Influence of hydrogen chloride addition on the catalytic isomerization activity of chlorinated alumina and chlorinated platinum–alumina solids. Superacid behaviour

Abstract

Alumina and alumina-supported platinum have been submitted to chlorination by carbon tetrachloride at 573 K. The addition of HCl during the n-butane isomerization reaction at 573 K strongly increases the catalytic activity when HCl is added to the reaction mixture during the early stage of the reaction. Preadsorption of hydrogen chloride at 573 K leads to the conversion of the strongest Lewis acid sites into superacid ones able to perform the isomerization of n-butane at temperatures as low as 373 K. In such conditions the reaction rate is not dependent on the presence of platinum: a superacid behaviour is proposed. At 573 K, the role of platinum in the isomerization reaction would be to produce important amounts of HCl by dechlorination of the support and to contribute to the formation of superacid centres. In the absence of platinum, the formation of HCl would be limited leading to a less active catalyst.