Influence of mild dealumination on physicochemical, acidic and catalytic properties of H-ZSM-5

Abstract

Mild dealumination of ZSM-5 using HCl, acetylacetone and ammonium hexafluorosilicate resulted in a slight increase in the XRD crystallinity and overall surface area, but there was a marginal decrease in the micropore area and a considerable increase in mesopore area. ²⁷Al MAS-NMR spectra showed very weak signals due to octahedral aluminium for the samples treated with HCl and acetylacetone. FTIR spectra revealed small amounts of extra framework Al and four bands due to OH stretching vibration. The nature and intensity of the bands due to different hydroxyl groups varied depending on the treatment. Dealumination resulted in an increase in m-xylene conversion but a decrease in isomerization selectivity. The activity was maximum for HCl- and acetylacetone-treated samples that is attributed to the increase in the overall acidity (both Lewis and Bronsted) of samples as well as to the creation of mesoporosity.