Kinetic Trapping of D2 in MIL-53(AL) Observed using Neutron Scattering

Published

July 14, 2014

Author(s)

Rachel Ann Pollock, Jae-Hyuk Her, Craig Brown, Yun Liu, Anne Dailly

Abstract

We have studied gas adsorption effects on the structure of a metal organic framework, MIL-53(Al), a material well known due to the controllable framework 'breathing¿ phenomenon. Neutron powder diffraction between 4 K and 77 K and up to 4.5 bar pressure D₂ confirms that a structural phase transition is responsible for the observed H₂/D₂ isotherm hysteresis at 77 K. We find two crystallographically distinct D₂ adsorption sites in MIL-53(Al) when the pores are fully opened, similar to those reported for D₂ in MIL-53(Cr), but in contrast with the previously published cases of CO₂ and H₂O. Upon desorption of D₂ at 77 K, we find strong evidence for the existence of D₂ molecules kinetically trapped in the center of the closed pore of MIL-53(Al). This 'molecular clamp¿ appears to be functional until approximately equal) 120 K, where the D₂ eventually desorbs under dynamic vacuum. Hydrogen diffusion constants calculated using quasielastic neutron scattering data collected along the isotherm are also consistent with H₂ being trapped in the closed pore structure. Diffraction experiments performed with N2 and He gases under similar conditions show the range of structural response from immediate pore opening at low N₂ pressures (< 1 bar) to no observable effect at 10 bar He.

Citation

Journal of Physical Chemistry C

Volume

118

Pub Type

Journals

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Keywords

MIL-53, neutron powder diffraction, hydrogen storage, quasielastic neutron scattering, metal-organic framework

Citation

Pollock, R. , Her, J. , Brown, C. , Liu, Y. and Dailly, A. (2014), Kinetic Trapping of D₂ in MIL-53(AL) Observed using Neutron Scattering, Journal of Physical Chemistry C, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=916223 (Accessed April 25, 2024)