Surface Technology , 26 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG (1985) 253 - 259 253 zyxwvut THE STANDARD BUT MISLEADING NITROGEN ADSORPTION ISOTHERM AND TEXTURE A SSESSMENT OF POROUS SILICAS AND ALUMINAS M. ABDELKHALIK Chemistry Department, Faculty of Science, Ain Shams University, Cairo (Egypt) M. I. ZAKI* Chemistry Department, Faculty of Science, M inia University , El-M inia (Egy pt) (Received January 14, 1985) Summary 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 o$ 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 impor- tance of having accurate standard data derived from an isotherm deter- mined on a reference solid virtually identical in surface structure with the solid being tested. 1. Introduction The concept of the standard isotherm, as defined precisely by Gregg [ 11, has proved increasingly useful in making allowance for the thickness t of the adsorbed film on pore walls, and in detecting both the onset of cap- illary condensation in mesopores and the presence of micropores. Various empirical methods have been devised for comparing experimental isotherms with the standard isotherm obtained on an appropriate non-porous reference solid, so as to assess the texture of a solid surface. The most widely adopted of these are probably the t method of Lippens and de Boer [2], the n meth- od of Mikhail and Cadenhead [ 31 and the oc, method of Sing [4]. Amongst these, however, the ol, method has proved exceedingly reliable, for it is almost independent of the theoretical limitations and restrictions of the BET method and makes less assumptions [ 51. *Present address: Institut fiir physikalische Chemie, Universitiit Miinchen, Sophien- str. 11,800O Miinchen 2, F.R.G. 0376-4583/85/$3.30 @ Elsevier Sequoia/Printed in The Netherlands