Effect of calcination temperature of alumina on the adsorption/impregnation of Pd(II) compounds

Abstract

A series of alumina supports derived from a common source material was subjected to a range of calcination temperatures and the results of this treatment on the adsorption of Pd(II) compounds were studied. Increasing calcination temperature lead to a decrease in BET surface area and produced a series of alumina samples carrying different inventories of hydroxyl groups. The surface chemistry of these hydroxyl groups was studied using mass and potentiometric titration techniques and from these data the protonation/deprotonation equilibrium constants for the surface hydroxyl groups were obtained. This allowed us to construct the pH-dependent surface charge distribution for each alumina sample. Cationic and anionic Pd(II) complexes were used to titrate the negative and positive surface charge sites. We find that the adsorption mechanism is primarily controlled by electrostatic effects in that saturation capacities of adsorbed complex showed a correlation with the surface charge density evaluated at the pH used for the adsorption/impregnation experiments.