Base-induced Brönsted Acid Sites on Dealuminated HY Zeolite: A Solid-state NMR Spectroscopy Study |
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Authors: | Wei Hu Qing Luo Shenhui Li Wanling Shen Yong Yue Feng Deng |
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Institution: | State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China |
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Abstract: | Using trimethylphosphine (TMP) and d5-pyridine(deuterated pyridine) as the basic probe molecules, the concentrations of Brönsted acid sites on both HY zeolite and dealuminated HY zeolite have been quantitatively determined using solid-state 1H and 31P magic-angle spinning (MAS) NMR. After adsorption of the probe molecules, the concentration of Brönsted acid sites on the dealuminated HY zeolite increases by about 25%, whereas that in the parent HY sample remains almost unchanged. The increase in the concentration of Brönsted acid sites is due to the appearance of base-induced Brönsted acid sites in the dealuminated HY zeolite. The terminal SiOH in the vicinity of the aluminum atom is “induced” to form a bridging hydroxyl group (SiOHAl) in the presence of the basic probe molecules. The mechanism of formation of the induced Brönsted acid sites has also been discussed. |
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Keywords: | HY zeolite NMR Dealumination Probe molecule Induced Brönsted acid site |
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