Gas adsorption studies and microcalorimetry on some iron oxides

Abstract

A volumetric gas adsorption apparatus uas built and calibrated with two surface area standards. The nitrogen adsorption and desorption isotherms were determined for five iron oxides and the specific surface area was calculated. Four of the oxides were found to be mesoporous. [alpha]s-plots were constructed using the non-porous sample (haematite) as the reference. An attempt was made to measure the effectiveness of an organic pretreatment on two of the porous samples by comparing their surface areas and pore size distributions before and after treatment. A commercial flow microcalorimeter was used to investigate the adsorption and desorption of 1-butanol and 1,2-epoxybutane on one of the porous samples and haematite. For haematite the adsorption of both 1-butanol and 1,2-epoxybutane were reversible. The surface area of both samples estimated from microcalorimetry were smaller than their measured specific surface areas, probably because of water precoverage. The heat of 1-butanol adsorption on sample 'A' was a function of concentration, the number of previous adsorption-desorption cycles and the volume of solvent passed over the surface prior to the adsorption. The adsorption of 1,2-epoxybutane on sample 'A' was substantially irreversible. Dilution effects became important for both samples for concentrations above ca. 1.0 wt.%. A speculative water vapour adsorption experiment was performed using the microcalorimeter. Comparisons were made of the water adsorption-desorption properties of all the samples. The observed effects could not be simply explained. The heats and rates of water adsorption and desorption increased with increasing sample temperature.