Characterization of Acidity and Porosity of Zeolite Catalysts by the Equilibrated Thermodesorption of n-Hexane and n-Nonane

Abstract

Thermodesorption of n-hexane and n-nonane from the acidic and non-acidic zeolites ZSM-5 and Y was studied by means of the thermogravimetric temperature programmed equilibrated desorption (TPED) and quasi-equilibrated temperature programmed desorption and adsorption (QE-TPDA). Micropore volumes determined from the adsorption capacity of n-hexane were close to those determined by N2 adsorption. Content and strength of acid sites in the acidic zeolites estimated by fitting the Arrhenius equation to the high temperature parts of QE-TPDA profiles of n-hexane attributed to its cracking were in agreement with their acidity characteristics obtained by IR spectroscopy of chemisorbed pyridine. The mesopore volume was determined from the QE-TPDA profiles of n-nonane. Coking observed only for QE-TPDA of n-nonane on H-USY zeolite resulted in blocking the micropores without affecting the mesopores.