Regulating the size and acidity of SAPO-34 zeolites using dual templates to enhance the selectivity of light olefins in MTO

• Published in: New journal of chemistry 2021-07, Vol.45 (26), p.11812-11822
• Main Authors: Yao, Jihui, Tian, Haifeng, Zha, Fei, Ma, Shizi, Tang, Xiaohua, Chang, Yue, Guo, Xiaojun
• Format: Article
• Language: English
• Subjects: Alkenes; Aluminum; Ammonia; Catalytic converters; Crystal growth; Crystallites; Crystallization; Fixed bed reactors; Fixed beds; Methanol; Morpholine; NMR spectroscopy; Selectivity; Silicon; Triethylamine; Zeolites
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d1nj01845k

To understand the relationship between the catalytic performance, crystallite size, and acidity of SAPO-34 zeolites better, a series of SAPO-34 zeolites were prepared by hydrothermal crystallization using palygorskite as silicon and partial aluminum source, and selecting two kinds of triethylamine, morpholine and tetraethylammonium hydroxide as dual templates. The obtained SAPO-34 zeolites were characterized via the methods of XRD, SEM, N 2 -adsorption-desorption, NH 3 -TPD, FTIR, XRF, 29 Si MAS NMR, 27 Al MAS NMR and TG. The properties of the templates affected the crystal growth rate that triethylamine and morpholine can cause a larger crystallite size while tetraethylammonium hydroxide can form small crystallite size particles. The number of acid sites of SAPO-34 zeolites first decreased and then increased with the increase of morpholine. The formation of Si islands can enhance the number of acid sites of SAPO-34 zeolites. The catalytic performance of SAPO-34 zeolites in methanol-to-olefins (MTO) reaction was investigated in a fixed bed reactor. Under reaction conditions, when the reaction temperature was 400 °C, the feed WHSV was 2.0 h −1 , the mass of the catalyst was 0.5 g, at atmospheric pressure, the sample with an amount of acid sites of 0.85 mmol g −1 and crystallite size of 0.84 μm exhibited the optimum catalytic performance with methanol conversion at 100%, light olefin selectivity at 97.15% and catalytic lifetime at more than 1050 min. To understand the relationship between the catalytic performance, crystallite size, and acidity of SAPO-34 zeolites, a series of SAPO-34 zeolites were prepared by hydrothermal crystallization using palygorskite and dual templates.