Preparation of the Phillips Catalyst

The Phillips catalyst is prepared by impregnating a chromium compoxmd into a high surface area silica, such as Davison Grade 952 silica, with a pore volume of about 1.6 cc/g and a surface area of about 300 mVg. The type of chromium compound used as the chromium source does not affect the behavior of the finished catalyst after the activation (oxidation) step [4]. Chromium(III) acetate, ammonium chromate or dichromate and chromium oxide (CrOj) are possible sources of chromium. Sufficient chromium is used to yield about 0.5 tol.O wt% Cr in the final catalyst. 

Hogan has postulated that a surface chromate species is formed by the interaction of surface hydroxyl groups (Si-OH) on the silica with CrOj[5]. 

Hydrogen is the least preferred reducing agent, as it forms water as the oxidation product which may remove the chromium species from the silica surface via a hydrolysis reaction. Carbon monoxide has been used in various studies to determine the final oxidation state(s) of the reduced 

Reduction of the Phillips catalyst with ethylene at 135 C was investigated by Carrick and Baker [8]. Their data are shown in Table 3.3. Oxidative cleavage of the ethylene double bond, with the formation of the 

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