Hierarchical ZSM-5, Beta and USY zeolites: Acidity assessment by gas and aqueous phase calorimetry and catalytic activity in fructose dehydration reaction

Abstract

The acidity of hierarchical USY, Beta and ZSM-5 zeolites obtained by alkaline treatment was investigated. Samples were characterized by low temperature nitrogen adsorption, X ray diffraction and solid-state (27)AI MAS NMR. Acidity of parent and mesoporous samples was estimated through the adsorption of typical probe molecules - measurements were conducted in both gas phase (microcalorimetry/volumetry of ammonia adsorption, FTIR spectrometry of pyridine adsorption/desorption) and aqueous phase (calorimetry of phenylethylamine adsorption). Quantitative distributions in strength of the acid sites were determined, as well as acid sites concentrations. No significant changes in total acidity were detected for ZSM-5. Acid sites strength was decreased in modified Beta and USY zeolites. The samples were probed as catalysts for the dehydration of fructose. Higher selectivities towards 5-hydroxymethylfurfural were detected for all modified zeolites, compared to the parent ones.