Ruthenium surface mobility

In the case of a Pt(l 11) single crystal covered by spontaneously deposited mthenium of 50%, the infrared spectra change to those of that in Figure 11.7. As a difference to the infrared spectra on clean Pt(lll), the linearly bonded carbon monoxide adsorbate is shifted to 2040 cm-1 due to the surface mobility of the adsorbate on platinum ruthenium islands. On the other hand, there is a... 

In this paper, we postulate that the primary role of an alkali promoter is to reduce the mobility of the chemisorbed hydrogen on the ruthenium surface based on the data obtained from NMR spectroscopy. We will examine the active hydrogen adsorption states (a and P) in supported ruthenium catalysts and report the effects of the alkali promoters on the population and the mobility of the adsorbed states. 

Maillard F, Gloaguen F, Hahn F, Leger J-M. Electrooxidation of carbon monoxide at ruthenium-modified platinum nano-particles evidence for CO surface mobility. Fuel Cells 2002 2 143-52. 

High catalyst activity and utilization of sputtered thin films was demonstrated in operating fuel cells. Optimal sputter-deposition conditions for platinum-ruthenium alloys have been determined. The effect of composition on the performance of Pt-Ru films was studied, and optimal composition has been determined. Novel methods of enhancing surface area and improving porosity have been identified. Co-sputtered ruthenium oxide has been demonstrated not to have any significant beneficial effect on the activity of the catalyst layers. While cost presents a major obstacle to commercialization of DMFCs for mobile applications, this project demonstrates novel means to reduce the catalyst costs in DFMC fuel cells. Efficiency enhancements that are also necessary for DMFCs to be viable will be addressed... 

In the case of the particles accommodating amine ligands, a new phenomenon has been evidenced, namely, a dynamic exchange at the NMR timescale between free and coordinated amines. It has been correlated to the TEM and HREM results, which show that, at the early stage of the reaction, the particles display a spherical aspect and a small size (ca. 2-3 nm), and that after a few hours, the particles coalesce into elongated wormlike particles, still constituted of pure, unoxidized hep ruthenium. This NMR observation is particularly interesting since it evidences for these particles a fluxionality similar to that of molecular clusters, which is well documented. The ruthenium nanoparticles contain coordinated mobile surface hydrides, as recently demonstrated by a combination of NMR techniques in solution, gas phase, and in the solid state. ... 

Characterization by wide-angle X-ray scattering (WAXS) evidenced crystalline NPs displaying the expected hep structure of bulk ruthenium. Reactivity smdies were carried out in particular with CO [17]. It has been observed that there is an influence of the reaction time on the coordination mode of CO on the surface of the NPs and that CO is mobile. Short reaction times give rise to CO adsorption in the bridging mode, while longer reaction times allow adsorption of more CO molecules only in the linear or multicarbonyl modes. 

Ruthenocene, and other ruthenium complexes were shown by Cluff et al, some of which were labelled with H, were adsorbed on silica surfaces by grinding the polycrystalline materials with silica. The progress was monitored by H, C, and solid-state NMR spectroscopy. The transition from the crystal lattice to the surface species that are highly mobile is proven by strongly reduced chemical shift anisotropies and diminished dipolar interactions. The MAS spectra of surface-adsorbed ferrocene-da prove that the motion of the metallocenes on the surfaces is fast and nearly isotropic, as in solution. ... 

---