Catalysis in SCFs

This chapter has focused on heterogeneous catalysis in supercritical media, but the relationship between supercritical fluids and catalysis is much broader. There have been numerous studies of homogeneous catalysis in SCFs. Examples include hydroformylation via cobalt carbonyl complexes in supercritical CO2, oxidation via metal salts dissolved in supercritical water, and acid-catalyzed dehydration of alcohols in supercritical water. 

After initial findings that some enzymes were active and stable in SCF s [1,2], several other studies on enzyme catalysis in SCF s have been carried out. The majority of systems explored to date have used model reactions [3,4] of which only a few show a possibility for practical and commercial purposes [5],... 

Enzymatic catalysis in SCFs exploits the ability to alter solvent strength with small changes in temperature and pressure in the near-critical region. The versatile solvation characteristics of SCFs, the extreme catalytic specificity of enzymes, and the ability to achieve complete removal of the SCF solvent by depressurization make enzymatic catalysis in SCFs attractive to the pharmaceutical and food industries. 

Heterogeneous catalysis in SCFs dates from the experiments of Ipatiev, Haber, and researchers at BASF (1). Although the advantages were not known at that time, SCFs are particularly appropriate as media for heterogeneous catalysis because of the extremely rapid diffusion rates of SCFs in... 

Syntheses of commercially important drugs, intermediates, and related compounds by asymmetric catalysis in SCFs have been reported (Table 1). There... 

Before discussing individual examples of metal catalysis in SCFs in detail (Sections 4.7.2-4.7.6), it is appropriate to outline briefly some experimental approaches to carrying out a metal-complex-catalyzed SI. ... 

The first reports of enzyme activity in SCFs were published almost simultaneously in 1985 and 1986 [1-3]. Great enthusiasm emerged and since this pioneering work more than 200 papers on enzymatic catalysis in SCFs have appeared. The subject has been reviewed in 1991 [4] and in 1995 [5]. 

Many enzymes are stable and catalyze reactions in supercritical fluids, just as they do in other non- or microaqueous environments. Many enzymes are more stable in supercritical fluids than in aqueous solutions. However, enzymes are not soluble in SCFs therefore enzymatic catalysis in SCFs is always heterogeneous. 

Catalysis is the key for efficient use of raw materials of a given chemical conversion. It is common knowledge that the performances of catalysts and the properties of catalytic reactions vary with the reaction media. Catalysis in SCFs... 

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