Preparation of CeO2-ZrO2 mixed oxide with high surface area and high thermal stability

Ceria-zirconia solid particles have been recognized as a key material of the automotive exhaust catalysts since they can release and uptake oxygen owing to the rapid reversible oxidation states of cerium between Ce³⁺ and Ce⁴⁺. Several methods have recently been described to prepare the CeO₂-ZrO₂ solid particles used in the catalysts. In this paper, a new coprecipitation method is used to prepare the CeO₂-ZrO₂ solid particles. The Ce-Zr alcogel is dried and calcined in flowing N₂ not in flowing air under atmospheric pressure. The results show that the ceria-zirconia sample calcined at 650 °C has high surface area over 90 m²g⁻¹, which drops to 40 m²g⁻¹ following treatment at 900°C.     

制备条件对铜铬催化剂酸性质的影响

为了研究制备条件对铜铬催化剂酸性质的影响,建立了铜铬催化剂酸性质的检测方法,并采用共沉淀方法研制了不同制备条件的铜铬催化剂,通过SEM 对晶貌的分析得出,催化剂的酸性质与催化剂晶貌有关。通过Thanable假说和Seiyama假说建立了铜铬二元氧化物模型,分析得出,处于无定形状态的铜铬催化剂,其酸中心主要由一元氧化物氧化铜和氧化铬本身带来的,而处于结晶态的铜铬催化剂,其酸中心除了由一元氧化物本身带来的之外,还由于氧化铜和氧化铬混合的不均匀引起的B酸中心的增加。从而表明,铜铬二元氧化物的晶粒越小,晶粒越均匀,催化剂的酸性质越弱,B酸比例越小,相反则越强。     

Ni-Ce-ZrO2催化剂在二氧化碳甲烷重整制合成气中的研究

采用XRD、氢化学吸附作用、TPR和XPS等技术研究了共沉淀方法制备N i-Ce-ZrO2催化剂对二氧化碳甲烷重整的性能。N i的载入量和CeO2与ZrO2的比率系统地被改变将使N i-Ce-ZrO2催化剂最优化。发现15w t%N i与Ce0.8Zr0.2O2共沉淀有体相的状态,在800℃用CH4制合成气超过97%,并且经过100h的反应,活性被维持没有重大的损失。     

Co3O4负载纳米Au催化剂的制备

利用共沉淀法（CP）和沉积-沉淀法（DP）制备了Au／C0304催化剂,考察了制备条件及不同制备方法对金粒子大小的影响。结果表明,负载量为1wt％Au／Co3O4金粒子最小,分散度最好,而焙烧温度太高不利于金粒子的分散,另外,DP法制备的金粒子比CP法制备的要小。     

Synthesis based structural and optical behavior of anatase TiO2 nanoparticles

The effect of synthesis method on optical and photoconducting properties of titanium dioxide (TiO₂) nanoparticles has been investigated. Sol–gel and co-precipitation methods have been employed to prepare pure anatase phased TiO₂ nanoparticles calcinated at different temperatures below 500 °C. The optimized value of average crystallite size is within the range of 19−21 nm for a common calcination temperature of 400 °C for both the methods. The redshift in optical band gap of 0.9 eV has been observed for the sample synthesized by co-precipitation method with respect to the sol–gel method. The photoluminescence spectrum exhibits broad visible emission in both routes of synthesis while photoconductivity shows fast growth and decay of photocurrent in TiO₂ prepared by co-precipitation method as compared to TiO₂ prepared by the sol–gel method under visible illumination. Crystal structure based Rietveld refinement of X-ray diffraction data, scanning electron microscopy as well as photoluminescence and photoconductivity measurements were performed to characterize nanocrystalline anatase TiO₂.     

Cr-doped WO3 nanosheets: Structural,optical and formaldehyde sensing properties

Co-precipitated undoped and Cr-doped WO₃ nanosheets have been investigated by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) in order to study the influence of Cr doping on their structural and morphological properties. XRD analyses confirm the monoclinic structure of nanocrystalline WO₃, whereas the FESEM and TEM images exhibit nanosheet-like morphology of the as-synthesized WO₃ materials. Among all the samples examined, the 1.5 at% Cr-doped WO₃ nanosheets exhibit the selective maximum response (~82%) to formaldehyde over methanol, ethanol, propan-2-ol and acetone at the operating temperature of 200 °C for 50 ppm concentration in air. The sensing mechanism has been explained based on chemisorption of oxygen on the WO₃ surface and the subsequent reaction between the adsorbed oxygen species and the formaldehyde molecules.     

