Self-assembly of silicoaluminophosphate nanocrystals in biphasic media with a water-insoluble structure-directing agent. Issue 15 (1st July 2021)

• Record Type: Journal Article
• Authors: Ding, Hongxin; Zhou, Qiuming; Li, Junfen; Zhu, Kake; Fan, Weibin
• Is Part Of: Catalysis science & technology. Volume 11:Issue 15(2021)
• Page Start: 5135
• Page End: 5146
• Publication Date: 2021-07-01
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/d1cy00655j
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : Toluene/water media enable the use of hydrophobic tri- n -heptylamine as an organic structure-directing agent for the synthesis of hierarchically porous SAPO-31 that outperforms conventional one in n -dodecane hydroisomerization. Abstract : The catalytic performance of silicoaluminophosphates is dependent on their acidity and diffusion properties, which can be altered by an organic structure-directing agent (OSDA) as a result of its dominant effect on crystallization. Generally, the solubility of an amine in aqueous media is an important factor for judging whether it is suitable to serve as an OSDA in hydrothermal synthesis of zeolites. This work demonstrates that a hydrophobic molecule, tri- n -heptylamine, could be used as an OSDA for synthesis of hierarchically porous SAPO-31 in biphasic toluene/water media. It provides not only a new method for synthesis of zeolites but also a simple, inexpensive, and porogen-free pathway to generate hierarchical SAPOs. The synthesis allows manipulation of the n Si /( n Al + n P + n Si ) ratio from 0.02 to 0.13 without noticeable change of morphological features. The self-assembled, nanocrystalline structure was revealed by combined XRD, SEM/TEM, N2 physisorption, and 27 Al, 31 P and 29 Si MAS NMR spectroscopy, and the acidity was measured with NH3 -IR. Catalytic evaluation in n -dodecane hydroisomerization shows that the isomer yield depends on the acid site density of the catalysts, and weak acid strength and high acid site density should be avoided to achieve high selectivity. On the optimized catalyst, the isomer yield has been significantly improved up to 79.7% in contrast to 58.1% for the sample derived from usual hydrothermal synthesis with di- n -hexylamine as an OSDA.