Mesoporous CeMnOx composite oxides catalysts were prepared by surfactant-assisted co-precipitation method and used for the catalytic oxidation of toluene.The effect of different cerium precursors[Ce(NO3)3 and(NH4)2 Ce...Mesoporous CeMnOx composite oxides catalysts were prepared by surfactant-assisted co-precipitation method and used for the catalytic oxidation of toluene.The effect of different cerium precursors[Ce(NO3)3 and(NH4)2 Ce(NO3)6] on catalyst structure,surface properties and toluene combustion activities of mesoporous CeMnOx catalysts were investigated.The Ce(Ⅲ)MnOx catalyst prepared from Ce(NO3)3 precursor shows higher catalytic activity,with a 90% conversion temperature of 240℃,which is better than the Ce(Ⅳ)MnOx catalyst derived from[(NH4)2 Ce(NO3)6] precursor.On the basis of characterizations,it reveals that abundant surface content of Mn4+,better redox behavior and larger concentration of surface active oxygen species are responsible for the excellent catalytic performance.展开更多
The synthesis of ultrafine cerium dioxide precursor via homogeneous precipitation was studied. Mixed aqueous solution of anhydrous cerium nitrate and urea was first heated to 85℃ for 2 h, and the prepared suspension ...The synthesis of ultrafine cerium dioxide precursor via homogeneous precipitation was studied. Mixed aqueous solution of anhydrous cerium nitrate and urea was first heated to 85℃ for 2 h, and the prepared suspension was then aged at room temperature for various periods of time. White precipitate was finally collected by centrifuging and washed with distilled water and anhydrous ethanol. The obtained cerium dioxide (CeO2) precursor was observed with SEM. It was found that the morphology and size of the precursor were strongly affected by aging time and stirring conditions (with or without stirring). The precipitated fine spherical particles of the precursor changed their shape from ellipse to slice or directly to slice. Fine spherical monodispersed (300 nm) precursor powders could be obtained by controlling the aging time. Stirring the solution also could change the reaction process and thus the morphology and size of the precursor were changed.展开更多
Cerium dioxide was used for the first time as reactive sorbent for the degradation of the organophosphate pesticides para-thion methyl, chlorpyrifos, dichlofenthion, fenchlorphos, and prothiofos, as well as of some ch...Cerium dioxide was used for the first time as reactive sorbent for the degradation of the organophosphate pesticides para-thion methyl, chlorpyrifos, dichlofenthion, fenchlorphos, and prothiofos, as well as of some chemical warfare agents-nerve gases soman and O-ethyl S-[2-（diisopropylamino） ethyl] methylphosphonothioate （VX）. CeO2 specimens were prepared by calcination of basic cerous carbonate obtained by precipitation from an aqueous solution. The CeO2 samples containing certain amounts （1 wt.%-5 wt.%） of the neighboring lanthanides （La, Pr, Nd） were prepared in a similar way from pure lanthanide salts. It was shown that ceria accelerated markedly the decomposition of parathion methyl causing the cleavage of the P-O-aryl bond in the pesticide molecule. A similar reaction mechanism was proposed for the degradation of other organophosphate pesticides and nerve agents. The degradation times （reaction half-times） were in an order of minutes in the presence of CeO2, compared to hours or days under common environ-mental conditions. The reaction in suitable organic solvents allowed conversions of about 90%for parathion methyl loading of 20 mg pesticide/g CeO2 within 2 h with a reactant half-life in the order of 0.1 min. The key parameter governing the degradation efficiency of CeO2 was the temperature during calcination. At optimum calcination temperature （about 773.15 K）, the produced ceria retained a sufficiently high surface area, and attained an optimum degree of crystallinity （related to a number of crystal defects, and thus poten-tial reactive sites）. The presence of other lanthanides somewhat decreased the reaction rate, but this effect was not detrimental and permitted the possible use of chemically impure ceria as a reactive sorbent. A fast organophosphate degradation was demonstrated not only in non-polar solvents （such as heptane）, but also in polar aprotic solvents （acetonitrile, acetone） that are miscible with water. This opens new possibilities for designing more versatile decontamination strategies. The cleavage of phosphate ester bonds is of a great importance not only for the degradation of dangerous chemicals （chemical weapons, pesticides）, but also for interactions of ceria （es-pecially the nano-sized one） in biologically relevant systems.展开更多
