6533b857fe1ef96bd12b4683

RESEARCH PRODUCT

Hysteresis in nitrogen sorption and mercury porosimetry on mesoporous model adsorbents made of aggregated monodisperse silica spheres

subject

description

Abstract An elucidation of the hysteresis phenomena in nitrogen sorption (NS) and mercury porosimetry (MP) on porous aggregates of non-porous silica spheres of particle diameter 90–1000 nm is presented. First, it is demonstrated that highly ordered and dense aggregates of a porosity of 26–30% are formed by gravity settling and centrifugation. A hexagonal and cubic close-packed structure within the layers and a vertical stacking between the layers were observed. Minor deteriorations were seen between the ordered domains. Second, the pore size distribution (PSD) curves calculated from the adsorption branch of the nitrogen isotherms by means of the Cohan equation and from the desorption branch by means of the Kelvin equation were quite similar for most of the aggregates. Furthermore, the values of 0.414 R (octahedrally shaped cavities, R is the radius of spheres), 0.225 R (tetrahedrally shaped cavities) and 0.155 R (pore throats) derived from close-packed sphere models were in the range of the PSD curves. Third, mercury porosimetry gave a pronounced hysteresis between the intrusion and retraction branch with normalized pressures P* of 5 (or 8) to 10 for the intrusion and 1.8–3 for retraction. The values correspond to those computed from packed sphere models, assuming the packing structure as seen at the aggregates by stereo electron scanning microscopy.