Rhodium catalysts preparation

Routinely used X-ray sources are Mg Ka (1253.6 eV) and A1 Ka (1486.3 eV). In XPS one measures the intensity of photoelectrons N(E) as a function of their kinetic energy. The XPS spectrum, however, is usually a plot of N(E) versus Ek, or, more often, versus the binding energy Eb. Figure 3.3 shows the XPS spectrum of an alumina-supported rhodium catalyst, prepared by impregnating the support with... 

The other three studies in the literature also deal with the asymmetric hydroformylation of styrene and all three applied water soluble rhodium -phosphine catalysts (Scheme 4.9). BINAS (44), sulfonated BIPHLOPHOS (43), tetrasulfonated (R,R)-cyclobutane-DIOP (37, m=0) and tetrasulfonated (S,S)-BDPP (36, m=0) were applied as ligands of the rhodium catalyst prepared in situ from [Rh(acac)(CO)2] or [ Rh( Li-OMe)(COD) 2] and the phosphines. The results are summarized in Table 4.4. 

Table 4J. Faraday magnetic balance study of the redox behaviour of two ccria-supported rhodium catalysts prepared from Rh(NO))j (N) and RhCi> (Cl) metal precursors. Metal loading and BET surface area of the catalysts were 3 wt% and 49 m g respectively. Data taken from(i95).

Table 4.8. Evolution of average diameter (dm) and dispersion (D) with reduction temperature of rhodium catalysts prepared from nitrate (N) and chloride (Cl) precursors.

Trisubstituted acrylic acids, such as alkene (2.52), where the carboxylic acid is believed to bind to the amino groups of the ligand (2.54), also undergo enantioselective rhodium-catalysed hydrogenation. a-Methyldimamic acid is reduced with 99% ee using the rhodium catalyst prepared from a 2 1 mixture of PipPhos (2.16c) andtriphenylphosphine. ... 

Grubbs and coworkers (35) while examining Rh and Co catalysts derived from 14 reported the loss of infrared CO stretches and visual darkening of the catalysts after use for hydrogenation of olefins, aldehydes or ketones, cyclohexene disproportionation to benzene and cyclohexane or the cyclotrimerization of a wide variety of acetylenes. Stille (36) using a rhodium catalyst prepared from 14 observed activity for the hydrogenation of benzene that increased with reuse, a phenomenon usually associated with metal crystallite formation. Rhodium catalysts of 15 and 16 used to hydroformylate octene-1 revealed a loss of carbonyl adsorptions and a loss in catalytic activity upon reuse (37). 

As mentioned earlier, a number of iridium compounds have been shown to be effeetive catafysts for the methanol earbonylation reaction [11,13]. Nickel catalysts have also been found to be effective, partieularfy when used with compounds of Sn, Cr, Mo, or W [10c,15]. Heterogenized rhodium catalysts, prepared by supporting rhodium eompounds on a solid or by anehoring a rhodium eomplex to a polymer matrix, are also catalysts. However, none of these have been commercialized. In the latter case, the slow dissolution of rhodium is a major problem. 

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