The effect of acid treatment on the properties of dealuminated Y zeolite

Abstract

Dealuminated Y zeolite has been prepared by treatment of the hydrogen form with SiCl₄ vapour at 720 K. Measurements of aluminium content, pore volume, crystallinity and infrared spectra, together with ²⁷Al and ²⁹Si magic-angle spinning nuclear magnetic resonance spectra, have been used to characterize the product following controlled acid treatments between pH 4.8 and 0.0. Extrastructural aluminium was progressively extracted with increasing acidity between pH 4.8 and 1.3, whilst the Si/Al ratio of the framework structure increased only slightly from its initial value of ca. 16. With acid treatment below pH 1.0 extraction of both extrastructural and structural aluminium was accompanied by loss of porosity and crystallinity. Measurements of the catalytic activity for dehydration of propan-2-ol at 380 K confirmed that mineral acid at ca. pH 1.0 provides the optimum pretreatment for moderately dealuminated Y zeolite. The investigation emphasizes the need to control activation procedures for dealuminated zeolite catalysts.