Rhodium zeolites kinetics

Table 1.4.1 Kinetic parameters for the simultaneous hydroformylation and hydrogenation of propene over a rhodium zeolite catalyst at 7" = 423 K and 1 atm total pressure [from Rode et al., J. Catal., 96 (1985) 563].

Carbonylation of organic substrates was investigated using these well defined complexes. These carbonyl compounds exhibited catalytic properties in the carbonylation of organic substrates. In particular methanol carbonylation to methyl acetate in the gas phase was successfully attempted. Mechanistic and kinetic studies of this reaction over rhodium and iridium zeolites showed the similarities between the homogeneous and the zeolite mediated reactions. Aromatic ni-tro compounds were also converted to aromatic isocyanates using similar catalytic systems. The mechanistic aspect of this reaction will be also examined. 

The differences displayed by rhodium and iridium zeolites when interacting with the reaction partners are consistent with their different kinetic behaviour. These differences seem to be independent upon the nature of the medium (solution or zeolitic) and appear to be essentially relevant to the chemistry of rhodium and iridium. 

Pti-x ZXjc supported on carbon or alumina, Kt/Kb is proportional to x, suggesting electron transfer from platinum to zirconium, as predicted by the Engel-Brewer theory, and (2) chemisorption of sulfur on platinum has been shown to decrease electron density of the surface, while carbon has the opposite effect. The ratio Kt/Kb was very large for ruthenium, about 10 for rhodium and about unity for palladium, which may help to explain their different activities in these and other reactions. An extensive kinetic study of the hydrogenation of mixtures of benzene and toluene on NiA zeolite has however revealed a situation of some complexity, and it is not certain that the original simple concept is totally valid. 

Carbonylation and decarbonylation reactions of alkyl complexes in catalytic cycles have been reviewed . A full account of the carbonylation and homologation of formic and other carboxylic acid esters catalysed by Ru/CO/I systems at 200 C and 150-200 atm CO/H2 has appeared. In a novel reaction, cyclobutanones are converted to disiloxycyclopentenes with hydrosilane and CO in the presence of cobalt carbonyl (reaction 4) . The oxidative addition of Mel to [Rh(CO)2l2] in aprotic solvents (MeOH, CHCI3, THF, MeOAc), the rate determining step in carbonylation of methyl acetate and methyl halides, is promoted by iodides, such as Bu jN+I", and bases (eg 1-methylimidazole) . A further kinetic study of rhodium catalysed methanol carbonylation has appeared . The carbonylation of methanol by catalysts prepared by deposition of Rh complexes on silica alumina or zeolites is comparable with the homogeneous analogue . 

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