Preparation, Characterization, and Catalysis of a Modified ZSM-5 Zeolite

Protonated and modified ZSM-5 zeolites were prepared, characterized and used in the conversion of methanol to gasoline and in hydrocarbon cracking. The modified ZSM-5 was prepared by heating Na-ZSM-5 with a protonated, sterically hindered amine salt such that only cationic sites external to the zeolite channels underwent exchange. Its constraint index number was significantly lower than that of the unmodified H-ZSM-5, reflecting external protonic sites. Also, its sodium content was higher due to retention of internal sodium. NMR spectrometry of 129Xe gas sorbed in the modified and slightly coked zeolite demonstrated coking occurred primarily on the surface; whereas, the H-ZSM-5 zeolite was shown to deposit coke internally. In the conversion of methanol to gasoline, the modified zeolite was significantly less reactive. However, both zeolites had comparable activity in hydrocarbon cracking reactions carried …