Study On Pd@SiO₂/?-Fe₂O₃ Catalyst For Lean Burn CNG Vehicle Exhaust Gas Purification

Fuel are more fully combusted in lean-burn CNG-fuelled vehicles because of excessive air.Exhaust pollutions are relatively less compared with other gasoline vehicles.However,the high content of unburned methane in exhaust of lean-burn CNG-fuelled vehicles poses a great potential threat to the environment.Results of research showed that Pd have the highest catalytic activity for methane combustion,but they are prone to high temperature sintering and sulfur poisoned,which resulted in a significant reduction in the catalytic activity for methane combustion.It is known that the research on the anti-sintering and sulfur resistance of Pd catalysts is particularly important.A new type of good performance Pd@SiO2/?-Fe2O3 catalysts were prepared accordingly,and the anti-sintering and sulfur resistance of catalysts were systematically studied.The main contents and conclusions were as follows:(1)A highly efficient synthesis method of Pd@SiO2 nanoparticles with similar size and similar morphology was developed.Controlled synthesis of Pd@SiO2 nanoparticles with uniform size and morphology was achieved by precise control of the reaction conditions.After calcination for 5 h at 700 ?,the Pd@SiO2 nanoparticles still maintained the integrity of the core-shell structure,which showed good resistance to sintering.(2)A synthesis method of ?-Fe2O3 nanorods was developed,and the ?-Fe2O3 nanorods with uniform morphology and size were synthesized.Pd/a-Fe2O3 and Pd/?-Al2O3 catalysts were prepared by using the ?-Fe2O3 and ?-Al2O3 as carriers.The sulfur resistance of carriers of ?-Fe2O3 and ?-Al2O3 was studied,and the regeneration of sulfur poisoning of two kinds of carriers was also studied.Results showed that ?-Fe2O3 showed better performance of sulfur resistance than ?-Al2O3.The active components of two carriers supported Pd catalysts were severely sintered during the process of regeneration at high temperature,which leads to a significant decrease in the activity of the catalysts.And the regeneration of sulfur poisoning was failed.(3)The Pd/?-Fe2O3 and Pd@Siv2/?-Fe2O3 catalysts were prepared,and the anti-sintering property of core-shell catalysts was studied by characterizations and the test of methane activity.Results showed that the catalysts with core-shell structure had good property of anti-sintering.Pd@SiO2/?-Al2O3 and Pd@SiO2/?-Fe2O3 catalysts were synthesized on the basis of the above research.The sulfur resistance and regeneration of sulfur poisoning of the two kinds of catalysts were studied.The sintering of active components at high temperature in the process of regeneration can be effectively eliminated by using core-shell nanoparticles as active components.The results showed that the Pd@SiO2/?-Fe2O3 catalysts had better properties of sulfur resistance and regeneration of sulfur poisoning than the Pd@SiO2/?-Al2O3 catalysts.The research provided some basic references for the design and preparation of good performance exhaust purifying catalysts for CNG automobiles under lean-burn condition.