Effect of oxidant treatment of date pit active carbons used as Pd supports in catalytic hydrogenation of nitrobenzene

Two active carbons from Algerian date pits prepared by chemical activation at moderate temperature (500-600 °C) with H3PO4 and ZnCl2 and one commercial active carbon (from Darco) have been oxidized with air at different temperatures (300-450 °C) and with nitric acid in severe conditions during a short time. It has been demonstrated that air treatment generates surface oxygenated groups (XPS) that have an acidic character (simplified Boehm titration), without degrading the specific surface area (BET). Each active carbon has an optimal oxidation temperature depending on its activation procedure and corresponding to 20% in weight loss during the oxidation process. This optimal temperature achieves the highest surface oxygen content, which is directly correlated to the global acidity. It also means that when the support is loaded with 5% Pd by incipient wetness method, the catalyst exhibits the best activity for the liquid phase hydrogenation of nitrobenzene to aniline. In general, the metallic dispersion of the catalysts (CO chemisorption) remained appreciable even after oxidizing treatments. Exception is noted when nitric acid is used as oxidant while the active carbon has been prepared using zinc chloride.