FREUNDLICH, LANGMUIR, TEMKIN AND HARKINS-JURA ISOTHERMS STUDIES OF H2 ADSORPTION ON POROUS ADSORBENTS

The hydrogen adsorption and desorption isotherms of multiwalled carbon nanotube sample (MWCNT), an iron loaded multiwalled carbon nanotube (Fe_MWCNT), two zeolites (Na_Y_Zeo and NH4_Y_Zeo) and MCM-41 were measured at 77 K and atmospheric pressure by using the volumetric adsorption apparatus. The adsorption data were evaluated by several isotherm equations such as Langmuir, Freundlich, Temkin and Harkins-Jura isotherm models but were best described by the Freundlich isotherm model as it gave the highest correlation. The amount of adsorbed hydrogen by weight depended on the micropore volume of the sample, except for MWCNT and Fe_MWCNT. The porous samples were characterized by scanning electron microscopy (SEM) and N-2 adsorption isotherms. The maximum hydrogen storage of 1.96 wt % at 77 K was achieved by Fe_MWCNT. Microporous Na_Y_Zeo and NH4_Y_Zeo showed higher hydrogen adsorption capacities than the mesoporous MCM-41. The hydrogen adsorption properties of these porous adsorbents may be further enhanced by different metal doping, thus paving the way for further study.