| Diesel engines have been widely used due to their high thermal efficiency,good economy,good structure,strong maneuverability,easy operation and maintenance.While diesel engines bring convenience to human beings,the nitrogen oxides?NOx?and soot particles?PM?emitted by diesel engines also bring serious harm to the atmospheric environment and human health.At present,the post-treatment technology of soot particles emitted by diesel engines is mainly diesel particulate filter?DPF?,but the exhaust temperature of diesel engines is relatively low?200-500°C?,which is not enough to make the soot,the main component in the particles,completely burn to achieve automatic regeneration.So,the soot can be catalyzed and combusted at a lower temperature while filtering by coating a suitable catalyst component on the DPF to eliminate the soot emission from diesel exhaust.In this paper,Bi2O3-Fe2O3 system catalysts were synthesized by hydrothermal method with different raw material molar ratios.Five catalysts with the main composition of Fe2O3,Bi2O3,Bi Fe O3,Bi2Fe4O9 and Bi25Fe O40 were successfully prepared.The physical and chemical properties of the catalysts were characterized and studied by using XRD,BET,SEM,H2-TPR,O2-TPD,XPS,and Raman and the catalytic combustion performance of soot was evaluated by programmed temperature oxidation experiments.XPS and O2-TPD show that the active oxygen content of the bismuth-iron composite catalysts is higher than that of a single Bi2O3 or Fe2O3 catalyst,and the active oxygen content of the Bi0.2Fe1.8 catalyst is the highest.The composite catalyst shows better low-temperature catalytic activity than single Bi2O3 or Fe2O3.Bi0.2Fe1.8 catalyst with the best catalytic performance has a T90of soot catalytic combustion in tight mode and loose mode of 422?and 560?,respectively.Bi2O3-Ce O2solid solution catalysts were synthesized by a simple co-precipitation method.A series of characterization methods were used to study the physical and chemical properties of the catalysts,and the soot catalytic combustion activity was evaluated on a temperature-programmed oxidation device.XPS,O2-TPD and Raman results show that the composite catalysts have higher active oxygen content than pure Bi2O3 and Ce O2,and Bi0.2Ce0.8O2-?has the highest content.All composite catalysts show superior low-temperature catalytic activity over single catalyst and Bi0.2Ce0.8O2-?catalysts have the best catalytic performance.The T90 of Bi0.2Ce0.8O2-?is 393?and536?in the tight contact and loose contact modes,respectively,and the T90 is 520?in the NO2 assisted loose contact mode.Analysis of the soot catalytic combustion mechanism of Bi2O3-Fe2O3and Bi0.2Ce0.8O2-?shows that the doping of Bi2O3 oxide with transition metal oxide Fe2O3and rare earth metal oxide Ce O2,respectively,accelerates the transfer rate of active oxygen,increases the oxygen vacancy and the content of active oxygen,improves the catalytic combustion performance of soot. |
PDF Full Text Request