The effects of templates and seeds on the properties of nanosheet SAPO-34 molecular sieves and their catalytic performance in the MTO reaction

Abstract

Nanoscale SAPO-34 molecular sieves were synthesized by adding different types of seed into hydrothermal synthesis systems with tetraethylammonium hydroxide (TEAOH) and triethylamine (TEA) & tetraethylammonium bromide (TEABr) as templates. The effects of different types of template and seed on the crystal structure, morphology, grain size and acidity of the molecular sieves were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 isothermal adsorption–desorption and ammonia temperature-programmed desorption (NH3-TPD). The methanol-to-olefins (MTO) reaction performance of the synthesized samples was investigated in a fixed-bed reactor. The results showed that crystalline supernatant and seed soaking solution could be used as liquid seeds to assist in the synthesis of SAPO-34 molecular sieves with a lamellar structure. The yield of SAPO-34 synthesized by seed increased from 38.64 to 59.68%, and the methanol conversion rate was significantly improved as compared with that of SAPO-34 synthesized without seed. The nano-thickness of SAPO-34 synthesized with TEA&TEABr instead of TEAOH as template decreased from 100–150 to 40–50 nm, and the lifetime increased from 360 to 400 min with the original yield kept constant.