Homogeneous Catalysts: Activity – Stability – Deactivation
Homogeneous catalysts have played a key role in the production of petrochemicals and coal-derived chemicals since the 1960s. In the last two decades, transition metal catalysts have revolutionized synthetic organic chemistry, both in the laboratory and in industrial production. The use of homogeneous catalysts in polyolefin synthesis started in the 1980s and triggered enormous R&D efforts, leading to hitherto inaccessible polymers and to greatly improved control over polymer structure and properties. The introduction of new processes and catalysts continues in bulk chemical production, as exemplified by new routes that have recently come on stream for the production of 1-octene and methyl methacrylate.
For all catalysts, selectivity and rates of reactions are crucial parameters and in the laboratory even the rate may not concern us that much, as catalyst loadings of 5% or more are often applied. For industrial applications, however, high turnover numbers are required for economic reasons, which may be more complex than simply catalyst costs. For the bulk chemical applications, studies of catalyst activation, activity, stability, deactivation, recycling and regeneration have always formed an integral part of catalysis research. A considerable research effort has been devoted to this, mainly in industry, but explicit publications are scarce, although some stability issues can be deduced from the patent literature. Catalyst stability has been a highly important factor in transforming advances in catalysis into practical applications, notably in the areas of polymer synthesis, cross-coupling chemistry, hydrogenation catalysis, carbonylation reactions and metathesis chemistry.
In heterogeneous catalysis, the study of activation, deactivation, and regeneration of catalysts has always been a major research activity. These topics have been addressed in many articles, books and conferences, and literature searches with these keywords give many relevant results. For homogeneous catalysts this is not the case, with the possible exception of metathesis. A wealth of knowledge can be found in a vast number of publications, but this is not easily retrieved. The approach in homogeneous catalysis is entirely different to that of heterogeneous catalysis, especially before industrial applications come into sight; in homogeneous catalysis, the general approach to improving the catalyst performance is variation of one of the catalytic components, without much attention being paid to the question of why other catalyst systems failed.
|May 30, 2020
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