Spectroscopic IR and NMR studies of hierarchical zeolites obtained by desilication of zeolite Y: Optimization of the desilication route

Optimization of the procedure of desilication of dealuminated zeolite Y in a NaOH/tetrabutylammonium hydroxide (NaOH/TBAOH) mixture was done in order to obtain zeolites of optimal crystallinity, porosity and acidity and therefore of promising catalytic properties in the isomerization of α-pinene. High-silica zeolite Y (Si/Al = 31) was treated with NaOH/TBAOH mixture of various TBAOH content (0–100 mol %). Desilication was carried out at temperatures from 293 to 373 K. It was shown, that the optimal crystallinity, acidity, porosity and catalytic properties was obtained if zeolite was treated with the NaOH/TBAOH mixtures containing 10–70% of TBAOH. However, taking into account the cost of a desilication route (TBAOH is an expensive agent), the most economic variant of desilication using 10 mol % of TBAOH only was chosen. The experiments performed at different temperatures revealed that the optimal catalytic properties of a resultant material were obtained after desilication carried out at 353 K. The conversion of α-pinene on this sample was nearly doubled in comparison with other zeolites desilicated at lower or higher temperatures. IR experiments showed also that desilication performed at higher temperatures (above 318 K) produced samples with a new kind of OH groups at 3600 cm−1. Finally, the experiments of pyridine adsorption demonstrated that this maximum is composed of the two kinds of OH groups exhibiting various properties, namely the acidic groups vibrating at 3600 cm−1 and the non-acidic ones at 3620 cm−1.