Iridium supported catalyst

Dehydrocyclization, 30 35-43, 31 23 see also Cyclization acyclic alkanes, 30 3 7C-adsorbed olefins, 30 35-36, 38-39 of alkylaromatics, see specific compounds alkyl-substituted benzenes, 30 65 carbene-alkyl insertion mechanism, 30 37 carbon complexes, 32 179-182 catalytic, 26 384 C—C bond formation, 30 210 Q mechanism, 29 279-283 comparison of rates, 28 300-306 dehydrogenation, 30 35-36 of hexanes over platintim films, 23 43-46 hydrogenolysis and, 23 103 -hydrogenolysis mechanism, 25 150-158 iridium supported catalyst, 30 42 mechanisms, 30 38-39, 42-43 metal-catalyzed, 28 293-319 n-hexane, 29 284, 286 palladium, 30 36 pathways, 30 40 platinum, 30 40 rate, 30 36-37, 39... 

Effect of Sulfur on the Hydrogen Adsorption Capacity and the Hydrogen Binding Energy of Platinum- and Iridium-Supported Catalysts... 

Rapoport s findings have been confirmed in the authors laboratory where the actions of carbon-supported catalysts (5% metal) derived from ruthenium, rhodium, palladium, osmium, iridium, and platinum, on pyridine, have been examined. At atmospheric pressure, at the boiling point of pyridine, and at a pyridine-to-catalyst ratio of 8 1, only palladium was active in bringing about the formation of 2,2 -bipyridine. It w as also found that different preparations of palladium-on-carbon varied widely in efficiency (yield 0.05-0.39 gm of 2,2 -bipyridine per gram of catalyst), but the factors responsible for this variation are not knowm. Palladium-on-alumina was found to be inferior to the carbon-supported preparations and gave only traces of bipyridine,... 

Rhodium-on-carbon has also been found to bring about the formation of 2,2 -biquinoline from quinoline, the yield and the percentage conversion being similar to that obtained with palladium-on-carbon. On the other hand, rhodium-on-carbon failed to produce 2,2 -bipyridine from pyridine, and it has not yet been tried with other bases. Experiments with carbon-supported catalysts prepared from ruthenium, osmium, iridium, and platinum have shown that none of these metals is capable of bringing about the formation of 2,2 -biquinoline from quinoline under the conditions used with palladium and rhodium. ... 

The catalyst powders were compressed to thin disks under a pressure of about 50 kg/cm2, with the exception of the alumina-supported catalysts which required a pressure of 1500 kg/cm2 to obtain reasonable transmittance. The samples were reduced in a stream of hydrogen supplied at a rate of 10 1 hr-1 (SV 30,000 hr-1). The temperatures of reduction were 350°-450°C for the nickel samples, 475°C for the palladium samples, and 425°C for the iridium catalysts. 

Abstract 1,3-Dipolar cycloaddition reactions (DCR) are atom-economic processes that permit the construction of heterocycles. Their enantioselective versions allow for the creation of up to four adjacent chiral centers in a concerted fashion. In particular, well-defined half-sandwich iridium (111) catalysts have been applied to the DCR between enals or methacrylonitrile with nitrones. Excellent yield and stereoselectivities have been achieved. Support for mechanistic proposals stems from the isolation and characterization of the tme catalysts. 

Panjabi, G., Argo, A. M., and Gates, B. C., Supported iridium cluster catalysts for propene hydrogenation Identification by X-ray absorption spectra measured during catalysis. Chem. Eur. J. 5,2417 (1999). 

Catalytic activities of the zeolite-supported clusters (Table 4) are reported as turnover frequencies these are rates per total iridium atom for such small clusters. Rates were also reported for conventional (structurally nonuniform) supported catalysts consisting of aggregates of metallic iridium on supports, these rates, per unit of metal surface area, are markedly greater than those observed for the supported clusters [15]. Changing the support from zeolite NaY to MgO had little effect on the activities of the decarbonylated clusters. 

