Heterogeneous catalysis carbonylation with carbon

Isolation and identification of surface-bonded acetone enolate on Ni(l 11) surfaces show that metal enolate complexes are key intermediates in carbon-carbon bond-forming reactions in both organometaUic chemistry and heterogeneous catalysis. Based on studies on powdered samples of defined surface structure and composition, most of the results were reported for acetone condensation over transition-metal oxide catalysts, as surface intermediate in industrially important processes. With the exception of a preoxidized silver surface, all other metal single-crystal surfaces have suggested that the main adsorption occurs via oxygen lone-pair electrons or di-a bonding of both the carbonyl C and O atoms. 

As shown by reaction 1.6.4.3, depending on the requirement for hydrogen, carbon monoxide could be further reacted with water to yield more hydrogen. This reaction is called water gas shift reaction and is of relevance in homogeneous catalyst-based carbonylation reactions (see Section 4.7.1). The heterogeneous industrial catalyst for water gas shift reaction contains copper and zinc oxide on alumina. By the standards of heterogeneous catalysis, it operates at a relatively low temperature ( 230°C). 

Although the homogeneous catalyst systems have been successfully applied in commercial practice, some intrinsic problems associated with catalyst separation remain. This has led to considerable interest in the development of a suitable heterogeneous analog. Rhodium compounds have been heterogenenized on substrates such as carbon (197), alumina (198, 199), and synthetic polymers (200). More recently, zeolites have also attracted quite some attention as a support material for carbonylation catalysis, as is discussed later. 

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