Systematic sorption studies on surface and pore size characteristics of different MCM-48 silica materials

摘要

We present results of a systematic study of the sorption- and phase behavior of argon, krypton and nitrogen at 77 K and 87 K on different pristine mesoporous MCM-48 silica phases of mean pore diameters 2-3 nm and on a MCM-48 silica/iron(III) oxide host-guest compound. Argon and krypton sorption isotherms on all MCM-48 silica materials revealed phase transition accompanied by sorption hysteresis of type H1 well below the bulk triple point temperature. Details of the sorption hysteresis depend on temperature and pore size, e.g. with increasing temperature and decreasing proe size a shrinkage of the hysteresis loops is observed. MCM-48 silica consists of two interwoven, but unconnected three dimensional pore system.s Because of this special structure the cubic MCM-48 silica phase is considered as a matrix to immobilize catalytic active species onto or within the silica walls. The analysis of nitrogen and argon sorption isotherms at 77 K and 87 K indicates that the impregnation of a prisitine MCM-48 silica phase with iron(III) oxide has led indeed to a coating of the inner surface of the silica walls.