Rhodium-alumina catalysts reactions over

Product Distributions from the Reaction of PropyUne with Deuterium over Rhodium-Alumina Catalysts (61)... 

The dehydrocyclization activity of rhodium-alumina is lower than that of platinum-alumina. Hydrogenolysis predominates over all the other reactions with this catalyst (57). The effect of temperature on the anthracene/phenanthrene ratio in the product from 2- -butylnaphthalene is the same over iridium-alumina catalyst as that observed over platinum-alumina more phenanthrene and less anthracene are formed at high temperatures (58). 

Reduction of benzene derivatives carrying oxygen or nitrogen functions in ben-zylic positions is complicated by the easy hydrogenolysis of such groups, particularly over palladium catalysts. Preferential reduction of the benzene ring in these compounds is best achieved with ruthenium or rhodium catalysts, which can be used under mild conditions. For example, mandelic acid is readily converted into the cyclohexyl derivative 29 over rhodium-alumina, whereas with palladium, hydrogenolysis to phenylacetic acid is the main reaction (7.18)... 

The intramolecular Buchner reaction of aryl diazoketones has been carried out using both copper(I) and rhodium(II) catalysts. For example, 1-diazo-4-phenylbutan-2-one 27a cyclizes in bromobenzene with copper(I) chloride catalysis, furnishing 3,4-dihydroazulen-l(2//)-one 30 in 50% yield after purification by chromatography over alumina. Trienone 30 is not the primary cyclization product, and the less conjugated isomeric trienone 29a is first produced, but contact with alumina causes isomerization to 30. The yield of this cyclization is further improved when rhodium(II) acetate is used as the catalyst instead of copper(I) chloride. Thus a catalytic amount of rhodium(II) acetate brings about the nearly quantitative conversion of 27a to 29a within minutes in hot dichloromethane. Compound 29a isomerizes to 30 on treatment with triethylamine, and rearranges to 2-tetralone 31a when exposed to silica gel or acid. 

Wanat et al. investigated methanol partial oxidation over various rhodium containing catalysts on ceramic monoliths, namely rhodium/alumina, rhodium/ceria, rhodium/ruthenium and rhodium/cobalt catalysts [195]. The rhodium/ceria sample performed best. Full methanol conversion was achieved at reaction temperatures exceeding 550 °C and with O/C ratios of from 0.66 to 1.0. Owing to the high reaction temperature, carbon monoxide selectivity was high, exceeding 70%. No by-products were observed except for methane. 

Pyrrole can be reduced catalyticaHy to pyrroHdine over a variety of metal catalysts, ie, Pt, Pd, Rh, and Ni. Of these, rhodium on alumina is one of the most active. Less active reducing agents have been used to produce the intermediate 3-pyrroline (36). The 2-pyrrolines are ordinarily obtained by ring-closure reactions. Nonaromatic pyrrolines can be reduced easily with to pyrroHdines. 

Oh, S.H. (1990) Effects of cerium addition on the CO-NO reaction kinetics over alumina-supported rhodium catalysts, J. Catal. 124, 477. 

Gasolines contain a small amount of sulfur which is emitted with the exhaust gas mainly as sulfur dioxide. On passing through the catalyst, the sulfur dioxide in exhaust gas is partially converted to sulfur trioxide which may react with the water vapor to form sulfuric acid (1,2) or with the support oxide to form aluminum sulfate and cerium sulfate (3-6). However, sulfur storage can also occur by the direct interaction of SO2 with both alumina and ceria (4,7). Studies of the oxidation of SO2 over supported noble metal catalysts indicate that Pt catalytically oxidizes more SO2 to SO3 than Rh (8,9) and that this reaction diminishes with increasing Rh content for Pt-Rh catalysts (10). Moreover, it was shown that heating platinum and rhodium catalysts in a SO2 and O2 mixture produces sulfate on the metals (11). 

Hydrogenations of acetylpyridines were carried out similarly, and yielded various products depending on the reaction conditions and especially on the catalyst used. Thus 4-acetylpyridine was hydrogenated over palladium oxide to form the corresponding alcohol, 4-(l-hydroxyethyl)pyridine, with a small amount of the pinacol (4), but it was converted mainly to the pinacol using palladium on charcoal or rhodium on alumina. However, under different conditions, the pyridyl ring of 3-acetylpyridine was reduced to a mixture of 3-acetyl-l, 4,5,6-tetrahydropyridine and 3-acetylpiperidine. 

