Solid support catalysts silicon compounds

The alumina or silica-alumina supports used in bifunctional catalysts have been shown to be acidic in nature. The acidic properties are readily demonstrated by the affinity of these solids for adsorption of basic compounds such as ammonia, trimethylamine, re-butylamine, pyridine, and quinoline (01, R5). Furthermore, adsorption of certain acid-base indicators such as butter yellow gives a coloration similar to that observed in acid media (B3, B4). With regard to the origin of the acidity, Tamele (Tl) has suggested in the case of silica-alumina that aluminum atoms replace silicon atoms in the surface of the silica structure, giving rise to surface sites of the form... 

The supported chromium oxide catalysts can be prepared by impregnating a silica-alumina support with a solution of chromium ions or by coprecipitating the oxides. The preferred impregnating solutions contain dissolved Cr(N03)s.9H20 or CrOs in nitric acid because catalysts made from chromium chlorides or sulfates retain some of the anions after calcination. The solid mixture of chromium-silicon-aluminum compounds is calcined in dry air at 400-700° C or higher to obtain the desired oxide. This probably results in the reaction of surface hydroxy groups in the support material with CrOs to form chromate (IV) and dichromate (V) species ... 

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