Effect of cobalt doping on ceria-zirconia mixed oxide： Structural characteristics, oxygen storage/release capacity and three-way catalytic performance

The effect of Co doping on ceria-zirconia mixed oxides was investigated for Co 0.1 Ce 0.6 Zr 0.3 O x sample prepared by sol-gel method. The Pd-only three-way catalyst (TWC) was obtained by incipient wetness impregnation with 0.5 wt.% Pd loading. The structural and oxygen handling properties were analyzed by X-ray diffraction (XRD), H 2 -temperature programmed reduction (H 2 -TPR) and the dynamic oxygen storage capacity (DOSC). The introduction of Co into ceria-zirconia lattice strongly modified the mobility of oxygen and enhanced the DOSC performance. Pd-only TWC based on the Co 0.1 Ce 0.6 Zr 0.3 O x support exhibited superior activity for water-gas shift and steam reforming and amplified amplitude of stoichiometric window.     

Structures and oxygen storage capacities of CeO2-ZrO2-Al2O3 ternary oxides prepared by a green route： supercritical anti-solvent precipitation

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 Al 3+ and Zr 4+ 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 aluminium isopropoxide concentration at 0.2 wt.% in the solution.     

Structure and high-temperature electrochemical properties of La_（0.60）Nd_（0.15）Mg_（0.25）Ni_（3.3）Si_（0.10） hydrogen storage alloys

The structure and high-temperature electrochemical properties of the as-cast and annealed (940 °C, 8 h) La0.60Nd0.15Mg0.25Ni3.3Si0.10 hydrogen storage alloys were investigated. The X-ray diffraction revealed that the multiphase structure of the as-cast alloy with LaNi5 phase as the main phase was converted into a double-phase structure with La2Ni7 phase as the main phase after annealing. The surface morphology studied by scanning electronic microscope (SEM) showed that the annealed alloy had a much higher anti-corrosion ability than the as-cast alloy. Both alloys presented excellent activation characteristics at all test temperatures. The maximum discharge capacity of the as-cast alloy decreased when the test temperature increased, while the temperature almost had no effect on the annealed alloy. As the test temperature increased, the cyclic stability and charge retention of both alloys decreased, and these properties were improved significantly by annealing.     

Synthesis kinetics and thermophysical properties of La_2（Zr_（0.7）Ce_（0.3））_2O_7 ceramic for thermal barrier coatings

La2(Zr0.7Ce0.3)2O7 (LZ7C3) ceramic was synthesized by solid state reaction with La2O3, ZrO2 and CeO2 as starting materials. The synthesis kinetics, phase structure, mass loss and microstructure were studied by thermo gravimetric-different thermal analyzer (TG-DTA), X-ray difference (XRD) and scanning electron microscopy (SEM). The thermal conductivity and thermal expansion coefficient were measured by laser-flash method and pushing-rod method, respectively. XRD results showed that LZ7C3 was a mixture of La2Zr2O7 (LZ, pyro- chlore) and La2Ce2O7 (LC, fluorite). The lowest synthesis temperature and time of LZ7C3 were 1400 oC and 5 h. There were no peaks of La2O3 when the powder granularity was about 0.82 μm in the synthesis process. The atom ratio La:Zr:Ce of prepared LZ7C3 powder was very close to 10:7:3 which was the theory value of LZ7C3. The thermal conductivity of LZ7C3 decreased gradually with the temperature increased up to 1200 oC, and was located within 0.79 to 1.02 W/(m·K), which was almost 50% lower than that of LZ, whereas its thermal expansion coefficient was larger and the value was 11.6×10-6 K-1.     

A study on hydrogen storage and electrochemical properties of La_（0.55）Pr_（0.05）Nd_（0.15）Mg_（0.25）Ni_（3.5） （Co_（0.5）Al_（0.5））_x （x=0.0, 0.1, 0.3, 0.5） alloys

The La0.55Pr0.05Nd0.15Mg0.25Ni3.5(Co0.5Al0.5)x(x=0.0, 0.1, 0.3, 0.5) alloys were prepared by magnetic levitation melting under an Ar atmosphere, and the effects of Co and Al on the hydrogen storage and electrochemical properties were systematically investigated by pressure composition isotherms, cyclic voltammetry, Tafel polarization and electrochemical impedance spectroscopy testing. The results showed that the alloy phases were mainly consisted of (La,Pr)(Ni,Co)5, LaMg2Ni9, (La,Nd)2Ni7 and LaNi3 phases, and the cell volumes of (La,Pr)(Ni,Co)5, LaMg2Ni9, (La,Nd)2Ni7 and LaNi3 phases expanded with Co and Al element added. The hydrogen storage capacity initially increased from 1.36 (x=0) to 1.47 wt.% (x=0.3) and then decreased to 1.22 wt.% (x=0.5). The discharge capacity retention and cycle stability of the alloy electrodes were improved with the increase of Co and Al contents. The La0.55Pr0.05Nd0.15Mg0.25Ni3.5(Co0.5Al0.5)0.3 alloy electrode possessed better electrochemical kinetic characteristic.     

