High-performance catalysts, structural

In summary, the compilation of relevant case studies shows that XRD of working catalysts is a widely applicable technique. It gives rich and useful information about synthesis and activation of catalysts as well as deactivation by structural transformations. The pertinent question about the structure of the active sites is not accessible directly by this method despite such claims in the literature. It must be pointed out that this shortcoming of a technique involving characterization of samples in reactive atmospheres is common to all methods when one is concerned with high-performance catalysts in which the active sites are a small fraction of the active surface. Model systems do a better job in this respect, provided that they are active for the reaction of interest and not only in proxy reactions. 

Titanium compounds with MAO or borate as co-catalysts effectively produce syndiotactic polystyrene from styrene monomer. The design of high-performance catalyst systems is now well demonstrated. The basic structure of the active site, the mechanism of coordination and insertion and the kinetics are also now well understood for this new polymerization. 

Xiong W, Du F, Liu Y, Perez A, Supp M, Ramakrishnan S, Dai L, Jiang L (2010) 3-D carbon nanotube structures used as high performance catalyst for oxygen reduction reaction. J Am Chem Soc 132 15839-15841... 

Equation 8.2 is sensitive to size, surface morphology, and the surfaee eleetronic structure of Pt nanoparticles as well as to the properties of the substrate [8, 71-75]. A better understanding of the relationships between partiele size and aetivity, including those effects, is critical in view of the design of highly performing catalyst systems [68, 76-78]. Obviously, a reduction in particle size improves the... 

Relationship of reduction process and catalytic activity. Prior to reduction, fused iron catalyst is a dense solid and without catalytic activity. The activity of the fused iron catalyst is not only related with the chemical components and preparation method, but also dependent upon the reduction process because all physical properties such as the surface area, porous structure, pore size and distribution, specific volume of pore, especially, size and formation of a-Fe crystallite etc. are produced during the reduction process. Different reduction processes produce different physical properties, and the surface area and porous structure are also different. The high performance catalysts can only be obtained when the reduction process are carefully controlled. Therefore, the reduction of the catalysts is the last step of the catalysts preparation, and also a key step. 

To enable a structure with high performance catalysts, the opted route in development included the following strategies ... 

Structured catalysts, including monoliths, are very promising as far as pressure drop and high performance for selective reactions are concerned. The perspectives for the use of monolithic catalysts in heterogeneous catalysis have been analysed by Cybulski and Moulijn (1994) and are further discus.sed in Section 5.4.7.7. 

The well balanced electronic and coordinative unsaturation of their Ru(II) center accounts for the high performance and the excellent tolerance of these complexes toward an array of polar functional groups. This discovery has triggered extensive follow up work and carbenes 1 now belong to the most popular metathesis catalysts which set the standards in this field [3]. Many elegant applications to the synthesis of complex target molecules and structurally diverse natural products highlight their truely remarkable scope. 

Allylruthenium(IV) complexes such as 23 convert into highly performing metathesis catalysts on treatment with ethyl diazoacetate (Fig. 3) [17]. Again,the structure of the active species is unknown and only applications to polymerization reactions have been reported so far. 

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