Ru systems

Equilibrium vapor pressures were measured in this study by means of a mass spectrometer/target collection apparatus. Analysis of the temperature dependence of the pressure of each intermetallic yielded heats and entropies of sublimation. Combination of these measured values with corresponding parameters for sublimation of elemental Pu enabled calculation of thermodynamic properties of formation of each condensed phase. Previ ly reported results on the subornation of the PuRu phase and the Pu-Pt and Pu-Ru systems are correlated with current research on the PuOs and Pulr compounds. Thermodynamic properties determined for these Pu-intermetallics are compared to analogous parameters of other actinide compounds in order to establish bonding trends and to test theoretical predictions. 

In addition to the W and Mo carbonyl complexes that have most commonly been used for the cycloisomerization of alkynols, an Rh-based catalyst system has recently been developed which uses substantially lower catalyst loadings (1.5-2.5 mol%) than have typically been required for the W and Mo systems (10-50 mol%).369 Among the various ligands studied, P(/>-F-C6H4)3 proved to be particularly effective. Interestingly, this ligand has also been found to be optimal for an Ru system that catalyzes the same type of cycloisomerization (Equation (104)).370,371... 

In the Cu/Ru system, ruthenium may function as a reservoir for atomic hydrogen, which is accessible via spillover to neighboring copper. Kinetically controlled spillover of hydrogen from ruthenium to copper (5) is consistent with the observed optimum reaction rate at an intermediate copper coverage. 

The transformation of RhCl(PH3)2(HC=CH) to RhCl(PH3)2(C=CH2) has been calculated (MP2) to be exothermic by 7.8 kcal.mol"1. The intraligand 1,2-hydrogen shift mechanism found in the Ru11 system is not relevant to the present rhodium case. Starting from a T 2 C=C complex, both systems give a metal-( T]2 C-H) species in a subsequent step. In the case of the d6 Ru system this ri2 C-H complex is an intermediate. In contrast, the T 2 C-H coordinated state is a transition state in the d8 Rh1 system, the oxidative addition being a very facile process. 

The rate enhancement observed for submonolayer Cu deposits may relate to an enhanced activity of the strained Cu film for this reaction due to its altered geometric and electronic properties. Alternatively, amechansim whereby the two metals cooperatively catalyze different steps of the reaction may account for the activity promotion. For example, dissociative Hj adsorption on bulk Cu is unfavorable due to an activation barrier of approximately 5 kcal/mol . In the combined Cu/Ru system, Ru may function as an atomic hydrogen source/sink via spillover to/from neighboring Cu. A kinetically controlled spillover of Hj from Ru to Cu, discuss above, is consistent with an observed optimum reaction rate at an intermediate Cu coverage. 

The use of carbonyl complexes has enabled proper study of the role of rhenium in Pt-Re bimetallic catalysts used in the reforming of naphtha [57-60] and tailoring of the preparation of Pt-Ru bimetallic particles. Pt-Ru systems are of interest in developing electrodes for fuel cell applications [61]. 

The predominance of the ruthenium iodocarbonyl over the cobalt carbonyl species in the bimetallic Co-Ru systems is evidenced by the I.R. spectra of the catalytic solutions of the methyl acetate homologation with cobalt and ruthenium catalysts used in about the same concentration or with an excess of ruthenium. The latter compositions actually show the highest activity for the homologation... 

Blum J.D., Wasserburg G.J., Hutcheon i.D., Beckett J.R., and Stolper E.M. (1989) Diffusion, phase equilibria and partitioning experiments in the Ni-Fe-Ru system. Geochim. Cos-mochim. Acta 53, 483-489. 

In bimetallic catalysts, Cu-Ru is an important system. Combinations of the Group Ib metal (Cu) and Group VIII metal (Ru)-based catalysts are, for example, used for the dehydrogenation of cyclohexane to aromatic compounds and in ethane hydrogenolysis involving the rupture of C-C bonds and the formation of C-H bonds (Sinfelt 1985). Here we elucidate the structural characteristics of supported model Cu-Ru systems by EM methods, including in situ ETEM. 

