Metal Modification Of Platinum-supported Catalysts And Their Catalytic Performance In Eliminating Nitrogen-containing Pollutants

Nitrogen oxides?NO_x?and ammonia?NH₃?have become the main control targets for the next stage of“haze chemical”pollution in China atmospheric.Source control is the fundamental way to solve atmospheric pollution.Automobile exhaust emissions are one of the important sources of NO_x and NH₃ pollution in the atmosphere.While strictly controlled NO_x pollutants,reduced emissions of NH₃ secondary pollutants is a major challenge for traditional automotive catalysts.In the field of NO_x and NH₃ purification,Pt-supported catalysts have shown good catalytic reaction characteristics,but it is difficult to meet the increasingly strict emission regulations.Non-stoichiometric oxides such as Ce O_2-x,Mn O_2-x,and Fe O_x can not only effectively stabilized the active species of Pt-supported catalysts,but also have good oxygen storage capacity,which plays an important role in improving catalyst performance.In this paper,the effects of modification of different metal elements on the composition,structure,and purification capacity of NO_x and NH₃of catalysts were studied for the purpose of improving the catalytic activity and N₂ yield?selectivity?of traditional Pt-supported catalysts,and established the structure-activity relationship of catalyst structure-capacity.?1?Pt/MBa Al?M=Mn,Ce,Mn-Ce?catalyst was prepared by multi-step impregnation method,and the structure-activity relationship of structure-NO_x storage capacity of Pt/MBa Al catalyst was established through various characterization and performance evaluation techniques.It was found that among all the catalysts,Pt/Mn Ba Al has the best NO_x storage and release capacity.Mn modification can not only promotes low-temperature NO oxidation into NO₂ for forming surface nitrates with a better thermal stability than nitrites,but also inhibits the formation of ionic nitrates to improve the stored NO_x release capacity.?2?M-Pt/USY?M=Mn,Ce,Fe,Pr?catalyst was prepared by multi-step impregnation method,and the structure activity relationship of structure-N₂ selectivity of M-Pt/USY catalyst was established through various characterization and performance evaluation techniques.The study found that the addition of Mn O_2-x,Ce O_2-x,Fe O_x and Pr O_x can effectively stabilized the structure of USY,improve the strength of acid sites and stability of acid sites on the surface of the Pt/USY catalyst,among which Fe O_ximproves the effect of acid sites better.Fe modification can not only promote the generation of oxidation state Pt⁴⁺,but also effectively inhibit the generation of Pt⁰.The Pt^?+/Pt value of catalysts decreases in the order of Fe-Pt/USY>Pt/USY>Ce-Pt/USY>Mn-Pt/USY>Pr-Pt/USY.Compared with other catalysts,Fe-Pt/USY catalyst can inhibit the formation of N₂O,NO,and NO₂ by-products while promoting the formation of N₂.It is the best catalyst material for NH₃oxidation.From the perspective of structure-activity relationship,controlling Pt^?+/Pt value and O-Pt bond content in the catalyst through metal elements modification can improve the N₂ selectivity of the catalyst and the effect is more obvious at at relatively high temperature.?3?Based on the best NO_x storage capacity of Pt/Mn Ba Al catalyst,a series of Pt/Mn Ba Al and Rh/Ce O₂ combined catalysts with different contents were prepared by physical mixing method,and its catalytic NO_x removal performance was studied.The research found that the combined catalyst not only has higher NO_x removal efficiency and N₂ yield,but also inhibit the generation of N₂O,Rh_0.1Ce-Pt_0.9Mn Ba Al catalyst is the optimal NO_x storage-reduction catalytic material.However,a large amount of NH₃produced by the Rh_0.1Ce-Pt_0.9Mn Ba Al catalyst in NO_x purification.At the same time,the catalyst stratification method was used to combine Fe-Pt/USY and Rh_0.1Ce-Pt_0.9Mn Ba Al to studied its purification performance for NO_x and NH₃.As a result,it was found that the combined catalyst not only effectively reduced the by-product NH₃production,but also improved the yield The N₂ yield and low-temperature NO_x removal efficiency.The mass ratio of the two catalytic materials should not be less than 1:9.