Transition metal pillared clay 4. A comparative study of textural, acidic and catalytic properties of chromia pillared montmorillonite and acid activated montmorillonite

Abstract

The preparation, characterisation and catalytic activities of chromia pillared montmorillonites were investigated. The Na-exchanged montmorillonite shows higher uptake of chromium(III) acetato complex than that of acid activated clay. However, in both the cases, stepwise ion-exchange process results in better intercalation compared to the single step process. Both the pillared materials are found thermally stable up to 773 K. Materials prepared from Na-exchanged clay show higher surface area, micropore volume and basal spacing, whereas the materials prepared from acid-activated clay possess higher mesopore volume, average pore diameter and surface acidity. A substantial increase in acidity due to acid activation before pillaring is observed in the 2-propanol and methanol dehydration reactions. Increase in cracking activity indicates the formation of an extra number of Bronsted acid sites due to the acid activation. However, with the increase in reaction temperature above 673 K, cracking activity decreases and dehydrogenation activity increases owing to the loss of Bronsted acid sites. Surface poisoning studies proved that alcohol dehydration and cumene cracking depend on the Bronsted acid sites, while dehydrogenation of cumene occurs on Lewis acid sites. (C) 1998 Elsevier Science B.V.