Catalytic Activity of Chlorozinc(II) Complex-Fixed Metal Oxides -The Reactions of o-Xylene and Cyclohexanone Oxime-

Abstract

The catalytic activity of metal oxides, on which chlorozinc (II) complexes were fixed, was investigated concerning with the isomerization(I) and disproportionation IO of o-xylene as well as the Beckmann rearrangement (III) and dehydration (IV)of cyclohexanone oxime. Of the various catalysts examined, Si0<₂ Al₂O₃ and Si0₂, on which chlorozinc (II) complex was fixed exhibited high catalytic activity toward the above reactions. On these systems, however, the fixation of chlorozinc(II) complexes changed the reaction selectivity to enhance (II) and (IV) and to diminish (I) and (IV). Surface acidity measurements by the Benesi method showed that, with increasing the amount of fixed zinc (II) complex, acid sites (-5.6 ≤ Ho ≤ 3.3) increased, while those (110≤ -5.6) decreased, and that such change in acidity corresponded closely with the observed change in catalytic activity. The thermal stability of the surface zinc(II)complex was examined by chemical analyses after various heat treatments. On the basis of the above result, it was proposed that the decrease of acid sites (H0 ≤-5.6) occurred -due to the loss of surface acidic protons during the fixation of zinc (II) complexes and that acid sites (-5.6≤ Ho ≤3.3) appeared due to the partial decomposition of the fixed complexes; the latter acid sites were either surface OH groups adjacent to zinc (II) or coordinatively unsaturated zinc (II) ions.