Of rhodium metal

The concept of continuous flow SILP hydroformylation was also tested in the biphasic, liquid-liquid hydroformylation of 1-octene using the Rh-norbos catalyst system [78], TOFs of 44 h"1 were achieved after 3-4 h with no sign of deactivation at prolonged reaction times. At steady-state conditions an n/iso ratio of 2.6 was obtained. No leaching of rhodium metal could be detected by ICP-AES analysis of product samples at least after these short reaction times. 

There is much current excitement and activity in the field of homogeneous hydrogenation using ruthenium catalysts. This is reflected in the recent, explosive increase in the number of research publications in this area, now rivaling those for rhodium catalysts (Fig. 3.1). Meanwhile, the price of rhodium metal has risen dramatically, becoming about ten times that of ruthenium, on a molar basis. The number of reports on the use of osmium catalysts has remained low, partly because of the higher price of osmium compounds - about ten times that of ruthenium - and partly because the activity of osmium catalysts is often lower. 

Figure 6.14 EXAFS and Fourier transform of rhodium metal, showing a) the measured EXAFS spectrum, b) the uncorrected Fourier Transform according to equation (6-10), c) the first Rh-Rh shell contribution being the inverse of the main peak in the Fourier Transform, and d) the phase- and amplitude-corrected Fourier Transform according to (6-11). The Fourier transform is a complex function, and hence the transforms give the magnitude of the transform (the positive and the negative curve are equivalent) as well as the imaginary part, which oscillates between the magnitude curves (from Martens (361).

The powder and dust of rhodium metal are flammable in air. Some of the compounds may cause skin irritations. It is best to use approved laboratory procedures when handling any of the six elements in the platinum family of metals. 

When the hydrogenation of citral is performed with supported nanoparticles of rhodium metal, for example Rh/Si02 under classical conditions [liquid phase, rhodium dispersion 80% (particles in the range of 1-2nm), citral/Rhs = 200, P(ti2) = 80bar, T = 340 K], the catalytic activity is very high but most of the above products are obtained and the reaction is totally non-selective, even if the major product was citronellal. 

Elemental composition (Rh203) Rh 81.09%, 0 18.91%. The oxide may be solubilized by treatment with alkali to form hydrated oxide, which may be dissolved in acid and diluted for analysis of rhodium metal by AA or ICP. The oxide may be characterized by x-ray diffraction, physical properties, and reaction with strong alkali to form yellow precipitate of pentahydrate, and in excess alkali a black precipitate of the trihydrate. 

Fig. 10.17. EXAFS and Fourier transforms of rhodium metal (a) measured EXAFS spectrum, (b) the uncorrected Fourier transform, (c) the inverse Fourier transform of the main contribution in (b), and (d) the phase and amplitude corrected Fourier transform [38],...

Logan AD, Sharoudi KS, Datye AK (1991) Oxidative restructuring of rhodium metal surfaces Correlations between single crystals and small metal particles. J Phys Chem 95 5568... 

The efficiency of the rhodium recycling system using the new amphiphilic ligands was determined by re-use of the catalyst solution in a second hydroformylation run and by determination of the absolute amount of rhodium (metal) recovered using ICP-AES. 

Complex hydrides of rhodium, Li4RhH4, and Li4RhH6 have been described (75). They were prepared by treatment of rhodium metal powder with lithium hydride at 600°C. The presence of transition metal-hydrogen bonds in either the latter complexes or those of Weichselfelder has yet to be unequivocally shown. Recent studies using a time-of-flight mass spectrometer have identified TiH4 and chlorohydride derivatives (29). 

ACUTE HEALTH RISKS possible respiratory sensitization, (note no toxic effects of rhodium metal fume and insoluble compounds have been reported in experimental animals or in man). 

For all reactions studied, the activity of the supported catalysts was higher than for the similar biphasic ionic liquid system, which was ascribed to improved mass transfer between the substrates and the ionic liquid phase. In addition, the observed product selectivities of 64-87% and enantioselectivity of 97% for the SILP-Ru-(S)-BINAP catalyzed reaction equalled those of the homogeneous reference reactions. No indication of rhodium metal leeching was found by AAS analysis of the reaction filtrate. 

Metal and Metal Oxide Catalysts. Only a few examples are known on application of metal and metal oxide catalysts for carbonylation reaction. For example, it has been reported that benzyl alcohol could be carbonylated with CO to phenylacetic acid (with 100% selectivity) in the presence of rhodium metal Rh(0) (72). Methyl formate was prepared by treatment of CH3OH with CO in the presence of alkali earth metal oxide catalysts. The oxide catalysts are preferably CaO catalysts supported on oxides of group Ila (except Ca), Ilb, Ilia, or IVa metals. CH3OH was autoclaved with CaO/ZnO under 50 atm of CO at 180°C for 2 h to give 9.7% of methyl formate at 99.9% selectivity (73). 

An interesting reaction is the oxidation of CO to CO2 and the reduction of NO to N2 in automotive exhaust gases as a smog-control measure. Figure 20-18 shows how this reaction is thought to occur on the surface of rhodium metal in a catalytic converter. In general, the reaction profile for a surface-catalyzed reaction resembles that shown in Figure 20-19. 

The degradation of phosphine also influences the performance of the catalyst. The degradation of TPPTS is initiated by the oxidative insertion of rhodium metal into the P-C bond, as shown in Scheme 14.3. Further reaction of 6 due to the oxidative insertion of rhodium metal may generate m-0HCCgH4S03Na (7) or C3H7P(m-CgH4S03Na)2 (8), which was confirmed via the separation of products and catalysts in the RCH/RP process [19, 20]. The appearance of 7 evidenced that metal rhodium indeed got inserted into the P-C bond, and the appearance of 8 indicated that the... 

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