Unusual adsorption behavior of volatile hydrocarbons on MOF-5 studied using thermodesorption methods

• Unusual thermodesorption profiles of volatile hydrocarbons observed for MOF-5.
• Number of thermodesorption peaks increasing with the size of a probe molecule.
• One adsorption state found for pentane and benzene, five for decane.
• Considerable adsorption–desorption hysteresis observed for isooctane.
• Thermodesorption profiles observed do not correspond to standard adsorption isotherms.

Adsorption of n-alkanes (C5–C10), isooctane, benzene, toluene and p-xylene on MOF-5 was studied by means of quasi-equilibrated temperature programmed desorption and adsorption (QE-TPDA) and temperature programmed desorption (TPD). Unusual thermodesorption profiles showing increasing complexity with the size of a probe molecule have been observed. Number of peaks in the thermodesorption profile increased from one for pentane or benzene to five for decane. Considerable adsorption–desorption hysteresis was found for isooctane. These unusual thermodesorption profiles were discussed in comparison to those obtained for zeolites and ordered mesoporous silicas.