The three way catalysts (TWCs) promoters (Ce Zr)O 2, (Pr Ce Zr)O 2 and (Pr Zr)O 2 were prepared by sol gel like method. They were characterized by XRD, EXAFS and BET surface area determination. The reduction ...The three way catalysts (TWCs) promoters (Ce Zr)O 2, (Pr Ce Zr)O 2 and (Pr Zr)O 2 were prepared by sol gel like method. They were characterized by XRD, EXAFS and BET surface area determination. The reduction features of the promoters were measured by temperature programmed reduction (TPR) of H 2 to access the potential for the promoters containing praseodymia as oxygen storage component in three way catalyst. The (Pr Zr)O 2 cubic solid solution is formed at high temperature up to 800 ℃, which makes it more reducible than the (Ce Zr)O 2 solid solution. For the (Pr Ce Zr)O 2 samples, the ternary solid solution plays an important role in the reduction process. The performance of the three way catalysts with fully formulated Pt, Pd and Rh is proceeded by using both light off temperature under a stoichiometric gas composition and the conversion of CO, C 3H 6 and NO under changing air/fuel ratio at a constant reaction temperature 400 ℃ . The results indicate that a small amount of praseodymia doping into (Ce Zr)O 2 favors the light off temperature of C 3H 6 and NO, and all the catalysts containing praseodymia obviously exhibits enhanced width of S value for NO conversion at lean region ( S ≥1.00).展开更多
Ce Zr O solid solution was prepared by four different methods, i.e., decomposition of nitrate, coprecipiation, hydroxysuainic acid sol gel as well as citrate sol gel, and characterized by using X ray powder diffr...Ce Zr O solid solution was prepared by four different methods, i.e., decomposition of nitrate, coprecipiation, hydroxysuainic acid sol gel as well as citrate sol gel, and characterized by using X ray powder diffraction, Raman and temperature programmed reduction. The phase composition and the reduction properties of Ce Zr O depend on the preparation method. A cubic Ce 0.5 Zr 0.5 O 2 solid solution can be obtained by using the sol gel method. The Ce Zr O solid solution prepared by using decomposition or coprecipiation was composed of cubic Ce 0.8 Zr 0.2 O 2 and tetragonal Ce 0.2 Zr 0.8 O 2 solid solution. The Ce Zr O solid solution prepared with different methods shows the different reduction properties owing to different phase composition. Results of differential thermal analysis and XRD show that Ce 0.5 Zr 0.5 O 2 solid solution is formed during the decomposition or combustion of the gel.展开更多
Monolithic catalysts of Pt/La-Al2O3 and Pt/Ce0.67Zr0.3302 were prepared to investigate methane selective catalytic reduction （SCR） of NO. The results indicate that Pt/Ce0.67Zr0.33O2 shows high activity and both NO a...Monolithic catalysts of Pt/La-Al2O3 and Pt/Ce0.67Zr0.3302 were prepared to investigate methane selective catalytic reduction （SCR） of NO. The results indicate that Pt/Ce0.67Zr0.33O2 shows high activity and both NO and CH4 can be converted completely at 450℃. Meanwhile, NO and CH4 can be converted completely when there exists excess oxygen. The Pt/Ce0.67Zr0.33O2 catalyst were further investigated by using methane as reducing agent to SCR NO in a novel equipment which combined the CH4 selective catalytic reduction of NO with methane combustion. The result shows that the catalyst is high active and the novel equipment is very effective. The conversion of NO is above 92% under the conditions used in this work. The prepared burner and catalysts have great potential for application.展开更多
Ce0.67Zr0.33O2-Al2O3 solid solution was prepared by the co-precipitation method. Fe2O3-based catalysts supported on the solid solution were obtained by the impregnation method. The article revealed that the optimal lo...Ce0.67Zr0.33O2-Al2O3 solid solution was prepared by the co-precipitation method. Fe2O3-based catalysts supported on the solid solution were obtained by the impregnation method. The article revealed that the optimal loading amount of Fe2O3 on Ce0.67Zr0.33 O2-Al2O3 in our experimental condition for catalytic combustion of methane was 8% （ mass fraction）. The prepared catalysts were characterized by BET, TPR, XRD analyses, and their catalytic activity was investigated after being calcined at 873 K and after being aged in water gas at 1273 K. When the loading amount of Fe203 was 8% （ mass fraction）, the catalyst held the highest activity, and the best temperature speciality and thermal stability. The complete-conversion temperature of methane for fresh and aged sample was 788 and 838 K, respectively. The range between the light-off temperature and the complete-conversion temperature was only 15 K. The characterization results of XRD indicated that Fe2O3 was well dispersed on the Ce0.67Zr0.33O2-Al2O3 matrix. The results of BET and TPR were in good harmony with the catalytic activity results.展开更多
