Impact of the support oxide and Ba loading on the sulfur resistance and regeneration of Pt/Ba/support catalysts

The influence of both the support oxide (Al2O3, SiO2, Al2O3-5.5 wt% SiO2 and Ce0.7Zr0.3O2) and the barium loading of Pt/Ba/Support model catalysts on sulfur resistance was investigated by hydrogen temperature programmed reduction (TPR), X-ray diffraction (XRD) and NOx storage capacity measurements. The sulfation of catalysts under lean conditions in the presence of water and carbon dioxide led to the formation of both surface and bulk sulfates, except for silica supported catalyst on which mainly bulk barium sulfates were formed. Sulfate stability was influenced by the support oxide and the Ba loading. For alumina containing catalysts, both the amount of deposited sulfur and the sulfate stability under hydrogen increase with the Ba loading. Conversely the same sulfates stability was observed for Ce-Zr supported samples, whatever the Ba loading. The thermal treatment of the sulfated catalysts under oxidizing conditions at 800 degrees C favored the formation of less reducible bulk barium sulfates on all the catalysts. Ceria-zirconia led to a decrease of bulk BaSO4 stability under hydrogen, their reduction temperature being about 100 degrees C lower than on alumina containing materials. The elimination of sulfates under rich conditions (H-2, CO2, H2O, N-2) was more effective on the ceria-zirconia supported sample compared to alumina containing catalysts, even after ageing at 800 degrees C. Sulfation of the catalysts induced a loss of NOx storage capacity depending on catalyst composition. All the catalysts recovered their initial NOx storage capacity after regeneration at 550 degrees C, even with an improvement in the case of the ceria-zirconia supported material. The ageing at 800 degrees C of sulfated catalysts before regeneration did not lower the performance of the Pt/10Ba/CeZr catalyst, contrary to the alumina containing samples. (C) 2007 Elsevier B.V. All rights reserved.