Hydrogen storage properties of mechanically milled La2Mg17-x wt.% Ni （x=0, 50, 100, 150 and 200） composites

Melting method was used to obtain La2Mg17 alloy,and then Ni powder was added by mechanical alloying method.The kinetics of hydriding process and electrochemical properties of La2Mg17-x wt.%Ni(x=0,50,100,150,200) composites were investigated.X-ray diffraction(XRD) and scanning electron microscopy(SEM) analyses showed that the crystal structure of composite alloy gradually transformed into amorphous phase by the effect of ball milling and Ni powders.The research of hydrogen absorption properties found that La2Mg 17-50 wt.%Ni reached the highest hydrogen absorption than other alloys with more addition of Ni content,reached to 5.796 wt.% at 3 MPa,and up to 5.229 wt.% merely in 2 min,which revealed that the amorphous phase reduced the H occupation of the lattice clearance,resulting in the decline of hydrogen absorption capacity.The electrochemical tests indicated that the maximum discharge capacity increased to 353.1 mAh/g at 30 oC,however,the cycle stability decreased considerably.A series of kinetic measurements demonstrated that the controlling steps of electrochemical process of La 2 Mg 17-x wt.%Ni alloys transferred from hydrogen diffusion on alloy bulk(x=50,100) to hydrogen diffusion on both alloy bulk and surface(x=150,200).     

Preparation of Ce0.65Zr0.35O2 by co-precipitation： The role of hydrogen peroxide

The effect of H2O2 on the properties of Ce0.65Zr0.35O2 was explored by treating cerium nitrate and zirconium nitrate with a mixed aqueous solution of ammonia and ammonia-carbonate 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-temperature-programmed 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.     

Influence of oxygen non-stoichiometry on physical properties of NdSr2Mn2O7±δ

Nd Sr2Mn2O7+δ compounds were synthesized by ceramic method under three different cooling conditions. The Nd Sr2Mn2O7+δ samples were characterized by powder X-ray diffraction(XRD). Oxygen non-stoichiometry data for the studied powders were determined by using gravimetric and X-ray photoelectron spectroscopy(XPS) methods. The correlation of cooling method and oxygen as non-stoichiometry was established. The electroconductivity in samples was studied by using four-point probe method, and the strong correlation with non-stoichiometry was found out. Magnetization measurements were carried out. It was found that the magnetic and transport properties of the samples were also influenced by oxygen non-stoichiometry. The evolution of the magnetic properties could be explained by the formation of magnetic clusters in the vicinity of oxygen vacancies(OV) and strong competition between the superexchange and double exchange interactions.     

Cone-shaped cylindrical Ce_（0.9）Gd_（0.1）O_（1.95） electrolyte prepared by slip casting and its application to solid oxide fuel cells

A cone-shaped gadolinium doped ceria(Ce0.9Gd0.1O1.95,GDC) electrolyte cylinder with a thin wall was fabricated using slip cast-ing technique.The diameter of the larger open end of the cone-shaped cylinder was 0.85 cm,the length was 1.0 cm,and the thickness of the wall was 0.026 cm after sintering.Both the electrolyte and electrode powders were fabricated by using a glycine-nitrate process.A single solid oxide fuel cell(SOFC) was prepared with the cone-shaped electrolyte,NiO-GDC(70:30 wt.%) anode and Sm0.5Sr0.5CoO3(SSC) cathode.Its electrochemical performance(I-V curve) and electrochemical impedance spectroscopy(EIS) were studied with humidified hydrogen as the fuel and air as the oxidant.The maximum output power density was about 300 ?mW/cm2 at 700 oC.The EIS results showed that the dominant loss of the SOFC was from the ohmic resistance of the electrolyte.     

