Atomic species catalysis

Adsorbed Atomic Species as Intermediates in Heterogeneous Catalysis Carl Wagner... 

C. Wagner, Adsorbed Atomic Species as Intermediates in Heterogeneous Catalysis, in Adv. Catal., (1970), pp. 323-381. 

Supported metal clusters play an important role in nanoscience and nanotechnology for a variety of reasons [1-6]. Yet, the most immediate applications are related to catalysis. The heterogeneous catalyst, installed in automobiles to reduce the amount of harmful car exhaust, is quite typical it consists of a monolithic backbone covered internally with a porous ceramic material like alumina. Small particles of noble metals such as palladium, platinum, and rhodium are deposited on the surface of the ceramic. Other pertinent examples are transition metal clusters and atomic species in zeolites which may react even with such inert compounds as saturated hydrocarbons activating their catalytic transformations [7-9]. Dehydrogenation of alkanes to the alkenes is an important initial step in the transformation of ethane or propane to aromatics [8-11]. This conversion via nonoxidative routes augments the type of feedstocks available for the synthesis of these valuable products. 

In order to avoid the unwanted dimerization, steric constraints were incorporated into the used ligands. This hinders the metal centres to approach each other, so either the equilibrium is shifted to the side of the monomeric molybdenum species or the dimerization completely prevented. One of the first bulky sulfur-containing ligands that was able to successfully promote oxygen atom transfer catalysis of its molybdenum complex was developed by Berg and Holm (Scheme 4.7 BuLNS = bis(4-tert-butylphenyl)-2-pyridylmethanthiolate). ... 

Platinum-thiourea complexes have been extensively studied because of their biological activity [54], but few have been used in catalysis. Neutral thioureas are able to coordinate to metal centres through their sulfur atom (Scheme 9) [55,56] monomeric (I) and oligomeric (II) species are known for Rh [57], and an X-ray structure has also been determined for the chiral complex III [58]. In many complexes hydrogen bonding has been observed... 

The dominant species of Ce(IV) existing under the reaction conditions is 00(804)3 and the activated complexes for the two paths must have compositions 0(804)2 Br and 00(804)261 . The latter path is subject to chloride-ion catalysis of the form = A q-1-A [OI ] which suggests an activated complex 0e(804)201Br2 . 8I0W oxidative breakdown of the complexes containing bromide gives Oe(III) and Br atoms or -BrJ. The latter go on to form molecular bromine however, their presence has been detected in this reaction from their ability to add to butadiene to form dibromooctadienes . 

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