CeO2-ZeO2 solid solutions are extensively used as oxygen storage promoters in the current automotive three-way catalysts. High thermal stability of the textural properties is one of the most important requirements for...CeO2-ZeO2 solid solutions are extensively used as oxygen storage promoters in the current automotive three-way catalysts. High thermal stability of the textural properties is one of the most important requirements for practical application since temperatures up to 1273 K are easily experienced by these materials under real working conditions. In the present paper, we investigated how hydrothermal treatments applied to cakes of doped and undoped ZrO2-rich CeO2-ZrO2 precursors might improve the thermal stability of the final CeO2-ZrO2 solid solution. A rationale was developed that allowed to correlate the morphology of the hydrothermaUy treated cake with the thermal stability at 1273 K of the final product, which did not depend on the composition of the mixed oxides.展开更多
The structure and catalytic desulfurization characteristics of CeO2-TiO2 mixed oxides were investigated by means ofX-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and catalytic activity tests. Acco...The structure and catalytic desulfurization characteristics of CeO2-TiO2 mixed oxides were investigated by means ofX-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and catalytic activity tests. According to the results, a CeO2-TiO2solid solution is formed when the mole ratio of cerium to titanium n（Ce）：n（Ti） is 5：5 or greater, and the most suitable n（Ce）：n（Ti） isdetermined as 7：3, over which the conversion rate of SO2 and the yield of sulfur at 500℃ reach 93% and 99%, respectively.According to the activity testing curve, Ce0.7Ti0.3O2 （n（Ce）：n（Ti）=7：3） without any pretreatment can be gradually activated by reagentgas after about 10 min, and reaches a steady activation status 60 min later. The XPS results of Ce0.7Ti0.3O2 after different time ofSO2＋CO reaction show that CeO2 is the active component that offers the redox couple Ce4＋/Ce3＋ and the labile oxygen vacancies, andTiO2 only functions as a catalyst structure stabilizer during the catalytic reaction process. After 48 h of catalytic reaction at 500℃,Ce0.7Ti0.3O2 still maintains a stable structure without being vulcanized, demonstrating its good anti-sulfur poisoning performance.展开更多
Four kinds of CeO2-ZrO2 mixed oxides, i.e., a physical mixture of ceria and zirconia （CZP）, zirconia-coated ceria （ZCC）, ceria-coated zirconia （CCZ） and a chemical mixture of celia and zirconia （CZC）, were pre...Four kinds of CeO2-ZrO2 mixed oxides, i.e., a physical mixture of ceria and zirconia （CZP）, zirconia-coated ceria （ZCC）, ceria-coated zirconia （CCZ） and a chemical mixture of celia and zirconia （CZC）, were prepared. The oxygen storage capacity （OSC） measurements at 500℃ were performed under transient and stationary reaction conditions. All the curves of CO2 evolution during CO-O2 cycles presented a bimodal shape. The fast peak was primarily the result of the reaction of CO with the oxygen from the oxides, which was mainly determined by the nature of the material The sec- ond peak was mostly related to the CO2 adsorption behavior and was highly influenced by the surface area and the number of surface active sites. As a result, OSC activity of the samples followed in the order of CZC 〉 CCZ 〉 ZCC=CZP.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
CeO2-ZrO2-Al2O3 ternary oxides were successfully prepared by a green route of supercritical anti-solvent precipitation with supercritical CO2 as anti-solvent and methanol as solvent. The structures and oxygen storage ...CeO2-ZrO2-Al2O3 ternary oxides were successfully prepared by a green route of supercritical anti-solvent precipitation with supercritical CO2 as anti-solvent and methanol as solvent. The structures and oxygen storage capacities of these ternary oxides were characterized by XRD, Raman spectra and oxygen storage capacity measurements. It was found that Al3＋ and Zr4＋ inserted into CeO2 lattice, forming CeO2-ZrO2-Al2O3 solid solution. The concentration of aluminium isopropoxide in the solution affected the concentration of oxygen vacancy and the distortion of oxygen sublattice which were responsible for the oxygen storage capacity. The rapidest oxygen uptake/release rate and maximum total oxygen storage capacity （122.0 mmolO2/molCeO2） were obtained with the aluminitun isopropoxide concentration at 0.2 wt.% in the solution.展开更多
CeO2-MOx (M=Cu, Mn, Fe, Co, and Ni) mixed oxide catalysts were prepared by a citric acid complexation-combustion method. CeO2-MOx solid solutions could be formed with M cations doping into CeO2 lattice, while NiO and ...CeO2-MOx (M=Cu, Mn, Fe, Co, and Ni) mixed oxide catalysts were prepared by a citric acid complexation-combustion method. CeO2-MOx solid solutions could be formed with M cations doping into CeO2 lattice, while NiO and Co3O4 phases were detected on the surface of CeO2-NiO and CeO2-Co3O4 by Raman spectroscopy. The presence of M in CeO2 could obviously promote its catalytic activity for CH4 catalytic combustion and CO oxidation. Among the prepared samples, CeO2-CuO exhibited the best performance for CO oxidatio...展开更多
