Characterization of aluminium siting in MOR and BEA zeolites by 27Al, 29Si NMR and FTIR spectroscopy

Abstract

Commercial and dealuminated mordenites (MOR) as well as home made and cobalt modified beta (BEA) zeolites have been characterized by 29Si and 27Al solid state Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy. The quantitative contributions of Si(nAl) and Si(OH)x sites to the NMR signal intensities were calculated from the various Si/Al ratios and relative 29Si and 27Al NMR signal intensities assuming twin, lone and no Al containing periodical building units of the zeolite framework. More lone compared to twin and silicate units were suggested for BEA than for MOR zeolites. Some octahedral Al transformed back to tetrahedral coordination due to ion-exchange of HBEA to Co/BEA zeolites. We conclude that we are able to distinguish the Si(OH)x groups which are original defect sites or produced in a dealumination or calcination process.