Effect of trivalent rare earth ions doping on the fluorescence properties of electron trapping materials SrS：Eu~（2＋）

Trivalent rare-earth ions (La3+,Pr3+,Nd3+,Sm3+,Gd3+,Tb3+,Dy3+,Ho3+,Er3+,Tm3+,and Yb3+) were investigated as the codoped auxiliary sensitizer for the electron trapping materials SrS:Eu2+ in order to enhance the fluorescence properties.It was found that Sm3+ and Tb3+ had the best photoluminescence stimulated luminescence (PSL) effect among the selected trivalent rare-earth ions.All the SrS:Eu2+ samples doped by different trivalent rare-earth ions could be stimulated by 980 nm laser after being exposed to the conventional sunlight,and they emitted PSL with the peak located at 615 nm.The result also indicated that some co-doped rare earth ions could increase fluorescence intensities of the traditional electron trapping materials SrS:Eu2+.     

Preparation and investigation of Ce_(0.4)Zr_(0.5–x)Y_(0.1)Mn_xO_2 oxygen-storage materials

A series of Ce0.4Zr0.5-xY0.1MnxO2(0     

Structure and oxygen storage capacity of Pd/Pr/CeO_2-ZrO_2 catalyst:effects of impregnated praseodymia

Praseodymium(Pr) was impregnated to CeO2-ZrO2 solid solution by an impregnation method.The as-obtained Pr modified CeO2-ZrO2 was impregnated with 1 wt.% Pd to prepare the catalysts.The structure and reducibility of the fresh and hydrothermally aged catalysts were characterized by X-ray diffraction(XRD),Raman,X-ray photoelectron spectroscopy(XPS),CO chemisorption and H2 temperature-programmed reduction(H2-TPR).The oxygen storage capacity(OSC) was evaluated with CO serving as probe gas.Effects of impregnated Pr on the structure and oxygen storage capacity of catalysts were investigated.The results showed that the aged Pr-impregnated samples had much higher OSC and better reducibility than the unmodified ones.The scheme of structural evolutions of the catalysts with and without Pr was also established.Partial of the impregnated Pr diffused into the bulk of CeO2-ZrO2 during ageing,which inhibited the sintering,and increased the amount of oxygen vacancies in CeO2-ZrO2 support.Furthermore,those impregnated Pr species which covered on the surface of the support obstructed the strong metal-support interaction between Pd and Ce so as to reduce the encapsulation of Pd as well as the back spill-over of the oxygen during the catalytic process.     

Enhanced thermal stability of Ce_(0.33)Zr_(0.55)(LaNdY)_(0.12)O_2 mixed oxides prepared by sulfate-aided coprecipitation method

Ceria-zirconia based mixed oxides(CZs) have been applied in three-way catalysts(TWCs) for their high surface area and oxygen storage capacity(OSC).In this work,enhanced thermal stability of Ce_(0.33)Zr_(0.55)(LaNdY)_(0.12)O_2 mixed oxides was realized via a facile and scalable approach,namely,sulfateaided coprecipitation method was labelled as CZ-S.Sulfate ion(SO_4~(2-)) was added into raw solution in the form of sulfuric acid and acted as coordination agent.The control sample was prepared by conventional coprecipitation method without sulfuric acid added and labelled as CZ.The promotion effect of sulfate ion was analyzed systematically by X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),N_2 adsorption-desorption,Fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),OSC and hydrogen temperatureprogrammed reduction(H_2-TPR) analysis.XRD and high resolution TEM results reveal that CZ-S have homogeneous distributions of elements.TEM and SEM images show that fresh samples of CZ-S have narrower distributions of grain sizes and larger pore sizes than those of CZ.Through cross analysis of structure and morphology of CZ and CZ-S,we find that the introduction of sulfate ions results in uniform distributions of elements,narrows distributions of grain sizes,and enables the formation of secondary loose packing of sub-particles,which lead to enhanced thermal stability of the samples of CZ-S upon aging process at high temperature.After aging treatment at 1100℃ for 10 h,aged samples of CZ-S present larger specific surface areas and pore volumes than the aged sample prepared by conventional coprecipitation method without sulfate ions added.Furthermore,the aged sample of CZ-S2(SO_4~(2-)/Zr=1)possesses the highest specific surface area of 21.9 m2/g and the biggest pore volume of 0.035 mL/g among all aged samples.     

