Heterogeneous catalysis olefins

The study of catalytic polymerization of olefins performed up to the present time is certain to hold a particular influence over the progress of the concepts of the coordination mechanism of heterogeneous catalysis. With such an approach the elementary acts of catalytic reaction are considered to proceed in the coordination sphere of one ion of the transition element and, to a first approximation, the collective features of solids are not taken into account. It is not surprising that polymerization by Ziegler-Natta catalysts is often considered together with the processes of homogeneous catalysis. 

The range of reactions which have been examined is wide (248) and includes hydrogenations (256), ammonia synthesis (257), polymerizations (257), and oxidations (258). Little activity has occurred in this area during the past few years. Recent reports of the effects of sonication on heterogeneous catalysis include the liquefaction of coal by hydrogenation with Cu/Zn (259), the hydrogenation of olefins by formic acid with Pd on carbon (260), and the hydrosilation of 1-alkenes by Pt on carbon (261). 

It is in the very nature of the catalytic process that the intermediate compound formed between catalyst and reactant is of extreme lability therefore not many cases are on record where the isolation by chemical means, or identification by physical methods, of intermediate compounds has been achieved concomitant with the evidence that these compounds are true intermediaries and not products of side reactions or artifacts. The formation of ethyl sulfuric acid in ether formation, catalyzed by HjSO , and of alkyl phosphates in olefin polymerization, catalyzed by liquid phosphoric acid, are examples of established intermediate compound formation in homogeneous catalysis. With regard to heterogeneous catalysis, where catalyst and reactant are not in the same... 

Heterogeneous Catalysis in the Anodic Oxidation of Olefins and Bisarene Sulfides... 

In discussing the mechanism of eliminations over solids, the nomenclature which has been developed for homogeneous reactions will be used. Therefore the basic mechanisms of olefin formation have first to be outlined and their meaning in heterogeneous catalysis defined. 

It is known [41] that partial oxidation reactions in heterogeneous catalysis involves redox properties of the solid catalysts, allowing the well known Mars-van Krevelen mechanism [42] to occur, or at least to be facilitated. Acid-base properties are also an important feature, as they play a determining role in the activation of the reactants and in the desorption of the intermediate compounds, for instance, an acid surface will favor desorption of acid products, thus avoiding further over-oxidation, while a basic surface will favor desorption of basic products as olefins. It follows that heteropolyoxometallate compounds, in particular TMSP, appear as potential... 

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