Improved Pd/γ-Al2O3–Ce catalysts for benzene combustion

The catalytic oxidation of benzene on Pd (0.5 wt%)/γ-Al2O3–Ce catalysts with 1, 5 and 10 wt% Ce was investigated. The alumina–Ce supports were prepared by adding a Ce-nitrate precursor to an aluminum boehmite. The presence of Lewis acid sites was determined by FTIR-pyridine adsorption spectroscopy. By FTIR-CO adsorption, it was found that the presence of Ce leads to the stabilization of PdO on the supports. The presence of the PdO species on the Pd/γ-Al2O3–Ce catalysts was confirmed by X-ray photoelectron spectroscopy (XPS). The combustion of benzene (2600 ppm) in air was carried out at atmospheric pressure. Two behaviors were observed: for the catalysts with low Ce content (1%) and without Ce, the combustion occurs in a broad temperature range 100–280 °C, meanwhile, catalysts with high Ce contents (5, 10%), the benzene combustion occurs in the range 220–280 °C. An activation treatment on Pd/γ-Al2O3–Ce catalysts with a reactant mixture at 250 °C for 20 h reduces the temperature of the total combustion to 250 °C. A better stability on Pd/γ-Al2O3–Ce catalysts containing 5 and 10% Ce was observed. These results suggest that the oxidative catalytic properties of cerium oxide are shown at temperatures higher than 220 °C, and that an activation treatment is needed to obtain an optimal Pd°/PdO ratio for these species. The stability showed by the catalysts is explained by the effect of the CeO2, which inhibits the deposition of carbonaceous species on the Pd surface.