A series of TiO 2-XSiO 2[X denotes the molar fraction(%) of silica in the mixed oxides] with different \{n(Ti)\}/n(Si) ratios was prepared with ammonia water as a hydrolysis catalyst. The photocatalysts prepared wer...A series of TiO 2-XSiO 2[X denotes the molar fraction(%) of silica in the mixed oxides] with different \{n(Ti)\}/n(Si) ratios was prepared with ammonia water as a hydrolysis catalyst. The photocatalysts prepared were characterized by XRD, thermal analysis, FTIR, UV-Vis and SPS. The characterization results of FTIR and UV-Vis spectra show that Ti atoms were gradually changed from octahedral coordination to tetrahedral coordination with the addition of silica, which is not beneficial for obtaining strong Brnsted acidity and higher photocatalytic activity. The photocatalytic activity experiments, which were conducted by using heptane(or SO 2) as the model reactant, showed that TiO 2-SiO 2 containing a suitable amount of silica can exhibit much higher photocatalytic activity than pure TiO 2. The enhanced photocatalytic activity can be attributed to three following factors: (1) smaller crystalline size; (2) higher thermal stability; (3) the new strong Brnsted acidity.展开更多
CeO_2-ZrO_2 mixed oxides are widely used in the three-way catalysts due to their unique reversible oxygen storage and release capacity. Large surface area, high oxygen storage capacity and good thermal stability of ce...CeO_2-ZrO_2 mixed oxides are widely used in the three-way catalysts due to their unique reversible oxygen storage and release capacity. Large surface area, high oxygen storage capacity and good thermal stability of cerium zirconium mixed oxides are the key properties for the automotive catalysts so as to meet the strict emission regulations. In this work, alumina modified CeZrLaNd mixed oxides were prepared by a co-precipitation method. The effects of moisture in precursor and inert N2 atmosphere during calcinations on the structure and properties were investigated by Brunauer-Emmett-Teller(BET) surface area measurements, X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), hydrogen temperature-programmed reduction(H_2-TPR), oxygen storage capacity(OSC), Raman spectroscopy, and X-ray photoelectron spectroscopy(XPS). The results show that the moisture in precursor during calcinations increases the crystal grain size of the cerium zirconium mixed oxides, improving the thermal stability. And the aged surface area of sample after being calcined at1000 ℃ for 4 h reaches 68.8 m^2/g(5.7% increase compared with the common sample). The inert N2 atmosphere endows a great pore-enlarging effect, which leads to high fresh surface area of 148.9 m2/g(13.5% increase compared with the common sample) and big pore volume of 0.5705 mL/g. The redox and oxygen storage capacity are also improved by inert N2 atmosphere with high OSC value of 241.06μmolO_2/g(41.3% increase compared with the common calcination), due to the abundant formation of the crystal defects and oxygen vacancies.展开更多
In this study,Pd-Mg(Al)-LDH/γ-Al2O3 and Pd-Mg(Al)Zr-LDH/γ-Al2O3 precursors were synthesized by impregnating Na2PdCl4 on Mg(Al)-LDH/γ-Al2O3 and Mg(Al)Zr-LDH/γ-Al2O3,and then the precursors were calcinated and reduc...In this study,Pd-Mg(Al)-LDH/γ-Al2O3 and Pd-Mg(Al)Zr-LDH/γ-Al2O3 precursors were synthesized by impregnating Na2PdCl4 on Mg(Al)-LDH/γ-Al2O3 and Mg(Al)Zr-LDH/γ-Al2O3,and then the precursors were calcinated and reduced to obtain Pd-Mg(Al)-MMO/γ-Al2O3 and Pd-Mg(Al)Zr-MMO/γ-Al2O3 catalysts.Compared with Pd/γ-Al2O3 catalyst,the hydrogenation efficiency of Pd-Mg(Al)-MMO/γ-Al2O3 and Pd-Mg(Al)Zr-MMO/γ-Al2O3 increased by 15.7%and 24.0%,respectively.Moreover,the stability of Pd-Mg(Al)Zr-MMO/γ-Al2O3 catalyst was also higher than that of Pd/γ-Al2O3.After four runs,the hydrogenation efficiency of Pd/γ-Al2O3 decreased from 12.1 to 10.0 g/L,while that of Pd-Mg(Al)Zr-MMO/γ-Al2O3 decreased from 15.0 to 14.3 g/L.The active aquinones selectivities of all catalysts were almost 99%.The structures of the catalysts were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),N2 adsorption–desorption,inductively coupled plasma-atomic emission spectrometry(ICP-AES),CO chemisorption analysis,transmission electron microscopy(TEM),temperature-programmed reduction with hydrogen(H2-TPR),and X-ray photoelectron spectroscopy(XPS).The results indicate that the improved catalytic performance is attributed to the stronger interaction between Pd and Mg(Al)Zr-MMO/γ-Al2O3,smaller Pd particle size and higher Pd dispersion.This work develops an effective method to synthesize highly dispersed Pd nanoparticles based on the layered double hydroxides(LDHs)precursor.展开更多
Ce x Ti 1- x O 2 mixed oxides of different mole ratios ( x =0, 0.1, 0.2～0.9, 1.0) were prepared by co precipitation of TiCl 4 with Ce(NO 3) 3 and then loaded with different amounts of CuO. The effe...Ce x Ti 1- x O 2 mixed oxides of different mole ratios ( x =0, 0.1, 0.2～0.9, 1.0) were prepared by co precipitation of TiCl 4 with Ce(NO 3) 3 and then loaded with different amounts of CuO. The effects of CuO on NO+CO reaction were investigated, and the structure and reductive properties of various CuO/Ce x Ti 1- x O 2 were characterized by the methodologies of BET, TPR and XRD. The results show that different Ce/Ti mole ratios and calcination temperatures induce changes of structure and reductive properties of the Ce x Ti 1- x O 2 mixed oxides. When x =0.1～0.5, amorphous CeTi 2O 6 phase mainly forms at 650 ℃ compared to the formation of CeTi 2O 6 which crystallizes at 800 ℃. When x >0.6, some TiO 2 enters the CeO 2 lattice and a CeO 2 TiO 2 solid solution is formed. The activity of 6%CuO/Ce x Ti 1- x O 2 calcined at 650 ℃ is largely affected by the x values, which is the highest when x =0.3, 0.4 and 0.9. The NO conversion reaches 70% at a reaction temperature of 150 ℃. By comparison, the x values have little effect on the activity of 6%CuO/Ce x Ti 1- x O 2 calcined at 800 ℃ . There are strong interactions between CuO and CeTi 2O 6, i.e., formation of the CeTi 2O 6 phase shifts the CuO reduction peak temperature from 380 to 200 ℃, and CuO, in turn, shifts the CeTi 2O 6 reduction peak temperature from 600 to 300 ℃.展开更多
