Modified H-Mordenites, ZSM-5, and heteropoly acids were prepared and subjected to reaction studies to gain an insight into their acid roles on the reactions. Modification steps for mordenites include steam-treatment and ion-exchange with transition metals.
Acid properties of the catalysts were investigated by the temperature programmed desorption of ammonia and pyridine and infrared spectra of pyridine adsorbed on the catalysts. TPD experiments showed that there were two kinds of active sites-weak and strong- on mordenite and ZSM-5 surfaces. IR experiments revealed that there were Lewis and Brönsted acids on mordenites and ZSM-5, while there was only Brönsted acid on heteropoly acids.
It was found that strong acids were responsible for the carbon deposits on the catalyst surface. It was also observed that strong acid played an imporatant role on the product selectivity for the xylene isomerization and toluene disproportionation, while weak acids were active for isomerization of n-butene and methanol conversion to dimethyl ether.