Abatement of diesel exhaust pollutants: NOx adsorption on Co,Ba,K/CeO2 catalysts

Abstract

Abstract The Co,Ba,K/CeO 2 system is a potential candidate to be used under the simultaneous abatement of soot and NO x in diesel exhausts. In this work, we study the interactions of NO x with the said solid. NO 2 is strongly adsorbed on the Ba,K/CeO 2 surface through the formation of Ba and K nitrate species which are stable under He atmosphere up to 490 °C. However, when Co is incorporated to the system (Co,Ba,K/CeO 2 catalyst), Ba nitrates become unstable at ca. 370 °C, under both NO+O 2 and He atmosphere. DRX, FTIR, and LRS characterization shows that potassium favors the formation of the BaCoO 2.93 perovskite in the Co,Ba,K/CeO 2 catalyst calcined at 400 °C. This perovskite structure is not detected when K is absent (Co,Ba/CeO 2 system). FTIR spectra of Co,Ba,K/CeO 2 treated with NO+O 2 indicate the formation of surface N-bound nitrate species (OBa- -NO 2 ), where NO 2 acts as a Lewis base. Since the said species are not detected in the samples without BaCoO 2.93 , it is suggested that they are related to the Ba atoms of the perovskite structure. Microbalance experiments combined with FTIR and mass spectroscopy characterization show that the nitrate species formed in the Co,Ba,K/CeO 2 sample can be readily decomposed to N 2 under a reducing atmosphere, making this system very interesting to be used as a NO x catalytic trap. On the other hand, under He atmosphere the decomposition of nitrates only produces gaseous NO x . In addition, when the Co,Ba,K/CeO 2 catalyst previously treated under NO+O 2 atmosphere is intimately mixed with the soot and then heated in He up to 490 °C, the soot particulates are partially oxidized by the surface nitrate species.