Quantification of Bronsted Acid Sites in Zeolites by Water Desorption Thermogravimetry

authors	Bornes, C; Amelse, J; Peacock, M; Marshall, CL; Schwartz, M; Geraldes, CFGC; Rocha, J; Mafra, L
nationality	International
journal	EUROPEAN JOURNAL OF INORGANIC CHEMISTRY
author keywords	Zeolites; Acidity; Water clusters; Thermogravimetry; ZSM-5; Structure elucidation
keywords	HAMS-1B
abstract	The many studies that have been conducted on water adsorption on zeolites were carried out in adsorption mode, from adsorption isotherms or single-point measurements, with the samples being first degassed at high temperature, and then exposed to water vapor at variable partial pressure. Here, we report Thermogravimetric Analysis (TGA) studies of HZSM-5 saturated with water at room temperature, thus studying water adsorption in desorption mode. TGA was used to ascertain the amount of water remaining as a function of the pretreatment temperature, and to identify the temperature at which one water molecule per framework Al atom persists. Solid-state H-1 NMR spectroscopy, combined with molecular modeling, provided evidence for water molecules hydrogen bonded to Bronsted acid sites and formation of oxonium species for distinct water per framework Al atom. TGA is shown to be a simple and expeditious technique to measure the number of Bronsted acid sites in aluminosilicate zeolites, with advantages over the traditional methods of IR or TPD of dangerous adsorbed ammonia or pyridine. TGA of adsorbed water also provides information on the water clusters formed at the acid sites of HZSM-5, which are proportional to the number of acid sites.
publisher	WILEY-V C H VERLAG GMBH
issn	1434-1948
isbn	1099-0682
year published	2020
volume	2020
issue	19
beginning page	1860
ending page	1866
digital object identifier (doi)	10.1002/ejic.202000050
web of science category	Chemistry, Inorganic & Nuclear
subject category	Chemistry
unique article identifier	WOS:000529235000001