| Recent years, the employment of ethanol gasoline fuels are getting widerand wider. Meanwhile, as a renewable clean energy, the ethanol developmentprospects are anticipated. The exhaust gases of different motor vehicles such asaldehyde, ether and incomplete combustion of ethanol exert great harm toenvironment and human body. The carriers can not only disperse and support theactive component, but affect the catalyst surface, mechanical strength, chemicalstability and thermal stability. In the ethanol fuel car exhaust gas catalyticpurification, titanium dioxide has obtained widespread attention as load typecatalyst.With good chemical and mechanical stability, resistance to lightcorrosion of field and non-toxic characteristics, TiO2has been applied inphotocatalysis, sterilization, flue gas denitration, SCR reaction and many otherfields. TiO2has many defect as small specific surface area, poor mechanical strength and poor stability of crystal structure. With many advantages, Al2O3make up for the deficiencies of titanium dioxide. Al2O3-TiO2composite oxideshave showed excellent carrier performance in various catalytic systems.Although Al2O3-TiO2composite carrier has been widely investigated, therewas few report concerning the effect of the addition and adding amount of Al2O3in TiO2carrier on what the phase transformation of TiO2and how the acidity andactive centers have been influenced. Our previous research has shown that1%Pd/γ-Al2O3-TiO2catalyst had a higher catalytic activity than other single carriercatalyst for the ethanol complete oxidation. The addition of Al2O3inPd/γ-Al2O3-TiO2(95%) influenced the crystal structure and catalytic activity ofTiO2has been discussed. However how the Al2O3proportion affects the carrierand catalyst need to be further researched. This study focuses on the influencesof different Al2O3amount on the Pd/TiO2catalyst. Meanwhile, discussion on themutual influence in crystal structure level between Al2O3and TiO2that mayexist was carried out, as well as the change of the catalyst performance onethanol catalytic oxidation. Finally, research on such as catalyst surfaceproperties, phase structure and mutual effect between different components wereaccomplished by means of XRD, N2adsorption/desorption, NH3-TPD, XPS,FT-IR characterization methods. Main conclusions in this thesis are as follows:(1) Ethanol online activity test show that catalysts with different Al2O3:TiO2mass ratio presented great difference in catalytic activity, and activity ofthe composite carrier catalyst was generally superior to single TiO2catalyst. Along with the increase of the content of Al2O3, Pd/Al-Ti(0.95) andPd/Al-Ti(0.10) showed the best performance at various different temperatures,and bimodal phenomena appeared in the temperature-activity figure.(2) Calcination temperature and time both affect the catalytic oxidation ofethanol. The sample that calcined at500℃showed an obviously better activitythan that calcined at700℃, better for CO2. In addition, the high Al2O3: TiO2ratio catalysts were affected more serious by temperature, and their catalyticactivity decreased bigger after calcination temperature increased.(3) The interaction between different carriers and different activecomponent may lead to the change of the catalyst performance. In the catalyticremoval process of ethanol and NOxat the same time, activity of catalystsloading Pd-V and Pd-Ce were higher than single Pd catalysts. And activity ofcatalyst with the carrier Al-Ti(0.92) was much better than that of Al-Ti(0.08)catalysts. The effect of catalyst support for activity of ethanol catalytic oxidationis greater than that of the difference of active component.(4) XRD results showed that the addition of Al2O3in TiO2inhibited theshift of crystal type from anatase to rutile phase. γ-Al2O3in Pd/Al-Ti(0.95) washighly dispersed on the surface of the carrier or Al atoms may incorporated intoTiO2lattice, and Ti atoms may enter into Al2O3lattice or occupy the O2-space incatalyst Pd/Al-Ti(0.10). The form of specific Al-O-Ti chemical bonds increasedthe TiO2crystal transition temperature obviously. The results of N2adsorptionalso showed that the TiO2in composite carriers existed in the form of anatase crystal, and part of the Ti-O-Ti bonds replaced by Al-O-Ti bonds.(5) The results of N2adsorption/desorption showed that both the additionand the amount of Al2O3in TiO2will affect the overall specific surface area andpore structure of the carrier. With the increasing addition ratio of Al2O3, specificsurface area and pore volume increased gradually, however, was not consistentwith the increase of catalyst activity completely, indicating that high catalyticactivity need appropriate specific surface area and pore structure characteristics.(6) The results of NH3-TPD showed that the Al2O3modified the weak acidenvironment of TiO2carrier, and increased the specific surface area of thecomposite catalyst carriers, which would provide more surface acid sites andchanged carrier acid characteristics at the same time.(7) The XPS results showed that the Ti exists in Ti+4price while Al exists inthe form of Al2O3in carrier. Changes of diffraction peaks and migration ofbinding energy indicated that Al-O-Ti had partially replaced Al-O-Al or Ti-O-Tichemical bonds in compound carrier. Surface Pd content in Pd/Al-Ti(0.95) andPd/Al-Ti(0.10) was relative high and advantageous for the oxidation of ethanol.(8) After the comparison of different Al2O3: TiO2ratio in the catalystcarrier, appropriate composite carrier is advantageous to combine advantages ofAl2O3and TiO2. Ions mutually embedded between these two components maydeveloped, causing changes in the crystal defect and oxygen storage capacity.Or due to the formation of solid solution structures between the two components,the catalysts showed excellent catalytic oxidation performance of ethanol. |
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