Catalytic methanol carbonylation supported

An alternative strategy for catalyst immobilisation uses ion-pair interactions between ionic catalyst complexes and polymeric ion exchange resins. Since all the rhodium complexes in the catalytic methanol carbonylation cycle are anionic, this is an attractive candidate for ionic attachment. In 1981, Drago et al. described the effective immobilisation of the rhodium catalyst on polymeric supports based on methylated polyvinylpyridines [48]. The activity was reported to be equal to the homogeneous system at 120 °C with minimal leaching of the supported catalyst. The ionically bound complex [Rh(CO)2l2] was identified by infrared spectroscopic analysis of the impregnated resin. 

A mechanistic study by Haynes et al. demonstrated that the same basic reaction cycle operates for rhodium-catalysed methanol carbonylation in both homogeneous and supported systems [59]. The catalytically active complex [Rh(CO)2l2] was supported on an ion exchange resin based on poly(4-vinylpyridine-co-styrene-co-divinylbenzene) in which the pendant pyridyl groups had been quaternised by reaction with Mel. Heterogenisation of the Rh(I) complex was achieved by reaction of the quaternised polymer with the dimer, [Rh(CO)2l]2 (Scheme 11). Infrared spectroscopy revealed i (CO) bands for the supported [Rh(CO)2l2] anions at frequencies very similar to those observed in solution spectra. The structure of the supported complex was confirmed by EXAFS measurements, which revealed a square planar geometry comparable to that found in solution and the solid state. The first X-ray crystal structures of salts of [Rh(CO)2l2]" were also reported in this study. 

Catalytic Features of Carbon-Supported Group VIII Metal Catalysts for Methanol Carbonylation... 

The catalytic activities of group VIII metals supported on activated carbon for methanol carbonylation were in the order as follows ... 

Methanol carbonylation has been the subject of numerous reviews [6-17], including the seminal mechanistic studies by Denis Forster at Monsanto. This chapter does not seek to repeat all the information included in those reviews, but instead is focused on the important recent advances in process development and mechanistic understanding along with recent research efforts to identify new ligand-modified, supported, or promoted catalysts. The increasing use of computational methods to model catalytic mechanisms and potential alternative catalytic routes to acetic acid are also summarized. 

In a further variation, the PVP-supported rhodium catalyst was used for methanol carbonylation in supercritical carbon dioxide [100]. This reaction medium has complete miscibility with CO and dissolves high concentrations of methanol and methyl iodide, while being a poor solvent for ionic metal complexes. Catalytic reaction rates up to half of those obtained in conventional liquid-phase catalysis were achieved with minimal catalyst leaching. 

The metal complexes most often studied as polymer-bound catalysts have been Rh(I) complexes, such as analogues of Wilkinson s complex. The catalytic activity of a bound metal complex is nearly the same as that of the soluble analogue. Rhodium complexes are active for alkene hydrogenation, alkene hydroformylation, and, in the presence of CH3I cocatalyst, methanol carbonylation, etc. Polymer supports thus allow the chemistry of homogeneous catalysis to take place with the benefits of an insoluble, easily separated catalyst . ... 

The effect of Pt particle size on oxidation of methanol has been studied by several researchers. Machida et al. [67] introduced several platinum-cluster-attached graphite electrodes and reported enhanced electrocatalytic activity in anodic methanol oxidation with Pt clusters ranging in size from Pt9 to Ptis [67]. The catalytic activity of supported Pt clusters is significantly higher than that of conventional Pt electrodes. They used platinum carbonyl clusters of the type Pt3n,(CO)6n (u= 3,5) as well as HRu3(CO)n. Modification of the graphite surface... 

This reaction mechanism is supported by model studies. Paricularly advantageous are the mild reaction conditions (30-40 bar, 150-200°C) and the high selectivity with respect to methanol (99 %) and CO (> 90 %) compared to the older cobalt process. Methanol carbonylation is one of the few industrially important catalytic reactions whose kinetics are known in full [7]. 

Methanol Carbonylation. Some researchers have described the possibility of supporting a rhodium compound on an ionic resin such as a copolymer of styrene and 4-vinylpyridine alkylated with methyl iodide forming a methylpyridinium-functionalized polymer (16). They have concluded that their ionic polymer-supported rhodium catalyst for methanol carbonylation in liquid phase is approximately equal in catalytic activity to the dissolved complex and that leaching of the complex could be minimized by suitable choice of solvent and by selecting high resin-to-rhodium ratios. However, experiments carried out only at low temperature (120°C) and low pressure were reported. 

The silica gel-supported IL-phase catalyst could be applied in the continuous methanol carbonylation [99]. A rhodium carbonyl-functionalized IL was produced inside the silica gel-supported [BMIm]I and used as the catalytically active species for the carbonylation reaction. Scheme 2.24. At 150 °C, the conversion of methanol reached 99% if Mel was used as an additive. The major products were acetic acid (21.4%), methyl acetate (74.4%), and dimethyl ether (4.2%). 

The selective production of methanol and of ethanol by carbon monoxide hydrogenation involving pyrolysed rhodium carbonyl clusters supported on basic or amphoteric oxides, respectively, has been discussed. The nature of the support clearly plays the major role in influencing the ratio of oxygenated products to hydrocarbon products, whereas the nuclearity and charge of the starting rhodium cluster compound are of minor importance. Ichikawa has now extended this work to a study of (CO 4- Hj) reactions in the presence of alkenes and to reactions over catalysts derived from platinum and iridium clusters. Rhodium, bimetallic Rh-Co, and cobalt carbonyl clusters supported on zinc oxide and other basic oxides are active catalysts for the hydro-formylation of ethene and propene at one atm and 90-180°C. Various rhodium carbonyl cluster precursors have been used catalytic activities at about 160vary in the order Rh4(CO)i2 > Rh6(CO)ig > [Rh7(CO)i6] >... 

In 1963, Imperial Chemical Industries (ICI) PLC announced an innovative process using Cu/Zn0/Al203 catalysts, later called low-pressure synthesis. The major constituents of this catalytic system are Cu (reduced form of CuO) and ZnO on an A1203 support. The reaction pressure and temperature are 220-270 °C and 5-10MPa, respectively. The catalysts have been found to be susceptible to sulfur and carbonyl poisoning, sintering, and thermal aging. Nowadays, almost all of commercial methanol syntheses are carried out by low-pressure processes. 

This hipothesis is supported by the following experimental observation when a- or y ZrP was added to a methanol solution of RhCl3 and the suspension was allowed to react for one hour with CO, the resulting filtered dark material tested for aniline carbonylation showed the same catalytic activity. 

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