Catalyst actinide

HDPE resias are produced ia industry with several classes of catalysts, ie, catalysts based on chromium oxides (Phillips), catalysts utilising organochromium compounds, catalysts based on titanium or vanadium compounds (Ziegler), and metallocene catalysts (33—35). A large number of additional catalysts have been developed by utilising transition metals such as scandium, cobalt, nickel, niobium, molybdenum, tungsten, palladium, rhodium, mthenium, lanthanides, and actinides (33—35) none of these, however, are commercially significant. 

Extremely high cistactic structures are obtained by catalysts systems based on 4f and 5f block elements of Periodic Table (lanthanides and actinides). Some of these catalysts systems are particularly interesting for saving energy in the polymerization process. 

As to the first route, we started in 1969 (1) in investigating unconventional transition metal complexes of the 5 and 4f block elements of periodic table, e.g., actinides and lanthanides as catalysts for the polymerization of dienes (butadiene and isoprene) with an extremely high cis content. Even a small increase of cistacticity in the vicinity of 100% has an important effect on crystallization and consequently on elastomer processability and properties (2). The f-block elements have unique electronic and stereochemical characteristics and give the possibility of a participation of the f-electrons in the metal ligand bond. 

Metal hydrides and acyl-like CO insertion products are two types of species likely to be present in any homogeneous or heterogeneous process for the catalytic reduction of carbon monoxide. The discovery and understanding of new types of reactivity patterns between such species are of fundamental interest. As discussed elsewhere (11,22,54-57), bis(pentamethylcyclo-pentadienyl) actinide hydrides (58) are highly active catalysts for olefin hydrogenation as well as H-H and C-H activation. 

In hydrogenation, early transition-metal catalysts are mainly based on metallocene complexes, and particularly the Group IV metallocenes. Nonetheless, Group III, lanthanide and even actinide complexes as well as later metals (Groups V-VII) have also been used. The active species can be stabilized by other bulky ligands such as those derived from 2,6-disubstituted phenols (aryl-oxy) or silica (siloxy) (vide infra). Moreover, the catalytic activity of these systems is not limited to the hydrogenation of alkenes, but can be used for the hydrogenation of aromatics, alkynes and imines. These systems have also been developed very successfully into their enantioselective versions. 

Hydrogenation Catalysts Based on Croup III, Lanthanide, and Actinide Complexes... 

Perovskites, 27 358 band structure, 38 131-132 crystal structure, 38 123-125 Perovskite-type oxides see also specific lanthanum-based catalysts actinide storage in radioactive waste, 36 315-316... 

The extraction properties of the BTBPs toward trivalent lanthanides and actinides have been intensively investigated as a function of the nature of the organic diluent or phase-transfer catalyst and as a function of the ionic strength and acidity of the aqueous phase (47, 210-215). 

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