Flame-derived Pt/Ba/CexZr1−xO2: Influence of support on thermal deterioration and behavior as NOx storage-reduction catalysts

Abstract

Pt/Ba catalysts for NOx storage-reduction (NSR) supported on ceria/zirconia were prepared by two-nozzle flame spray pyrolysis. Emphasis was placed on the effect of the support composition on the thermal deterioration and the related behavior during NOx storage and reduction. The materials were characterized by X-ray diffraction (XRD), nitrogen adsorption (BET), electron microscopy (TEM), and temperature-programmed decomposition (TPD). The as-prepared material consisted of intimately mixed agglomerates of BaCO3 and Cex Zr1 - x O2 particles. Low thermal stability of BaCO3 resulted in high NOx storage capacity. The support composition (Cex Zr1 - x O2) strongly affected the NOx reduction activity of Pt. Higher Ce content favored the formation of stable Pt oxides exhibiting lower reduction activity. Thermal deterioration was investigated in different atmospheres. At 800 °C, BaCO3 transformed into inactive Ba zirconate and Ba cerate. At high Ce content, BaCO3 was reformed when exposed to CO2 at high temperatures, recovering its high NOx storage capacity. During the high-temperature treatment, however, Pt strongly deactivated, resulting in a loss of the catalyst's NOx reduction activity.