A new method called ultrasonic-assisted membrane reaction(UAMR)was reported for the fabrication of ceria-zirconia solid solution.A series of ceria-zirconia solid solutions with different Ce/Zr molar ratios were prepared by the UAMR method and characterized by Xray diffraction(XRD),N2 adsorption,hydrogen temperature-programmed reduction(H2-TPR),scanning electron microscope(SEM),and transmission electron microscopy(TEM)techniques.The UAMR method proved to be superior,especially when the Ce/Zr molar ratio was lower than 1,in fabricating ceria-zirconia solid solutions with large BET surface area,high oxygen storage capacity(OSC),and low reduction temperature.
Lijing MENGLicheng LIUXuehong ZIHongxing DAIZhen ZHAOXinping WANGHong HE
Ce-Al2O3 catalysts prepared by co-precipitation are investigated both in NO oxidation by O2 and in selective catalytic reduction of NO by C2H2(C 2 H 2-SCR).It is found that C2H2-SCR is initiated and controlled by NO oxidation to NO 2 over Al2O3.Ce loading on Al2O3 is almost inactive for NO oxidation below 350 C,since NO2 strongly adsorbs on cerium oxide,leading to the active sites being blocked,which was characterized by temperature-programmed desorption of NO and NO 2 and Fourier transform infrared spectroscopy after NO+O 2 coadsorption over the samples.However,in the case of C2H2-SCR,Ce loading on Al 2 O 3 significantly improves the reaction by accelerating the NO oxidation step in the temperature range of 250-450 C,since the nitrate species produced by NO 2 adsorption is an active intermediate required by C2H 2-SCR.
The nanometer CeO2 powder was prepared by the method of microwave-assisted heating hydrolysis,and the nanometer CeO2-supported or ordinary CeO2-supported vanadia catalysts with different vanadium loadings(atomic ratios:100V/Ce=0.1,1,4,10,and 20) were prepared by an incipient-wetness impregnation method.Spectroscopic techniques(XRD,FT-IR,Raman and UV-Vis DRS) were utilized to characterize the structures of VOx/CeO2 catalysts.The results showed that the structures of CeO2-supported vanadium oxide catalysts de-pended on the vanadium loading.Isolated mono-vanadate species were present on the surface of catalysts at low V loading,and poly-vanadate species existed at medium V loading,but CeVO4 crystallites were formed at high V loading(V10 and V20).The catalytic performances of these catalysts for diesel soot oxidation were investigated with temperature-programmed oxidation reaction(TPO).For soot oxidation,the poly-vanadate species were mainly active sites in ordinary CeO2-supported vanadyl catalysts,but nanometer CeO2 was mainly active components in nanometer CeO2-supported vanadium oxide catalysts.Due to the nanometer effect and the good contact between the catalyst and the soot,nanometer CeO2 exhibited a very high catalytic activity for soot combustion.
