The Application Of Porous KCC-1 And SSZ-13 Materials For The Elimination Of Haze Cauising CO And NO_x Pollutants

Over recent years,due to the fast development of global industry and auto industry,air pollution incidents have taken place frequently.NO_x and CO,which are two major air pollutants,can degrade the air quality and harm people’s health severely.Therefore,it is extremely urgent to suppress their pollutions.Due to its high efficiency and low cost,ammonia selective catalytic reduction of NO_x（NH₃-SCR）has currently become a major technique for the elimination of NO_x for mobile systems.Because of its unique microporous（3.8 ?）structure,good hydrothermal stability and reistance to sulfur deactivation,Cu-SSZ-13 zeolite catalysts have attracted much attention.However,it still suffers from low temperature activity.It is reported that by co-exchanging Cu and Fe cations,Cu-Fe-SSZ-13 catalyst with improved low temperature activity can be prepared.Based on this idea and the fact that Mo addition can improve the NH₃-SCR performance of Ce-Zr and Ce-Ti catalysts,the modification effects of Mo on Cu-SSZ-13 zeolite catalysts has been investigated in this study.On the other hand,catalytic CO oxidation has been proved to be an effective technique for the removal of CO pollution.High surface area mesoporous silica materials are good supports,which can generally disperse the active components well to obtain highly active catalysts for CO oxidation.Therefore,Ag supported on mesoporous silica materials with different morphologies has been investigated for this reaction.The main results of this thesis are summarized here:First,a series of mesoporous SiO₂ with different morphologies,such as KCC-1,SBA-15,MCM-41 and regular SiO₂ powder,have been synthesized and used as supports for Ag to prepare catalysts（7% Ag/KCC-1,7% Ag/SBA-15,7% Ag/MCM-41 and 7% Ag/ SiO₂）for CO oxidation.It is found that the morphologies of the SiO₂ supports influence the dispersion of the supported Ag species,thus resulting in catalysts with different Ag grain sizes and active metallic surface areas,as proved by XRD and H₂ adsorption-desorption results.With fibrous KCC-1 silica spheres as the support,the mobilization and aggregation of the Ag particles can be effectively hindered by the open access surface mesopores.Therefore,compared with SBA-15 and MCM-41,Ag nanoparticles with much smaller grain sizes have been achieved,thus resulting in a catalyst with significantly improved activity.Furthermore,a strict linear relationship has been found between the differential CO oxidation rates and the Ag crystallite size/the active metal surface area,indicating the Ag crystallite size/the metallic Ag surface area is the determining factor for the activity of the catalysts.Second,Cu-Mo-SSZ-13 zeolite catalysts have been prepared for NH₃-SCR reaction to remove NO_x.XRD results illustrate that the structure of the SSZ-13 zeolite can be changed by excess Mo addition.With too much Mo,its structure could be eventually damaged completely.H₂-TPR results indicate that the Cu2+ cations are located on two sites,one on the six-membered rings and another inside the large cages of the CHA structure.With the increase of Mo loading,the first kind of Cu2+ cations become less,while the second kind become more.While with the further increase of the Mo loading,these two kinds of Cu2+ cations disappear,with the formation of CuO,which could be owing to the pores blockage by the excess Mo species.XPS results confirm the change of the chemical environments of Cu2+ cations,which are well consistent with the H₂-TPR results.NH₃-TPD results demonstrate that the addition of appropriate amount of Mo addition can increase the amount of surface acidic sites,hence improving the NO_x conversion at the high temperature and decreasing the selectivity of the side product N2 O.