考察了铈及其前驱物对乙苯脱氢制苯乙烯催化剂性能的影响,并采用程序升温还原(TPR)、X 射线衍射(XRD)、扫描电子显微镜(SEM)、热重-差热分析(TG-DTA)和 X 射线能谱(EDAX)等技术对催化剂进行了表征。结果表明,不含铈的脱氢催化剂活性较低...考察了铈及其前驱物对乙苯脱氢制苯乙烯催化剂性能的影响,并采用程序升温还原(TPR)、X 射线衍射(XRD)、扫描电子显微镜(SEM)、热重-差热分析(TG-DTA)和 X 射线能谱(EDAX)等技术对催化剂进行了表征。结果表明,不含铈的脱氢催化剂活性较低,苯乙烯收率为53.8%。添加铈后,可以较大幅度地提高乙苯脱氢反应中苯乙烯的收率。不同的铈源会影响到催化剂表面的形貌、铈的分布和催化剂的抗还原性,其中以硝酸铈作为前驱物所得的催化剂具有较高的活性和选择性。CeO_2在脱氢反应条件下,部分被还原,可能与三价铁形成了新的活性中心。从而大幅度地提高了乙苯脱氢催化剂的活性。展开更多
CeO2 precursors were prepared by the homogeneous precipitation method, hydrothermal synthesis method and hydrothermal precipitation coupling method using urea as a precipitator.The results indicated that urea was a re...CeO2 precursors were prepared by the homogeneous precipitation method, hydrothermal synthesis method and hydrothermal precipitation coupling method using urea as a precipitator.The results indicated that urea was a reserve resource of CO 2- <sub>3.CeO2 precursors were orthorhombic Ce2O（CO3） 2·H2O, hexagonal Ce（OH）（CO3） , orthorhombic CeO（CO3）2·H2O respectively when the homogeneous precipitation method, hydrothermal synthesis method and hydrothermal precipitation coupling method were used.The synthesis technology had a great effect on the precursors.Different precursors were synthesized through various processes and mechanisms.When heated up to the temperature of 500℃, the precursors were all finally changed into face centred cubic CeO 2 powders.展开更多
Homogenous precipitation and subsequent calcination has been used tosynthesize ultrafine ceria from cerium nitrate and urea solution. The ceria calcined from theprecursor inherit the size and morphology of it. The siz...Homogenous precipitation and subsequent calcination has been used tosynthesize ultrafine ceria from cerium nitrate and urea solution. The ceria calcined from theprecursor inherit the size and morphology of it. The size and morphology of the precursor areclosely related to the preparation process. The morphology, size and distribution of the precursorcould be tailored by changing the reaction condition and the ageing time. Monodispersed 200 nm sizedspherical particles is prepared by this method. The powder is used in the chemical-mechanicalpolishing of Si wafer. The average surface roughness of the polished Si wafer is 0.171 nm measuredby AFM.展开更多
Sm3+-doped CeO2 (denoted as Ce1-xSmxO2) powders with different morphologies were successfully synthesized via a precursor-growth-calcination approach, in which precursor was first synthesized by a hydrothermal method ...Sm3+-doped CeO2 (denoted as Ce1-xSmxO2) powders with different morphologies were successfully synthesized via a precursor-growth-calcination approach, in which precursor was first synthesized by a hydrothermal method and Ce1-xSmxO2 powders were finally obtained through a calcination process. The products were characterized with X-ray diffractometry(XRD), field emission scanning electron microscopy(FE-SEM) and fluorescence spectroscopy. The results reveal that the Ce1-xSmxO2 powders obtained by calcining the precursors prepared in the absence and presence of poly(vinyl pyrrolidone) (PVP) exhibit bundle- and sphere-like morphology, respectively. The possible growth process was proposed by preparing a series of intermediate morphologies during the shape evolution of CeO2 based on the SEM image observation. It is also found that the luminescence intensity of bundle-like Ce1-xSmxO2 is enhanced in comparison with that of sphere-like one due to its special morphology.展开更多
基金Project supported by the National Natural Science Foundation of China(21503184)the Natural Science Foundation of Jiangsu ProvinceGeneral Program(BK20171273)+1 种基金the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(18KJA610004)the Opening Project of the Jiangsu Key Laboratory for Environment Functional Materials(SJHG1806)