Potassium-modified ceria-zirconia catalyst was synthesized by wetness impregnation method. The ageing treatment was performed in static air at 800℃ for 20 hr to evaluate the thermal stability of the catalyst. The cat...Potassium-modified ceria-zirconia catalyst was synthesized by wetness impregnation method. The ageing treatment was performed in static air at 800℃ for 20 hr to evaluate the thermal stability of the catalyst. The catalysts were characterized by X-ray diffraction, BET surface area, oxygen storage capacity, NOx-temperature programmed desorption and soot-temperature programmed oxidation measurements. By introduction of potassium, the maximum soot oxidation rate temperature （Tin） of the ceria-zirconia based catalyst decreased from 525 to 428℃ in the presence of NO under a loose contact mode. The shift of Tm of the K-modified catalyst after ageing is only 15℃. The enhanced activity of the aged catalyst mainly lies in the promotional effect of potassium on the NOx/oxygen storage capacity as well as the soot-catalyst contact.展开更多
A series of CexPr1-xO2-δ (x=0, 0.5, 0.9, 1.0) mixed oxide calcined at different temperatures were synthesized by sol-gel method and characterized by Raman, XRD and O2-TPD techniques. When x=0.9, only a cubic phase Ce...A series of CexPr1-xO2-δ (x=0, 0.5, 0.9, 1.0) mixed oxide calcined at different temperatures were synthesized by sol-gel method and characterized by Raman, XRD and O2-TPD techniques. When x=0.9, only a cubic phase CeO2 is observed. When x=0.5, the compound was combined by Pr6O11 and CeO2 mixed oxides. For CexPr1-xO2-δ (x=0.5, 0.9)samples 465 cm-1 Raman peak is attributed to the Raman active F2g mode of CeO2. The broad peak at about 570 cm-1 can be linked to lattice defects resulting in oxygen vacancies. The crystallite size of the samples increased as increasing the calcined temperature. But the increased value of Ce0.9Pr0.1O2-δ and Ce0.5Pr0.5O2-δ is smaller than single CeO2 and Pr6O11 obviously. It reveals that the insertion of Pr atom into the ceria lattice could enhance the sintering resistance and thermal stability of the mixed oxides. Calcination temperatures had great effect on the peak intensity for CeO2 but less effect on Ce0.8Pr0.2O2-δ in Raman spectra, and it may be caused by the colors transformation of the mixed oxides. The result of O2-TPD experiment indicates that the formation of solid solution has elevation the stabilization and thermal stability of the mixed oxides.展开更多
Nickel catalysts supported on CeO2-ZrO2-CeO2,ZrO2-Al2O3 and Al2O3 were prepared and characterized by means of X-ray diffraction（XRD）,BET areas,H2 temperature-programmed reduction（H2-TPR）,and X-ray photoelectron sp...Nickel catalysts supported on CeO2-ZrO2-CeO2,ZrO2-Al2O3 and Al2O3 were prepared and characterized by means of X-ray diffraction（XRD）,BET areas,H2 temperature-programmed reduction（H2-TPR）,and X-ray photoelectron spectroscopy（XPS）.Through the test of catalytic partial oxidation of methane（CPOM）,Ni/CeO2-ZrO2-Al2O3 displayed the highest activity,which resulted from its largest BET area and best NiO dispersion.Furthermore,Ni/CeO2-ZrO2-Al2O3 maintained a long-time stability in CPOM,which was attributed to its best coking resistance among all the prepared catalysts.展开更多
Hairong Wang, Yaoqiang Chen, Qiulin Zhang, Qingchao Zhu, Maochu Gong, Ming Zhao（ Key Laboratory of Green Chemistry ＆ Technology of Ministry Education, College of Chemistry, Sichuan University, Chengdu 610064, Sichua...Hairong Wang, Yaoqiang Chen, Qiulin Zhang, Qingchao Zhu, Maochu Gong, Ming Zhao（ Key Laboratory of Green Chemistry ＆ Technology of Ministry Education, College of Chemistry, Sichuan University, Chengdu 610064, Sichuan, China展开更多
Composite supports CeO2-ZrO2-Al2O3（CZA） and CeO2-ZrO2-Al2O3-La2O3（CZALa） were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and N...Composite supports CeO2-ZrO2-Al2O3（CZA） and CeO2-ZrO2-Al2O3-La2O3（CZALa） were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles （NGVs） operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction （XRD） and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperatnre-programmed reduction （H2-TPR） and oxygen storage capacity （OSC） measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. The catalysts reported in this work also have significant potential in industrial application because of their high performance and low cost.展开更多
