Homogeneous, Heterogeneous, and Biocatalysis

In contrast to heterogeneous catalysis, classical homogeneous catalysis takes place in the bulk of a solvent. However, due to the lack of a phase boundary it is much more complicated in this case to isolate the fully dissolved transition metal complex from the desired reaction product. Often, distillation fails due to the thermal instability of the dissolved catalyst or the fact that unselective reactions occur in the bottom of the distillation column. Catalyst recovery and recycling strategies for homogeneous catalytic processes can therefore sometimes be rather complicated 

Selectivity High, molecularly defined active centers Variable, often undefined active sites 

Variability of steric and electronic properties Possible by bgand effects Difficult 

Understanding Plausible imder random conditions Often very difficult (pressure material gap) 

Catalyst/product separation Difficult, often expensive Straightforward 

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This book is thus organized in three parts. The first five chapters discuss the principles and tools needed to realize a sustainable industrial chemistry. Chapter 1 discusses the general principles and emphasizes the differences between green and sustainable industrial chemistry approaches. It is also an introductory chapter to the topic. Chapter 2 discusses the role of catalysis as a main enabling factor to achieve sustainability through chemistry. Several examples of homogeneous, heterogeneous and biocatalysis are discussed, with emphasis on industrial aspects, to provide a comprehensive view of the possibilities offered by this tool. 

Recent achievements of Baeyer-Villiger reaction in homogeneous, heterogeneous and biocatalysis reactions have been reviewed the relation between catalyst substrate and mechanism is clarified for different systems and future development of the... 

This chapter outlines the principles of green chemistry, and explains the connection between catalysis and sustainable development. It covers the concepts of environmental impact, atom economy, and life-cycle analysis, with hands-on examples. Then it introduces the reader to heterogeneous catalysis, homogeneous catalysis, and biocatalysis, explaining what catalysis is and why it is important. The last two sections give an overview of the tools used in catalysis research, and a list of recommended books on specialized subjects in catalysis. 

Here we discuss catalysis and its relevance for chemical technology. Catalysis is applied industrially in the form of heterogeneous catalysis, homogeneous catalysis, and biocatalysis. All three forms follow the same general principles. However, the... 

In homogeneous catalysis and biocatalysis the catalyst molecules are present in solution. The rate is then usually determined by the turn over frequency, which is defined as the number of reactant molecules reacting per active center and time. For a batch reactor, the amount converted up to the time t is called the turn over number. (In heterogeneous catalysis, TOP and TON values are seldom used as knowledge of the number of active sites is usually limited.)... 

The objective of this NoE is to strengthen research in catalysis by the creation of a coherent framework of research, know-how and training between the various disciplinary catalysis communities (heterogeneous, homogeneous, and biocatalysis) with the objective of achieving a lasting integration between the main European Institutions in this area. IDECAT will create the virtual European Research Institute on Catalysis (ERIC) that is intended to be the main reference point for catalysis in Europe. 

Before any catalysis can occur, at least one of the substrates must coordinate to the catalyst. This means that the catalyst must have a vacant active site. In homogeneous metal complex catalysis and biocatalysis, this will be a vacant coordination site at the metal atom. In heterogeneous catalysis, the vacant site could be a metal crystallite or an ion on the surface. For the latter, we speak of desorption and adsorption instead of dissociation and coordination. Remember that our reactions are not in vacuum, so there is no vacant site . Thus, before any chemical species can coordinate to the metal complex (or to the active site in heterogeneous catalysis or biocatalysis) the species already occupying this space must first vacate it. This happens constantly, as the system is dynamic (Figure 3.3) [15]. At any given moment... 

Energy diagram 3.7 is of course very similar in heterogeneous, homogeneous and biocatalysis, since kinetics is similar. A difference to be taken into accoxmt is that in the liquid phase adsorption is to be considered with respect to the liquid phase. 

Solid-catalyzed reactions are generally examined in continuous-flow reactors, while homogeneously catalyzed reactions (including reactions catalyzed by non-immobilized biocatalysts) are usually studied in batch reactors. An important difference between chemical catalysis and biocatalysis is that it is relatively easy to study the biocatalyst either as a homogeneous or a heterogeneous catalyst, as desired. 

The nanoreactor can thus provide a confined 3D environment for optimal integration between heterogeneous, homogeneous and biocatalysis. By combining advances in knowledge in homo-, hetero- and biocatalysis it is thus possible to design... 

Fig. 2.1-2 Classification of catalysis into the three important classes of heterogeneous, homogeneous, and biocatalysis.

In this book, my main objective is to present an overview on catalysis, so that both the student and the experienced practitioner can see the broad picmre. It was the intention to compile a text of about 500 pages surveying the whole area of catalysis, that means homogeneous catalysis, heterogeneous catalysis, biocatalysis and special topics of apphed catalysis. It is felt that sufficient information is given here for a rational approach to be applied in a basic understanding of the phenomenon catalysis. 

Special attention is given to the integration of biocatalysis with chemocatalysis, i.e., the combined use of enzymatic with homogeneous and/or heterogeneous catalysis in cascade conversions. The complementary strength of these forms of catalysis offers novel opportunities for multi-step conversions in concert for the production of speciality chemicals and food ingredients. In particular, multi-catalytic process options for the conversion of renewable feedstock into chemicals will be discussed on the basis of several carbohydrate cascade processes that are beneficial for the environment. 

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