A rationale for the development of thermally stable nanostructured CeO_2-ZrO_2-containing mixed oxides

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.

Comparative structural and electrochemical properties of mixed P2/O′3-layered sodium nickel manganese oxide prepared by sol-gel and electrospinning methods:Effect of Na-excess content

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.

Catalytic reduction of SO_2 by CO over CeO_2-TiO_2 mixed oxides

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.

Properties of TiO_2-SiO_2 Mixed Oxides and Photocatalytic Oxidation of Heptane and Sulfur Dioxide

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.

Highly Dispersed Pd Nanoparticles Supported on Zr-Doped MgAl Mixed Metal Oxides for 2-Ethylanthraquinone Hydrogenation

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.

Ce_xTi_(1-x)O_2 Mixed Oxides Supported CuO Catalyst for NO Reduction by CO

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 ℃.

Effect of Calcination Temperature on Structure and O_2 Desorption Properties of Ce_xPr_(1-x)O_(2-δ) Mixed Oxides

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.

Preparation of Mesoporous Ce_(0.5)Zr_(0.5)O_2 Mixed Oxide by Hydrothermal Templating Method

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.

MOLECULAR BEAM STUDIES ON OXIDATION OF CO ON Pd WITH DIFFERENT MIXED RATIOS OF P_(CO) TO P_(O2) ~*

Here some steady-state experiments on oxidation of CO on Pd were performed on a molecular beam apparatus. It is found that the characteristics of the rate of CO_2 formation r versus substrate temperature T are dependent on the ratio P=P_(CO)/P_(O2) in the mixed beam. These characteristics are related to the complicated interactions of co-adsorbed CO and O particles on Pd surface.

氧化石墨烯掺杂UO_(2)芯块制备工艺及性能研究

氧化石墨烯(Graphene Oxide,GO)掺杂改性二氧化铀(UO_(2))芯块是高性能核燃料研究的重点方向之一。为实现GO在UO_(2)芯块中的均匀分布及掺杂量的有效控制,利用固-液混合法和重铀酸铵(Ammonium Diuranate,ADU)共沉淀法制备了不同GO掺杂量的UO_(2)粉末,研究了制粉方法及GO掺杂量对GO在UO_(2)中混合均匀性的影响。采用放电等离子烧结制备了不同GO掺杂量的UO_(2)-GO芯块,探索了不同烧结参数的影响,并对燃料芯块的性能进行测试。结果表明,固-液混合法制备的GO掺杂UO_(2)粉末混合均匀度更好;放电等离子烧结得到的UO_(2)-GO芯块密度最高可达97.6%T.D.;GO掺杂量为1.5 wt.%的芯块在1000℃下的热导率较常规UO_(2)芯块提高了85.9%;制备的UO_(2)-GO芯块晶粒尺寸较为均匀,GO均匀分布在晶界处并形成了桥联导热网络,有效提升了掺杂芯块的热导率。

Effect of Manganese Doping on Oxygen Storage Capacity of Ceria-Zirconia Mixed Oxides

CeO2-ZrO2-MnOx mixed oxide series were prepared by sol-gel method. CO pulse and CO-O2 cycle measurements were carried out to examine the oxygen storage complete capacity （OSCC） and dynamic oxygen storage capacity （OSC） of the samples. The doping method brought about strong interactions between manganese oxide and ceria, both in the bulk and on the surface. Only a small part of Mn cations are incorporated into the ceria lattice to form solid solutions and the remaining are left on the surface as finely dispersed Mn3O4. The OSC behaviors of the materials are influenced by the doping amount of Mn and the solubility of Mn in the CeO2 lattice. The OSC is more easily affected by available contents of oxygen storage components when the measurement frequency is low. Comparatively, the concentration of lattice defects, which affects the mobility of bulk oxygen, is the determining factor under high frequency.

Catalytic Partial Oxidation of Methane over Ni/CeO_2-ZrO_2-Al_2O_3

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.

