Heterogeneous catalysts overview

Rauter and her coauthors Xavier, Lucas, and Santos (Lisbon) present here a detailed overview of the potential for heterogeneous catalysts in useful synthetic transformations of carbohydrates. Such silicon-based catalysts as zeolites are easy to handle and recover, are nontoxic, and can offer interesting possibilities for exercising stereo- and regio-control in many established carbohydrate transformations. 

The chapter Characterization of Heterogeneous Catalysts [82] in Surface and Nanomolecular Catalysis gives an overview on the methods (i.e., structural techniques,... 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

The present chapter has given an overview with selected examples and techniques on the potential and opportunities but also limitations for in situ characterization of heterogeneous catalysts. A multitude of different characterization techniques are available nowadays, and more and more ways are being found to further adapt... 

Another approach towards asymmetric heterogeneous catalysts is the immobilization of chiral homogeneous complexes via different methods. In this way the advantages of homogeneous catalysts (high activity and selectivity) and heterogeneous catalysts (easy recovery) can be combined. For a complete overview of this active research field the reader is referred to several reviews on this topic [50, 51]. The practical applicability of these catalysts is hampered by the fact that severe demands of recyclability and stability need to be obeyed. In certain cases promising results have been obtained as outlined here. 

Baleizao C, Garcia H. Chiral salen complexes an overview to recoverable and reuseable homogeneous and heterogeneous catalysts. Chem. Rev. 2006 106 3987-4043. 

Figure 2.53 Overview of some of the possibilities for developing enantioselective heterogeneous catalysts, including a model of cinchonidine adsorbed on an Pt surface.

This contribution provides an overview of known heterogeneous catalysts for Diels-Alder reactions with emphasis on methods which enable efficient synthesis of fine chemicals. It covers the literature up to the end of 1998. 

The application of organic modifiers is an important strategy for influencing the properties, mainly selectivity, of heterogeneous catalysts. Freifelder [13] has published a good overview of the effect of a wide variety of additives used in hydrogenation reactions. This approach will be discussed in more detail in Section... 

Because this book is devoted to fine chemical synthesis by heterogeneous catalysis, homogeneously catalyzed metathesis reactions will not be discussed. After a short overview of heterogeneous metathesis catalysts, the synthesis of fine chemicals from normal (unfunctionalized) olefins in the presence of these heterogeneous catalysts will be discussed. This is followed by a discussion of fine chemicals synthesized from functionalized olefins. 

Reductive alkylation is an effective method to synthesize secondary and tertiary amines from primary amines and hence is practiced commercially for the synthesis of a variety of fine and specialty chemicals. These inclnde corrosion inhibitors snch as the derivatives of cyclohexylamine, mbber chemicals such as A-(l,3-dimethylbutyl)-A -phenyl-p-phenylenediamine (6-PPD see Figure 15.13), pharmaceutical intermediates, dye intermediates, and pesticides [66-70]. The reaction starts ont as the condensation of an amine with a carbonyl compound followed by rednction of the intermediate imine (a Schiff base) to the desired amine. If the carbonyl componnd has an a-proton that can be abstracted, this secondary amine can be further reduced to tertiary amine [65]. Dne to the relatively small volume of such chemicals, the production is nsnally achieved in a batch process over a heterogeneous catalyst at pressures of 5 to 35 bar and temperatures of 323 to 423 K. Nishimura [71] provides an excellent overview of the literature for the synthesis of primary, secondary, and tertiary amines via reductive alkylation. 

Aromatic organosulfur compounds such as thiophenes, benzothiophenes and dibenzothiophenes are frequently contained in fossil oil and their sulfur atoms are generally difficult to remove in HDS process [106], In the industrial HDS process, Mo/Co/S or Ni/Mo/S heterogeneous catalysts supported on alumina are widely employed. In order to obtain ideas to develop more efficient catalysts as well as to shed some light on their mechanisms at a molecular level, transition metal complex-mediated cleavages of C-S bond are extensively studied. On the other hand, thiiranes and thietanes are frequently employed for preparation of transition metal sulfides, in which their C-S bonds are smoothly cleaved. In this section, the C-S bond cleavages of thiophene derivatives, thiiranes, thietanes, vinylic sulfides, allylic sulfides, thiols and dithioacetals are overviewed. 

Particularly intensive investigations have been carried out on catalysts for reactions with CO or alkenes. These reactions, which are typical transition metal catalyzed conversions, provide the best possibility for assessing the properties of heterogenized catalysts. Examples are given in the following overview (Table 6-1). AU the examples show that the reaction mechanisms with homogeneous and heterogeneous catalysis are in many respects similar. However, care must be taken in... 

Futter C, Prasetyo E, Schunk SA. (2013) Liquid phase oxidation and the use of heterogeneous catalysts—a critical overview. Chem. Ing. Technol. 85(4) 1-18. 

Infiltration is a weU-known method in heterogeneous catalyst applications. Infiltration, also known as impregnation, is commonly used for the preparation of supported catalyst systems. It involves the dispersion of a metal salt component into a support. It has recently been appHed to produce enhanced SOFC electrodes in order to solve the problems mentioned above. This chapter is intended to provide an overview of the application of infiltration in manufacturing SOFC electrodes, the procedures that are implemented to impregnate the electrode materials and the improvements achieved with infiltrated electrodes. 

JulkapU NM, Bagheri S. Graphene supported heterogeneous catalysts an overview. Int J Hydr En 2015 46 948-79. 

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