Rietveld structure refinement,cations distribution and magnetic features of CoFe2O4 nanoparticles synthesized by co-precipitation,hydrothermal, and combustion methods

Cobalt ferrite nanoparticles were synthesized by chemical co-precipitation, hydrothermal and sol gel auto-combustion methods. X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometer (VSM) were used to investigate the structural characteristics and magnetic properties of cobalt ferrite nanocrystals. X-ray patterns revealed the production of a broad single cubic phase with the average crystallite size of 16, 18 and 178 nm for co-precipitation, hydrothermal and combustion methods, respectively. The FTIR measurements between 400 and 4000 cm⁻¹ confirmed the intrinsic cation vibrations of spinel structure. The FE-SEM micrographs of the synthesized samples indicated the presence of two distinct groups of grains exhibiting different sizes and, different shapes for hydrothermal route. The results of magnetic hysteresis at a room temperature showed that the magnetic properties depend on the particle size and shape of particles, whereas the role of particle size is more significant.     

Bivalent tin ion assisted reduction for preparing graphene/SnO2 composite with good cyclic performance and lithium storage capacity

Co-precipitation method of SnCl₂·2H₂O and graphene oxide (GO) solution was performed to fleetly prepare graphene/SnO₂ composite. The structure and composition of the nanocomposite were detected by means of XRD, SEM, TEM and FT-IR. The GO was reduced by bivalent tin ions to graphene nanosheet (GNS) via solution reaction and SnO₂ nano-crystals with size of 4–6 nm were homogeneously distributed on the matrix of GNS. It was found that the disorder degree of graphene in GNS/SnO₂ composite prepared by the bivalent tin ion assisted reduction method was much lower than that of GNS obtained via pyrolysis reduction. The possible mechanism for this phenomenon was discussed in detail. The N₂ adsorption tests showed an ink-bottle-like pore structure of GNS/SnO₂ and the SnO₂ nanoparticles were confined in the interlayer of GNS without agglomeration. These structural features were desirable and enabled GNS/SnO₂ an excellent anode material in lithium ion battery. The electrochemical tests showed that the composite could deliver a reversible capacity of 775.3 mAh/g and capacity retention of 98% after 50 cycles.     

Physical and photoelectrochemical characterizations of hematite α-Fe2O3: Application to photocatalytic oxygen evolution

The physical properties and photoelectrochemical characterization of α-Fe₂O₃, synthesized by co-precipitation, have been investigated in regard to solar energy conversion. The optical gap is found to be 1.94 eV and the transition is indirectly allowed. The chemical analysis reveals an oxygen deficiency and the oxide exhibits n-type conductivity, confirmed by a negative thermopower. The plot log σ vs 1/T shows linearity in the range (400-670 K) with the donor levels at 0.14 eV below the conduction band and a break at ∼590 K, attributed to the ionization of the donors. The conduction occurs by small polaron hopping through mixed valences Fe^2+/3+ with an electron mobility μ_400 K of 10⁻³ V cm² s⁻¹. α-Fe₂O₃ exhibits long term chemical stability in neutral solution and has been characterized photoelectrochemically to assess its activity as bias-free O₂-photoanode. The flat band potential V_fb (−0.45V_SCE) and the electron density N_D (1.63 × 10¹⁸ cm⁻³) were determined, respectively, by extrapolating the linear part to C⁻² = 0 and the slope of the Mott Schottky plot. At pH 6.5, the valence band (+1.35V_SCE) is suitably positioned with respect to the O₂/H₂O level (+0.62 V) and α-Fe₂O₃ has been evaluated for the chemical energy storage through the photocatalytic reaction: (, ΔG = 213.36 kJ mol⁻¹). The best photoactivity occurs in solution (0.025 M, pH 8) with an oxygen rate evolution of 7.8 cm³ (g catalyst)⁻¹ h⁻¹.     

Conventional and field-assisted sintering of nanosized Gd-doped ceria synthesized by co-precipitation

Gadolinium-doped ceria is an attractive electrolyte for potential application in SOFCs operating at intermediate temperature; for such use, the fundamental compositions typically contain 10–20 mol% Gd₂O₃. In this work, we produced nanosized 10 mol% gadolinium-doped ceria powder by co-precipitation, starting from Ce and Gd nitrate solutions and using ammonia solution as precipitating agent. The co-precipitate was characterized by DTA-TG, TEM, XRD and nitrogen adsorption analyses. We studied the behavior of the nanopowder under both conventional and Flash sintering. Very different behavior was seen: the conventional sintering cycle produced a poorly densified material, while Flash sintering allowed production of a perfectly densified material, with uniform sub-micrometric grain size.