Study On NO_x Adsorption-reduction Performance And Deactivation Process Of Fe Modified Hydrotalcite-based Catalyst

Lean NO_x Trap technology is one of the most potential aftertreatment technologies to reduce the NO_x emission from diesel engines.The conventional LNT catalyst has disadvantages such as poor stability in high temperature,bad sulfur resistance and poor adsorption performance in low temperature,which restrict its wide acceptance.Therefore,the development of new materials like modified hydrotalcite to improve the NO_x purification performance,the stability in high temperature and sulfur-resistance capability of LNT catalyst attracts much more attention in the related research field.In this paper,a series of iron-magnesium hydrotalcite-based catalyst with well dispersed noble metal for the lean NO_x trap（LNT）was prepared by co-precipitation and impregnation methods.The effect of modified metal ratio on catalyst performance was investigated by analytical techniques to find out the best new type LNT catalyst.Meanwhile,the study on the thermal deactivation and sulfur poison process of the catalyst was developed to reveal the main factor and mechanism for the deactivation of Fe modified hydrotalcite-based catalyst.Through this research,the design and optimization theory for modified hydrotalcite-based LNT catalyst was established initially,which provides a beneficial research foundation for its wide acceptance in automobile field.The main results from this research are as follow:The hydrotalcite-based catalyst with well dispersed noble metal as well as BaO for the lean NO_x trap（LNT）can be prepared by co-precipitation and impregnation methods.Analysis of physicochemical properties show that the increase of Fe/Al ratio can enhance the NO_x adsorption ability and lower the stability of adsorbed nitrate,thus widen the NO_x desorption temperature and improve the NO_x desorption concentration.With Fe modified,the reduction performance of LNT catalyst improves,more N₂ was created.The crystalline structure of the catalyst remains stable when the heat treatment temperature is less than 700°C.The sintering of catalyst prepared and the conglobation of Pt particles appear on the catalyst surface after calcination at 800°C.With the increase in heat treatment temperature from 500 to 800°C,the desorption amounts of NO_x increases after an initial decrease,while the corresponding peak temperature shows a marginal change.DRIFTs results indicate that the NO_x adsorbed species and the adsorption pathways over the catalyst after calcination at 800°C differs from those at 500°C.And the ratio of NH₃/N₂ released from the reduction of adsorbed NO_x species over the catalyst calcinated at 800°C decreased.Bulk sulphate species are observed on sulfur poisoned Pt/BaO/MgFeO catalyst,leading to the decrease of adsorption sites.Meanwhile,the NO_x adsorption species move to more stable natrite ones,leading to worse of catalyst performance.Compared with Pt/BaO/Al₂O₃ catalyst,the Pt/BaO/MgFeO catalyst shows better sulfur resistance capability.And the temperature of regeneration phase on sulfur poisoned catalyst is lower,shows better desulfurization ability.