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

• Published in: Microporous and mesoporous materials Vol. 236; pp. 85 - 93
• Main Authors: Borges, Luciana Diniz, de Macedo, Julio Lemos
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-12-2016
• Subjects: Ammonium hexafluorosilicate; Calorimetry; Dealumination; Solid-state; Zeolite Y; Zeolite Y; Calorimetry; Dealumination; Solid-state; Ammonium hexafluorosilicate
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2016.08.031

Zeolite Y was dealuminated in the solid-state at several degrees (5, 10, 15 and 20%) using (NH4)2SiF6 as dealumination agent. The materials were heated to 80, 100, 120, 140, 160, 180 and 200 °C to investigate the best temperature at which the samples retain their crystallinity and acidity. The solids obtained were characterized by XRD, FTIR, TG/DTG, XRF, 27Al and 29Si MAS NMR and N2 physisorption. They were also subjected to pyridine adsorption and calorimetric experiments. Structural and textural results showed that lower temperatures (80 and 100 °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 Brønsted 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.
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•Zeolite Y solid-state dealumination with AHFS was studied at several temperatures.•The surface area and porosity of dealuminated zeolites increased at lower temperatures.•The calorimetric enthalpy data showed high values for the dealuminated materials.•The dealumination with AHFS at 80 and 100 °C favored the substitutive mechanism.