Study On Adsorption And Desorption Of NO_x And Catalytic Oxidation Of Soot For Barium-modified Iron-cerium Oxides Catalysts

The catalytic diesel particulate filter?CDPF?,combined with the In-engine cleaning technologies,is one of the most important technical routes to meet the emission regulation in the future.Nowadays,the cost of commercial CDPF catalysts is high and the low-temperature activity is poor.However,the non-precious metal CDPF catalysts are cheap and can greatly reduce the oxidation combustion temperature of soot particulates.Therefore,non-precious metal CDPF catalysts have great potential for the application on PM removal.In this paper,the storage component barium with strong NO_x adsorption and desorption capacity was loaded on FeCeO_2-?catalyst samples.The changes of soot oxidation activities for FeCeO_2-?and BaFeCeO_2-?catalyst samples were investigated.The results show that much higher catalytic soot combustion activity can be observed on BaFeCeO_2-?catalyst.The soot ignition temperatures of the Ba?5%?FeCe,Ba?10%?FeCe,and Ba?20%?FeCe catalysts decrease to 296°C,284°C,and 299°C when1,000 ppm NO is introduced,which is superior to the catalytic performance of the FeCeO_2-?catalyst with the soot ignition temperature of 305°C.However,in the field of physical structure,redox capacity and NO_x storage capacity,the results show that the introduction of barium to FeCeO_2-?catalyst causes agglomeration on the surface of BaFeCeO_2-?catalyst and the specific surface area of BaFeCeO_2-?catalyst decreases.Moreover,the barium loading is bad for the redox performance of the catalysts and the contents of Ce³⁺and adsorbed oxygen on the surface of catalysts are greatly reduced,which has a not good effect on the catalytic performance.For further investigating the NO_x adsorption and desorption behavior,the NO_x storage tests and NO-TPD experiments were carried out.The results show that the introduction of barium to FeCeO_2-?improves the NO_x adsorption and desorption ability in a high temperature range.NO-TPD experiments show that NO is the main desorption product in the temperature of 50°C to 200°C for FeCeO_2-?catalyst and the NO desorption for BaFeCeO_2-?catalyst mainly occurs in the range of 300°C to550°C.It is the behavior of storing a large amout of NO_x in the low temperature and releasing NO_x in the high temperature that makes BaFeCeO_2-?catalyst exhibits good activity for soot oxidation.Combined with the NO_x adsorption-desorption tests and catalytic performance for soot oxidation,the reaction mechanism of NO_x storage and desorption on BaFeCeO_2-?catalyst and NO_x assisted for soot oxidation of BaFeCeO_2-?catalyst were proposed.The reaction process of NO_x storage and desorption can be divided into four steps.Firstly,NO is oxidized to NO₂by the active site.Secondly,the NO and NO₂ in the reaction gas are stored in the form of NO₂^-and NO₃^-.Thirdly,when the reaction temperature reaches350°C,a more stable species Ba?NO₃?₂ occurs on the surface of BaFeCeO_2-?catalyst.Finally,Ba?NO₃?₂ gradually decomposes and desorbs to generate a large amount of NO_x.The last step is the most critical step of BaFeCeO_2-?catalyst for NO_x assisted for soot oxidation.