Rare earths as catalysts

The patenting activity in the field of rare earth catalysts during 1970 and 1985 is illustrated in Fig. 12.3a. The vertical scale is arbitrary and is based on a total of 580 publications in 1985. As compared to 1970, the total published papers increased by four times and the patents by three times. Further, the patent activity showed a shift in emphasis from petroleum refining to pollution control activity. Other commercial catalyst systems are ammoxidation and dehydrogenation in which rare earths play a crucial role. 

In Tables 12.2 to 12.5 the lanthanide component used as the catalyst and the corresponding purpose are given. 

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Some of the applications of the organometallic compounds of lanthanides are as catalysts for (i) stereo specific polymerization of diolefins and in particular to obtain high yields of 1,4-ci.v-polybutadiene and 1,4-cw-polyisoprene and copolymer of the two monomers. The order of effectiveness of the rare earths as catalysts is Nd > Ce, Pr < Sm, Eu. The nature of halogen of the Lewis acid affecting the catalytic activity is in the order Br > Cl > I > F. Detailed work on the activity of cerium octanoate-AlR3-halide showed stereo specificity with cerium as the primary regulator. Cerium is thought to form jr-allyl or 7r-crotyl complexes with butadiene. 

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