the cluster and the zeolite frame. This is plausible since the size of the Pt 13 cluster amounts to about three atomic diameters (three Pt-Pt bond lengths), ca. 8 Å, which is slightly more than the open diameter of the 12-ring window of the supercage (Figure 11f).…”

“…The hydrogen adsorption energies per H 2 molecule were calculated as the difference between the energy of Pt clusters covered with n hydrogen atoms and the sum of the energies of the bare Pt cluster and the gas-phase hydrogen molecule. They are given by where E Pt+nH , E Pt , and E H2 represent the total energies of the hydrogen-reduced Pt 13 cluster, the bare Pt 13 cluster, and a gasphase hydrogen molecule, respectively. In the following, the desorption energy E des ) -E ads will be quoted, and it should…”

“…In contrast, for free clusters, special numbers (so-called "magic numbers") of atoms occur much more frequently than others since elements exhibiting electron deficient metallic bonding prefer a maximum coordination resulting in various close-packed polyhedral structures. 35 In the case of platinum, Pt 13 is one of the smallest magic clusters in which 12 equivalent Pt nuclei surround a central Pt atom.…”