Noble metal catalysts hydrogen activation

As of now no details of the synthesis of optically active tritiated compounds produced under microwave-enhanced conditions have been published. Another area of considerable interest would be the study of solvent effects on the hydrogenation of aromatic compounds using noble-metal catalysts as considerable data on the thermal reactions is available [52]. Comparison between the microwave and thermal results could then provide useful information on the role of the solvent, not readily available by other means. 

It is well established that commercially important supported noble metal catalysts contain small metal crystallites that are typically smaller than a few nanometers. The surface of these crystallites is populated by different types of metal atoms depending on their locations on the surface, such as comers, edges, or terraces. In structure sensitive reactions, different types of surface metal atoms possess quite different properties. For example, in the synthesis of ammonia from nitrogen and hydrogen, different surface crystallographic planes of Fe metal exhibit very different activities. Thus, one of the most challenging aspects in metal catalysis is to prepare samples containing metal particles of uniform shape and size. If the active phase is multicomponent, then it is also desirable to prepare particles of uniform composition. 

Due to the absence of electron withdrawing groups the aromatic amines are hydrogenated with difficulty. Supported noble metal catalysts (Pd, Pt, Ru, Rh, Ir) are usually active at elevated temperature and pressure. The perhydrogenation of aromatic amines is mainly accompanied by two side reactions, i.e. the... 

The deoxo reaction, performing the reduction of dioxygen with hydrogen, usually catalysed by a noble metal catalyst, was also reported to occur with NaY encapsulated complexes of Cu(embelin) (18) and 2-aminobenzimidazole (19).[134] The Cu(embelin) complex entrapped in NaY is a stable catalyst, that showing enhanced activity compared with the homogeneous case and may be reused many times, the corresponding benzimidazole complex is deactivated rapidly. 

The important application of SPC in organic synthesis is their conversion into the gem-dimethyl group, which is a common fragment in many natural products as well as in synthetically made, physiologically active compounds. This transformation utilizes hydrogenation of the cyclopropyl fragment over a noble metal catalyst. Equation 20 presents a typical example of the introduction of the g m-dimethyl group into a complex molecule via a SPC intermediate ... 

I. M. Keen With regard to your first question, I would agree with you that the noble metal is the active catalyst component for hydrogenating olefins and aromatics, the zeolite acting as a high-surface-area support for the metal. 

Saturation of a carbohydrate double bond is almost always carried out by catalytic hydrogenation over a noble metal. The reaction takes place at the surface of the metal catalyst that absorbs both hydrogen and the organic molecule. The metal is often deposited onto a support, typically charcoal. Palladium is by far the most commonly used metal for catalytic hydrogenation of olefins. In special cases, more active (and more expensive) platinum and rhodium catalysts can also be used [154]. All these noble metal catalysts are deactivated by sulfur, except when sulfur is in the highest oxidation state (sulfuric and sulfonic acids/esters). The lower oxidation state sulfur compounds are almost always catalytic poisons for the metal catalyst and even minute traces may inhibit the hydrogenation very strongly [154]. Sometimes Raney nickel can... 

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