Effect of barium loading on CuOx–CeO2 catalysts: NOx storage capacity, NO oxidation ability and soot oxidation activity

A series of Ba–Cu–Ce catalysts were prepared by loading different amounts of Ba(Ac)2 on the sol–gel-synthesized CuOx–CeO2 mixed oxides. The activities of the catalysts for soot oxidation were evaluated in 1000 ppm NO/10% O2/N2 under loose contact conditions. The catalysts were characterized by XRD, BET, H2-TPR, in situ-DRIFTS and NO-TPO measurements. When Ba loading is between 6 and 10 mol.% of Cu + Ce, the catalysts exhibit an onset temperature (Ti) as low as 376 °C. NO is oxidized at Cux+ and Cex+ sites and then stored on the adjacent Ba species in form of barium nitrate. Ba(NO3)3 begins to decompose, releasing abundant NO2 at around 370 °C under the driving of soot as the reductant. The nitrate-derived NO2 and the NO-derived NO2 initiate the soot combustion over the Ba-modified catalysts with a significantly lowered Ti. The ternary catalysts lose their NOx storage capacity after hydrothermally aged at 800 °C for 10 h due to the formation of BaCeO3. However, Ba restrains the sintering of (Cu,Ce)Ox, resulting in relatively more favorable redox properties and thus higher activity for NO oxidation. The barium-modified catalysts show lower onset temperatures (470–480 °C) of soot oxidation than pure CuCe (509 °C) after aging.