The three-way catalysts （TWCs） promoters Ce0.6Zr0.4- x TbxO2-y were prepared by sol-gel method. BET surface areas analysis indicated that an increase of the dopant Tb content from x = 0.05 to x = 0.15 favors an incr...The three-way catalysts （TWCs） promoters Ce0.6Zr0.4- x TbxO2-y were prepared by sol-gel method. BET surface areas analysis indicated that an increase of the dopant Tb content from x = 0.05 to x = 0.15 favors an increase of surface area from 66.8 to 80.4 m^2· g^-1 compared with the undoped sample Ce0 .6oZr0.40O2 65.1 m^2·g^- 1 after calcination at 650℃. Transmission electron microscopy （TEM） observation indicated that the doped samples have a higher thermal stability. The XRD and Raman spectra confirmed that the Ce0.6Zr0.4-xTbxO2-y cubic solid solution is formed. XPS analysis revealed that Ce and Tb mainly existed in the form of Ce^4＋ and Tb^3 ＋ , and Zr existed in the form of Zr^4＋ on the surface of the samples. The doped samples were homogenous in composition ; the introduction of Tb into the CeO2-ZrO2 promoters resuited in the formation of a solid solution, and the concentration of surface lattice oxygen was increased.展开更多
Ce1-xZrxO_(2) composite oxides(molar,x=0-1.0,interval of 0.2)were prepared by a cetyltrimethylammonium bromide-assisted precipitation method.The enhancement of silver-species modification and catalytic mechanism of ad...Ce1-xZrxO_(2) composite oxides(molar,x=0-1.0,interval of 0.2)were prepared by a cetyltrimethylammonium bromide-assisted precipitation method.The enhancement of silver-species modification and catalytic mechanism of adsorption-transformationdesorption process were investigated over the Ag-impregnated catalysts for lowtemperature selective catalytic oxidation of ammonia(NH_(3)-SCO).The optimal 5 wt.%Ag/Ce_(0.6)Zr_(0.4)O_(2) catalyst presented good NH_(3)-SCO performancewith>90% NH_(3) conversion at temperature(T)≥250°C and 89% N_(2) selectivity.Despite the irregular block shape and underdeveloped specific surface area(∼60m2/g),the naked and Ag-modified Ce_(0.6)Zr_(0.4)O_(2) solid solution still obtained highly dispersed distribution of surface elements analyzed by scanning electron microscope-energy dispersive spectrometer(SEM-EDS)(mapping),N_(2) adsorptiondesorption test and X-ray diffraction(XRD).H2 temperature programmed reduction(H2-TPR)and X-ray photoelectron spectroscopy(XPS)results indicated that Ag-modification enhanced the mobility and activation of oxygen-species leading to a promotion on CeO_(2) reducibility and synergistic Ag0/Ag+and Ce^(4+)/Ce^(3+)redox cycles.Besides,Ag+/Ag_(2)O clusters could facilitate the formation of surface oxygen vacancies that was beneficial to the adsorption and activation of ammonia.NH3-temperature programmed desorption(NH_(3)-TPD)showed more adsorption-desorption capacity to ammoniawere provided by physical,weakandmedium-strong acid sites.Diffused reflectance infrared Fourier transform spectroscopy(DRIFTS)experiments revealed the activation of ammonia might be the control step of NH3-SCO procedure,during which NH3 dehydrogenation derived from NHx-species and also internal selective catalytic reduction(i-SCR)reactions were proposed.展开更多
基金Project supported by the Natural Science Basic Research Plan in Shaanxi Province of China (2004B13)
文摘The three-way catalysts （TWCs） promoters Ce0.6Zr0.4- x TbxO2-y were prepared by sol-gel method. BET surface areas analysis indicated that an increase of the dopant Tb content from x = 0.05 to x = 0.15 favors an increase of surface area from 66.8 to 80.4 m^2· g^-1 compared with the undoped sample Ce0 .6oZr0.40O2 65.1 m^2·g^- 1 after calcination at 650℃. Transmission electron microscopy （TEM） observation indicated that the doped samples have a higher thermal stability. The XRD and Raman spectra confirmed that the Ce0.6Zr0.4-xTbxO2-y cubic solid solution is formed. XPS analysis revealed that Ce and Tb mainly existed in the form of Ce^4＋ and Tb^3 ＋ , and Zr existed in the form of Zr^4＋ on the surface of the samples. The doped samples were homogenous in composition ; the introduction of Tb into the CeO2-ZrO2 promoters resuited in the formation of a solid solution, and the concentration of surface lattice oxygen was increased.
基金financially supported by National Natural Science Foundation of China (No.U20A20130)Fundamental Research Funds for the Central Universities (No.06500152)
文摘Ce1-xZrxO_(2) composite oxides(molar,x=0-1.0,interval of 0.2)were prepared by a cetyltrimethylammonium bromide-assisted precipitation method.The enhancement of silver-species modification and catalytic mechanism of adsorption-transformationdesorption process were investigated over the Ag-impregnated catalysts for lowtemperature selective catalytic oxidation of ammonia(NH_(3)-SCO).The optimal 5 wt.%Ag/Ce_(0.6)Zr_(0.4)O_(2) catalyst presented good NH_(3)-SCO performancewith>90% NH_(3) conversion at temperature(T)≥250°C and 89% N_(2) selectivity.Despite the irregular block shape and underdeveloped specific surface area(∼60m2/g),the naked and Ag-modified Ce_(0.6)Zr_(0.4)O_(2) solid solution still obtained highly dispersed distribution of surface elements analyzed by scanning electron microscope-energy dispersive spectrometer(SEM-EDS)(mapping),N_(2) adsorptiondesorption test and X-ray diffraction(XRD).H2 temperature programmed reduction(H2-TPR)and X-ray photoelectron spectroscopy(XPS)results indicated that Ag-modification enhanced the mobility and activation of oxygen-species leading to a promotion on CeO_(2) reducibility and synergistic Ag0/Ag+and Ce^(4+)/Ce^(3+)redox cycles.Besides,Ag+/Ag_(2)O clusters could facilitate the formation of surface oxygen vacancies that was beneficial to the adsorption and activation of ammonia.NH3-temperature programmed desorption(NH_(3)-TPD)showed more adsorption-desorption capacity to ammoniawere provided by physical,weakandmedium-strong acid sites.Diffused reflectance infrared Fourier transform spectroscopy(DRIFTS)experiments revealed the activation of ammonia might be the control step of NH3-SCO procedure,during which NH3 dehydrogenation derived from NHx-species and also internal selective catalytic reduction(i-SCR)reactions were proposed.
