Reduced transition metal oxide catalysts on support

Reduced Transition Metal Oxide Catalysts on Support 

For an Al203-Si02 support, a 3% metal nitrate solution is used. The saturated bed is heated to 500 °C to decompose the nitrate. This is followed by a reduction. Many modifications of the above procedure have been developed since. 

Preparations based on molybdenum oxide are called Standard Oil Co. catalysts, while those based on chromium oxide are known as the Phillips Petroleum Co. catalysts. Below is a description of a preparation of a molybdenum-based catalyst. Alumina is saturated with a solution of anunonium molybdate and then subjected to heating in air at 500 to 600 °C. The oxide that forms is reduced with hydrogen at 430 to 480 °C. Reducing agents like CO, SO, or hydrocarbons are also used. Hydrogen, however, is preferred at pressures of approximately 75 psi. The catalyst may contain between 5 and 25% of the molybdenum compound dispersed on the surface.  

A typical chromium-based catalyst is prepared similarly. It is usually supported by a 9 1 of Si02 Al203 carrier. Either Cr(N03)3 9H20 or C1O3 solutions in nitric acid are used to impregnate the support. The nitrates are decomposed in air at 400 to 1000 An optimum chromium content 

The mechanism of polymerization was initially believed to be as follows. Cr-O-Si bonds are present on the catalyst surface. Contact with ethylene results in an oxidation-reduction reaction and formation of an ethylene-chromium complex. The initiations are accompanied by gains of hydride ions and formations of terminal methyl groups. Polymer growth was pictured according to the reactions shown in Fig. 3.6  

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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