Modification of textural and acidic properties of -SVR zeolite by desilication

Abstract

Desilication conditions (concentration of NaOH and TPAOH solution, duration of the treatment) of -SVR zeolite were varied and related to the textural and acidic properties of the obtained materials. The treatment of -SVR zeolite with NaOH solution led to the formation of mesopores and also the increasing of the concentration of surface acid sites, accessible for bulky molecules (e.g. 2,6-ditertbutyl-pyridine). The volume of mesopores as well as the concentration of accessible acid centres in desilicated materials depends mainly on the concentration of the alkaline solution. The increase in the pH of the treatment resulted in moderate decrease of both micropore volume and Brønsted acid sites concentration, while the volume of mesopores increased significantly. Independently of the duration and pH of the treatment with NaOH solution, all desilicated -SVR zeolites are characterized by broad pore-size distribution in the range of 5–20nm with the maximum around 14nm. At fixed pH of the treatment with TPAOH, the volume of mesopores and their average size decreased, while the Si/Al ratio and the concentration of Brønsted acid sites in desilicated materials increased which indicates the inhibiting effect of TPA+ cations on the extraction of Si from -SVR zeolite.