The electrocatalytic activity and stability of Pt/C catalyst modified by using CeO_2-ZrO_2 mixed oxides for the alcohols electrochemical oxidation as probes were investigated. The catalyst samples were characterized b...The electrocatalytic activity and stability of Pt/C catalyst modified by using CeO_2-ZrO_2 mixed oxides for the alcohols electrochemical oxidation as probes were investigated. The catalyst samples were characterized by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The electrochemical properties were measured by a three electrode system on electrochemical workstation（IVIUM）. The results showed that the presence of CeO_2-ZrO_2 might be associated with the presence of Pt, which indicated that possibly there was synergistic effect between CeO_2-ZrO_2 and Pt nanoparticles. The electrocatalytic activity and stability of Pt-MO_x/C（M=Ce, Zr） for methanol and ethanol oxidation was better than that of Pt-CeO_2/C, which was attributed to that CeO_2-ZrO_2 composited oxides enhanced oxygen mobility and promoted oxygen storage capacity（OSC）. Furthermore, the best performance was found when the molar ratio of CeO_2 to ZrO_2 was 2：1 for the oxidation of methanol and ethanol. The forward peak current density of Pt-MO_x/C（M=Ce, Zr, Ce：Zr=2：1） towards the methanol electrooxidation was about 3.8 times that of Pt-CeO_2/C. Pt-MO_x/C（M=Ce, Zr） appeared to be a promising and less expensive methanol oxidation anode catalyst.展开更多
The influences of CeO2-ZrO2 and γ-Al2O3 mixing methods on the catalytic activity and stability of partial oxidation of methane （POM） were investigated over Ni/Ce0.7Zr0.3O2-Al2O3 catalysts. The catalysts were charac...The influences of CeO2-ZrO2 and γ-Al2O3 mixing methods on the catalytic activity and stability of partial oxidation of methane （POM） were investigated over Ni/Ce0.7Zr0.3O2-Al2O3 catalysts. The catalysts were characterized by XRD, TPR, H2-chemsorption, and TG-DTA. For fresh catalysts, the results showed that the salt precursor mixing catalyst （ATOM） presented better performance than the catalysts prepared by the precipitator mixing method （MOL） and the powder mechanically mixing method （MECH）. The result of XRD suggested that the interaction between CeO2-ZrO2 and Al2O3 in ATOM sample was stronger than the others, which led to more lattice defects and thereby better initial activity. Moreover, the MECH sample had the best stability and the least coke deposition in 24 h stability tests. The results of TPR and H2-chemsorption indicated that the intimate contact of Ni-Al in MECH sample enhanced the ability of resisting coke deposition and metal sintering.展开更多
The effect of Na-excess content in the precursor on the structural and electrochemical performances of sodium nickel manganese oxide(NNMO)prepared by sol-gel and electrospinning methods is investigated in this paper.X...The effect of Na-excess content in the precursor on the structural and electrochemical performances of sodium nickel manganese oxide(NNMO)prepared by sol-gel and electrospinning methods is investigated in this paper.X-ray diffraction results of the prepared NNMO without adding Na-excess content indicate sodium loss,while the mixed phase of P2/O′3-type layered NNMO presented after adding Na-excess content.Compared with the sol-gel method,the secondary phase of NiO is more suppressed by using the electrospinning method,which is further confirmed by field emission scanning electron microscope images.N_(2) adsorption-desorption isotherms show no remarkably difference in specific surface areas between different preparation methods and Na-excess contents.The analysis of X-ray absorption near edge structure indicates that the oxidation states of Ni and Mn are+2 and+4,respectively.For the electrochemical properties,superior electrochemical performance is observed in the NNMO electrode with a low Na-excess content of 5wt%.The highest specific capacitance is 36.07 F·g^(-1)at0.1 A·g^(-1)in the NNMO electrode prepared by using the sol-gel method.By contrast,the NNMO electrode prepared using the electrospinning method with decreased Na-excess content shows excellent cycling stability of 100%after charge-discharge measurements for 300 cycles.Therefore,controlling the Na excess in the precursor together with the preparation method is important for improving the electrochemical performance of Na-based electrode materials in supercapacitors.展开更多
Mesoporous Ce0.5Zr0.5O2 mixed oxide with high specific surface area was synthesized under basic condition in the presence of non-ionic surfactant PEG-4000. The effect of synthesis conditions, such as synthesis tempera...Mesoporous Ce0.5Zr0.5O2 mixed oxide with high specific surface area was synthesized under basic condition in the presence of non-ionic surfactant PEG-4000. The effect of synthesis conditions, such as synthesis temperature and the molar ratio of PEG-4000/（[ Ce] ＋ [ Zr] ）, on specific surface area were investigated. The products were characterized by transmission electron microscopy, powder X-ray diffraction, and nitrogen adsorption-desorption measurements, respectively. The results showed that synthesis temperature and the molar ratio of PEG-4000/（[ Ce] ＋ [ Zr] ） had great influence on specific surface area. Under the optimum synthesis conditions, the prepared Ce0.5Zr0.5O2 mixed oxide presented cubic fluorite-type structure and possessed high surface area of 148.6 m2·g^-1 with wormlike pores.展开更多