Pd/Ce0.67Zr0.33O2 catalyst was pretreated in different atmosphere respectively, and characterized by CO chemical adsorption, XPS, HR-TEM, H2-TPR, Raman, OSC and in situ DRIFTS to investigate the effect of the structur...Pd/Ce0.67Zr0.33O2 catalyst was pretreated in different atmosphere respectively, and characterized by CO chemical adsorption, XPS, HR-TEM, H2-TPR, Raman, OSC and in situ DRIFTS to investigate the effect of the structure properties of PdOx species on the catalytic performance for CO, HC and NOx elimination. The results show that Pd/CZ catalyst pretreated in air atmosphere has higher oxidation activity of HC due to having high Pd dispersion and strong interaction between PdOx and CZ support. Pd/CZ-H catalyst pretreated in reducing atmosphere exhibits better catalytic performance of NOx elimination because of having relatively big Pd particle size, more Pd species in metallic state and higher concentration of oxygen vacancies. While for the Pd/CZ-RG catalyst pretreated in reactant atmosphere, strong adsorption of HC species on the surface of catalysts would lead to a part of active sites being covered, which inhibits HC and NO conversions.展开更多
A series of Ceo.sFeo.30Zr0.20O2 catalysts were prepared by different methods （co-precipitations method, citric acid sol-gel method, impregnation method, physical mixed method, and hydrotherrnal method） and character...A series of Ceo.sFeo.30Zr0.20O2 catalysts were prepared by different methods （co-precipitations method, citric acid sol-gel method, impregnation method, physical mixed method, and hydrotherrnal method） and characterized by X-ray diffraction （XRD）, Raman spectroscopy, Brunauer-Emmett-Teller （BET） and H2-TPR measurements. Potential of the catalysts in the soot oxidation was evaluated in a temperature-programmed oxidation （TPO） apparatus. The results showed that all the Fe3＋ and Zr4＋ were incor- porated into ceria lattice to form a pure Ce-Fe-Zr-O solid solution for the co-precipitation sample, but two kinds of Fe phases ex- isted in the Ce-Fe-Zr-O catalysts prepared by other methods： Fe3＋ incorporated into CeO2 lattice and dispersed Fe2O3 clusters. The free Fe2O3 clusters could improve the activity of catalysts for soot oxidation comparing with the pure Ce-Fe-Zr-O solid solution owing to the synergetic effect between free Fe2O3 and surface oxygen vacancies. In addition, the activity of catalysts strongly relied on the surface reducibility of free Fe2O3 particles. Holding both abundant free Fe2O3 particles and high oxygen vacancy concentration, the hydrothermal Ce0.5Fe0.3Zr0.202 catalyst presented the lowest Ti （251℃, ignition temperature of soot oxidation） and Tm （310 ℃, maximum oxidation rate temperature） for soot combustion （with tight-contact between soot and catalysts） among the five samples. Even after aging at 800 ℃ for 10 h, the Ti and Tm were still relatively low, at 273 and 361 ℃, respectively, indicating high catalytic stability.展开更多
Ceria-zirconia-alumina （CZA） solid solution was prepared by sol-gel method in the present study. 0.5 wt.% Pd supported on CZA was prepared by incipient wetness impregnation. The steam effects for CO and C3H8 oxidati...Ceria-zirconia-alumina （CZA） solid solution was prepared by sol-gel method in the present study. 0.5 wt.% Pd supported on CZA was prepared by incipient wetness impregnation. The steam effects for CO and C3H8 oxidation, three-way catalytic activity and stoichiometric window property were studied. The light-off temperature of the CO oxidation reaction shifted to a lower temperature due to the water-gas shift （WGS） reactions. The oxidation of C3H8 was enhanced due to the steam reforming （SR） reactions. The steam promoted the C3H8 oxidation and NO reduction in three-way catalytic reaction. The amplitude of stoichiometric window was amplified by the addition of water to the feed stream.展开更多
The effect of H2O2 on the properties of Ce0.65Zr0.35O2 a mixed aqueous solution of ammonia and was explored by treating cerium nitrate and zirconium nitrate with in the presence/absence of H2O2. The resultant products...The effect of H2O2 on the properties of Ce0.65Zr0.35O2 a mixed aqueous solution of ammonia and was explored by treating cerium nitrate and zirconium nitrate with in the presence/absence of H2O2. The resultant products were characterized by X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, nitrogen adsorption/desorption, oxygen storage capacity （OSC） and H2- reduction （H2-TPR）. The presence of H2O2 was found to have profound effect on powder properties such as surface area, crystallite size of the samples. It was also shown that the addition of H2O2 favored the incorporation of Zr4＋ into CeO2 lattice, which facilitated the formation of CeO2-ZrO2 solid solution, and enhanced the thermal stability of the samples. OSC and H2-TPR studies indicated that the use of H2O2 enhanced the OSC and redox properties. Catalytic activity tests showed that as a support, the Ce0.65Zr0.35O2 prepared in the presence of H2O2 was more suitable for three-way catalyst. The corresponding Pd-only three-way catalyst demonstrated outstanding performance： wide air to fuel operation window, low light-off and total conversion temperature for the conversion of C3H8, NO and CO.展开更多
