III International Conference

361PP-II-1070.75, 1) were prepared by the direct anionic exchange (DAE) method developed by Ivanova etal. (5) for Au/Al 2 O 3 and next, in the cooperation with that group, adapted by us for thepreparation of Au/Mg 4 Al 2 (6). In order to remove the remaining Cl - ions, part of the catalystwas washed in either warm water or 4M ammonia solution. After drying at 120 °C overnight,the catalysts were calcined under air at 300 °C for 4 hours.The obtained systems were characterized by XRD, BET, H 2 -TPR, CO-TPR, AAS, TEM,SEM-EDS, TOF-SIMS and tested in the CO oxidation reaction, using a gas mixture containing1.6 vol.% CO and 3.3 vol.% O 2 (He as an eluant gas).The activity of unsupported mixed oxides was found to be dependant on Ce/Zr molarratio. The CO conversion increases with the increasing cerium content. Ce 0.75 Zr 0.25 O 2 (Ce/Zrmolar ratio = 3), with the total CO conversion at 420 °C presents the highest activity. Takinginto consideration the TPR results, one can say that the sequence of the increasing activityclearly follows the sequence of the increasing reducibility of the oxides.This study confirms the poisoning effect of the residual chloride on the catalyticperformance of Au/Ce 1-x Zr x O 2 catalysts. The average Au particle size is bigger for thecatalysts containing residual chloride. All the procedures used for washing allow to decreasethe average Au particle size. Depending on the washing procedure, one can observe differentactivities and different Au particle sizes. TEM measurements show the smallest Au particlesfor the series of catalysts washed in ammonia. Those catalysts were active at relatively lowtemperatures. The activity of Au/Ce 1-x Zr x O 2 depends on Ce/Zr molar ratio, with a maximumobtained for Au/Ce 0.75 Zr 0.25 O 2 (Ce/Zr molar ratio = 3). The samples with the higher zirconiumcontent were found less active. The lowest activity was observed for Au/ZrO 2 .The presence of Au particles facilitates the reduction of the supports as indicated by thedecrease in the temperature of the maximum of the reduction peak, as confirmed by TPRmeasurements. It suggests the activation of H 2 molecule on Au nanoparticles. The sequence ofthe increasing activity clearly follows the sequence of the increasing reducibility of thecatalysts. It indicates the role of the support properties, especially reducibility, in the creationof catalytic performance of Au/oxide catalysts. CeO 2 -ZrO 2 mixed oxides are promisingsupports for Au nanoparticles in CO oxidation.This research has been supported by Grant PBZ-KBN-116/T09/2004 (No.K124/1B/2005). Izabela Dobrosz is a holder of a fellowship of the Mechanism WIDDOKprogram supported by European Social Fund and Polish State (contract numberWIDDOK/SM/2006/7).References1. Haruta M., Yamada N., Kobayashi T., Iijima S., J. Catal. 115 (1989) 3012. Haruta, M., Daté M., Appl. Catal. A: General 222 (2001) 4273. Trovarelli A. (ed.), Catalysis of Ceria and Related Materials. ICP, 20024. Gomez-Garcia M.A., Pitchon V., Kiennemann A., Env. Int. 31 (2005) 445 (and references therein)5. Ivanova S., Petit C., Pitchon V., Appl. Catal. A: General, 267 (2004) 1916. Dobrosz I., Jiratova K, Pitchon V., Rynkowski J.M., J. Mol. Catal. A: Chemical, 234 (2005) 187