CeO2-based oxygen materials were prepared with co-precipitation method and characterized via Brunauer-Emmet Teller(BET)method,X-ray diffraction(XRD)and temperature-programmed reduction(H2-TPR).This paper revealed that...CeO2-based oxygen materials were prepared with co-precipitation method and characterized via Brunauer-Emmet Teller(BET)method,X-ray diffraction(XRD)and temperature-programmed reduction(H2-TPR).This paper revealed that three CeO2-based oxygen storage materials are all forming homogeneous solid solution.Among the samples,CeO2-ZrO2-Al2O3(CZA)has the best textural properties and excellent thermal stability.The specific surface area and pore volume of aged CZA are 90 m2/g and 0.29 mL/g.We proposed a viewpoint:Al3+ might insert among the interspace of fluorite structure or highly dispersal in solid solutions.展开更多
基金PRIN 2006, "Caratterizzazione spettroscopica e morfologica di Me-POSS eterogeneizzati", MEL Chemicals
文摘CeO2-ZeO2 solid solutions are extensively used as oxygen storage promoters in the current automotive three-way catalysts. High thermal stability of the textural properties is one of the most important requirements for practical application since temperatures up to 1273 K are easily experienced by these materials under real working conditions. In the present paper, we investigated how hydrothermal treatments applied to cakes of doped and undoped ZrO2-rich CeO2-ZrO2 precursors might improve the thermal stability of the final CeO2-ZrO2 solid solution. A rationale was developed that allowed to correlate the morphology of the hydrothermaUy treated cake with the thermal stability at 1273 K of the final product, which did not depend on the composition of the mixed oxides.
文摘The structure and catalytic desulfurization characteristics of CeO2-TiO2 mixed oxides were investigated by means ofX-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS） and catalytic activity tests. According to the results, a CeO2-TiO2solid solution is formed when the mole ratio of cerium to titanium n（Ce）：n（Ti） is 5：5 or greater, and the most suitable n（Ce）：n（Ti） isdetermined as 7：3, over which the conversion rate of SO2 and the yield of sulfur at 500℃ reach 93% and 99%, respectively.According to the activity testing curve, Ce0.7Ti0.3O2 （n（Ce）：n（Ti）=7：3） without any pretreatment can be gradually activated by reagentgas after about 10 min, and reaches a steady activation status 60 min later. The XPS results of Ce0.7Ti0.3O2 after different time ofSO2＋CO reaction show that CeO2 is the active component that offers the redox couple Ce4＋/Ce3＋ and the labile oxygen vacancies, andTiO2 only functions as a catalyst structure stabilizer during the catalytic reaction process. After 48 h of catalytic reaction at 500℃,Ce0.7Ti0.3O2 still maintains a stable structure without being vulcanized, demonstrating its good anti-sulfur poisoning performance.
基金Project supported by the National"973"Project (2004CB719503)"863"Project (2006AA060303)the National Natural Science Foundation of China (50502023)
文摘Four kinds of CeO2-ZrO2 mixed oxides, i.e., a physical mixture of ceria and zirconia （CZP）, zirconia-coated ceria （ZCC）, ceria-coated zirconia （CCZ） and a chemical mixture of celia and zirconia （CZC）, were prepared. The oxygen storage capacity （OSC） measurements at 500℃ were performed under transient and stationary reaction conditions. All the curves of CO2 evolution during CO-O2 cycles presented a bimodal shape. The fast peak was primarily the result of the reaction of CO with the oxygen from the oxides, which was mainly determined by the nature of the material The sec- ond peak was mostly related to the CO2 adsorption behavior and was highly influenced by the surface area and the number of surface active sites. As a result, OSC activity of the samples followed in the order of CZC 〉 CCZ 〉 ZCC=CZP.
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National Natural Science Foundation of China(20976120)the Natural Science Foundation of Tianjin(09JCYBJC06200)
文摘CeO2-ZrO2-Al2O3 ternary oxides were successfully prepared by a green route of supercritical anti-solvent precipitation with supercritical CO2 as anti-solvent and methanol as solvent. The structures and oxygen storage capacities of these ternary oxides were characterized by XRD, Raman spectra and oxygen storage capacity measurements. It was found that Al3＋ and Zr4＋ inserted into CeO2 lattice, forming CeO2-ZrO2-Al2O3 solid solution. The concentration of aluminium isopropoxide in the solution affected the concentration of oxygen vacancy and the distortion of oxygen sublattice which were responsible for the oxygen storage capacity. The rapidest oxygen uptake/release rate and maximum total oxygen storage capacity （122.0 mmolO2/molCeO2） were obtained with the aluminitun isopropoxide concentration at 0.2 wt.% in the solution.
基金Project supported by the National Basic Research Program of China (2010CB732300)the National Key Technologies R&D Program of China (2007BAJ03B01)the National Natural Science Foundation of China (20601008)
文摘CeO2-MOx (M=Cu, Mn, Fe, Co, and Ni) mixed oxide catalysts were prepared by a citric acid complexation-combustion method. CeO2-MOx solid solutions could be formed with M cations doping into CeO2 lattice, while NiO and Co3O4 phases were detected on the surface of CeO2-NiO and CeO2-Co3O4 by Raman spectroscopy. The presence of M in CeO2 could obviously promote its catalytic activity for CH4 catalytic combustion and CO oxidation. Among the prepared samples, CeO2-CuO exhibited the best performance for CO oxidatio...
