Sorption Properties of Aluminas in Relation to Adsorbate—Adsorbent Interaction

Abstract

Five calcination products AI–AV were obtained by the calcination of alumina gel in the temperature range 673–1473 K. The adsorption of nitrogen at 77 K on these products was determined volumetrically. The chemisorption of H₂, CO, CO₂ and CH₄ at 300, 320 and 340 K was also determined for each alumina sample.

Increasing calcination temperature caused phase changes with formation of the most stable phase α-Al₂O₃ starting at 1273 K and predominating at 1473 K. Chemisorption depends on the nature of the adsorbent and the adsorbate molecules. The amount adsorbed was related to the critical temperature of the gas involved while the heat of adsorption was related to the strength of the interaction between the adsorbent and the adsorbate. The polarizability of the adsorbed gas molecule is a determining factor in its chemisorption, particularly on polar surfaces.