Study On The Oxidation Characteristics And The Evolution Of Surface Functional Groups Of The Soot Particles For Gasoline Engines

Studying the oxidation behavior of the soot particles in gasoline particulate filters is conducive to the development of reasonable regeneration control strategies and the efficient regeneration of deposited soot particles,which can reduce the back pressure of engine exhaust and improve the fuel economy of engines.In this paper,the model carbon,whose physicochemical properties was similar with the soot particles of gasoline engines,was utilized to ensure the consistency of oxidation properties of the soot used in the experiment.The oxidation characteristics of the model carbon under different oxygen and nitric oxide contents were studied by means of a thermogravimetric analyzer.A series of cerium modified hydrotalcite catalysts were prepared by coprecipitate and step impregnation methods,and the adsorption and desorption performance for the catalysts were studied using the chemisorption analyzer manufactured by Quantachrome Instrument.The effects of the Pt/Ba O/MAC20 catalyst with the best desorption ability on the oxidation characteristics of the soot particles were analyzed.Finally,the evolution of the surface functional groups on soot during the non-catalytic and the catalytic processes were studied using infrared analysis technology,which further elaborated the oxidation of the soot particles.The results of this paper provided necessary theoretical basis for the regeneration of gasoline particulate filters.The main conclusions were listed as follows:At low oxygen contents of 0.5%and 1%,the ignition and burn out temperatures of the soot paricles were above 545 and 700°C,respectively.The addition of NO promoted the oxidation of soot under low temperature conditions（<550°C）,but the oxidation of soot under high temperature conditions（>550°C）was restrained.The Pt/Ba O/MAC20 catalyst could effectively reduce the light-off and the burn-out temperatures,and simultaneously enhance the maximum oxidation rate of soot.This catalyst had the best performance in catalytic oxidation of the soot particles.As compared to O₂ atmosphere,the catalytic performance of the Pt/Ba O/MAC20catalyst could be further improved in the presence of oxygen and nitric oxide.The relative content of aliphatic hydrocarbon functional group on the surface of soot decreased gradually with the oxidation process.The addition of NO promoted the conversion of hydrocarbon functional group.The variation tendencies of the carbonyl functional group on soot was related to the reaction temperatures,and the addition of NO exhibited opposite effects on the conversion of the carbonyl functional group under different temperature conditions.The content of C=O functional group on the surface of soot in the presence of Pt/Ba O/MAC20 catalyst was the highest among all the soot-catalyst samples,which indicated that the catalyst possessed the best performance of catalytic oxidation.In the presence of Pt/Ba O/MAC20 catalyst,the content of C=O functional group on the surface of soot under NO+O₂ atmosphere decreased initially and then increased as compared to that under O₂ atmosphere.The catalytic mechanism of Pt/Ba O/MAC20catalyst conformed to the principle of Langmuir-Hinshelwood heterogeneous catalysis.