The decomposition of n-propylammonium precursors of silicates with ZSM-5 structure containing Al, Band Ga, respectively, and the acidity and thermal stability of the resulting hydrogen forms were studied by infrared spectroscopic, x-ray diffractometric and thermal methods. The acidity of the as-synthesized products decreases in the substitution sequence B>Al> Ga. The hydrogen form of the boron analogue of ZSM-5 was found to be thermally instable, the decomposition of the precursor results in a silicalite-like product containing extra-framework boron oxide species. After heat treatment the acidity decreases in the substitution sequence Al> Ga >B. contrary to the boron counterpart the hydrogen form of ZSM-5 zeolite and of its Ga analogue are active and highly selective transalkylation catalysts. The catalytic conversion of the systems cumene-benzene, cumene-toluene and ethylbenzene-toluene were studied. Only acid sites of the Bronsted type seem to be involved in the transalkylation. Pretreatment of the catalysts under "selfsteaming" conditions favours side reactions, e.g. cumene cracking. Steaming results in dramatic' changes in activity and selectivity.
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry