Trimetallic systems

Significant (and even spectacular) results were contributed by the group of Norskov to the field of electrocatalysis [102-105]. Theoretical calculations led to the design of novel nanoparticulate anode catalysts for proton exchange membrane fuel cells (PEMFC) which are composed of trimetallic systems where which PtRu is alloyed with a third, non-noble metal such as Co, Ni, or W. Remarkably, the activity trends observed experimentally when using Pt-, PtRu-, PtRuNi-, and PtRuCo electrocatalysts corresponded exactly with the theoretical predictions (cf. Figure 5(a) and (b)) [102]. 

Under certain symmetry conditions, Eq. (6.3) can be rearranged in order to allow for analytical solutions3. In trimetallic systems, when J 2 J13 = J23, Eq. (6.3) becomes [1]... 

The copper-nickel couple works well also in the heterodimetallic system based on molecule 15 [37]. Here, a 2, 2,-bipyridine fragment is covalently linked to the carbon backbone of a [Ni(II) (cyclam) ]2+ subunit. Two bpy fragments coordinate a Cu(II) center, giving rise to the trimetallic system 16... 

The bimetallic systems Ni-Pt/A O- have the same activity for CO --COj whatever the impregnation order is. The light-off is about 210°C at 40cm5.min 1. The 0,2% Pt/A Oj catalyst has a half conversion temperature of 195°C the trimetallic system Ce-Pt-Ni/Al O where cerium was the last deposited metal did not significantly improve the activity. The light-off was around 190°C. Furthermore, the Pt-Co where Co... 

Kirkendall Effect The Kirkendall effect is a phenomenon observed frequently in solid materials [38]. It refers to a vacancy counter diffusion process through an interface of two solid materials, metals in particular, to compensate the unequal material flow formation at the interface [38a]. In metals and metallic alloys, the vacancy is atomic defect, that is, empty lattice site. Combination of excess vacancies can lead to the formation of void within the fast-diffusion side of the interface [39]. While this phenomenon has been known for a very long time, synthesis of hollow nanostructures based on Kirkendall effect was realized fairly recently [40]. Ym studied the time evolution in the formation of hollow nanospheres and found that Kirkendall diffusion followed the Tick s law [41]. This means that the diffusion of atoms and vacancies is driven by the difference in atom concentration. Wu et al. synthesized hollow nanostructures of CoCuPt alloy catalyst by using Co nanoparticles as the sacrificial templates. For this trimetallic system, Co atoms diffused faster than those of Pt or Cu to form core-shell like Co CuPt hollow nanoparticles and then the CoCuPt hollow spheres (Fig. 2.10) [42]. 

Recently, Balzani et al. have investigated two tiimetallic systems using three 2,2 2"-terpyridine ligands linked together with -CH -CH - or -CH=CH-groups (Fig. 17) [59]. The -CHj-CHj- bridged system was found to behave almost Identically to [Ru(tpy)2] with no emission at room temperature and a lifetime of 9.4 ps at 77 K. The -CH=CH- bridged trimetallic system had a detectable... 

Trimetallic systems that contain Fe and two different coinage metals are accessible through two synthetic routes, as shown in Schemes 1 and Electronic structures of [Fe4M4(GO)i6] (M = Gu, Ag, Au) have been studied... 

Trimetallic catalysts try to combine the individual advantages in a single system. However, there are controversial positions on whether they are more cost-effective than the use of stacked-bed reactors. Several formulations are offered in the market CoNiMo, CoNiW, and NiMoW, so far they are seldom employed. 

The selective hydrogenation of organic compounds which contain a C=C and a C=0 double bonds into unsaturated alcohols is a very challenging subject from an industrial and from a fundamental point of view. Recent studies have shown that some catalytic systems are suitable for a selective hydrogenation in particular bi or trimetallic supported catalysts but no clear conclusion could be drawn concerning the mechanism and the respective effects of the support and the alloying (ref.1). 

The most common bridging mode of coordination is syn-syn (47). The nature of the metal-metal interactions in such systems has been the subject of much study, with interaction varying from the relatively weak in dimeric Cu complexes, to strongly M-M bonded species such as Mo2(02CR)4, which contains a formal quadruple bond. The two systems that have been most studied are the bimetallic (52) and trimetallic (53) complexes, often referred to as paddle-wheel and triangular complexes respectively. These structural motifs have been widely utilized in the constraction of coordination polymers and metal-organic frameworks. 

The reductive homocoupling of chlorobenzene to biphenyl is efficiently catalyzed by a recyclable, heterogeneous trimetallic catalyst in the presence of PEG 400 in H2O (Scheme 14.81) [164]. Bismuth is believed to trap the surplus hydrides and retard undesired side-reactions. A ternary metal redox system, BiCl3-Al-NiCl2(bpy), mediates the reductive coupling of /flirornoslyrene [165]. 

Although there are a comparatively large number of binuclear systems which contain a II —CO, a limited number of polynuclear species have been characterized. The only example of a trimetallic cluster with a n —CO is Cp3Nb3(CO)7 (182,183). Equation (30) gives the synthesis for this species,... 

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