基金Supported by the National Natural Science Foundation of China(No.2 0 2 770 15 )
文摘A series of TiO 2-XSiO 2[X denotes the molar fraction(%) of silica in the mixed oxides] with different \{n(Ti)\}/n(Si) ratios was prepared with ammonia water as a hydrolysis catalyst. The photocatalysts prepared were characterized by XRD, thermal analysis, FTIR, UV-Vis and SPS. The characterization results of FTIR and UV-Vis spectra show that Ti atoms were gradually changed from octahedral coordination to tetrahedral coordination with the addition of silica, which is not beneficial for obtaining strong Brnsted acidity and higher photocatalytic activity. The photocatalytic activity experiments, which were conducted by using heptane(or SO 2) as the model reactant, showed that TiO 2-SiO 2 containing a suitable amount of silica can exhibit much higher photocatalytic activity than pure TiO 2. The enhanced photocatalytic activity can be attributed to three following factors: (1) smaller crystalline size; (2) higher thermal stability; (3) the new strong Brnsted acidity.
基金Project supported by the China National Key Research and Development Program(2017YFC0211002)
文摘CeO_2-ZrO_2 mixed oxides are widely used in the three-way catalysts due to their unique reversible oxygen storage and release capacity. Large surface area, high oxygen storage capacity and good thermal stability of cerium zirconium mixed oxides are the key properties for the automotive catalysts so as to meet the strict emission regulations. In this work, alumina modified CeZrLaNd mixed oxides were prepared by a co-precipitation method. The effects of moisture in precursor and inert N2 atmosphere during calcinations on the structure and properties were investigated by Brunauer-Emmett-Teller(BET) surface area measurements, X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), hydrogen temperature-programmed reduction(H_2-TPR), oxygen storage capacity(OSC), Raman spectroscopy, and X-ray photoelectron spectroscopy(XPS). The results show that the moisture in precursor during calcinations increases the crystal grain size of the cerium zirconium mixed oxides, improving the thermal stability. And the aged surface area of sample after being calcined at1000 ℃ for 4 h reaches 68.8 m^2/g(5.7% increase compared with the common sample). The inert N2 atmosphere endows a great pore-enlarging effect, which leads to high fresh surface area of 148.9 m2/g(13.5% increase compared with the common sample) and big pore volume of 0.5705 mL/g. The redox and oxygen storage capacity are also improved by inert N2 atmosphere with high OSC value of 241.06μmolO_2/g(41.3% increase compared with the common calcination), due to the abundant formation of the crystal defects and oxygen vacancies.
基金supported by the National Natural Science Foundation of China (Nos. 21276179, 21576205)the Program for Changjiang Scholars, Innovative Research Team in University (IRT_15R46)
文摘In this study,Pd-Mg(Al)-LDH/γ-Al2O3 and Pd-Mg(Al)Zr-LDH/γ-Al2O3 precursors were synthesized by impregnating Na2PdCl4 on Mg(Al)-LDH/γ-Al2O3 and Mg(Al)Zr-LDH/γ-Al2O3,and then the precursors were calcinated and reduced to obtain Pd-Mg(Al)-MMO/γ-Al2O3 and Pd-Mg(Al)Zr-MMO/γ-Al2O3 catalysts.Compared with Pd/γ-Al2O3 catalyst,the hydrogenation efficiency of Pd-Mg(Al)-MMO/γ-Al2O3 and Pd-Mg(Al)Zr-MMO/γ-Al2O3 increased by 15.7%and 24.0%,respectively.Moreover,the stability of Pd-Mg(Al)Zr-MMO/γ-Al2O3 catalyst was also higher than that of Pd/γ-Al2O3.After four runs,the hydrogenation efficiency of Pd/γ-Al2O3 decreased from 12.1 to 10.0 g/L,while that of Pd-Mg(Al)Zr-MMO/γ-Al2O3 decreased from 15.0 to 14.3 g/L.The active aquinones selectivities of all catalysts were almost 99%.The structures of the catalysts were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),N2 adsorption–desorption,inductively coupled plasma-atomic emission spectrometry(ICP-AES),CO chemisorption analysis,transmission electron microscopy(TEM),temperature-programmed reduction with hydrogen(H2-TPR),and X-ray photoelectron spectroscopy(XPS).The results indicate that the improved catalytic performance is attributed to the stronger interaction between Pd and Mg(Al)Zr-MMO/γ-Al2O3,smaller Pd particle size and higher Pd dispersion.This work develops an effective method to synthesize highly dispersed Pd nanoparticles based on the layered double hydroxides(LDHs)precursor.
