Acidity and Local Confinement Effect in Mordenite Probed by Solid-State NMR Spectroscopy

Ke Gong; Zhengmao Liu; Lixin Liang; Zhenchao Zhao; Meiling Guo; Xuebin Liu; Xiuwen Han; Xinhe Bao; Guangjin Hou

doi:10.1021/acs.jpclett.0c03610

Acidity and Local Confinement Effect in Mordenite Probed by Solid-State NMR Spectroscopy

J Phys Chem Lett. 2021 Mar 11;12(9):2413-2422. doi: 10.1021/acs.jpclett.0c03610. Epub 2021 Mar 4.

Authors

Ke Gong^{1

2}, Zhengmao Liu^{1

2}, Lixin Liang^{1

2}, Zhenchao Zhao¹, Meiling Guo³, Xuebin Liu³, Xiuwen Han¹, Xinhe Bao¹, Guangjin Hou¹

Affiliations

¹ State Key Laboratory of Catalysis, National Laboratory for Clean Energy, 2011-Collaborative Innovation Center of Chemistry for Energy Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China.
² University of Chinese Academy of Sciences, Beijing 100049, China.
³ Energy Innovation Laboratory, BP (China) Dalian Office, Dalian 116023, China.

PMID: 33661009
DOI: 10.1021/acs.jpclett.0c03610

Abstract

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.