Acidity and Local Confinement Effect in Mordenite Probed by Solid-State NMR Spectroscopy
journal contributionposted on 04.03.2021, 15:04 by Ke Gong, Zhengmao Liu, Lixin Liang, Zhenchao Zhao, Meiling Guo, Xuebin Liu, Xiuwen Han, Xinhe Bao, Guangjin Hou
Herein, utilizing acetonitrile as the probe molecule, the acidity and host–guest interactions of H-mordenite (H-MOR) zeolites are investigated comprehensively by solid-state NMR spectroscopy and theoretical calculation. The locations and local configurations of Brønsted acid sites (BASs) in H-MOR are revealed by multinuclear and multidimensional NMR experiments with adsorption/coadsorption of acetonitrile (CD3CN) and trimethylphosphine (TMP). Moreover, the confinement effect of dual pores in MOR has been characterized via the quantitative determination of host–guest interactions between CH3CN and BASs. The 1H–15N dipolar measurement results and DFT calculations demonstrate that there are two kinds of acetonitrile molecules adsorbed in 12-membered ring (12MR) main channels with distinct mobility, where acetonitrile undergoes either partially restricted or highly flexible motion in the time scale of nanoseconds to microseconds. These two types of acetonitrile can exchange with temperature rising. In contrast, the mobility of acetonitrile in 8-membered ring (8MR) channels is very restricted due to the confinement of the framework.