Ruthenium oxide, single crystals

The modification of platinum catalysts by the presence of ad-layers of a less noble metal such as ruthenium has been studied before [15-28]. A cooperative mechanism of the platinurmruthenium bimetallic system that causes the surface catalytic process between the two types of active species has been demonstrated [18], This system has attracted interest because it is regarded as a model for the platinurmruthenium alloy catalysts in fuel cell technology. Numerous studies on the methanol oxidation of ruthenium-decorated single crystals have reported that the Pt(l 11)/Ru surface shows the highest activity among all platinurmruthenium surfaces [21-26]. The development of carbon-supported electrocatalysts for direct methanol fuel cells (DMFC) indicates that the reactivity for methanol oxidation depends on the amount of the noble metal in the carbon-supported catalyst. 

Ruthenium bipyridyl complexes are suitable photosensitizers because then-excited states have a long lifetime and the oxidized Ru(III) center has a longterm chemical stability. Therefore, Ru bipyridyl complexes have been studied intensively as photosensitizers for homogeneous photocatalytic reactions and dye-sensitization systems. The Ru bipyridyl complex, bis(2,2 -bipyridine)(2,2 -bipyri-dine-4, 4,-dicarboxylate)ruthenium(II), having carboxyl groups as anchors to the semiconductor surface was synthesized and single-crystal Ti02 photoelectrodes sensitized by this Ru complex were studied in 1979 and 1980 [5,6]. 

A, bonds twisted by 31° to give a non-centrosymmetric ion. Reaction of [Ru302(NH3)14]6+ with en yields [Ru3O2(NH3)l0(en)2]6+,568 the single crystal X-ray structure of which shows a linear backbone with the en ligands bound to the central Ru.573 The central Ru—N bonds are eclipsed with respect to the Ru—N (equatorial) bonds of both end groups, which are themselves eclipsed relative to one another.573 Ruthenium red is also identified as the product when [Ru(NH3)sN2]2+ is oxidized in air on Y-type zeolite.342... 

An economical process for the low-temperature non-oxidative coupling of methane to give higher hydrocarbons would be commercially attractive. Direct observation of surface intermediates would be valuable in improving the efficiency of the process. The reaction has been characterized on ruthenium single-crystal surfaces by surface science techniques including HREELS 32) and references cited therein). 

A number of electro-oxidation studies on ruthenium-modified, platinum singlecrystal surfaces have recently appeared. Ruthenium has most commonly been deposited from solution on single-crystal platinum surfaces through spontaneous deposition or under electrochemical control [80-82,88-93]. In some cases MVD... 

In order to demonstrate the importance of a local ensemble in the promotion by ruthenium of the L-H oxidation of CO, a number of experiments were carried out on stepped platinum surfaces [98]. The results of these experiments also provide an interesting comparison between surfaces modified by MVD ruthenium and through deposition from solution. Experiments were carried out [98] on Pt(lll), Pt(533), and Pt(311) single-crystal surfaces. Ruthenium was dosed from an aged solution of 5 X 10 RuCls in 0.5 M H2SO4 (believed to contain the complex Ru0(H20)] by spontaneous deposition at open-circuit potential) [80]. Experiments were carried out on the clean surfaces, following the spontaneously deposition of ruthenium, and on surfaces where the deposited ruthenium was reduced in a 10% H2 in Ar gas mixture. CO was adsorbed on the variously prepared surfaces from solution and stripped in CO-free H2SO4 electrolyte. 

While many studies have been performed for the oxidation of methanol and carbon monoxide on supported catalyst systems [66,99-103] and Pt-Ru bulk alloys [61,104— 107], relatively few studies have been initiated on single-crystal platinum surfaces modihed with ruthenium. Of those performed these have largely involved the investigation of platinum single crystals modihed by ruthenium dosed electro-chemically [92,93] or spontaneously [80-82,90,91] from aqueous chloride solutions. This approach is discussed in Section 5.4. 

The study of a sublayer or a monolayer of ruthenium or osmium on platinum allows for an understanding of the role of the surface composition in the electrocatalysis of organic fuels, such as methanol oxidation. Interesting papers about ruthenium and osmium deposition on platinum single crystals and pc surfaces have been published [26,124—126],... 

---