Investigation of the Strong Br酶nsted Acidity in a Novel SAPO-type Molecular Sieve, DNL-6

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• 作者：Xiong Su ; Shutao Xu ; Peng Tian ; Jinzhe Li ; Anmin Zheng ; Qiang Wang ; Miao Yang ; Yingxu Wei ; Feng Deng ; Zhongmin Liu
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：February 5, 2015
• 年：2015
• 卷：119
• 期：5
• 页码：2589-2596
• 全文大小：375K
• ISSN：1932-7455

文摘

By applying analysis of multiple solid-state MAS NMR spectra, the atomic coordination environment and acidity of a novel SAPO-type molecular sieve, DNL-6, are studied. ²⁷Al MQ-MAS NMR and ³¹P鈥?sup>27Al MQ-HETCOR NMR spectra reveal the existence of a Si鈥揂l鈥揝i region with Al(OSi)_n (n = 1鈥?) species in the framework of DNL-6, explaining well the high concentration of single Si(OAl)₄ species (3 mmol/g) accommodated in the sample. ¹³C MAS NMR of 2-¹³C-acetone adsorption indicates that there exist two kinds of strong Br酶nsted acid sites in DNL-6. One of them has similar strength as those in HZSM-5 and the other is even stronger, which is unusual in SAPO-type molecular sieves. Also, a discrepancy in Br酶nsted acid concentration between the theoretical and ¹H NMR experimental results has been found, revealing the occurrence of a dehydoxylation process during the calcination. The origin of the extremely strong Br酶nsted acid sites in DNL-6 is investigated by density functional theory calculations, which suggest that the dehydroxylation process may lead to a local structure deformation and remarkably enhance the Br酶nsted acidity. More importantly, DNL-6 exhibits excellent catalytic activity in the synthesis of methylamines due to its stronger acidity.