In the present study, the synthesis of template free zeolite P under hydrothermal condition was investigated. The effects of parameters such as Si/Al ratios (3–45), crystallization temperatures (80–160°C), and cry (40–60 h) on the synthesis of zeolite P were studied. The phase transformation of zeolite P to two types of high crystallinity Y and analcime zeolites due to change of temperature was observed. The effect of temperature on the achievement of two different zeolite types (Y and analcime) with a constant initial synthetic composition under organic free synthesis of zeolite P was studied. The zeolitic products were characterized by X-ray diffraction, scanning electron microscopy, and IR spectroscopy techniques.
Zeolitic materials are microporous high-internal-surface crystalline and hydrated aluminosilicates of alkali and alkaline earth cations with an infinite open and rigid three-dimensional structure [
Phase transformation processes include the transition from one structure or symmetry into another structure or symmetry, and the intermediate phases can be observed by analysis techniques. This means that from an initial gel with defined composition, one can obtain two or more pure types of zeolite depending on the conditions of crystallization such as alkalinity, crystallization temperature and time, and organic additives (template). However, such a possibility may represent a serious disadvantage in the attempt to achieve the desired group of zeolite in pure form without admixtures of alternative types of zeolite. Then it is possible to know the conditions under which a certain type of zeolite transform into other ones, in order to determine useful crystallization conditions for synthesis of zeolites in pure form. The role of organic template on phase transformation process of Y zeolite to zeolite P and analcime was reported in our previous work [
The reagents silicic acid, sodium hydroxide, and aluminum powder (all purchased from Merck) were used in the synthesis. All aqueous solutions were prepared using deionized doubly distilled water. The zeolite was synthesized from gel with initial Si/Al molar ratio in composition of 14.5. The sol-gel mixture was prepared by mixing an aluminate and a silicate solution. Then the synthesis gel was introduced to Teflon-lined stainless steel autoclave and sealed autoclave was put into an air oven and heated for 60 hours at 100°C. The solid products were filtered and washed with deionized water, dried overnight at 100°C, and calcinated at 550°C for 5 h in an electric furnace.
The X-ray powder diffraction (XRD) patterns were collected on a GBC MMA instrument. The patterns were run with Ni-filtered CuK
The crystallization temperature was varied from 80°C to 160°C in order to find the appropriate temperature for the formation of each pure zeolitic phase. The results indicated that the pure zeolite P was obtained at 100°C whereas the pure phase zeolite Y was produced at 90°C and changing temperature to 95–97°C resulted in a mixture of zeolites Y and P. By increasing temperature from 100°C up to 110°C a mixture of zeolites P and analcime was produced. The pure phase analcime can be obtained at 130°C. All investigations about the effect of temperature were carried out with a same initial gel composition without using any organic additive. The scanning electron micrographs and XRD patterns, which showed the effect of temperature on the synthesis of three types of mentioned zeolites, are illustrated in Figures
Scanning electron micrographs of synthesized zeolites at different temperatures: (a) 90°C, (b) 96°C, (c) 100°C, (d) 110°C, and (e) 130°C.
X-ray patterns of synthesized zeolites at different temperatures: (a) 85°C, (b) 90°C, (c) 96°C, (d) 100°C, (e) 110°C, and (f) 130°C.
The crystallization of zeolite P from initial gel composition of 30 SiO2 : Al2O3 : 24 Na2O : 1360 H2O with different crystallization times at a temperature of 100°C was followed by X-ray powder diffraction (Figure
X-ray patterns of synthesized P zeolites after different crystallization times: (a) 30 h, (b) 40 h, and (c) 60 h.
In order to synthesize zeolite P the initial gel composition 30 SiO2 :
X-ray patterns of synthesized zeolites from initial synthetic gel with various Si/Al mole ratios: (a) 3, (b) 5, (c) 15, (d) 30, and (e) 45.
SEM images of synthesized zeolites from initial synthetic gel compositions with Si/Al mole ratios of (a) 15 and (b) 30.
Figure
FT-IR spectra of synthesized three types of zeolites under template free condition from the same initial gel compositions (a) zeolite Y, (b) zeolite P, and (c) analcime.
In this study a new method for organic free synthesis of zeolite P under hydrothermal condition was investigated. The effect of temperature on the phase transformation of the structure of zeolite p to analcime and to zeolite Y was studied. By changing temperature, the Y and analcime zeolitic phases were observed. The organic free synthesis of analcime and zeolite Y through synthesis of zeolite P with changing temperature for the first time in this study was reported. The effect of heating time, Si/Al ratios in the initial gel, and heating temperature on the obtained zeolite were investigated. A mixture of P and Y zeolites was obtained in 95–97°C and this mixture was transferred to high crystalline zeolites P and analcime phases with the increase of temperature to 100° and 130°C, respectively.