Hydroxyl Groups of Exceptionally High Acidity in Desilicated Zeolites Y

Abstract

The desilication of dealuminated zeolite Y in NaOH/tetrabutylammonium hydroxide mixtures produces hierarchical zeolite Y containing a micropore system as well as mesopores of significant volume and surface. IR studies evidenced that a new kind of hydroxyls was formed if desilication was realized above 318 K. This new kind of acidic hydroxyls is characterized by IR band at 3600 cm^-1 . IR studies showed, that these new hydroxyls showed extremely high acidity. This was evidenced by very high frequency shifts of IR bands of OH interacting with probe molecules: CO and N₂ : ${\Delta \nu }_{OH···CO}$ =411 cm^-1 and ${\Delta \nu }_{OH···N_2}$ =164 cm^-1 , resp. These frequency shift are the highest in all the chemistry of zeolites including very strongly acidic dealuminated mazzite and steamed zeolite USY ( ${\Delta \nu }_{OH···CO}$ =ca. 380 cm^-1 ) indicating that 3600 cm^-1 hydroxyls are the most acidic in all the zeolites.

Keywords: IR spectroscopy; acidity; dealumination; desilication; zeolites.