On the other hand, the selective dehydrocyclization, which does not allow the formation of secondary-primary C-C bonds, must involve only two methylic carbon atoms in the 1 and 5 positions. Although the reverse reaction (selective hydrogenolysis of methylcyclopentane) could be observed on platinum catalysts of low dispersion at 220°C (86), the selective dehydrocyclization of methylpentanes on these catalysts is detectable only at higher temperatures (280°-300°C), where it competes with another process, ascribed to Mechanism C (33). Fortunately, it was found recently that iridium supported on AI2O3 or SiOj selectively catalyzes at 150°C the cyclic type interconversion of 2-methyl- and 3-methylpentanes (88). n-Hexane under the same conditions yields only cracked products (702) (Scheme 52). Similarly,... 

There have been multiple efforts toward supported catalysts for asymmetric transfer hydrogenation, and the 4 position on the aryl sulfonate group of 26 has proven a convenient site for functionalization. Thus far, this ligand has been supported on dendrimers [181,182], polystyrenes [183], silica gel [184], mesoporous siliceous foam [185], and mesoporous siliceous foam modified with magnetic particles [186]. The resulting modified ligands have been used in combination with ruthenium, rhodium, and iridium to catalyze the asymmetric transfer of imines and, more commonly, ketones. 

Iridium was supported on different types of metal oxides by deposition precipitation (DP) and liquid phase grafting (LG) methods and was examined for the oxidation of CO and Hz. From these experiments, it was found that iridium supported on TiOz prepared by DP was much more active for CO oxidation than Ir/AIzOj and Ir/FezOy, and furthermore was active below room temperature. TEM observations showed that Ir was spread over the TiOz surface as a thin layer of 2 nm thickness, the structure of which was completely different from those of other noble metal catalysts. 

Figure A3.10.22 Relationship between selectivity and surface structure for w-butane hydrogenolysis on iridium, (a) Illustrations of the Ir(l 10)-(1 x 2) and Ir(l 11) surfaces. The z-axis is perpendicular to the plane of the surface, (b) Selectivity for 2 production (mol% total products) for w-butane hydrogenolysis on both Ni single crystals and supported catalysts at 475 K. The effective particle size for the single crystal surfaces is based on the specified geometric shapes [43]. A Ir/Al203 Ir/Si02-...

Results, using cluster complexes of nickel or iridium, support the proposal that hydrogenation of triple-bonded substrates can be more readily achieved by the use of polynuclear homogeneous catalysts than by use of mononuclear catalysts.The requirement for multinuclear centers to heterogeneously catalyze the hydrogenation of CO has also been proposed. Consequently, complexes of transition metals in which the metal atoms are constrained to be proximate are potentially of interest as catalysts. 

Itsimo [25] has also shown that polymer-supported OPEN monosulfonamides containing sulfonated pendent group (Scheme 16) are able to catalyze the HTR reduction of ketones in water with sodium formiate as hydrogen donor (S/C = 100). However, TsDPEN immobilized on polystyrene crosslinked or not, polymer 30 and 31 respectively, shrank in water. Sodium /j-styrene sulfonate was copolymerized with chiral A-(vinylbenzene-p-sulfonyl)-DPEN (20) imder radical polymerization conditions with or without DVB leading respectively to ligand 32 and 33. Control of the balance hydrophilicity/hydrophobieity of the polymer support is carried out by changing the salt from Na to quaternary ammonium. All of these polymers swelled in water, and their respective ruthenium, rhodium or iridium complexes were prepared. Compared to sodium salt polymer-supported catalyst from 32a and 33a, ammonium... 

To understand the role of the y-alumina support, two experiments were carried out (i) variation ofthe molar ratio ofIr/Re and (ii) the direct addition ofy-alumina to the system. Increasing the molar amount of the Re20y catalyst (molar ratio of 1 1.8) led to a better activity. An additional amount of y-alumina provided better productivity, but parallel studies on either Ir-2(H2) or supported Ir-17(C2H4) with the olefin metathesis catalyst Mo-1 in the presence of y-alumina were found to be detrimental to the reaction selectivity [143]. All of these results strongly support that the adsorption of iridium pincer catalysts on y-alumina could prevent the... 

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