Effect of silica/alumina ratio and structure-directing agent on the physical and chemical properties of SAPO-34

This work describes how the silica/alumina ratio (SAR) affects the framework, texture, chemical composition, and acidity of SAPO-34 molecular sieves synthesized via hydrothermal crystallization using morpholine (MOR) or triethylamine (TEA) as structure-directing agents (SDA’s). The solids were chara...

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Bibliographic Details
Published in:	Journal of sol-gel science and technology Vol. 100; no. 3; pp. 466 - 476
Main Authors:	dos Anjos, William Lima, Morales, Sergio Andres Villalba, Oliveira, Natália Maira Braga, Valença, Gustavo Paim
Format:	Journal Article
Language:	English
Published:	New York Springer US 01-12-2021 Springer Nature B.V
Subjects:	Alumina Aluminum oxide Ammonia Catalysis Ceramics Chemical composition Chemical properties Chemical synthesis Chemistry and Materials Science Composites Crystal structure Crystallinity Crystallization Desorption Engineering Fourier transforms Glass Infrared analysis Infrared spectroscopy Inorganic Chemistry Laboratories Materials Science Molecular sieves Morpholine Morphology Nanotechnology Natural Materials NMR spectroscopy Optical and Electronic Materials Original Paper: Industrial and technological applications of sol-gel and hybrid materials Radiation Scanning electron microscopy Silicon dioxide Surface area Thermogravimetric analysis Triethylamine X-ray fluorescence Silica/alumina ratio Morpholine Structure-directing agent SAPO-34 Triethylamine
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Summary:	This work describes how the silica/alumina ratio (SAR) affects the framework, texture, chemical composition, and acidity of SAPO-34 molecular sieves synthesized via hydrothermal crystallization using morpholine (MOR) or triethylamine (TEA) as structure-directing agents (SDA’s). The solids were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N 2 adsorption-desorption isotherms, thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), X-ray fluorescence spectrometry (XRF), silicon-29 MAS NMR spectroscopy ( 29 Si MAS NMR), aluminum-27 MAS NMR spectroscopy ( 27 Al MAS NMR), and temperature-programmed desorption of ammonia (NH 3 -TPD). The solids synthesized in this work had crystalline phases, vibrational modes, and morphology characteristics of silicoaluminophosphate (SAPO) materials. Pure SAPO-34 was obtained only with morpholine, while SAPO-18/34 was crystallized with TEA. The SAPO-34 synthesized with MOR had the higher relative crystallinity and incorporation of Si into the framework. The SAPO-18/34 prepared with TEA had the larger surface areas. The solids prepared with SAR 0.3 had only Si(4Al) coordination, independently of the SDA used. The SAPO-34 synthesized with MOR and SAR 0.6 had the highest total acidity (9.75 μmol NH 3 m −2 ). SAPO molecular sieves were synthesized hydrothermally with different structure-directing agents and silica/alumina ratios. The effects of both variables on the physical and chemical properties of the samples obtained were evaluated. Pure SAPO-34 was obtained with morpholine, while SAPO-18/34 was crystallized with TEA. The SP34T-0.6 sample prepared with triethylamine and SAR 0.6 showed promising characteristics for use as catalyst in MTO reactions: AEI/CHA intergrowths, the lowest acidity, the smallest crystallite size, and a large BET surface area. Highlights Simultaneous effects of SAR and MOR or TEA on the SAPO-34 properties were studied. SAPO-34 synthesized with morpholine (MOR) had the higher relative crystallinity. AEI/CHA intergrowths were synthesized with triethylamine (TEA) and had the larger surface areas. SAPO prepared with a silica/alumina ratio (SAR) of 0.3 had only the Si(4Al). The SAPO-18/34 synthesized with TEA and SAR 0.6 had the lowest total acidity.
ISSN:	0928-0707 1573-4846
DOI:	10.1007/s10971-021-05669-w