Ruthenium surface structure

Asakura K, Yamada M, Iwasawa Y, Kuroda H (1985) Spectroscopic studies on the surface structures of ruthenium catalysts derived from triruthenium dodecacarbonyl/y-aluminum oxide or -silicon dioxide. Chem Lett 14 511... 

The newest trend has been to deposit controlled amounts of ruthenium on the well-defined platinum single-crystal substrates of different crystallographic orientations. This approach allows one to investigate surface-structure effects in PtRu... 

W. Chrzanowski, A. Wieckowski, Surface structure effects in platinum/ruthenium methanol oxidation electrocatalysis. Langmuir 1998, 14, 1967-1970. 

As this review is intended to illustrate, the interplay between metal and oxygen leads to a richness of reactivity that is reflected in the surface structure of oxides. Much of this richness can be rationalised as varying proportions of ionic and covalent character in the metal-oxygen bonding, and is manifest in a variety of non-stoichiometric surfeces. We therefore focus on the prototypical transition metal oxide smface rutile Ti(>2 (1 1 0). This is contrasted with computational results for one of the most widely-studied p-block oxide surfaces - corundum Al2O3-(0 0 0 1) - and we refer also to computational surface studies on oxides of ruthenium, iron, vanadium, tin and silver, as well as ternary oxides. 

A surface structure of the type discussed for the rhodium-silica system, where two CO molecules adsorb on one surface metal atom, appears to be possible for some metals existing in certain ranges of crystallite sizes. Guerra and Schulman (112) have, in fact, questioned the existence of this adsorption complex on their rhodium-silica samples, but have suggested a similar type of adsorption mechanism occurring on their rhenium and ruthenium silica supported samples. 

Surface-science studies using nickel single-crystal surfaces revealed that the methanation reaction is surface-structure-insensitive. Both the (111) and (100) crystal faces yield the same reaction rates over a wide temperature range. These specific rates are also the same as those found for alumina-supported nickel, further proving the structure insensitivity of the process. This is also the case for the reaction over ruthenium, rhodium, molybdenum, and iron. 

Fiechter S, Dorbandt I, Bogdanoff P, Zehl G, Schulenburg H, Tributsch H, Bron M, Radnik J, Fieber-Erdmann M (2007) Surface modified ruthenium nanoparticles structural investigation and surface analysis of a novel catalyst for oxygen reduction. J Phys Chem C 111 477-487... 

The effect of alkaline earth metal as promoter still has disputation. Some researchers considered °dii pjjat barium as a structural promoter can modify the ruthenium surface and is beneficial to form high active B5 sites. Others considered that barium is an electronic promoter. Although there is disputation on promoting mechanism of barium, generally, barium atom is uniformly distributed on the surface of ruthenium atom in the form of (Ba- -0) under the condition of ammonia synthesis.Kowalczyk et proposed the existence forms of cesium and (Ba + O) on the ruthenium surface as Fig. 6.18. 

When fuel contains heavier hydrocarbons than methane, or it is biofuel, or contains alcohols, the feedstock often contains additional compounds such as sulphur and phosphorus, that is, fertiliser impurities. In the petrochemical industry, gas-borne reactive spedes (i.e., sulphur, arsenic, chlorine, mercury, zinc, etc.) or unsaturated hydrocarbons (i.e., acetylene, ethylene, propylene and butylene) may act as contaminating agents (Deshmukh et al, 2007). These impurities cause catalyst deactivation by poisoning. The effect of a poison on an active surface is seen as site blockage or atomic surface structure transformation (Babita et a/., 2011). Therefore, it is important to choose poisoning-resistant catalyst materials. For example, nickel is not the most effective MSR catalyst although it is widely used in industry due to its low market price compared to ruthenium and rhodium. Both Ru and Rh are more effective in MSR and less carbon is formed in these systems, than in the case of Ni. However, due to the cost and availability of precious metals, these are not widely used in industrial applications. 

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 ruthenium-copper and osmium-copper systems represent extreme cases in view of the very limited miscibility of either ruthenium or osmium with copper. It may also be noted that the crystal structure of ruthenium or osmium is different from that of copper, the former metals possessing the hep structure and the latter the fee structure. A system which is less extreme in these respects is the rhodium-copper system, since the components both possess the face centered cubic structure and also exhibit at least some miscibility at conditions of interest in catalysis. Recent EXAFS results from our group on rhodium-copper clusters (14) are similar to the earlier results on ruthenium-copper ( ) and osmium-copper (12) clusters, in that the rhodium atoms are coordinated predominantly to other rhodium atoms while the copper atoms are coordinated extensively to both copper and rhodium atoms. Also, we conclude that the copper concentrates in the surface of rhodium-copper clusters, as in the case of the ruthenium-copper and osmium-copper clusters. 

These conclusions from the infrared reflectance spectra recorded with Pt and Pt-Ru bulk alloys were confirmed in electrocatalysis studies on small bimetallic particles dispersed on high surface area carbon powders.Concerning the structure of bimetallic Pt-Ru particles, in situ Extended X-Ray Absorption Fine Structure (EXAFS>XANES experiments showed that the particle is a true alloy. For practical application, it is very important to determine the optimum composition of the R-Ru alloys. Even if there are still some discrepancies, several recent studies have concluded that an optimum composition about 15 to 20 at.% in ruthenium gives the best results for the oxidation of methanol. This composition is different from that for the oxidation of dissolved CO (about 50 at.% Ru), confirming a different spatial distribution of the adsorbed species. 

Williams ED, Weinberg WH. 1979. The geometric structure of carbon monoxide chemisorbed on the ruthenium (001) surface at low temperatures. Surf Sci 82 93. 

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