Phase Transition Behavior of Zeolite Y under Hydrothermal Conditions

Abstract

The phase transition behavior of zeolite Y (HY and NaY) to zeolite MER in the KOH solution under hydrothermal conditions was systematically investigated. Zeolite MER has four types of 8-membered ring channels (3.1 Å×3.5 Å, 2.7 Å×3.6 Å, 3.4 Å×5.1 Å, 3.3 Å×3.3 Å) and important potential applications in small molecule catalysis and separation. Seven to ten days are needed to synthesize highly crystalline zeolite MER with traditional hydrothermal synthesis. With phase transition of zeolite Y in the KOH solution under hydrothermal treatment, highly crystalline zeolite MER can be obtained within two days. The synthetic system contains zeolite Y (HY and NaY), KOH, and water, where KOH/SiO2 and H2O/SiO2 are changeable. Hydrothermally treating the equivalent amorphous aluminosilicate gel resulted in the mixture of zeolite MER and zeolite LTL (for HY) or zeolite CHA (for NaY) with low degree of crystallinity. Phase transition of HY can be conducted at either 100 or 150℃, whereas that of NaY can only be conducted at 150℃.As a common process for the hydrothermal phase transition of zeolite Y to zeolite MER in the absence of organic templates, potassium hydroxide was first dissolved into deionized H2O. After stirring at room temperature for 5 min, zeolite Y (HY or NaY) as aluminum and silicon sources was introduced into the potassium hydroxide solution. After further stirring for 1 h, the mixture was transferred into an autoclave for crystallization at elevated temperature (i.e.100 or 150℃). After filtrating, washing with deionized water and drying, zeolite products were obtained. The zeolite products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and inductively coupled plasma emission spectrometer (ICP). KOH/SiO2 and H2O/SiO2 have significant influence on the phase transition behavior of zeolite Y. Highly crystalline zeolite MER can only be obtained with the optimized KOH/SiO2 and H2O/SiO2. With this method, the synthesis period of zeolite MER is greatly reduced, which might be applied to the synthesis of other industrially important zeolites in a shortened time.