文摘Ce x Ti 1- x O 2 mixed oxides of different mole ratios ( x =0, 0.1, 0.2～0.9, 1.0) were prepared by co precipitation of TiCl 4 with Ce(NO 3) 3 and then loaded with different amounts of CuO. The effects of CuO on NO+CO reaction were investigated, and the structure and reductive properties of various CuO/Ce x Ti 1- x O 2 were characterized by the methodologies of BET, TPR and XRD. The results show that different Ce/Ti mole ratios and calcination temperatures induce changes of structure and reductive properties of the Ce x Ti 1- x O 2 mixed oxides. When x =0.1～0.5, amorphous CeTi 2O 6 phase mainly forms at 650 ℃ compared to the formation of CeTi 2O 6 which crystallizes at 800 ℃. When x >0.6, some TiO 2 enters the CeO 2 lattice and a CeO 2 TiO 2 solid solution is formed. The activity of 6%CuO/Ce x Ti 1- x O 2 calcined at 650 ℃ is largely affected by the x values, which is the highest when x =0.3, 0.4 and 0.9. The NO conversion reaches 70% at a reaction temperature of 150 ℃. By comparison, the x values have little effect on the activity of 6%CuO/Ce x Ti 1- x O 2 calcined at 800 ℃ . There are strong interactions between CuO and CeTi 2O 6, i.e., formation of the CeTi 2O 6 phase shifts the CuO reduction peak temperature from 380 to 200 ℃, and CuO, in turn, shifts the CeTi 2O 6 reduction peak temperature from 600 to 300 ℃.
基金supported by the Ministry of Science and Technology,China (No.2009AA064801,2010CB732304)
文摘Potassium-modified ceria-zirconia catalyst was synthesized by wetness impregnation method. The ageing treatment was performed in static air at 800℃ for 20 hr to evaluate the thermal stability of the catalyst. The catalysts were characterized by X-ray diffraction, BET surface area, oxygen storage capacity, NOx-temperature programmed desorption and soot-temperature programmed oxidation measurements. By introduction of potassium, the maximum soot oxidation rate temperature （Tin） of the ceria-zirconia based catalyst decreased from 525 to 428℃ in the presence of NO under a loose contact mode. The shift of Tm of the K-modified catalyst after ageing is only 15℃. The enhanced activity of the aged catalyst mainly lies in the promotional effect of potassium on the NOx/oxygen storage capacity as well as the soot-catalyst contact.
文摘A series of CexPr1-xO2-δ (x=0, 0.5, 0.9, 1.0) mixed oxide calcined at different temperatures were synthesized by sol-gel method and characterized by Raman, XRD and O2-TPD techniques. When x=0.9, only a cubic phase CeO2 is observed. When x=0.5, the compound was combined by Pr6O11 and CeO2 mixed oxides. For CexPr1-xO2-δ (x=0.5, 0.9)samples 465 cm-1 Raman peak is attributed to the Raman active F2g mode of CeO2. The broad peak at about 570 cm-1 can be linked to lattice defects resulting in oxygen vacancies. The crystallite size of the samples increased as increasing the calcined temperature. But the increased value of Ce0.9Pr0.1O2-δ and Ce0.5Pr0.5O2-δ is smaller than single CeO2 and Pr6O11 obviously. It reveals that the insertion of Pr atom into the ceria lattice could enhance the sintering resistance and thermal stability of the mixed oxides. Calcination temperatures had great effect on the peak intensity for CeO2 but less effect on Ce0.8Pr0.2O2-δ in Raman spectra, and it may be caused by the colors transformation of the mixed oxides. The result of O2-TPD experiment indicates that the formation of solid solution has elevation the stabilization and thermal stability of the mixed oxides.
基金Project supported by State Key Fundamental Research Project(G1999022400)
文摘Nickel catalysts supported on CeO2-ZrO2-CeO2,ZrO2-Al2O3 and Al2O3 were prepared and characterized by means of X-ray diffraction（XRD）,BET areas,H2 temperature-programmed reduction（H2-TPR）,and X-ray photoelectron spectroscopy（XPS）.Through the test of catalytic partial oxidation of methane（CPOM）,Ni/CeO2-ZrO2-Al2O3 displayed the highest activity,which resulted from its largest BET area and best NiO dispersion.Furthermore,Ni/CeO2-ZrO2-Al2O3 maintained a long-time stability in CPOM,which was attributed to its best coking resistance among all the prepared catalysts.
基金the National Natural Science Foundation of China (20773090)the Specialized Research Fund for the Doctoral Program of Higher Education of China (20070610026, 200806100009)
文摘Hairong Wang, Yaoqiang Chen, Qiulin Zhang, Qingchao Zhu, Maochu Gong, Ming Zhao（ Key Laboratory of Green Chemistry ＆ Technology of Ministry Education, College of Chemistry, Sichuan University, Chengdu 610064, Sichuan, China
基金supported by the National Natural Science Foundation of China (No. 20773090, 20803049)the National High Technology Researchand Development Program of China (863 Program, No. 2006AA06Z347)the Specialized Research Fund for the Doctoral Program of Higher Education(20070610026)
文摘Composite supports CeO2-ZrO2-Al2O3（CZA） and CeO2-ZrO2-Al2O3-La2O3（CZALa） were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles （NGVs） operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction （XRD） and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperatnre-programmed reduction （H2-TPR） and oxygen storage capacity （OSC） measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. The catalysts reported in this work also have significant potential in industrial application because of their high performance and low cost.