文摘The three way catalysts (TWCs) promoters (Ce Zr)O 2, (Pr Ce Zr)O 2 and (Pr Zr)O 2 were prepared by sol gel like method. They were characterized by XRD, EXAFS and BET surface area determination. The reduction features of the promoters were measured by temperature programmed reduction (TPR) of H 2 to access the potential for the promoters containing praseodymia as oxygen storage component in three way catalyst. The (Pr Zr)O 2 cubic solid solution is formed at high temperature up to 800 ℃, which makes it more reducible than the (Ce Zr)O 2 solid solution. For the (Pr Ce Zr)O 2 samples, the ternary solid solution plays an important role in the reduction process. The performance of the three way catalysts with fully formulated Pt, Pd and Rh is proceeded by using both light off temperature under a stoichiometric gas composition and the conversion of CO, C 3H 6 and NO under changing air/fuel ratio at a constant reaction temperature 400 ℃ . The results indicate that a small amount of praseodymia doping into (Ce Zr)O 2 favors the light off temperature of C 3H 6 and NO, and all the catalysts containing praseodymia obviously exhibits enhanced width of S value for NO conversion at lean region ( S ≥1.00).
文摘Ce Zr O solid solution was prepared by four different methods, i.e., decomposition of nitrate, coprecipiation, hydroxysuainic acid sol gel as well as citrate sol gel, and characterized by using X ray powder diffraction, Raman and temperature programmed reduction. The phase composition and the reduction properties of Ce Zr O depend on the preparation method. A cubic Ce 0.5 Zr 0.5 O 2 solid solution can be obtained by using the sol gel method. The Ce Zr O solid solution prepared by using decomposition or coprecipiation was composed of cubic Ce 0.8 Zr 0.2 O 2 and tetragonal Ce 0.2 Zr 0.8 O 2 solid solution. The Ce Zr O solid solution prepared with different methods shows the different reduction properties owing to different phase composition. Results of differential thermal analysis and XRD show that Ce 0.5 Zr 0.5 O 2 solid solution is formed during the decomposition or combustion of the gel.
基金Supported by the National High Technology Research and Development Program of China (863 Program, 2006AA06Z347)the NationalNatural Science Foundation of China (20773090).
文摘Monolithic catalysts of Pt/La-Al2O3 and Pt/Ce0.67Zr0.3302 were prepared to investigate methane selective catalytic reduction （SCR） of NO. The results indicate that Pt/Ce0.67Zr0.33O2 shows high activity and both NO and CH4 can be converted completely at 450℃. Meanwhile, NO and CH4 can be converted completely when there exists excess oxygen. The Pt/Ce0.67Zr0.33O2 catalyst were further investigated by using methane as reducing agent to SCR NO in a novel equipment which combined the CH4 selective catalytic reduction of NO with methane combustion. The result shows that the catalyst is high active and the novel equipment is very effective. The conversion of NO is above 92% under the conditions used in this work. The prepared burner and catalysts have great potential for application.
基金Project supported by the National Natural Science Key Foundation of China (20333030)
文摘Ce0.67Zr0.33O2-Al2O3 solid solution was prepared by the co-precipitation method. Fe2O3-based catalysts supported on the solid solution were obtained by the impregnation method. The article revealed that the optimal loading amount of Fe2O3 on Ce0.67Zr0.33 O2-Al2O3 in our experimental condition for catalytic combustion of methane was 8% （ mass fraction）. The prepared catalysts were characterized by BET, TPR, XRD analyses, and their catalytic activity was investigated after being calcined at 873 K and after being aged in water gas at 1273 K. When the loading amount of Fe203 was 8% （ mass fraction）, the catalyst held the highest activity, and the best temperature speciality and thermal stability. The complete-conversion temperature of methane for fresh and aged sample was 788 and 838 K, respectively. The range between the light-off temperature and the complete-conversion temperature was only 15 K. The characterization results of XRD indicated that Fe2O3 was well dispersed on the Ce0.67Zr0.33O2-Al2O3 matrix. The results of BET and TPR were in good harmony with the catalytic activity results.
