Pore Condensation and Hysteresis
An empirical classification of hysteresis loops, given by IUPAC (1985), correlates the hysteresis loops (types H1 - H4) with the texture of the adsorbent. Schematics of hysteresis types H1 and H2 are shown in Figure 1.
Type H1 hysteresis had been associated with porous materials exhibiting a narrow distribution of relatively uniform (cylindrical pores), whereas materials that give rise to H2 hysteresis contain more complex pore networks consisting of pores with ill-defined shape and wide pore size distribution.
The hysteresis loop shape reflects the underlying pore condensation-evaporation mechanism which can indeed be similar even in systems which consist of different pore topologies.