Nitrogen adsorption study of organised mesoporous alumina

Abstract

As the arrangement of pores generally achieved in organised mesoporous alumina is not completely regular, gas adsorption methods appear important for characterisation of this material. One of the promising approaches to adsorption data analysis is based on the comparison of the adsorption isotherm of nitrogen at −196 °C on the porous solid under study with the standard adsorption isotherm of the same adsorbate on a reference non-porous solid. To obtain reliable standard nitrogen adsorption data for characterisation of the alumina porous structure, nitrogen adsorption isotherms on Degussa Aluminiumoxid C and α-alumina were carefully measured at −196 °C with ASAP 2010 and modified Accusorb 2100E instruments. Standard nitrogen adsorption data (adsorbed amount divided by surface area) were listed for 41 points in the relative pressure range 0.001 to 0.95. Their applicability was tested on organised mesoporous aluminas of various structural parameters using the comparison plot method. Although some samples of organised mesoporous alumina were calcined at relatively high temperatures, only the standard data on Degussa Aluminiumoxid C proved suitable for the comparative analysis of adsorption isotherms. The standard adsorption data on Degussa Aluminiumoxid C transformed to the statistical film thickness curve were used for calculation of Barrett–Joyner–Halenda (BJH) pore size distributions. The determined material parameters of the organised mesoporous aluminas were also supported by X-ray diffraction data and were consistent with the conditions of synthesis and heat treatment of these materials.