Effects of ceria/zirconia ratio on properties of mixed CeO_2-ZrO_2-Al_2O_3 compound

A series of CexZr0.50-xAl0.50O1.75(0.05≤x≤0.45) mixed oxides with different Ce/Zr ratio were prepared by co-precipitation method and characterized by means of X-ray diffraction(XRD),Brunauer-Emmet Teller method(BET),temperature-programmed reduction(H2-TPR) and oxygen pulsing technique.The XRD results showed that all samples kept the single CeO2 cubic fluorite structure after calcination at 600 and 1000 oC for 5 h.The results of BET revealed that CexZr0.50-xAl0.50O1.75 with Ce/Zr molar ratio 1/1 exhibited higher specific surface area(212 m2/g) and larger pore volume(0.40 ml/g).For all aged samples,CZA with Ce/Zr molar ratio 3/7 presented the highest specific surface area(104 m2/g) and pore volume(0.34 ml/g).The compounds could still keep prominent structural and textural stability with excellent redox properties even calcined at 1000 oC.     

XPS study of surface absorbed oxygen of ABO3 mixed oxides

Perovskite-type complex oxides ABO3 （A=Sr, La; B=Mn, Fe, Co） were prepared by citric acid method. The degradation of water-solubilized dyes was carried out using the mixed oxides as photocatalyst. The surface absorbed oxygen was analyzed using X-ray photoelectron spectroscopy （XPS）. The results indicated that there was a relationship between the photocatalytic activity and the content of the surface absorbed oxygen. The higher the content of the surface absorbed oxygen was, the better the performance of the photocatalyst.     

Oxygen Storage Capacity and Adsorptive Property of Praseodymium Oxides

Ceriumoxideisusedwidelyinthree waycatalystduetoitsoxygenstoragecapabilitywhichenablesthecatalysttooperatemoreefficientlybymakingitlesssensitivetothevariationofoxygenconcentrationinex haustgasstream[1～ 3] .TheoxygenstoragecapabilityofceriastemsfromthevalencechangebetweenCe3+andCe4 +[1,2 ] .Thereareafewotherelementswithvariableoxidationstatewithinthewholeseriesofrareearth .Praseodymiumisoneoftheelementswhichcanformaspectrumofoxygen deficientornonstoi chiometricPrOx.Ontheotherhand ,theproperti…     

Effect of refining slag containing Ce_2O_3 on steel cleanliness

The effect of pre-melting refining slag containing different contents of Ce2O3 on the absorption and modification of Al2O3 inclusion in an Al-killed steel was investigated through the slag/steel reaction experiment at 1600 oC.It was found that the replacement of 10 wt.% Al2O3 with Ce2O3 for 50 wt.%CaO-33 wt.%Al2O3-7 wt.%MgO-10 wt.%SiO2 refining slag promoted the slag absorption ability of alumina inclusion,which made the total oxygen content determined by infrared absorption method decrease from 100 to 25 ppm in 15 min.The Mg-Al-Ce-O type inclusion was also detected in the as-solidified samples by scanning electron microscopy(SEM).Thermodynamic analysis indicated that the Ce2O3.Al2O3 type inclusions would be formed with the cerium content in the range of 6.9 ppb to 3.6 ppm when the content of aluminum was 0.01 wt.%.     

Preparation of Well Dispersed and Ultra-Fine Ce （Zr）O2 Mixed Oxide by Mechanochemical Processing

Ultra-fine CeO2-ZrO2 mixed oxide was successfully synthesized by wet-solid phase mechanochemical processing, Ce2(CO3)3·8H2O, ZrOCl2·xH2O and ammonia were used as reactants. It is found that the crystalline Ce2(CO3)3·8H2O and ZrOCl2·xH2O are changed to amorphous cerium and zirconium hydroxide precursor after milling with ammonia, and Ce0.15Zr0.85O2 mixed oxide with pure tetragonal phase structure and medium particle size(D50)less than 1μm is formed by calcining precursor over 673 K. The XRD patterns indicate that the crystal unite size increases with rising calcining temperature due to crystal growth. However, the particle size and BET surface area of the Ce(Zr)O2 mixed oxide decreases with rising calcining temperature, which may be attributed to the contract of particles and the vanish of holes inside grains.     

Quaternary Oxide of Cerium, Terbium, Praseodymium and Zirconium for Three-Way Catalysts

Inthelastdecadethethree waycatalystshave beenremarkablyimproved.Oxygenstoragecapacity(OSC)ofthecatalystwasdeterminedbyTPR.The measuredvalueisactuallyapartoftheoxygentransfer capacity(OTC)offluorite typeoxidescontainingCe,and orPr,and orTb[1,2].Theseoxides,Ce1-x-y PrxTbyO2-δ(0≤x≤1,0≤y≤1,0≤δ≤0.5)can releasetheirlatticeoxygenwhenthetemperatureisin creasedunderdifferentoxygenpartialpressureinclud inghydrogenflow,buttheywillabsorboxygenfromits vicinityenvironmentwhenthetemperatureisde…