Selectivity of gas phase adsorption of propene and propane onto mesoporous silica materials derivatised with Ag(I) and Cu(II) at low surface coverages:: comparison between equilibrium adsorption and flow microcalorimetry studies

Adsorption selectivity for propene over propane of mesoporous alummosilicate monoliths derivatised with Ag(I) and Cu(II) has been studied from the gas phase at low surface coverages at 298 K. The insertion of transition metals was achieved by ion exchange, incipient wetness impregnation or direct incorporation during the synthesis stage. The overall transition metal content in the samples ranged between 2 and 20 wt.%. Two-cycle adsorption of each gas measured at pressures up to 300 mbar was used to determine the reversible and irreversible contributions to the amount adsorbed under equilibrium conditions. Flow microcalorimetry measurements allowed estimates of the reversible and irreversible enthalpy components to be made under flow conditions. Adsorption selectivity of the derivatised alummosilicates changes when passing from one adsorption system to another. Both Ag(l) and Cu(II) can give selective adsorption of propene over propane under experimental conditions close to the adsorption equilibrium, whereas only Ag-containing samples are selective under flow conditions. (C) 2005 Elsevier B.V. All rights reserved.