基金supported by National Natural Science Foundation of China(51474133,21407084)Talent Incubation Funding of School of Materials and Metallurgy(2014CY012)
文摘The electrocatalytic activity and stability of Pt/C catalyst modified by using CeO_2-ZrO_2 mixed oxides for the alcohols electrochemical oxidation as probes were investigated. The catalyst samples were characterized by X-ray diffraction（XRD） and scanning electron microscopy（SEM）. The electrochemical properties were measured by a three electrode system on electrochemical workstation（IVIUM）. The results showed that the presence of CeO_2-ZrO_2 might be associated with the presence of Pt, which indicated that possibly there was synergistic effect between CeO_2-ZrO_2 and Pt nanoparticles. The electrocatalytic activity and stability of Pt-MO_x/C（M=Ce, Zr） for methanol and ethanol oxidation was better than that of Pt-CeO_2/C, which was attributed to that CeO_2-ZrO_2 composited oxides enhanced oxygen mobility and promoted oxygen storage capacity（OSC）. Furthermore, the best performance was found when the molar ratio of CeO_2 to ZrO_2 was 2：1 for the oxidation of methanol and ethanol. The forward peak current density of Pt-MO_x/C（M=Ce, Zr, Ce：Zr=2：1） towards the methanol electrooxidation was about 3.8 times that of Pt-CeO_2/C. Pt-MO_x/C（M=Ce, Zr） appeared to be a promising and less expensive methanol oxidation anode catalyst.
基金973 Program (2004CB719503)Key Program of Natural Science Foundation of Tianjin (07JCZDJC01600)Program for New Century Excellent Talents in University (NCET-06-0243)
文摘The influences of CeO2-ZrO2 and γ-Al2O3 mixing methods on the catalytic activity and stability of partial oxidation of methane （POM） were investigated over Ni/Ce0.7Zr0.3O2-Al2O3 catalysts. The catalysts were characterized by XRD, TPR, H2-chemsorption, and TG-DTA. For fresh catalysts, the results showed that the salt precursor mixing catalyst （ATOM） presented better performance than the catalysts prepared by the precipitator mixing method （MOL） and the powder mechanically mixing method （MECH）. The result of XRD suggested that the interaction between CeO2-ZrO2 and Al2O3 in ATOM sample was stronger than the others, which led to more lattice defects and thereby better initial activity. Moreover, the MECH sample had the best stability and the least coke deposition in 24 h stability tests. The results of TPR and H2-chemsorption indicated that the intimate contact of Ni-Al in MECH sample enhanced the ability of resisting coke deposition and metal sintering.
基金financially supported by (i) Suranaree University of Technology,(ii) Thailand Science Research and Innovation,and (iii) National Science,Research and Innovation Fund(project codes 90464 and 160363)。
文摘The effect of Na-excess content in the precursor on the structural and electrochemical performances of sodium nickel manganese oxide(NNMO)prepared by sol-gel and electrospinning methods is investigated in this paper.X-ray diffraction results of the prepared NNMO without adding Na-excess content indicate sodium loss,while the mixed phase of P2/O′3-type layered NNMO presented after adding Na-excess content.Compared with the sol-gel method,the secondary phase of NiO is more suppressed by using the electrospinning method,which is further confirmed by field emission scanning electron microscope images.N_(2) adsorption-desorption isotherms show no remarkably difference in specific surface areas between different preparation methods and Na-excess contents.The analysis of X-ray absorption near edge structure indicates that the oxidation states of Ni and Mn are+2 and+4,respectively.For the electrochemical properties,superior electrochemical performance is observed in the NNMO electrode with a low Na-excess content of 5wt%.The highest specific capacitance is 36.07 F·g^(-1)at0.1 A·g^(-1)in the NNMO electrode prepared by using the sol-gel method.By contrast,the NNMO electrode prepared using the electrospinning method with decreased Na-excess content shows excellent cycling stability of 100%after charge-discharge measurements for 300 cycles.Therefore,controlling the Na excess in the precursor together with the preparation method is important for improving the electrochemical performance of Na-based electrode materials in supercapacitors.
基金Project Supported by Open Fund of Key Laboratory of Catalysis Materials and Science of Hubei Province (CHCL0501)
文摘Mesoporous Ce0.5Zr0.5O2 mixed oxide with high specific surface area was synthesized under basic condition in the presence of non-ionic surfactant PEG-4000. The effect of synthesis conditions, such as synthesis temperature and the molar ratio of PEG-4000/（[ Ce] ＋ [ Zr] ）, on specific surface area were investigated. The products were characterized by transmission electron microscopy, powder X-ray diffraction, and nitrogen adsorption-desorption measurements, respectively. The results showed that synthesis temperature and the molar ratio of PEG-4000/（[ Ce] ＋ [ Zr] ） had great influence on specific surface area. Under the optimum synthesis conditions, the prepared Ce0.5Zr0.5O2 mixed oxide presented cubic fluorite-type structure and possessed high surface area of 148.6 m2·g^-1 with wormlike pores.
文摘CeO2-based oxygen materials were prepared with co-precipitation method and characterized via Brunauer-Emmet Teller(BET)method,X-ray diffraction(XRD)and temperature-programmed reduction(H2-TPR).This paper revealed that three CeO2-based oxygen storage materials are all forming homogeneous solid solution.Among the samples,CeO2-ZrO2-Al2O3(CZA)has the best textural properties and excellent thermal stability.The specific surface area and pore volume of aged CZA are 90 m2/g and 0.29 mL/g.We proposed a viewpoint:Al3+ might insert among the interspace of fluorite structure or highly dispersal in solid solutions.
