TY - JOUR
T1 - Neutron scattering and spectroscopic studies of hydrogen adsorption in Cr3(BTC)2-A metal-organic framework with exposed Cr 2+ sites
AU - Sumida, Kenji
AU - Her, Jae Hyuk
AU - Dincǎ, Mircea
AU - Murray, Leslie J.
AU - Schloss, Jennifer M.
AU - Pierce, Christopher J.
AU - Thompson, Benjamin A.
AU - Fitzgerald, Stephen A.
AU - Brown, Craig M.
AU - Long, Jeffrey R.
PY - 2011/4/28
Y1 - 2011/4/28
N2 - Microporous metal-organic frameworks possessing exposed metal cation sites on the pore surface are of particular interest for high-density H2 storage at ambient temperatures, owing to the potential for H2 binding at the appropriate isosteric heat of adsorption for reversible storage at room temperature (ca. -20 kJ/mol). The structure of Cr3(BTC) 2 (BTC3- = 1,3,5-benzenetricarboxylate) consists of dinuclear paddlewheel secondary building units connected by triangular BTC 3- bridging ligands to form a three-dimensional, cubic framework. The fully desolvated form of the compound exhibits BET and Langmuir surface areas of 1810 and 2040 m2/g, respectively, with open axial Cr2+ coordination sites on the paddlewheel units. Its relatively high surface area facilitates H2 uptakes (1 bar) of 1.9 wt % at 77 K and 1.3 wt % at 87 K, and a virial-type fitting to the data yields a zero-coverage isosteric heat of adsorption of -7.4(1) kJ/mol. The detailed hydrogen loading characteristics of Cr3(BTC)2 have been probed using both neutron powder diffraction and inelastic neutron scattering experiments, revealing that the Cr2+ site is only partially populated until a marked elongation of the Cr-Cr internuclear distance occurs at a loading of greater than 1.0 D 2 per Cr2+ site. Below this loading, the D2 is adsorbed primarily at the apertures of the octahedral cages. The H-H stretching frequency corresponding to H2 molecules bound to the primary site is observed in the form of an ortho-para pair at 4110 and 4116 cm-1, respectively, which is significantly shifted compared to the frequencies for free H2 of 4155 and 4161 cm-1. The infrared data have been used to compute a site-specific binding enthalpy for H2 of -6.7(5) kJ/mol, which is in agreement with the zero-coverage isosteric heat of adsorption derived from gas sorption isotherm data.
AB - Microporous metal-organic frameworks possessing exposed metal cation sites on the pore surface are of particular interest for high-density H2 storage at ambient temperatures, owing to the potential for H2 binding at the appropriate isosteric heat of adsorption for reversible storage at room temperature (ca. -20 kJ/mol). The structure of Cr3(BTC) 2 (BTC3- = 1,3,5-benzenetricarboxylate) consists of dinuclear paddlewheel secondary building units connected by triangular BTC 3- bridging ligands to form a three-dimensional, cubic framework. The fully desolvated form of the compound exhibits BET and Langmuir surface areas of 1810 and 2040 m2/g, respectively, with open axial Cr2+ coordination sites on the paddlewheel units. Its relatively high surface area facilitates H2 uptakes (1 bar) of 1.9 wt % at 77 K and 1.3 wt % at 87 K, and a virial-type fitting to the data yields a zero-coverage isosteric heat of adsorption of -7.4(1) kJ/mol. The detailed hydrogen loading characteristics of Cr3(BTC)2 have been probed using both neutron powder diffraction and inelastic neutron scattering experiments, revealing that the Cr2+ site is only partially populated until a marked elongation of the Cr-Cr internuclear distance occurs at a loading of greater than 1.0 D 2 per Cr2+ site. Below this loading, the D2 is adsorbed primarily at the apertures of the octahedral cages. The H-H stretching frequency corresponding to H2 molecules bound to the primary site is observed in the form of an ortho-para pair at 4110 and 4116 cm-1, respectively, which is significantly shifted compared to the frequencies for free H2 of 4155 and 4161 cm-1. The infrared data have been used to compute a site-specific binding enthalpy for H2 of -6.7(5) kJ/mol, which is in agreement with the zero-coverage isosteric heat of adsorption derived from gas sorption isotherm data.
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U2 - 10.1021/jp200638n
DO - 10.1021/jp200638n
M3 - Article
AN - SCOPUS:79955388727
SN - 1932-7447
VL - 115
SP - 8414
EP - 8421
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 16
ER -