Acid strength distribution and catalytic properties of H-ZSM-5: effect of deammoniation conditions of NH₄-ZSM-5

Abstract

Acid strength distribution, catalytic activity in cumene cracking and o-xylene isomerization reactions, and the distribution of hydrocarbons formed in methanol and ethanol conversion reactions on H-ZSM-5 zeolites obtained from NH₄-ZSM-5 under different deammoniation conditions (i.e., by varying temperature, period, atmosphere and heating rate in the deammoniation) have been studied. The catalytic properties of the zeolites are correlated to their acidity. The acid strength distribution, the cracking and isomerization activities, and the distribution of hydrocarbons in the alcohol conversion reactions on the zeolites are affected by the changes in the temperature, period, and atmosphere employed in the deammoniation, the effect produced by the higher deammoniation temperatures (< 873 K) being very drastic. The heating rate employed for attaining the deammoniation temperature has no significant effect on either the acidity distribution or the catalytic properties of the zeolite. The conversion of cumene, the xylene isomerization activity, and the extent of aromatization in the alcohol conversion reactions on the zeolites could be very satisfactorily correlated to the number of strong acid sites on which pyridine is adsorbed irreversibly at 673 K.