The standard but misleading nitrogen adsorption isotherm and texture assessment of porous silicas and aluminas

Standard nitrogen adsorption isotherms were determined on largely dehydroxylated silica and alumina references, prepared by calcination at 1200 °C for 72 h. The reliability of the reduced adsorption data α_s derived was checked for use in the analysis of experimental isotherms determined on a series of porous silicas and aluminas, prepared by calcination of Davison silica gel and Degussa aluminium oxide C in the range 400–800 °C for 5 h, by comparison with existing standard adsorption data of hydroxylated silica and alumina references. The results obtained demonstrate the importance of having accurate standard data derived from an isotherm determined on a reference solid virtually identical in surface structure with the solid being tested.