Ruthenium bulk properties

Ruthenium-copper and osmium-copper clusters (21) are of particular interest because the components are immiscible in the bulk (32). Studies of the chemisorption and catalytic properties of the clusters suggested a structure in which the copper was present on the surface of the ruthenium or osmium (23,24). The clusters were dispersed on a silica carrier (21). They were prepared by wetting the silica with an aqueous solution of ruthenium and copper, or osmium and copper, salts. After a drying step, the metal salts on the silica were reduced to form the bimetallic clusters. The reduction was accomplished by heating the material in a stream of hydrogen. 

The results of the EXAFS studies on osmium-copper clusters lead to conclusions similar to those derived for ruthenium-copper clusters. That is, an osmium-copper cluster Is viewed as a central core of osmium atoms with the copper present at the surface. The results of the EXAFS investigations have provided excellent support for the conclusions deduced earlier (21,23,24) from studies of the chemisorption and catalytic properties of the clusters. Although copper is immiscible with both ruthenium and osmium in the bulk, it exhibits significant interaction with either metal at an interface. 

A series of ruthenium(II) phthalocyanines with one or two pyridyl dendritic olig-othiophene axial substituent(s) have also been reported (compounds 50 and 51) [50], The dendritic ligands absorb in the region from 380 to 550 nm, which complements the absorptions of the phthalocyanine core. This combination results in better light harvesting property and enhancement in efficiency of the corresponding solar cells. The solution-processed photovoltaic devices made with these compounds and fullerene acceptor give efficiencies of up to 1.6%. These represent the most efficient phthalocyanine-based bulk heterojunction solar cells reported so far. 

The data in Fig. 11.1 show that all of the shaded metals, except ruthenium, have an fee crystal structure for the bulk metal. As implied above, ruthenium has some catalytic properties that are different from those of the other catalytically active metals. This may be the result of the hep crystal structure of ruthenium which would give surface sites different from those shown in Schemes 4.1-4.4. It could also be a manifestation of the specific electronic configuration of ruthenium, or, it could arise from a combination of both factors. 

It was discovered that the ability of metals to form solid solutions (alloys) in the bulk is not necessary for a bimetallic system to be of interest as a catalyst. An example is the ruthenium-copper system, in which the two components are virtually completely immiscible in the bulk. This system exhibits an effect of the copper (in particular, selective inhibition of hydrocarbon hydrogenoly-sis) similar to that exhibited by the nickel-copper system, in which the components are completely miscible. Although ruthenium and copper do not form solid solutions in the bulk, they do exhibit a strong interaction at copper-ruthenium interfaces. The copper tends to cover the surface of the ruthenium, analogous to a chemisorbed layer. As a result, the copper has a marked effect on the chemisorption and catalytic properties of the ruthenium. 

Any notion that the components of a bimetallic catalyst should form a complete series of solid solutions in the bulk, or even that they should be moderately miscible, has been found to be much too restrictive. Indeed, pairs of metallic elements that are completely immiscible in the bulk, for example, ruthenium-copper and osmium-copper (6), may form bimetallic aggregates whose surface properties reveal extensive interaction between the two elements (2,4). 

Thus although ruthenium and copper are immiscible in the bulk, ruthenium-copper aggregates can be prepared that have surface properties very different from those of pure ruthenium. The ruthenium-copper aggregates exhibit chemisorption and catalytic properties which would not be expected for simple physical mixtures of ruthenium and copper granules. The presence of the copper clearly has a marked effect on surface processes occurring on ruthenium. On the basis of the chemisorption and catalytic results, we conclude that the copper tends to cover the ruthenium surface. We thus adopt the view that copper is chemisorbed on the ruthenium. 

The elimination of sample luminescence using a diode laser was demonstrated by measuring SER spectra of tris(2,2 -bipyridine)ruthenium(II), [RB,], in bulk solution. RBj is a highly luminescent compound that has lecdved considerable interest because of its unique excited state properties (24-26). However, because of its intense visible luminescence, it is difficult to obtain luminescence-free Raman spectra even with SER enhancement. Further, visible-wavelength Raman spectra of this compound are usually complicated by resonance Raman contributions to the spectrum. 

It has been established that the charge transport—which occurs by electron hopping between the ruthenium ions in the mixed-valence compound—is substantially enhanced by the presence of the conductive polymer. The results of the thermopower study indicate a bulk-metal-like conductivity which is controlled by the conductive polymer. (PANI)x(RuCl3)y shows a room temperature conductivity of ca. 1 Scm It was suggested that the combination of the high conductivity of the polyaniline with the wide-ranging catalytic properties of RuCls could provide new materials with valuable electrocatalytic properties [136]. 

Anion Retention. Transition metal chlorides are often favored as catalyst precursors because of their ready availability, high solubility, and their ease of reduction. However, residual chloride anions (from incomplete catalyst reduction) can have a very marked effect on the properties of the catalysts. While the platinum group metal chlorides are, from a thermodynamic standpoint, very easy to reduce (Pt > Ru > Ir > Rh), residual chloride ions on the metal surface can be tenaciously bonded. The severity necessary to remove all the surface chloride reflects the surface energy of the metal (Ru, Mo, Ir > Rh > Pt > Pd). In the case of ruthenium, although bulk reduction apparently occurs at around 470 K, extended reduction above 700 K can be necessary to remove all chloride anions. The presence... 

The properties typically specified for metal or conductive oxide powders may include particle size and size distributions, surface area, tap and/or bulk densities, critical impurity levels, loss on ignition, and morphological characteristics. Metal powders can be utilized in various shapes, including spheres, flakes, and combinations of both. Their particle sizes can range from submicrometer to 20 /tm. In the case of conductive oxides such as ruthenium oxide used in resistor formulations, the surface areas can approach 100 mVg, which translates to a particle size of less than 10 /tm. The state of agglomeration becomes particularly important for these types of powders. 

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