Effect of contributing factors on microwave-assisted hydrothermal synthesis of nanosized SAPO-34 molecular sieves

Microwave synthesis has been shown to dramatically enhance the reaction rate of many zeolite syntheses. In this study, crystals of nanosized SAPO-34 molecular sieves were synthesized by using microwave-assisted hydrothermal heating with different synthesis conditions to elucidate the effect of these contributing factors on the SAPO-34 formation, in terms of the size and morphology of crystals. All samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thermal gravimetric analysis (TGA). It was found that microwave-assisted hydrothermal heating was required to obtain fully crystalline SAPO-34 crystals. The hydrothermal heating time played a crucial role in the shape and size control of nanosized SAPO-34 crystals, while the aging time had a negligible effect. The smaller pure SAPO-34 crystals were formed when using a higher concentrated solution as the initial gel. Smaller crystals were produced at higher microwave power, whereas the crystal morphology was found to be independent of the microwave power levels. The crystal size and morphology of SAPO-34 could be controlled by microwave irradiation time and an optimum microwave irradiation time for the preparation of nanosized SAPO-34 crystals was found.