文摘Mesoporous CeMnOx composite oxides catalysts were prepared by surfactant-assisted co-precipitation method and used for the catalytic oxidation of toluene.The effect of different cerium precursors[Ce(NO3)3 and(NH4)2 Ce(NO3)6] on catalyst structure,surface properties and toluene combustion activities of mesoporous CeMnOx catalysts were investigated.The Ce(Ⅲ)MnOx catalyst prepared from Ce(NO3)3 precursor shows higher catalytic activity,with a 90% conversion temperature of 240℃,which is better than the Ce(Ⅳ)MnOx catalyst derived from[(NH4)2 Ce(NO3)6] precursor.On the basis of characterizations,it reveals that abundant surface content of Mn4+,better redox behavior and larger concentration of surface active oxygen species are responsible for the excellent catalytic performance.
基金the Natural Science Foundation of Jiangsu Province under pro ject No.BK2002010.
文摘The synthesis of ultrafine cerium dioxide precursor via homogeneous precipitation was studied. Mixed aqueous solution of anhydrous cerium nitrate and urea was first heated to 85℃ for 2 h, and the prepared suspension was then aged at room temperature for various periods of time. White precipitate was finally collected by centrifuging and washed with distilled water and anhydrous ethanol. The obtained cerium dioxide (CeO2) precursor was observed with SEM. It was found that the morphology and size of the precursor were strongly affected by aging time and stirring conditions (with or without stirring). The precipitated fine spherical particles of the precursor changed their shape from ellipse to slice or directly to slice. Fine spherical monodispersed (300 nm) precursor powders could be obtained by controlling the aging time. Stirring the solution also could change the reaction process and thus the morphology and size of the precursor were changed.
基金Project supported by Czech Science Foundation(P106/12/1116)
文摘Cerium dioxide was used for the first time as reactive sorbent for the degradation of the organophosphate pesticides para-thion methyl, chlorpyrifos, dichlofenthion, fenchlorphos, and prothiofos, as well as of some chemical warfare agents-nerve gases soman and O-ethyl S-[2-（diisopropylamino） ethyl] methylphosphonothioate （VX）. CeO2 specimens were prepared by calcination of basic cerous carbonate obtained by precipitation from an aqueous solution. The CeO2 samples containing certain amounts （1 wt.%-5 wt.%） of the neighboring lanthanides （La, Pr, Nd） were prepared in a similar way from pure lanthanide salts. It was shown that ceria accelerated markedly the decomposition of parathion methyl causing the cleavage of the P-O-aryl bond in the pesticide molecule. A similar reaction mechanism was proposed for the degradation of other organophosphate pesticides and nerve agents. The degradation times （reaction half-times） were in an order of minutes in the presence of CeO2, compared to hours or days under common environ-mental conditions. The reaction in suitable organic solvents allowed conversions of about 90%for parathion methyl loading of 20 mg pesticide/g CeO2 within 2 h with a reactant half-life in the order of 0.1 min. The key parameter governing the degradation efficiency of CeO2 was the temperature during calcination. At optimum calcination temperature （about 773.15 K）, the produced ceria retained a sufficiently high surface area, and attained an optimum degree of crystallinity （related to a number of crystal defects, and thus poten-tial reactive sites）. The presence of other lanthanides somewhat decreased the reaction rate, but this effect was not detrimental and permitted the possible use of chemically impure ceria as a reactive sorbent. A fast organophosphate degradation was demonstrated not only in non-polar solvents （such as heptane）, but also in polar aprotic solvents （acetonitrile, acetone） that are miscible with water. This opens new possibilities for designing more versatile decontamination strategies. The cleavage of phosphate ester bonds is of a great importance not only for the degradation of dangerous chemicals （chemical weapons, pesticides）, but also for interactions of ceria （es-pecially the nano-sized one） in biologically relevant systems.