Al-Ammar AS, Webb G (1978) Hydrogenation of acetylene over supported metal catalysts Part 1 - Adsorption of [ C] Acetylene and [ C] ethylene on silica supported rhodium, iridium and palladium and alumina supported palladium. J Chem Soc Earaday Trans 74 195 Al-Ammar AS, Webb G (1979) Hydrogenation of acetylene over supported metal catalysts Part 3 - [ C] tracer studies of the effect of added ethylene and carbon monoxide on the reaction catalyzed by silica-supported palladium, rhodium and iridium. J Chem Soc Faraday Trans 75 1900... 

Hydrogenation of carbocyclic aromatic compounds requires only mild conditions over Rh catalysts. Rhodium is an outstandingly active catalyst for reduction of benzene. Catalyst efficiency is influenced by trace materials that act as inhibitors or promoters. Hydrogen halides are strong inhibitor for reductions in MeOH over Rh-on-carbon or on alumina. Small amounts of acetic acid promote reduction of aromatics over Rh-on-alumina. In a clean medium, 5% Rh-on-carbon or Rh-on-alumina in MeOH reduces alkyl benzenes at room temperature, under 500 kPa . Reaction is facilitated at higher T or by adding glacial acetic acid. 

Primary amine formation is equally well promoted in alkaline medium, e.g., aqueous ethanolic NaOH solution, that selectively poisons the catalyst for hydrogenolysis reactions. However, saturated NH3/alcohol solutions best afford almost quantitative yields of primary amines from catalytic reduction of nitriles. Ammonia adds to imine 1 to give a 1,1-diamine, which is hydrogenolyzed to the primary amine. In the presence of NHj, finely divided Ni can be used, platinized finely divided Ni for the hydrogenation of hindered nitriles, and rhodium-on-alumina for sensitive compounds. Mild reduction of 3-indoleacetonitrile to tryptamine [equation (c)] is effected at RT over 5% rhodium-on-alumina in 10% ethanolic NH3 with little side reaction , and branched chain amino sugars are conveniently prepared using this selective hydrogenation [equation (d)] . 

Catalytic reductions have been carried out under an extremely wide range of reaction conditions. Temperatures of 20 C to over 300 C have been described. Pressures from atmospheric to several thousand pounds have been used. Catal3rsts have included nickel, copper, cobalt, chromium, iron, tin, silver, platinum, palladium, rhodium, molybdenum, tungsten, titanium and many others. They have been used as free metals, in finely divided form for enhanced activity, or as compounds (such as oxides or sulfides). Catalysts have been used singly and in combination, also on carriers, such as alumina, magnesia, carbon, silica, pumice, clays, earths, barium sulfate, etc., or in unsupported form. Reactions have been carried out with organic solvents, without solvents, and in water dispersion. Finally, various additives, such as sodium acetate, sodium hydroxide, sulfuric acid, ammonia, carbon monoxide, and others, have been used for special purposes. It is obvious that conditions must be varied from case to case to obtain optimum economics, yield, and quality. 

Ethanol steam reforming catalysts were developed by Men et al. [24]. Nickel, rhodium and ruthenium catalysts on different carrier materials such as alumina, silica, magnesia and zinc oxide were tested at a S/C ratio of 1.5 and WHSV 90 Lh g J in the temperature range 400-600 °C. All the monometallic catalysts were mainly selective for acetaldehyde and ethylene. Over the rhodium catalyst, a reaction temperature of 600 °C was required to achieve 80% hydrogen selectivity. 

Specchia et al. performed partial oxidation of methane over rhodium/a-alumina fixed catalyst beds for short contact times over a time range of between 10 and 40 ms [64]. With increasing catalyst particle sizes, conversion decreased, which was attributed to transport limitations. Fligher reactor temperature was observed for larger particles and thus more exothermic reactions took place. When increasing the particle size and the weight hourly space velocity (see Section 4.1), the water content in the product increased, while less carbon monoxide was found and carbon dioxide remained at an unchanged low concentration. Similar to the results of Lyubovski discussed above, steam seemed to be a primary product of the reaction. 

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