Study Of Catalytic Combustion Of Soot On Fe-based Catalysts

In recent years,particulate matter is one of the major air pollution in China.Soot particles produced by fossil fuel combustion is an important component of particulate matter.Soot particles not only seriously pollute the atmosphere,but also endanger human health and lead to high incidence of cardiovascular diseases.Therefore,it is necessary to control the pollution of soot particles.Exhaust emissions from car engines,kitchens and factories are an important source of soot particles.Particulate filters are commonly used to purify soot particles from vehicle exhaust.The regeneration of the filter is the key to the purification efficiency,which has been the focus of scholars.There are two main solutions to solve the passive regeneration of the filter:adding fuel additives and coating catalyst on the filter.The addition of catalysts in the fuel not only solve the problem of soot emissions from automobile exhaust,but also can be used in general burners,so it is the focus of this paper.In addition,the catalytic effect of solid catalysts on soot particles was also studied in this paper.Iron-based catalyst has been an important research object in the field of catalytic combustion,owing to its good catalytic effect,low price and no harm to human body.In this paper,the effect of ferrocene on the formation of soot particles in propane oxygen diffusion flame was studied.Moreover,we measured the effect of ferrocene on the flame temperature,the basic morphology of soot particles,the chemical composition and the physical structure of soot particles.We also studied the catalytic effect of iron oxide supported noble metal on soot particles in this paper.First,the effects of ferrocene on the flame temperature and the basic characteristics of soot particles were studied.Ferrocene is added to the propane oxygen diffusion flame by heating in a water bath.The distribution of flame temperature in the axial direction was measured by primary-color pyrometry after adding ferrocene.The soot particles were collected at different flame locations by thermophoretic sampling and analyzed by TEM,XRD and TGA.It was found that the addition of ferrocene in propane could reduce the flame temperature,especially for the temperature at the end of the flame.With the increase of the concentration of ferrocene in propane,the temperature decreased more significantly.At the same height of the flame,the effect of ferrocene on the temperature of propane flame is various for different equivalence ratios.When the equivalent ratio is 2.1,the temperature drops by 260 K,the greater the equivalent ratio,the less the temperature drop.Iron atoms were separated from ferrocene and reacted with the free radicals such as OH to form iron oxides.Transmission electron microscopy(TEM)shows that the soot particles grow with iron oxide as the nucleus,and the diameter of the soot particles was two times larger than that without ferrocene addition.Thermogravimetric analysis(TGA)shows that the addition of ferrocene can improve the oxidation activity of soot particles,which can be easily oxidized at low temperature.Second,the effects of ferrocene on polycyclic aromatic hydrocarbons(PAHs)and the carbon bond mode in the soot particles were studied.PAHs are important precursors for the formation of soot particles.The polycyclic aromatic hydrocarbons in soot particles were dissolved in organic solution by ultrasonic extraction.Qualitative analysis of PAHs was studied by gas chromatography mass spectrometry,and quantitative analysis of the change of aromatics quality was studied by gas chromatography after adding ferrocene.It was found that the addition of ferrocene to the fuel did not change the type of polycyclic aromatic hydrocarbons in soot particles,but it increased the quality of small PAHs and reduced the quality of big PAHs.Ferrocene inhibited the growth of PAHs in the flame.In addition,the effect of ferrocene on the bonding mode and the oxygen-containing functional groups of soot particles was studied by near edge X-ray absorption fine structure(NEXAFS).The results show that ferrocene reduces peak height ratios Iπ/Iσ of soot particles and promotes the formation of aliphatic hydrocarbon.Ferrocene also reduces the formation of oxygen-containing functional groups such as phenols,ketones and carboxyl groups of soot particles.Third,the effect of ferrocene on the nanostructure of soot particles was studied.Based on the MATLAB software platform,the image processing program was compiled for the high resolution transmission electron microscope image processing.Through the negative transformation,contrast enhancement,top-hat transformation,binarization,skeletonization,breaking triple or quadruple joints and ruling out artifacts,the characterization parameters of the nanostructure of soot particles were extracted.Fringe length,tortuosity and fringe separation distance were used to characterize the effect of two ferrocene on the nanostructure of soot particles.The results show that ferrocene causes the decrease of fringe length,the increase of tortuosity and fringe separation distance,and the decrease of graphitization degree,which is favorable for the oxidation of soot at low temperature.Finally,iron oxide supported noble metal catalysts were prepared and mixed with soot particles in tight contact and loose contact,respectively.The effect of the catalyst on soot particles was tested on the thermogravimetric analyzer,and the catalysts were characterized by TEM,XPS and XRD.The results show that the iron oxide has catalytic effect on soot particles,and the catalytic effect is better after loading the noble metal Au,and the conversion temperature of soot particles can be reduced by about 100℃.It is proved that the iron-based catalyst has a very good catalytic effect on soot particles,whether in the form of fuel addition or loading on the filter.