Hierarchical zeolite mazzite: Physicochemical properties and α-pinene isomerization

Abstract

Dealuminated mazzite shows very high acid strength of SiOHAl groups. The aim of our study was to produce hierarchical mazzite, containing mesopore system, but preserving strong acidity. This was done by desilication of dealuminated mazzite (Si/Al = 30), carried out using NaOH/TBAOH solutions. Desilication of zeolite as strongly acidic as mazzite was not done before. During desilication ca. 50% of silicon was extracted, the structural microporosity was indeed preserved, and large volume of mesopores was formed too. IR studies evidenced that very high acid strength of SiOHAl groups was preserved. According to NMR results five types of Al species were present in the desilicated material. Distribution of aluminium between two tetrahedral sites was non-random, with high preference toward occupying T2 positions located in the six-membered rings. The desilicated sample showed very high Brønsted acidity and high catalytic activity in the liquid-phase isomerization of α-pinene. Retention of the sample crystallinity, increased amount of Brønsted acid sites, their high acid strength and formation of large volume of 3D mesopores improving transport of reactants, all contributed to the enhanced catalytic activity of the desilicated mazzite.