Immobilized catalysts, industrial application

End N, Schoning K-U (2004) Immobilized Catalysts in Industrial Research and Application. 242 241-271... 

The recovery of the photocatalyst from the reaction environment represents one of the main problems of the photocatalytic process that limits its industrial application. Although this process step can be obviated by the use of immobilized catalyst, the suspended system has more attractive features [76]. Therefore, the separation of the photocatalyst from the treated solution and its recycle is one of the challenges in further development of this technology. 

Although the AD process has found widespread use on the lab scale, industrial applications are obstructed owing to the toxicity and the high cost of the osmium catalyst and the risk of contamination of the products by toxic osmium residues. To address this issue, several research groups have developed immobilized osmium catalysts for use in the osmium-catalyzed dihydroxylations [30]. 

First, we address the use of immobilized catalysts. Literature on immobilized homogeneous catalysts is extensive and reaches back to the 1970s. Notwithstanding the large effort, there seems to be only one industrial application of this technique, namely [Rhl2(CO)2], that is electrostatically anchored to an ion-exchange resin for the carbonylation of methanol vide infra) 113). 

The last strategy is the use of supramolecular binding in catalyst immobilization. Immobilization of efficient homogeneous catalysts has been investigated extensively. Except for one case, the thousands of publications and patents have not led to industrial applications. In the s)m-thesis of fine chemicals, homogeneous catalysts may be removed in a column, but crystallization of the product is the preferred operation. In bulk chemical s)mthesis, we find all the unit operations applied to effect separation of the catalyst from the product mixture. 

Much work is still in progress to improve the Ru-carbene complexes. Considerable attention has recently also been directed at efforts to immobilize a Ru-based metathesis catalyst on solid supports, which could make the metathesis reaction even more attractive for industrial applications. 

In other reactions, particularly where strongly complexing reactants, e. g., carbon monoxide, are involved, leaching of the immobilized metal center may take place. Generally, the parameters to be considered in a polymer-anchored metal complex catalyst are of a manifold nature. It is still an unsolved problem and an incompatible situation that, on the one hand, a leaching process should be avoided while, on the other hand, sufficient activity and the selectivity necessary for industrial applications are to be maintained. As a consequence it has become... 

Both polymer-supported (immobilized) catalysts [19] and two-phase reactions (water-soluble phosphine co-ligands) were described for aryl iodides only [20]. However, aryl iodides are not attractive starting materials for large-scale industrial applications. 

Even though the results with the immobilized catalyst in hydrogenation experiments with a substrate/catalyst ratio of 100 1 were good, their industrial application failed because with a substrate/catalyst ratio of 1000 1 re-use of the immobilized catalyst for the second run was impossible. 

Abstract The present state of the art of the application of immobUized/heterogenized homogeneous catalysts in industrial research and production will be introduced. Special attention is drawn to catalysts which have been tested for the synthesis of chiral compounds. In a second part, commercially available immobilized catalyst systems wiU be presented, giving the reader an impression of what the favored directions of industrial development are and where future applications of such systems are most likely to occur. 

In order for the immobilized version of the homogeneous catalyst to be successful in an industrial chemical process, it must not negatively impact the economics of the process in view of its cost, activity, selectivity, and lifetime. According to Hagen [1] the ideal immobilized metal complex for industrial applications has not yet been found, as was shown by weighing up the advantages and disadvantages of different types of catalysts. 

---