Solid-state dealumination of zeolite Y: Structural characterization and acidity analysis by calorimetric measurements

Zeolite Y was dealuminated in the solid-state at several degrees (5, 10, 15 and 20%) using (NH4)(2)SiF6 as dealumination agent. The materials were heated to 80, 100, 120, 140, 160, 180 and 200 degrees C to investigate the best temperature at which the samples retain their crystallinity and acidity. The solids obtained were characterized by XRD, FTIR, TODTG, XRF, Al-27 and Si-29 MAS NMR and N-2 physisorption. They were also subjected to pyridine adsorption and calorimetric experiments. Structural and textural results showed that lower temperatures (80 and 100 degrees C) and smaller degrees of dealumination (5 and 10%) maintained the zeolite crystallinity and increased its specific surface area, microporosity and mesoporosity. The study of the materials acidity indicated the presence of Bronsted acid sites with different strength, hydrogen bonding sites and Lewis sites originated from acid leaching. The calorimetric measurements showed higher enthalpy values for some of the dealuminated materials than for the parent zeolite. It also evidenced an increase for the number of acid sites between -160 and -140 kJ mol(-1) and a reduction for the other sites, between -140 and -80 kJ mol(-1). (C) 2016 Elsevier Inc. All rights reserved.