CeO_2-ZrO_2-La_2O_3-Al_2O_3 composite oxide and its supported palladium catalyst for the treatment of exhaust of natural gas engined vehicles

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.

Physico-Chemical Properties and Catalytic Behavior of LnSrNiO_4 Mixed Oxides for NO Decomposition

A series of LnSrNiO_4(A_2BO_4, Ln=La, Pr, Nd, Sm, Gd) mixed oxides with K_2NiF_4 structure, in which Asite(Sr) was partly substituted by individual light rare earth element, was prepared. The solid state physicochemical properties including crystal structure, defect structure, IR spectrum, valence state of Bsite ion, nonstoichiometric oxygen, oxygenous species, the properties of oxidation and reduction etc. as well as the catalytic behavior for NO decomposition on these mixed oxides were investigated. The results show that all of these mixed oxide catalysts have high activity for the direct decomposition of NO(at 900 ℃ the conversion of NO is more than 90%). The effect of the substitution of light rare earth elements at Asite on catalytic behavior for NO decomposition was elucidated.

New insight into the design of highly dispersed Pt supported CeO_(2)-TiO_(2) catalysts with superior activity for VOCs low-temperature removal

A series of CeO_(2)-TiO_(2)mixed oxides supports with various Ce/Ti molar ratio were synthesized by modified coprecipitation method. The corresponding Pt loaded(0.5 wt% Pt) catalysts were prepared by electronless deposition method and evaluated for the deep oxidation of n-hexane as a model VOCs. The results show that the CeO_(2)and TiOxnanoparticles can highly disperse into each other and form Ce_(2)Ti_(2)O_(7)solid solution with appropriate Ce/Ti molar ratio, which significantly improves their redox ability by enhancing the interaction between CeO_(2)and TiO_(x). The dispersibility of Pt species can also be adjusted by altering the Ce/Ti molar ratio, and Pt/CeTi-2/1 catalyst with Ce/Ti molar ratio of 2:1 exhibits the best Pt dispersibility that Pt species mainly exist as Pt single atoms. The high dispersion of Pt species in the Pt/CeO_(2)-TiO_(2)catalysts would promote the catalytic activity of VOCs oxidation with low T90% values(1000 ppm, GHSV = 15,000 h^(-1)), such as for n-hexane degradation with T90% of 139℃. The characterizations reveal that the superior activity is mainly related to possessing the more Pt2+species,adsorbed oxygen species and higher low-temperature reducibility owing to the strong interaction between highly dispersed Pt species and CeO_(2)-TiO_(2)as well as the promoted migration of lattice oxygen by the formation of more Ce_(2)Ti_(2)O_(7)species. Furthermore, the Pt/CeTi-2/1 catalyst also exhibits excellent stability for chlorinated and other non-chlorinated VOCs oxidation, making it very promising for real application under various operating conditions.

Elimination of 1,2-dichloroethane over(Ce,Cr)_x O_2/Nb_2O_5 catalysts: synergistic performance between oxidizing ability and acidity

A series of(Ce,Cr)xO2/Nb2O5 catalysts with different(Ce,Cr)xO2 to Nb2O5 mass ratios were synthesized by the deposition-precipitation method for use in deep catalytic oxidation of 1,2-dichloroethane(DCE), which is one of the typical chlorinated volatile organic compound pollutants. The textural properties were characterized by X-ray diffraction, N2 adsorption/desorption isotherms, UV-Raman spectroscopy, and scanning electron microscopy. The surface acidity and the redox properties were characterized by ammonia temperature-programmed desorption and H2 temperature-programmed reduction, respectively. The results show that the addition of a proper amount of(Ce,Cr)xO2 over Nb2O5 significantly improves the intrinsic catalytic activity towards the deep oxidation of DCE, and only a very small amount of C2H3Cl is detected as the byproduct of the oxidation process. Further study reveals the existence of an obvious synergistic effect between Nb2O5, with abundant strong acid sites, and(Ce,Cr)xO2, with strong oxidation sites, as the strong acid sites of Nb2O5 promote the adsorption and dehydrochlorination of DCE, while the strong oxidation sites of(Ce,Cr)xO2 contribute to the deep oxidation of the reactant, intermediates, and byproducts.

