Impact of cationic lanthanum species on zeolite Y: an infrared, excess infrared and Raman spectroscopic study

Abstract

The recently proposed technique of excess infrared spectroscopy was extended for the first time to a solid system to explore the host–guest interactions between the framework of zeolite Y and the encapsulated lanthanum species. By employing infrared, excess infrared and Raman spectroscopies, the physical insights into the band shifts/intensity variations of asymmetric TO₄ (T = Si, Al) stretching and T–O–T bending were revealed. In the ion-exchange process, the ring distortions were sensitively distinguished by the red shift of the T–O–T bending bands. Upon dehydration, the strengthening effect on the T–O bond was demonstrated by the absorption of the interaction pair between the zeolite framework and dehydrated lanthanum species ([La(OH)_n]⁽³⁻ⁿ⁾⁺ (n = 1, 2) and La³⁺), revealing the mechanism of the stabilization effect of lanthanum species on the zeolite framework. Also, the Raman band located at 362 cm⁻¹ was found to be directly related to the 6-membered rings in the hexagonal prisms of zeolite Y. Moreover, Raman spectroscopy showed the capability to describe the distinction between rare earth oxides within and outside the microporous zeolites. XPS, ²⁷Al and ²⁹Si MAS NMR were also performed for further validations.