文摘考察了铈及其前驱物对乙苯脱氢制苯乙烯催化剂性能的影响,并采用程序升温还原(TPR)、X 射线衍射(XRD)、扫描电子显微镜(SEM)、热重-差热分析(TG-DTA)和 X 射线能谱(EDAX)等技术对催化剂进行了表征。结果表明,不含铈的脱氢催化剂活性较低,苯乙烯收率为53.8%。添加铈后,可以较大幅度地提高乙苯脱氢反应中苯乙烯的收率。不同的铈源会影响到催化剂表面的形貌、铈的分布和催化剂的抗还原性,其中以硝酸铈作为前驱物所得的催化剂具有较高的活性和选择性。CeO_2在脱氢反应条件下,部分被还原,可能与三价铁形成了新的活性中心。从而大幅度地提高了乙苯脱氢催化剂的活性。
文摘CeO2 precursors were prepared by the homogeneous precipitation method, hydrothermal synthesis method and hydrothermal precipitation coupling method using urea as a precipitator.The results indicated that urea was a reserve resource of CO 2- <sub>3.CeO2 precursors were orthorhombic Ce2O（CO3） 2·H2O, hexagonal Ce（OH）（CO3） , orthorhombic CeO（CO3）2·H2O respectively when the homogeneous precipitation method, hydrothermal synthesis method and hydrothermal precipitation coupling method were used.The synthesis technology had a great effect on the precursors.Different precursors were synthesized through various processes and mechanisms.When heated up to the temperature of 500℃, the precursors were all finally changed into face centred cubic CeO 2 powders.
基金This project is supported by Provincial Natural Science Foundation of Jiangsu (No.BK2002010).
文摘Homogenous precipitation and subsequent calcination has been used tosynthesize ultrafine ceria from cerium nitrate and urea solution. The ceria calcined from theprecursor inherit the size and morphology of it. The size and morphology of the precursor areclosely related to the preparation process. The morphology, size and distribution of the precursorcould be tailored by changing the reaction condition and the ageing time. Monodispersed 200 nm sizedspherical particles is prepared by this method. The powder is used in the chemical-mechanicalpolishing of Si wafer. The average surface roughness of the polished Si wafer is 0.171 nm measuredby AFM.
基金Project(20676153)supported by the Science Foundation of Guangxi Provincial Education Department,ChinaProject(0728107)supported by the Science and Technology Bureau of Guangxi Province,ChinaProject(08JJ3104)supported by the Natural Science Foundation of Hunan Province,China
文摘Sm3+-doped CeO2 (denoted as Ce1-xSmxO2) powders with different morphologies were successfully synthesized via a precursor-growth-calcination approach, in which precursor was first synthesized by a hydrothermal method and Ce1-xSmxO2 powders were finally obtained through a calcination process. The products were characterized with X-ray diffractometry(XRD), field emission scanning electron microscopy(FE-SEM) and fluorescence spectroscopy. The results reveal that the Ce1-xSmxO2 powders obtained by calcining the precursors prepared in the absence and presence of poly(vinyl pyrrolidone) (PVP) exhibit bundle- and sphere-like morphology, respectively. The possible growth process was proposed by preparing a series of intermediate morphologies during the shape evolution of CeO2 based on the SEM image observation. It is also found that the luminescence intensity of bundle-like Ce1-xSmxO2 is enhanced in comparison with that of sphere-like one due to its special morphology.
