TY - JOUR

T1 - Dynamics of xylene isomers in MIL-53 (Al) MOF probed by solid state 2H NMR

AU - Khudozhitkov, Alexander E.

AU - Arzumanov, Sergei S.

AU - Kolokolov, Daniil I.

AU - Stepanov, Alexander G.

N1 - Funding Information: This work was supported by Russian Foundation for Basic Research (grant № 18-29-04009 ) and in part by the Ministry of Science and High Education of the Russian Federation (Project no. AAAA-A17-117041710084-2 ). DIK also acknowledges the support from the Russian Science Foundation , project № 17-73-10135 . Publisher Copyright: © 2020 Elsevier Inc. Copyright: Copyright 2020 Elsevier B.V., All rights reserved.

PY - 2020/6/15

Y1 - 2020/6/15

N2 - With regard to understanding the effect of the dynamics of xylenes confined in the MOFs pores on the origin of xylene isomers separation, the mobility of para and ortho isomers of xylene in MIL-53(Al) MOF has been studied by solid-state 2H NMR. It is inferred that both isomers perform rotational and librational motions of the aromatic ring plane. The geometry, rates and energy barriers of the detected rotational modes for the molecules confined in the channels have been determined. The rotation around the axis perpendicular to the plane of aromatic ring is obliged with pairwise arrangement of xylene molecules along 1D channels of the MOF. The evolution of motional patterns with temperature shows that the pairwise arrangement of ortho isomer in the channels is held till 300 K, whereas the pairs are stable up to 405 K for the para isomer. This was rationalized by stronger interaction of o-xylene with the channel walls, while π–π intermolecular interaction is stronger for p-xylene. Due to stronger interaction between the unpaired molecules and MOF walls o-xylene exhibits notably higher temperature of the molecules desorption from the channels (494 K). In contrast, the p-xylene is capable to leave the channels of MIL-53 already at 405 K, moving in the channels predominantly in pairs. The different motional behavior of xylene isomers provides the conditions for a faster translational mobility along the MOF channel of para compared to the ortho isomer, thus accounting for the molecular mechanism behind the separation selectivity for xylene isomers.

AB - With regard to understanding the effect of the dynamics of xylenes confined in the MOFs pores on the origin of xylene isomers separation, the mobility of para and ortho isomers of xylene in MIL-53(Al) MOF has been studied by solid-state 2H NMR. It is inferred that both isomers perform rotational and librational motions of the aromatic ring plane. The geometry, rates and energy barriers of the detected rotational modes for the molecules confined in the channels have been determined. The rotation around the axis perpendicular to the plane of aromatic ring is obliged with pairwise arrangement of xylene molecules along 1D channels of the MOF. The evolution of motional patterns with temperature shows that the pairwise arrangement of ortho isomer in the channels is held till 300 K, whereas the pairs are stable up to 405 K for the para isomer. This was rationalized by stronger interaction of o-xylene with the channel walls, while π–π intermolecular interaction is stronger for p-xylene. Due to stronger interaction between the unpaired molecules and MOF walls o-xylene exhibits notably higher temperature of the molecules desorption from the channels (494 K). In contrast, the p-xylene is capable to leave the channels of MIL-53 already at 405 K, moving in the channels predominantly in pairs. The different motional behavior of xylene isomers provides the conditions for a faster translational mobility along the MOF channel of para compared to the ortho isomer, thus accounting for the molecular mechanism behind the separation selectivity for xylene isomers.

KW - H NMR

KW - Dynamics

KW - MIL-53

KW - MOF

KW - Xylene

KW - P-XYLENE

KW - MOBILITY

KW - WATER DYNAMICS

KW - MIXTURES

KW - EQUILIBRIA

KW - DIFFUSION

KW - H-2 NMR

KW - SEPARATION

KW - LIQUID-PHASE ADSORPTION

KW - PAREX PROCESS

KW - ZEOLITE

UR - http://www.scopus.com/inward/record.url?scp=85081678141&partnerID=8YFLogxK

U2 - 10.1016/j.micromeso.2020.110155

DO - 10.1016/j.micromeso.2020.110155

M3 - Article

AN - SCOPUS:85081678141

VL - 300

JO - Microporous and Mesoporous Materials

JF - Microporous and Mesoporous Materials

SN - 1387-1811

M1 - 110155

ER -