Alumina heterogeneous polymerization catalysts

Gfoup 4 bis(arene) complexes (arene = mesitylene) have also been used as precursors for heterogeneous polymerization catalysts. Their reaction with alumina gives 1 equiv. of mesitylene/grafted M, and it has been proposed that this reaction yields [(AlsO)M(C6H3Me3) (H)] (Scheme... 

Phillips (1) A process for polymerizing ethylene and other linear olefins and di-olefins to make linear polymers. This is a liquid-phase process, operated in a hydrocarbon solvent at an intermediate pressure, using a heterogeneous oxide catalyst such as chromia on silica/ alumina. Developed in the 1950s by the Phillips Petroleum Company, Bartlesville, OK, and first commercialized at its plant in Pasadena, TX. In 1991, 77 reaction fines were either operating or under construction worldwide, accounting for 34 percent of worldwide capacity for linear polyethylene. 

As the scope of the reaction increased, the name Olefin Metathesis was introduced by Goodyear, who also pioneered the use of homogeneous catalysts. The reaction had first been recognized during experiments on the development of a heterogeneous catalyst to replace mineral acids in alkylation reactions. Molybdenum hexacarbonyl catalyst supported on alumina produced 2-pentene (40%) from mixed n-butenes together with propylene (51%) and hexene (9%). Tungsten hexacarbonyl was less active than the molybdenum catalyst, and in total contrast, it was found that chromium hexacarbonyl acted as a polymerization catalyst. 

The exopolyhedral metaHacarborane complex Ti(C2B2QH22)4, which is prepared by the reaction of TiCl and 1-Li-1,2-C2B2QH22, has also been reported to be an active heterogeneous catalyst for the polymerization of olefins when supported on alumina and in the presence of (C2H3)2A1C1 co-catalyst (230). 

Alcohols and jlkenes are also primary products and are not shown in the simplified Eq. 15.182. The overall reaction is complicated and, as a result, its mechanism has been the subject of considerable debate.188 The reaction may be viewed as the reductive polymerization of carbon monoxide, with molecular hydrogen as the reducing agent. A variety of heterogeneous catalysts, such as metallic iron and cobalt on alumina, have been used. It is believed that carbon monoxide dissociates on the catalytic surface to give carbides and that these are in turn hydrogenated to give surface carbenes 1 " n ... 

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