Ruthenium-Silica

L. Schmid, M. Rohr and A. Baiker, A mesoporous ruthenium silica hybrid aerogel with outstanding catalytic properties in the synthesis... 

Ruthenium compounds, 19 637-641 synthesis of, 19 640 uses for, 19 640—641 Ruthenium-copper clusters, 16 70 Ruthenium initiators, 26 934 Ruthenium plating, 9 823 Ruthenium-silica... 

Raney nickel. Ruthenium-Silica. Sodium hydride-Nickel aoetate-f-Amyl oxide. 

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. 

Chloro-2-(3-methyl-4H-1,2,4-triazol-4-yDbenzophenone (Oxidation of 7solution prepared by adding sodium periodate (2 g) to a stirred suspension of ruthenium dioxide (200 mg) in water (35 ml). The mixture became dark. Additional sodium periodate 18 g) was added during the next 15 minutes. The ice-bath was removed and the mixture was stirred for 45 minutes. Additional sodium periodate (4 g) was added and the mixture was stirred at ambient temperature for 18 hours and filtered. The solid was washed with acetone and the combined filtrate was concentrated in vacuo. The residue was suspended in water and extracted with methylene chloride. The extract was dried over anhydrous potassium carbonate and concentrated. The residue was chromatographed on silica... 

From the reaction of 5-0-benzoyl-l,2-0-isopropylidene-o -D-en/t/iro-pentofuranos-3-ulose (prepared in 80% yield by oxidation of 5-0-benzoyl-l,2-0-isopropylidene- -D-xylofuranose (35,36) with ruthenium tetroxide) with an excess of diazomethane in methanol-ether, two main products (m.p. 44°-45°C. and 76°-77°C.), both epoxides, could be isolated by chromatography of the product on a silica column. An... 

The ruthenium complexes were prepared in 50-80% yield by treatment of the imidazolium salts with potassium hexafluoro-t-butoxide, and then by (PCy3)2Cl2Ru = CHPh. A single phosphine is displaced by the carbene affording the desired complexes as air-stable solids that were purified by silica gel... 

To select the metal to be incorporated into the substrate porphyrin unit, the following basic properties of metalloporphyrins should be considered. The stability constant of MgPor is too small to achieve the usual oligomeric reactions and purification by silica gel chromatography. The starting material (Ru3(CO)i2) for Ru (CO)Por is expensive and the yield of the corresponding metalation reaction is low. Furthermore, the removal of rutheniirm is difficult, and it is likewise difficult to remove the template from the obtained ruthenium CPOs. Therefore, ZnPor is frequently used as a substrate in this template reaction, because of the low prices of zinc sources (zinc acetate and/or zinc chloride), the high yield in the metalation reaction, the sufficient chemical stability of the ZnPor under con-... 

Proven, industrially used catalysts are mostly based on either iron or cobalt. Ruthenium is an active F-T catalyst but is too expensive for industrial use. Both Fe and Co are prepared by several techniques including both precipitation and impregnation of (e.g. alumina or silica) supports. The more noble Ni catalyst produces nearly exclusively methane and is used for the removal of trace of CO in H2. 

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. 

Figure 1. X-ray absorption spectrum of a silica supported ruthenium-copper catalyst at 100 K In the vicinity of the K absorption edge of ruthenium. Reproduced with permission from Ref. 8. Copyright 1980, American Institute of Physics.

The copper EXAFS of the ruthenium-copper clusters might be expected to differ substantially from the copper EXAFS of a copper on silica catalyst, since the copper atoms have very different environments. This expectation is indeed borne out by experiment, as shown in Figure 2 by the plots of the function K x(K) vs. K at 100 K for the extended fine structure beyond the copper K edge for the ruthenium-copper catalyst and a copper on silica reference catalyst ( ). The difference is also evident from the Fourier transforms and first coordination shell inverse transforms in the middle and right-hand sections of Figure 2. The inverse transforms were taken over the range of distances 1.7 to 3.1A to isolate the contribution to EXAFS arising from the first coordination shell of metal atoms about a copper absorber atom. This shell consists of copper atoms alone in the copper catalyst and of both copper and ruthenium atoms in the ruthenium-copper catalyst. 

An example for a non-structure-sensitive reaction is provided by Davis et al. [102], who investigated the liquid-phase hydrogenation of glucose over carbon and silica based ruthenium catalysts with particle sizes between 1.1 and 2.4 run. Depending on catalyst loading which was between 0.56 wt.% and 5 wt.%, dispersion decreased from 91% to 43%. At the same time, TOFs varied only insignificantly in a range between 0.21 1/s and 0.32 1/s. 

Supported (alumina, silica) Ru catalysts The Mossbauer data show that RuCl3 (l-3)H20 reacts chemically when supported onto alumina, but does not when impregnated on a silica support. The study further shows that a supported ruthenium catalyst converts quantitatively into RUO2 upon calcination, and that the reduction of a supported ruthenium catalyst converts all of the ruthenium into the metallic state... 

Other metals on silica supports have been investigated less extensively than platinum and nickel, and average particle diameters have only been estimated by gas adsorption methods, supported in a few cases by X-ray line broadening data. Thus, rhodium, iridium, osmium, and ruthenium (44, 45) and palladium (46) have all been prepared with average metal particle diameters <40 A or so, after hydrogen reduction at 400°-500°C. 

The ruthenium complex of NH-benzyH 17T2,S )-norephedrine covalently tethered to silica showed a high activity and enantioselectivity in the reduction of acetophenone.310... 

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