Effect of Co addition to Pt/Ba/Al2O3 system for NOx storage and reduction

A comparative study of Pt/Ba/Al2O3, Co/Ba/Al2O3, Pt/Co/Al2O3 and Pt/Co/Ba/Al2O3 was performed in regards to their NOx storage capacities and NO oxidation abilities as a function of temperature. The nitrate stability and dynamic behaviors of NOx storage reduction during lean/rich fuel cycles using hydrogen as a reductant were also investigated over these catalysts. It was found that Pt/Co/Ba/Al2O3 possessed the largest NOx storage capacity within the temperature range of 200–350 °C. The existence of Co not only improved the oxidation of NO to NO2 under lean conditions, but also enhanced the release and reduction of NOx during the rich phase. The Pt and Co co-supported catalysts showed better NOx storage reduction activity and higher N2 selectivity than Pt supported Ba/Al2O3 catalysts within the tested temperature range. As for Pt/Co/Ba/Al2O3, high conversion was obtained at either a low reductant concentration with long duration time or a high reductant concentration with short duration time during the rich phase. In situ FTIR studies showed that NOx adsorption over Co-containing catalysts takes “nitrite route” as an important pathway. The intimate contact of Co and Ba/Al could accelerate nitrite/nitrate formation and the synergistic effect of Pt and Co could accelerate NOx reduction.

. Co containing catalysts (Co/Ba/Al2O3, Pt/Co/Al2O3 and Pt/Co/Ba/Al2O3) show much higher NO oxidation ability than Pt/Ba/Al2O3 between 250 °C and 400 °C. The effective NO oxidation ability of Co oxides and the intimate contact between Co and Ba/Al species improve the NOx storage capacity of Co containing catalysts during the lean condition.Figure optionsDownload as PowerPoint slideResearch highlights▶ The existence of Co significantly improves the oxidation of NO to NO2 under lean conditions. ▶ Co addition also enhances the release and reduction of NOx during the rich phase. ▶ Pt/Co/Ba/Al2O3 shows better NOx storage reduction activity and higher N2 selectivity than Pt/Ba/Al2O3. ▶ The intimate contact of Co and Ba/Al can accelerate nitrite/nitrate formation.