Post-synthesis modification of TUN zeolite: Textural, acidic and catalytic properties

Dealumination, desilication and silylation of TUN zeolite was investigated and related to the catalytic behavior in toluene disproportionation and its alkylation with isopropyl alcohol. Only negligible concentration of acid sites was identified on the “external” surface of parent TUN zeolite and this concentration increased with increasing desilication. Silylation resulted in channel narrowing and probably some plugging. As a result, significant increase in the para-selectivity in toluene disproportionation and its alkylation with isopropyl alcohol was achieved. No changes in toluene conversion were observed for all parent and modified samples in toluene alkylation confirming diffusion and transport of products as the rate determining step in 10-ring zeolites. Selectivity to cymenes and p-cymene decreased with dealumination as well as desilication. In contrast, silylation increased both cymene (80%) and p-cymene (90%) selectivity in toluene alkylation.