TY - JOUR
T1 - Understanding hydrocarbon adsorption in the uio-66 metal-organic framework
T2 - Separation of (un)saturated linear, branched, cyclic adsorbates, including stereoisomers
AU - Duerinck, T.
AU - Bueno-Perez, R.
AU - Vermoortele, F.
AU - De Vos, D.E.
AU - Calero, Sofia
AU - Baron, G.V.
AU - Denayer, J.F.M.
PY - 2013/6/20
Y1 - 2013/6/20
N2 - The low coverage adsorption properties of alkanes, alkenes, and aromatics of the linear, branched, and cyclic type (ca. 70 molecules) were studied using inverse pulse gas chromatography at zero coverage on the zirconium metal-organic framework UiO-66 and its functionalized analogues UiO-66-Me, UiO-66-NO 2, UiO-66-Me2 in the temperature range 433-573 K. In our study, we determined and analyzed the adsorption enthalpy, Henry constants, and entropic factors. Preferential adsorption of bulky molecules is observed with specific adsorbate and cage size effects, yielding very specific, preferential adsorption. Remarkably high adsorption selectivity factors (up to 14) for cyclo- compared to n-alkanes were found. The presence of additional groups (methyl, nitro) on the linkers in the framework influences adsorption properties significantly, mainly by reducing the effective pore size. Whereas increased selectivity is observed for UiO-66-Me, this effect decreases again upon addition of a second methyl group, UiO-66-Me2. The latter allows for tuning confinement factors inside the pores, thus adsorption properties of the metal-organic framework. The selective adsorption results from the interaction in the smallest octahedral cage. The extreme confinement in the tetrahedral cage allows for stereoselective separation of disubstituted cycloalkanes and cis/trans alkenes. Monte Carlo simulations were performed for the unfunctionalized UiO-66 framework. First, a comparative study between the force fields Dreiding and UFF is performed with n-alkanes to obtain accurate and reproducible values. The simulations show adsorbate molecular size-adsorbent cage size effects similar to window/cage effects reported for zeolites (e.g., silicalite). Second, adsorption properties were simulated for selected cases, including stereoisomers. Careful analysis of the adsorbate's molecular positioning in the framework confirms the experimental data. The framework's selectivity results from adsorption in the tetrahedral cage at zero coverage. Furthermore, simulations show important contributions of entropic factors to the observed adsorption selectivity.
AB - The low coverage adsorption properties of alkanes, alkenes, and aromatics of the linear, branched, and cyclic type (ca. 70 molecules) were studied using inverse pulse gas chromatography at zero coverage on the zirconium metal-organic framework UiO-66 and its functionalized analogues UiO-66-Me, UiO-66-NO 2, UiO-66-Me2 in the temperature range 433-573 K. In our study, we determined and analyzed the adsorption enthalpy, Henry constants, and entropic factors. Preferential adsorption of bulky molecules is observed with specific adsorbate and cage size effects, yielding very specific, preferential adsorption. Remarkably high adsorption selectivity factors (up to 14) for cyclo- compared to n-alkanes were found. The presence of additional groups (methyl, nitro) on the linkers in the framework influences adsorption properties significantly, mainly by reducing the effective pore size. Whereas increased selectivity is observed for UiO-66-Me, this effect decreases again upon addition of a second methyl group, UiO-66-Me2. The latter allows for tuning confinement factors inside the pores, thus adsorption properties of the metal-organic framework. The selective adsorption results from the interaction in the smallest octahedral cage. The extreme confinement in the tetrahedral cage allows for stereoselective separation of disubstituted cycloalkanes and cis/trans alkenes. Monte Carlo simulations were performed for the unfunctionalized UiO-66 framework. First, a comparative study between the force fields Dreiding and UFF is performed with n-alkanes to obtain accurate and reproducible values. The simulations show adsorbate molecular size-adsorbent cage size effects similar to window/cage effects reported for zeolites (e.g., silicalite). Second, adsorption properties were simulated for selected cases, including stereoisomers. Careful analysis of the adsorbate's molecular positioning in the framework confirms the experimental data. The framework's selectivity results from adsorption in the tetrahedral cage at zero coverage. Furthermore, simulations show important contributions of entropic factors to the observed adsorption selectivity.
UR - http://www.scopus.com/inward/record.url?scp=84879431078&partnerID=8YFLogxK
U2 - 10.1021/jp402294h
DO - 10.1021/jp402294h
M3 - Article
AN - SCOPUS:84879431078
SN - 1932-7447
VL - 117
SP - 12567
EP - 12578
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 24
ER -