Shape-selectivity changes in high-silica zeolites
Y-type, ZSM-5 and ZSM-11 zeolites with the same chemical composition have been prepared. Peak indexation and microscopic examination were used to identify the phases and to examine the samples for degree of crystallinity. The acidity was measured by temperature-programmed desorption of NH3 and infrared examination of OH groups upon interaction with hydrogen-bond-acceptor molecules. These data were consistent with the results derived from total activity and selectivity measurements of the isomerization and hydrocracking of n-decane on the Pt-loaded zeolites.
The distribution of the feed isomors served to distinguish between HZSM-5 and HZSM-11 type structures, while the cracked products could be predicted using simple reaction schemes. 2,2,4-Trimethylpentane was not able to enter the pores of the Pentasil zeolites, reacting near the pore mouth or entering the pores after dehydrocyclisation on Pt clusters external to the zeolite.