Iron-platinum cluster

Iron-only hydrogenase, dithiolate-bridged compounds as biomimetic models, 6, 239 Iron oxide films, synthesis, 12, 51 Iron-palladium nanoparticles, preparation, 12, 74 Iron-platinum bimetallic clusters, with isocyanide clustes,... 

Iron-platinum carbonyl clusters, characteristics, 8, 415 Iron reagents, in Kumada-Tamao-Corriu reaction, 11, 21 Iron-rhodium clusters, as heterogeneous catalyst precursors,... 

Clusters of vanadium, chromium, nickel, ° iron, platinum, pal-... 

Platinum-iron on alumina catalysts were characterized by Mbssbauer spectroscopy (Section 4) and their activity tested. Iron in clusters with high Pt Fe ratios, about 5, and fully combined with platinum, was catalytically inert for the CO-H2 synthesis reaction, attributed to a decrease in the electron density of the iron as indicated by the Mbssbauer isomer shift. The direction of electron transfer was opposite to that proposed for alkali-metal promoted iron catalysts. At low Pt Fe ratio, 0.1, ferromagnetic iron as well as Fe " ions and PtFe clusters were produced and dominated the activity/selectivity pattern. Rhodium on silica catalysts produced C2-compounds containing oxygen, specifically acetic acid, acetaldehyde and ethanol, with methane as the other major product. The addition of iron moved the C2-product formation sharply in favour of ethanol and now methanol was also formed. ... 

The evidence for association of the iron atoms with platinum in samples similar to B has been discussed elsewhere in some detail (55). Incorporation of iron atoms into the platinum clusters is indicated by the agreement of the isomer shift for iron in the catalyst with that for iron in a PtFe bulk alloy of similar composition. In addition, it is found that the iron in samples such as B, after reduction at 500°C, exhibits a unique chemical behavior in that it can be reversibly oxidized and reduced at room temperature. This property appears to be characteristic of iron in association with metals such as platinum and palladium (54-57). It is not observed when the iron is present by itself on alumina. 

Sample B-600 gives a spectrum similar to that of sample B in Figure 4.32, and the Mossbauer parameters for these samples in Table 4.2 are also similar. These results indicate that sample B-600 also consists of platinum clusters with iron atoms incorporated therein. 

The spectrum of sample D-600 resembles that of sample B in Figure 4.32 more closely than it resembles the spectrum of sample D. The Mossbauer parameters in Table 4.2, especially the ratios A 2M, and W2IWU show substantial differences between samples D and D-600. The iridium in sample D-600 is largely present in the same poorly dispersed form as the iridium in sample C-600, as has been found from X-ray diffraction studies of similar samples. Sample D-600 therefore can be characterized approximately as consisting of highly dispersed platinum clusters incorporating iron atoms and separate iridium crystallites of much lower dispersion that are not significantly associated with iron atoms. This characterization is consistent with chemisorption data (41). 

The data indicate that platinum clusters associated with iron are altered by addition of iridium to the sample. We conclude that the added iridium is incorporated in the platinum clusters to give Ptlr clusters containing the iron probe atoms. If the added iridium was present as separate iridium clusters... 

Colloidal metal clusters, which offer a high surface area for better activity, have been stabilized by polymers. Thus, a homogeneous dispersion of a cobalt-modified platinum cluster was stabilized by a coordinating polymer, poly(/V-vinyl-2-pyrrolidone).74 Addition of the cobalt(II) [or iron(III)] doubled the activity and increased the selectivity from 12 to 99% when the catalyst was used to reduce cin-namaldehyde (5.23). 

A number of iron-platinum bimetallic clusters with isocyanide ligands have been studied those, such as 129, bridged by a dppm ligand have proved to be versatile (Scheme 30). " Both charged, 129, and uncharged, 130, complexes are possible, depending on the reaction route taken Fe-Pt bond lengths are typically 2.80 A. 

This Study has shown that reasonably uniform platinum crystallites can be made on y-alumlna, and that platinum and palladium can be segregated and maintained In that form for the most part even after exposure to high temperature oxidation-reduction conditions. Highly dispersed clusters of palladium, nickel, cobalt, and Iron can be observed. Cluster size determination could not be accurately made because of the lack of contrast between the cluster and the support. The marginal detectability by EDS for these clusters enabled elemental Identification to be made, however, mass uniformity determinations could not be made. 

Heteronuclear Clusters Containing Platinum and the Metals of the Iron, Cobalt, and Nickel Triads... 

Dimercaptobenzene, with trinuclear Os clusters, 6, 745 Dimeric bis(alkyl) complexes, with iron, 6, 79 Dimesityl complexes, with platinum(III), 8, 568... 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

Ketenyl complexes, in Ru-Os mixed-metal clusters, 6, 1080 Ketenylidenes, in iron cluster compounds, 6, 301 Ketenylidenetriphenylphosphoranes, with platinum, 8, 632 Ketimines... 

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