Supported and Heterogeneous Catalysts

Many attempts have been carried out to graft most of the previously described catalysts onto organic or inorganic supports, in order to combine the outstanding selectivity of these systems with the easy recovery of 

Generally, the performances (turnover number) of such catalysts are good. The main drawbacks concern poorer selectivities due to diffusion hmitations with regard to the products, and sometimes deactivation. This latter is ascribed to elution either of a ligand or a Lewis acid (for cationic complexes) due to the dissociation equihbria  

This can be avoided by using crystalline oxides such as alumina. 

Three main industrial processes for monoolefin oligomerization have been developed. Each of them represents one of the three abovementioned families of catalysts. 

In the Dimersol process [22] a cationic nickel complex (Ni VAlEtCl2 and Table II) transforms propylene and/or w-butenes into a mixture of di, tri-, and tetramers of various structures (Tables III and IV), consisting of all possible olefinic isomers. The process works in a well mixed liquid phase. 

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Both homogeneous and heterogeneous (or supported) catalytic systems have been used in ATRP. However, polymerization with homogeneous catalysts yields a polymer with much lower polydispersity than that with heterogeneous and supported catalysts. Explain, giving reason. 

The most common route to cyclic carbonates is the reaction of epoxides with CO2, which is promoted by a variety of homogeneous, heterogeneous and supported catalysts either cyclic carbonates or polymers are obtained [89]. Main group metal halides [90a] and metal complexes [90b], ammonium salts [91] and supported bases [92], phosphines [93], transition metal systems [88, 94], metal oxides [95], and ionic liquids [96] have been shown to afford monomeric carbonates. A1 porphyrin complexes [97] and Zn salts [89, 94, 98] copolymerize olefins and CO2. 

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