The Effect of Nb Loading on Catalytic Properties of Ni/Ce_(0.75)Zr_(0.25)O_2 Catalyst for Methane Partial Oxidation

In this study, the effect of Nb loading on the catalytic activity of Ce0.75Zr0.25O2-supported Ni catalysts was studied for methane partial oxidation. The catalysts were characterized by BET, H2 chemisorption, XRD, TPR, TEM and tested for methane partial oxidation to syngas in the temperature range of 400-800 ℃at atmospheric pressure. The results showed that the activity of methane partial oxidation on the catalysts was apparently dependent on Nb loading. It seemed that the addition of Nb lowered the catalytic activity for methane partial oxidation and increased the extent of carbon deposition. This might be due to the strong interaction between NiO and Nb-modified support and reduction of surface oxygen reducibility.

CONDUCTING BLENDS OF POLY (2-VINYL PYRIDINE) AND POLYETHYLENE OXIDE WITH HIGH MOLECULAR WEIGHT

Ionic, electronic and mixed (ionic-electronic) conductivities of blends of poly(2-vinyl pyridine) (P2VP) and poly(ethylene oxide) (PEO) with high molecular weight after doped with LiClO4, TCNQ or LiClO4 and TCNQ were investigated. Effects of LiClO4 and TCNQ concentrations on the conductivity of PEO/P2VP/LiClO4 or TCNQ blend were studied. The ionic conductivity of PEO/P2VP/LiClO4 blend increases with increasing PEO content. At a Li/ethylene bride molar ratio of 0.10 and a TCNQ/2-vinyl pyridine molar ratio of 0.5, the mixed conductivity of PEO/P2VP/LiClO4/TCNQ is higher than the total of ionic conductivity of PEO/P2VP/LiClO4 and electronic conductivity of PEO/P2VP/TCNQ when the weight ratio of PEO and P2VP is 6/4 or 5/5. Scanning electron microscopy (SEM) on the broken cross-section of the PEO/P2VP/LiClO4 blend and differential scanning calorimetry (DSC) results show that LiClO4 could act as a compatibilizer in the blend.

Effect of Al Addition on Properties of Al_2O_3-SiC-C Dry Ramming Mixes for BF Trough

Aluminium powders were introduced to Al2O3-SiC-C dry ramming mixes in order to improve sintering properties and oxidation resistance according to their service conditions and installation methods. Properties such as bulk density, porosity, modulus of rupture, crushing strength and hot modulus of rupture as a function of aluminium addition were investigated in the present work. The microstructure and thermodynamics for the heat treated specimens were also analyzed. The results show that as aluminium addition increasing, the bulk density of the specimen treated at 220℃ tends to decrease and the apparent porosity increases, the strength of the specimens treated at 1100℃ and 1450℃ increases markedly, the bulk density tends to increase, apparent porosity and linear shrinkage decrease. The HMOR at 1400℃ is enhanced from 1.0 MPa to 3.5 MPa with 3% aluminium. Aluminium is served as sintering agent and anti-oxidant and it will react with CO and CO2 forming Al2O3 , which is helpful to enhance the strength, densify the structure and improve the overall properties.

硬脂酸法制备SO_4^(2-)/Fe_2O_3-SiO_2固体酸及其催化性能的初步探讨

首次用硬脂酸法制备了 Fe2 O3 -Si O2 混合氧化物 ,经浸渍 H2 SO4后再焙烧得 SO2 - 4 /Fe2 O3 -Si O2 固体酸催化剂 .用 TEM,XRD,N2 吸附 /脱附和 TG-DTA等手段对其进行了表征 ,结果显示制得的 Fe2 O3 -Si O2 混合氧化物具有多孔结构 ,且随着 Si含量的增大 ,其比表面积明显增大 ,但孔径减小 .用乙酸