Vickerman and Ertl (1983) have studied H2 and CO chemisorption on model Cu-on-Ru systems, where the Cu is deposited on single-crystal (0001) Ru, monitoring the process using LEED/Auger methods. However, the applicability of these studies carried out on idealized systems to real catalyst systems has not been established. Significant variations in the electronic structure near the Eermi level of Cu are thought to occur when the Cu monolayer is deposited on Ru. This implies electron transfer from Ru to Cu. Chemical thermodynamics can be used to predict the nature of surface segregation in real bimetallic catalyst systems. 

Despite numerous screening studies, the literature contains little evidence that homogeneous catalyst systems based on metals other than Co, Rh, or Ru have significant activity for catalytic CO reduction. As seen for the known active catalytic systems, however, properties of solvents and additives or promoters can have enormous effects on catalytic activities. Solvents and additives can serve many roles in these catalytic systems. One important function of promoters in the Rh and Ru systems appears to be that of stabilizing metal oxidation states involved in catalytic chemistry. Other... 

A diruthenium bisporphyrin, Ru2(DBP)(l-tBu-5-PhIm)2, which does not carry an axial ligand within the diporphyrin site, directly binds dihydrogen in benzene to form a bimetallic bridging dihydrogen complex, Ru2(H2XDBP)-(l-tBu-5-PhIm)2 [231], From NMR spectra it is deduced that there is a linear array of the Ru-H-H-Ru system in this compound. 

For the Ru system the thiol hydride could not be detected, while for the Rh system and also [IrH2(HS(CH2)3SH)(PCy3)2]+(which similarly catalyzes D2/H + exchange (79)), the H2 complex could not be seen but is a transient. A related system, Ni(NHP Pr3)(S3) clearly shows that heterolysis of D2 can also occur at nickel sites, which may be relevant to H2 activation in [FeNi] hydrogenases (78). 

The effects of pressure, temperature, and tertiary amine in the Ru system are similar to those observed in the Rh catalyst systems. These effects are illustrated in tables 3 and 4. 

DMF)Ru(0EP)02 (8, 135) can be formed from molecular 02, while Ti(0EP)02 (136) and Mo(TPP)(02)2 (137) can be made from peroxide addition [TPP = tetraphenylporphyrin, OEP = octaethylporphyrin]. The Ru system is ineffective for oxidation of terminal olefins at least under the mild conditions (1 atm 02, 35°C) studied thus far even the ubiquitous substrate triphenylphosphine is not oxidized catalytically because of formation of a relatively inert Ru(OEP)(PPh3)2 complex (138). The catalytic potential for 02 activation by Ru(II) porphyrins compared with Fe(II) porphyrins seems considerable, at least in principle, in view of a more readily accessible oxidation state of IV (139) this could circumvent the unfavorable one-electron reduction of 02 to superoxide (140). Such systems seem promising generally in terms of the multi-electron redox processes that 02 displays (141). 

One of the drawbacks of DMFCs is the relatively slow rate of the anodic oxidation of methanol even on highly active platinum electrodes. It was shown that the Pt-Ru system is much more catalytically active than pure platinum (pure ruthenium is inert towards this reaction) (-> platinum-ruthenium -> electrocatalysis). The so-called bifunctional mechanism is broadly accepted to describe this synergistic effect, according to which organic species are chemisorbed predominantly on platinum centers while ruthenium centers more readily adsorb species OH, required for the oxidation of the organic intermediates. Usually the composition of such alloys is Pto.sRuo.s and the metal loading is 2-4 mg cm-2. 

Ruthenium-catalyzed allylic alkylation falls between known catalysis with respect to regioselectivity and chirality of products. Like Pd, Mo, and W-but unlike Rh regioselectivity is not highly dependent on the nature of the starting carbonate. However, unlike Pd and Mo, but similar to Rh and W, substitution of the chiral substrate occurs with high retention of configuration, (equation 75). Hence the Ru system compliments other metal-catalyzed allylic systems well. ... 

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