469056 Adsorption Energies of Light Hydrocarbons in Functionalized Uio-66(Zr)

Thursday, November 17, 2016: 9:13 AM
Union Square 21 (Hilton San Francisco Union Square)
Michael D. Gross and Jennifer Buchanan, Chemistry, Wake Forest University, Winston-Salem, NC

Differential adsorption energies of ethane, ethylene, and acetylene on the metal-organic framework (MOF) UiO-66(Zr) and UiO-66(Zr) functionalized with –NH2 and –NO2 were measured by adsorption calorimetry at 293K using a Tian-Calvet calorimeter. Measurements were taken at low coverage ranging from 0.05 mmol/g to 1.2 mmol/g. In all cases the MOFs were heated under vacuum to dehydroxylate the MOFs prior to testing. The adsorption energy of ethylene was highest for UiO-66(Zr)-NO2 and was lowest for UiO-66(Zr). For UiO-66(Zr)–NO2, the adsorption energy of ethane was higher than ethylene and only slightly lower than acetylene. Given that the overall molecular polarity of ethane is lower than ethylene and that the kinetic diameter of ethane is larger than ethylene, confinement effects may be a dominating factor for ethane adsorption in the -NO2 case. For adsorption of both ethane and acetylene on UiO-66(Zr)-NO2, the adsorption energies decreased by ~5 kJ/mol as the coverage increased from 0.05 mmol/g to ~0.6 mmol/g. For ethylene, the adsorption energies were essentially constant over the entire range of coverage investigated. The change in adsorption energy for ethane and ethylene at low coverage may indicate that UiO-66(Zr)-NO2 has multiple types of adsorption sites. We are currently investigating low-temperature calorimetry measurements for this system, which will allow one to more clearly isolate the energies of stronger and weaker adsorption sites.

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