Surface to bulk characterization of phosphate modified aluminas

gamma-Al2O3, dried alumina gel, as well as their phosphated forms using (NH 4)(2)HPO4 were prepared by wet impregnation and calcined at 870 K. Resulted samples were subjected to investigate the consequent bulk [X-ray powder di ffractometry (XRD), diffuse reflectance spectroscopy (DRS) and infrared spe ctroscopy (IR)] and surface (texture, N-2-adsorption and surface acid prope rties, pyridine adsorption). Results indicated no detectable bulk phase cha nges due to phosphation. However, the phosphated gel sample reveals the hig hest S-BET. Surface stabilization of phosphate species by gamma-Al2O3 or ge l is indicated, leading to modifications on surface hydroxyl and hence surf ace acidity. The phosphated gel sample exhibits the strongest acidity (both Bronsted and Lewis). (C) 2000 Elsevier Science B.V. All rights reserved.