Improved Pd/gamma-Al2O3-Ce catalysts for benzene combustion

摘要

The catalytic oxidation of benzene on Pd (0.5 wt%)/gamma-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/gamma-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/gamma-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/gamma-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.