Heterogeneous catalytic processes industrial practices

In industry, heterogeneous catalytic reactions are frequently performed not only at elevated temperatures but also at higher pressure. For EPR spectroscopy of catalysts under such practical conditions, suitable high-pressure/high-temperature reactors are needed, but there are only a few examples of EPR spectroscopy cells meeting these requirements. Moreover, they are more than 20 years old and were developed primarily for non-catalytic pyrolysis processes. Nevertheless, they seem to be suited without notable modifications for heterogeneous catalytic reactions, although no such applications are reported in the recent literature. 

The development of the ammonia production process was also beginning of systematic catalytic research and widespread use of catalysts in industrial chemistry. Many subsequent achievments in theoretical understanding and practical application of heterogeneous catalysis have their roots in the ammonia synthesis reaction with probably can be considered to be the best understood catalytic process, as demonstrated by the enormous number of publications. 

H. Bartholomew, Fundamentals of Industrial Catalytic Processes, Blackie Academic and Professional, London, 1997 J. M. Thomas, W. J. Thomas, Principle and Practice of Heterogeneous Catalysis, VCH, Weinheim, 1997 C. R. Henry, Appl. Surf. Sci. 2000, 164, 252 T. P, St Qair, D. W. Goodman, Top. Catal. 

The development of the synthesis of ammonia was a landmark for the entire world and for the chemical industry in particular, since it not only solved the problem of securing food supply to the ever increasing world population, but it also had a significant impact on the industrial chemistry and laid the foundation for the theory and further developments in the industrial practice of heterogeneous catalysis. The ammonia industry has contributed significantly to improvements within chemistry and chemical engineering, and the very high R D activity with ammonia catalysts had a major effect on other catalyst based chemical industries. The ammonia synthesis reaction is probably the best fundamentally understood and documented catalytic process. 

The examples described in the previous paragraphs were all carried out as batch reactions. For practical applications in industry, however, the ideal process would involve a continuous-flow system in which the substrates are continuously fed into the reactor, where they react in the presence of the catalyst, and the products are collected at the other end. The catalyst remains in the reactor at all times. Such systems were previously exclusively applied for heterogeneous catalytic reactions. Nowadays, the use of SILP systems allows the desired homogeneous catalysts to be used in continuous flow. 

In addition to practical applications, metal cluster-derived catalysts, particularly intrazeolite metal cluster compounds, may aid in the identification of catalytically important bonding and structural patterns and thereby further our molecular understanding of surface science and heterogeneous catalysis. The ship-in-bottle technique for the synthesis of bulky metal-mixed metal cluster compounds inside zeolites and/or interlayered minerals has gained growing attention for the purpose of obtaining catalytic precursors surrounded by the interior constraint, imposing molecular shape selectivity. Such approaches may pave the way to offer the molecular architecture of hybrid (multifunctional) tailored catalysts to achieve the desired selectivity and stability for industrial processes. 

This article will be concerned with the mechanisms of some of these reactions and with some of the general principles that underly this relatively new and rapidly developing field of chemistry. The subject in question has attracted much interest in recent years both because of the novelty of much of the chemistry it reveals and because of its potential practical applications, exemplified by at least two processes (the Oxo and Wacker processes) which have already achieved considerable industrial importance. The possible relevance of many of the catalytic reactions in this field as model systems for related heterogeneous and enzymic process also lends interest to the subject although attempts to exploit this theme have thus far met with only limited success. 

This chapter summarizes some of the most characteristic results obtained with the use of mainly homogeneous metal complex eatalysts either in the industry or in processes recommended for practical use. These are large seale processes of asymmetric synthesis of the herbicide metolachlor, synthesis of optically pure menthol with the use of chiral iridium and rhodium phosphine complexes, consideration of the synthesis of ethyl 2-hydroxybutyrate as a monomer for the preparation of biodegradable polyesters with use of heterogeneous ehiral modified nickel catalyst, the manufacturing of (fJ)-pantolactone by means of a possible eata-IjTic systems for enantioselective hydrogenation of ketopantolactone, and catalytic systems for the preparation of other pharmaceuticals. 

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