Catalytic mechanisms on supported metals

The non-ideality of catalyst surfaces has ever been one the major difficulties in understanding the detailed mechanisms of contact catalysis. The Advances in Catalysis were opened in 1948 by an article of Taylor on the heterogeneity of catalyst surfaces for chemisorption [4] that the matter was not easy to model is understood by observing that 41 years later the role of particle size on the catalytic activity of supported metals was the subject of of another review in the same series [5] moreover, the family of solids of catalytic interest has since Taylor s review been increased by the availability of new techniques for the preparation of highly dispersed solids, like crystalline zeolites and amorphous aerogels. 

Concerning the mechanisms how gold, inert as a metal, can exhibit surprisingly high catalytic activities and se-lectivities, several hypotheses have been proposed. They can be classified in terms of active sites or reaction sites [38], which may change in some cases depending on support materials even for the same reactions. 

An alternative approach for the preparation of supported metal catalysts is based on the use of a microwave-generated plasma [27]. Several new materials prepared by this method are unlikely to be obtained by other methods. It is accepted that use of a microwave plasma results in a unique mechanism, because of the generation of a nonthermodynamic equilibrium in discharges during catalytic reactions. This can lead to significant changes in the activity and selectivity of the catalyst. 

Industrial heterogeneous catalysts and laboratory-scale model catalysts are commonly prepared by first impregnating a support with simple transition metal complexes. Catalytically active metal nanoparticles (NPs) are subsequently prepared through a series of high temperature calcination and / or reduction steps. These methods are relatively inexpensive and can be readily applied to numerous metals and supports however, the NPs are prepared in-situ on the support via processes that are not necessarily well understood. These inherent problems with standard catalyst preparation techniques are considerable drawbacks to studying and understanding complex organic reaction mechanisms over supported catalysts. (4)... 

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