Catalysis homogeneous and heterogeneous

Research has shown that heterogeneous catalysis is most likely responsible for the annual formation of an ozone hole over Antarctica. After the discovery of the Antarctic ozone hole in 1985, scientists wondered why there was such a dramatic drop in ozone over Antarctica but not over the rest of the planet. After aU, the chlorine from chlorofluorocar-bons that catalyzes ozone destruction is evenly distributed throughout the entire atmosphere. 

As it turns out, most of the chlorine that enters the atmosphere from chlorofluoro-carbons gets bound up in chlorine reservoirs, substances such as CIONO2 that hold chlorine and prevent it from catalyzing ozone destruction. The unique conditions over Antarctica—especially the cold isolated air mass that exists during the long dark winter— result in clouds that contain solid ice particles. These unique clouds are called 

Source U.S. Environmental PmtectionAsency, Our Nation s Air Status and Trends through 2010.  

A Polar stratospheric clouds contain ice particles that catalyze reactions by which chlorine is released from its atmospheric chemical reservoirs. 

A homogeneous catalyst exists in the same phase as the reactants. A heterogeneous catalyst exists in a different phase than the reactants. Often a heterogeneous catalyst provides a sohd surface on which the reaction can take place. 

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Biphasic catalysis in a liquid-liquid system is an ideal approach through which to combine the advantages of both homogeneous and heterogeneous catalysis. The reaction mixture consists of two immiscible solvents. Only one phase contains the catalyst, allowing easy product separation by simple decantation. The catalyst phase can be recycled without any further treatment. However, the right combination of catalyst, catalyst solvent, and product is crucial for the success of biphasic catalysis [22]. The catalyst solvent has to provide excellent solubility for the catalyst complex without competing with the reaction substrate for the free coordination sites at the catalytic center. 

However, research into transition metal catalysis in ionic liquids should not focus only on the question of how to make some specific products more economical or ecological by use of a new solvent and, presumably, a new multiphasic process. Since it bridges the gap between homogeneous and heterogeneous catalysis, in a novel and highly attractive manner, the application of ionic liquids in transition metal catalysis gives access to some much more fundamental and conceptual questions for basic research. 

In comparison with traditional biphasic catalysis using water, fluorous phases, or polar organic solvents, transition metal catalysis in ionic liquids represents a new and advanced way to combine the specific advantages of homogeneous and heterogeneous catalysis. In many applications, the use of a defined transition metal complex immobilized on a ionic liquid support has already shown its unique potential. Many more successful examples - mainly in fine chemical synthesis - can be expected in the future as our loiowledge of ionic liquids and their interactions with transition metal complexes increases. 

Abbenhuis H. C. L. Advances in Homogeneous and Heterogeneous Catalysis With Metal-Containing Sdsesquioxanes Chem. Eur. J. 2000 6 25 32... 

Research into cluster catalysis has been driven by both intrinsic interest and utilitarian potential. Catalysis involving "very mixed -metal clusters is of particular interest as many established heterogeneously catalyzed processes couple mid and late transition metals (e.g., hydrodesulfurization and petroleum reforming). Attempts to model catalytic transformations arc summarized in Section II.F.I., while the use of "very mixed -metal clusters as homogeneous and heterogeneous catalysis precursors are discussed in Sections I1.F.2. and I1.F.3., respectively. The general area of mixed-metal cluster catalysis has been summarized in excellent reviews by Braunstein and Rose while the tabulated results are intended to be comprehensive in scope, the discussion below focuses on the more recent results. 

Explain the differences and similarities between homogeneous and heterogeneous catalysis. 

J.L Margitfalvi J and M. Hegedus, 8th International Congress on the Relation Between Homogeneous and Heterogeneous Catalysis, Balatonfured, Hungary, Sept. 1995 N°21 oral presentation accepted for publication in J. Mol Cat... 

Keywords Elementary steps Homogeneous and heterogeneous catalysis ... 

In 1982, Laine reviewed simple chemical tests and application of some techniques to distinguish between homogeneous and heterogeneous catalysis. He proposed five criteria for detecting homogeneous cluster catalysts ... 

The main issue of the book is application of nanosized particles in both homogeneous and heterogeneous catalysis. A variety of reactions catalyzed by metal colloids or supported nanosized metals is discussed. The most intriguing reaction seems to be ethane hydrogenolysis catalyzed by Pt clusters on porous carrier and studied by G. A. Somorjai and his group. Another challenging observation by this group is shape isomerization of Pt metal particles affected by the addition of silver ions. 

Transition metal NPs dispersed in ILs are recognized as suitable catalyst systems for many reaction types with both typical homogeneous and heterogeneous catalysis (see Sections 1.3.1-1.3.5). The most investigated reactions are the hydrogenation of multiple bonds and arenes [1, 5, 12, 13, 43, 44, 54, 80, 89, 92], carbon-carbon cross-... 

Shi, F., Tse, M.K., Pohl, M.M., Bruckner, A., Zhang, S.M. and Beller, M. (2007) Tuning catalytic activity between homogeneous and heterogeneous catalysis improved activity and selectivity of free nano-Fe203 in selective oxidations. Angewandte Chemie International Edition, 46 (46), 8866-8868. 

In comparison to traditional biphasic catalysis using water, fluorous phases or polar organic solvents, transition metal catalysis in ionic liquids represents a new and advanced way of combining the specific advantages of homogeneous and heterogeneous catalysis. 

Branching reactions appear to be a unique indication of the existence of spatial constraints at growth sites. Analogies between homogeneous and heterogeneous catalysis are pertinent. 

Crabtree described the use of dibenzo[a,e]cyclooctatetraene, a potent selective poison of homogeneous hydrogenation catalysts, as a tool to distinguish between homogeneous and heterogeneous catalysis in the hydrogenation of hexene with a range of catalysts [24]. 

The Intermediate Compound Theory in Homogeneous and Heterogeneous Catalysis. 51... 

Cascade catalysis without recovery of intermediate products may require more than two steps, involving enzymatic, homogeneous, and heterogeneous catalysis. Several examples of this approach have been given [72, 73] one of the most representative consists of a four-step conversion of glucoside into aminodeoxysugar without intermediate product recovery. 

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