A Novel Zeolite MCM-22: Sorption Characteristics

Abstract

Synthetic zeolites of MCM-22 type with different framework SiO2/Al2O3 ratios (ranging from 40 to 140) obtained by direct hydrothermal crystallisation were studied using different probe molecules. The influence of framework aluminium content on the BET surface area and on the micropore void volume was examined using low-temperature argon sorption. Sorption uptake using different probe molecules such as water, n-hexane, cyclohexane, m-xylene and 1,3,5-trimethylbenzene (mesitylene) was measured at 298 K. Considerable sorption (> 7.5 wt%) of bulky molecules such as m-xylene and mesitylene was observed suggesting the possible access from the crystal surface to some 12 membered-ring cages. The sorption energetics in zeolite MCM-22 as a function of the framework SiO2/Al2O3 ratio were discussed on the basis of NH3 sorption isotherms in the temperature range 303–453 K. The sorption data were analysed in terms of different sorption isotherm equation models. The ammonia sorption studies indicated that the acid sites were not uniform and were distributed heterogeneously.