Electron spin resonance and electron spin echo modulation studies of Cu(II) cation locations and adsorbate interactions in ionexchanged Cu-MCM-22 zeolite

Abstract

MCM-22 is a medium-pore high-silica-containing zeolite. Its unique structure contains two noninterconnected channel systems with potential for transition metal-based heterogeneous catalysis. Paramagnetic Cu(II) cation is ionexchanged into MCM-22 to act as a probe for electron spin resonance and electron spin echo modulation spectroscopic methods to verify the location of the ion-exchangeable sites. The electron spin resonance spectra of dehydrated Cu-MCM-22 are strikingly well-resolved and exhibit features related to both ⁶³Cu and ⁶⁵Cu nuclei. Interactions with water, ammonia, methanol, pyridine, benzene, cyclohexylamine and triethylamine adsorbed on Cu-MCM-22 are studied. Three types of ion-exchangeable extra framework site are identified.