Synthesis of nanosheet SSZ-39 zeolite with enhanced catalytic performance in methanol-to-olefins reaction

• Published in: Reaction kinetics, mechanisms and catalysis mechanisms and catalysis, 2024-08, Vol.137 (4), p.1885-1897
• Main Authors: Guo, Niandong, Wang, Yaquan, Liu, Wenrong, Bu, Lingzhen, Sang, Juncai, Chu, Kailiang, Qu, Liping, Huang, Yitong, Zhang, Xian, Su, Xuemei, Li, Yaoning
• Format: Article
• Language: English
• Subjects: Catalysis; Chemistry; Chemistry and Materials Science; Industrial Chemistry/Chemical Engineering; Physical Chemistry
• ISSN: 1878-5190; 1878-5204
• DOI: 10.1007/s11144-024-02616-y

In order to improve the mass transfer rate of SSZ-39 and prolong its catalytic lifetime, peculiar nanosheet SSZ-39 zeolites were prepared by hydrothermal synthesis using N , N -dimethyl-3,5-dimethylpiperidinium as an organic structure-directing agent and cetyltrimethylammonium bromide (CTAB) as a crystal growth regulator. The nanosheet SSZ-39 zeolites with different CTAB/SiO 2 ratios in the initial gels were synthesized and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), nitrogen adsorption–desorption, Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), 27 Al nuclear magnetic resonance ( 27 Al NMR), temperature programmed desorption of ammonia (NH 3 -TPD) and thermogravimetric analysis (TGA). The addition of CTAB changed the morphology of SSZ-39 zeolite. Compared to conventional SSZ-39 without CTAB addition, the nanosheet SSZ-39 had a higher SiO 2 /Al 2 O 3 ratio (18.5 vs 16.7), a larger specific surface area (482 m 2  g −1 vs 433 m 2  g −1 ) and a higher strong acid density of (0.411 mmol g −1 vs 0.317 mmol g −1 ). Intensive research about the formation process of nanosheet SSZ-39 revealed that CTAB adsorbed on [001] crystal plane to inhibit the growth of the crystals along the c-axis, which played a crucial role in the formation of nanosheets. The nanosheet SSZ-39 with shorter diffusion path exhibited an enhanced performance in the methanol-to-olefins reaction. The sample with a CTAB/SiO 2 ratio of 0.01 in synthesis possessed a lower Hydrogen Transfer Index, indicating higher mass transfer efficiency, which endowed it a longer catalytic lifetime of 360 min and higher ethylene plus propylene selectivity than conventional SSZ-39.