The relative importance of heterogeneous and homogeneous methanol carbonylation using supported rhodium catalysts in the liquid phase

Carbonylation of methanol in supercritical CO2 catalysed by a supported rhodium complex

“…2 We have recently reported studies of a catalyst consisting of [RhI 2 (CO) 2 ] 2 supported on polyvinylpyrrolidone (PVP). 3,4 In the liquid phase, we showed that the rate constant for the homogeneous reaction was only 2.2 times that for the heterogeneous reaction but that significant leaching of Rh occurs. 3 In the gas phase, after activation, stable activity was observed over long periods, there was no leaching, but the overall methanol consumption rate is low because of the low concentration of methanol that can be attained in the gas phase.…”

“…3,4 In the liquid phase, we showed that the rate constant for the homogeneous reaction was only 2.2 times that for the heterogeneous reaction but that significant leaching of Rh occurs. 3 In the gas phase, after activation, stable activity was observed over long periods, there was no leaching, but the overall methanol consumption rate is low because of the low concentration of methanol that can be attained in the gas phase. 4 We reasoned that supercritical CO 2 might be an ideal vector for this reaction since it dissolves large quantities of methanol and methyl iodide, is totally miscible with CO, has gas-like diffusion properties and is a poor solvent for ionic species such as [RhI 2 (CO) 2 ] 2 so that leaching should be minimised.…”

Entre la comprensión y la predicción del funcionamiento de catalizadores sólidos

“…Uno de los principales problemas era que el metal no se anclaba de manera suficientemente estable sobre el soporte, por lo que normalmente lixiviaba en condiciones de reacción. El grupo de Cole-Hamilton (De Blasio et al, 1998) reportó la carbonilación de metanol catalizada por rodio soportado en PVP y en poliestireno entrecruzado modificado con ligantes de fosfinas. Los autores llevaron a cabo la reacción alimentando los reactivos en fase gas y demostraron que, en esas condiciones, el rodio permanecía en la superficie de los soportes.…”

Heterogenisation of a carbonylation catalyst on dispersible microporous polymer nanoparticles

“…17,18 Another approach to minimise problems with solubility at low water concentration is to heterogenise the catalyst by immobilisation on a solid support. 5,16,19 A range of support materials that bind the Rh catalyst directly through a covalent interaction have been investigated, including inorganic oxides, 20,21 zeolites, [22][23][24][25] polymers, [26][27][28][29][30][31] carbon 32 and covalent triazine frameworks. 33 Many of these systems exhibit reaction rates slower than that of the homogeneous process, likely due, in part, to the covalent tethering of the catalyst, which modifies the first coordination sphere of the Rh complex.…”