基金Project supported by the Key Program of Science Technology Department of Zhejiang Province(2018C03037)
文摘Pd/Ce0.67Zr0.33O2 catalyst was pretreated in different atmosphere respectively, and characterized by CO chemical adsorption, XPS, HR-TEM, H2-TPR, Raman, OSC and in situ DRIFTS to investigate the effect of the structure properties of PdOx species on the catalytic performance for CO, HC and NOx elimination. The results show that Pd/CZ catalyst pretreated in air atmosphere has higher oxidation activity of HC due to having high Pd dispersion and strong interaction between PdOx and CZ support. Pd/CZ-H catalyst pretreated in reducing atmosphere exhibits better catalytic performance of NOx elimination because of having relatively big Pd particle size, more Pd species in metallic state and higher concentration of oxygen vacancies. While for the Pd/CZ-RG catalyst pretreated in reactant atmosphere, strong adsorption of HC species on the surface of catalysts would lead to a part of active sites being covered, which inhibits HC and NO conversions.
基金Project supported by National Natural Science Foundation of China(51374004,51204083,51174105,51104074)Natural Science Foundation of Yunnan Province(2010ZC018)
文摘A series of Ceo.sFeo.30Zr0.20O2 catalysts were prepared by different methods （co-precipitations method, citric acid sol-gel method, impregnation method, physical mixed method, and hydrotherrnal method） and characterized by X-ray diffraction （XRD）, Raman spectroscopy, Brunauer-Emmett-Teller （BET） and H2-TPR measurements. Potential of the catalysts in the soot oxidation was evaluated in a temperature-programmed oxidation （TPO） apparatus. The results showed that all the Fe3＋ and Zr4＋ were incor- porated into ceria lattice to form a pure Ce-Fe-Zr-O solid solution for the co-precipitation sample, but two kinds of Fe phases ex- isted in the Ce-Fe-Zr-O catalysts prepared by other methods： Fe3＋ incorporated into CeO2 lattice and dispersed Fe2O3 clusters. The free Fe2O3 clusters could improve the activity of catalysts for soot oxidation comparing with the pure Ce-Fe-Zr-O solid solution owing to the synergetic effect between free Fe2O3 and surface oxygen vacancies. In addition, the activity of catalysts strongly relied on the surface reducibility of free Fe2O3 particles. Holding both abundant free Fe2O3 particles and high oxygen vacancy concentration, the hydrothermal Ce0.5Fe0.3Zr0.202 catalyst presented the lowest Ti （251℃, ignition temperature of soot oxidation） and Tm （310 ℃, maximum oxidation rate temperature） for soot combustion （with tight-contact between soot and catalysts） among the five samples. Even after aging at 800 ℃ for 10 h, the Ti and Tm were still relatively low, at 273 and 361 ℃, respectively, indicating high catalytic stability.
基金Project supported by National High-Tech Research and Development Program of China(2011AA03A405)the Key Program of TianjinNatural Science Foundation(09JCZDJC26600)
文摘Ceria-zirconia-alumina （CZA） solid solution was prepared by sol-gel method in the present study. 0.5 wt.% Pd supported on CZA was prepared by incipient wetness impregnation. The steam effects for CO and C3H8 oxidation, three-way catalytic activity and stoichiometric window property were studied. The light-off temperature of the CO oxidation reaction shifted to a lower temperature due to the water-gas shift （WGS） reactions. The oxidation of C3H8 was enhanced due to the steam reforming （SR） reactions. The steam promoted the C3H8 oxidation and NO reduction in three-way catalytic reaction. The amplitude of stoichiometric window was amplified by the addition of water to the feed stream.
基金supported by National Natural Science Foundation of China(21173153)Foundation of Science and Technology of Sichuan Province(2011GZ0035)Foundation of Environmental Protection of Sichuan Province(2011HB002)
文摘The effect of H2O2 on the properties of Ce0.65Zr0.35O2 a mixed aqueous solution of ammonia and was explored by treating cerium nitrate and zirconium nitrate with in the presence/absence of H2O2. The resultant products were characterized by X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, nitrogen adsorption/desorption, oxygen storage capacity （OSC） and H2- reduction （H2-TPR）. The presence of H2O2 was found to have profound effect on powder properties such as surface area, crystallite size of the samples. It was also shown that the addition of H2O2 favored the incorporation of Zr4＋ into CeO2 lattice, which facilitated the formation of CeO2-ZrO2 solid solution, and enhanced the thermal stability of the samples. OSC and H2-TPR studies indicated that the use of H2O2 enhanced the OSC and redox properties. Catalytic activity tests showed that as a support, the Ce0.65Zr0.35O2 prepared in the presence of H2O2 was more suitable for three-way catalyst. The corresponding Pd-only three-way catalyst demonstrated outstanding performance： wide air to fuel operation window, low light-off and total conversion temperature for the conversion of C3H8, NO and CO.
