Nature, strength and accessibility of acid sites in micro/mesoporous catalysts obtained by recrystallization of zeolite BEA

Micro/mesoporous materials with different contribution of micro- and mesoporosity were prepared by recrystallization of zeolite BEA in alkaline solution in the presence of cethyltrimethylammonium bromide. The materials were characterized by XRD, nitrogen adsorption–desorption and IR spectroscopy of adsorbed probe molecules. It has been demonstrated that the degree of recrystallization can be adjusted by variation of concentration of NaOH in solution. Recrystallization in mild conditions did not significantly affect the amount and strength of acid sites but resulted in the improvement of their accessibility for bulky probe molecules due to the creation of mesopores. The increase of the degree of recrystallization led first to partial and then to complete transformation of BEA into MCM-41 followed by a gradual decrease of the amount and strength of Brønsted sites and the increase of the contribution of Lewis sites to the total amount of sites.