Alumina and Alumina–Baria Supported Cobalt Catalysts for DeNO x : Influence of the Support and Cobalt Content on the Catalytic Performance

Co/Al₂O₃ and Co/Al₂O₃–BaO catalysts with low cobalt loading (0.1, 0.3 and 1 wt%) for the selective catalytic reduction (SCR) of NO _x by C₃H₆ were prepared. The distribution of cobalt species was investigated by UV–vis diffuse reflectance spectroscopy and by H₂-TPR in order to identify the active cobalt species in hydrocarbons (HC)-selective catalytic reduction (SCR). It was found that the nature of cobalt species strongly depends on the cobalt loading as well as on the properties of the support. The barium addition to the alumina slows down solid state diffusion processes, improving the thermal stability of the support and preventing diffusion of cobalt into the bulk. Highly dispersed surface Co²⁺ species over alumina were identified as active sites in the NO-SCR process. Accordingly, a high concentration of surface Co²⁺ sites in Co 1 wt%/Al₂O₃ improves the catalytic performance in NO-SCR, the long term stability as well as the water tolerance. On the contrary, the formation of Co₃O₄ particles in Co 1 wt%/Al₂O₃–BaO promotes the propylene oxidation by oxygen, decreasing the activity and selectivity of the catalyst in NO reduction.     

Effect of Composition on Electrical and Optical Properties of Thin Films of Amorphous GaxSe100?x Nanorods

We report the electrical and optical studies of thin films of a-Ga _x Se_100−x nanorods (x = 3, 6, 9 and 12). Thin films of a-Ga _x Se_100−x nanorods have been synthesized thermal evaporation technique. DC electrical conductivity of deposited thin films of a-Ga _x Se_100−x nanorods is measured as a function of temperature range from 298 to 383 K. An exponential increase in the dc conductivity is observed with the increase in temperature, suggesting thereby a semiconducting behavior. The estimated value of activation energy decreases on incorporation of dopant (Ga) content in the Se system. The calculated value of pre-exponential factor (σ₀) is of the order of 10¹ Ω⁻¹ cm⁻¹, which suggests that the conduction takes place in the band tails of localized states. It is suggested that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. On the basis of the optical absorption measurements, an indirect optical band gap is observed in this system, and the value of optical band gap decreases on increasing Ga concentration.     

Sol–gel synthesis of La0.6Sr0.4CoO3−x and Sm0.5Sr0.5CoO3−x cathode nanopowders for solid oxide fuel cells

Nano-powders of La_0.6Sr_0.4CoO_3?x (LSC) and Sm_0.5Sr_0.5CoO_3?x (SSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) with La(Sr)Ga(Mg)O_3?x (LSGM) as the electrolyte, were synthesized by low-temperature sol–gel method using metal nitrates and citric acid. Thermal decomposition of the citrate gels was followed by simultaneous DSC/TGA methods. Development of phases in the gels, on heat treatments at various temperatures, was monitored by X-ray diffraction. Sol–gel powders calcined at 550–1000 °C consisted of a number of phases. Single perovskite phase La_0.6Sr_0.4CoO_3?x or Sm_0.5Sr_0.5CoO_3?x powders were obtained at 1200 °C and 1300 °C, respectively. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy. The average crystallite size of the powders was ～15 nm after 700 °C calcinations and slowly increased to 70–100 nm after heat treatments at 1300–1400 °C.     

Influence of the Reduction of Graphene Oxide with Hydroiodic Acid on the Structure and Photoactivity of CdS–rGO Hybrids

The temperature used in the chemical reduction of graphene oxide (GO) with hydroiodic acid has a significant influence on the removal of surface oxygenated functional groups, on the residual iodine species and on the rupture, stacking and graphitization of the graphene sheets in the reduced graphene oxides. The modification in the characteristics of the reduced graphene oxides induces changes in the surface area, the exposition of reduced graphene oxide entities and in the concentration of small CdS nanocrystals with strong confinement effect on the CdS-reduced graphene oxide hybrids. The hybridization of the reduced graphene oxide with CdS modifies in different way their photocatalytic behavior for hydrogen production from aqueous solutions of Na₂S and Na₂SO₃ under simulated sunlight irradiation. Only the hybrid formed between the CdS and the reduced graphene oxide treated at higher temperature showed improved hydrogen production rate respect to the bare CdS reference associated with the better conductivity of the reduced graphene oxide and with the increase in the concentration of small CdS nanocrystals sith strong confinement effect observed in the hybrid.     

Passage of the Roughening Temperature Influence on the Crystalline Structure and Morphology of a Nano Metal–Organic Material

The reactions between 2-mercaptobenzothiazole (HMBT) and AgNO₃ in ultrasonic bath with low and high concentrations of initial reagents provided yellow precipitates of [Ag₆(MBT)₆] (1), which can be considered as 1L and 1H, respectively. Powder XRD patterns of them showed that they have crystalline structure and SEM images of 1L and 1H approved that microblocks and nanosheets of 1 were formed, respectively. Similar studies after mechanical and thermo-mechanical treatment of 1L and 1H indicated that compound 1 with nanoparticle and agglomerated nanoparticle morphologies were obtained. As a result of heat and energy created from the friction process and also external heat source a roughening transition was occurred and the crystalline samples of 1L and 1H, loses their facets. This can be understood by considering compound 1 surface above the roughening temperature as a liquid surface.     

Highly Active La1−x K x CoO3 Perovskite-type Complex Oxide Catalysts for the Simultaneous Removal of Diesel Soot and Nitrogen Oxides Under Loose Contact Conditions

The nanometric La_1?x K _x CoO₃ (x = 0–0.30) perovskite-type oxides were prepared by a citric acid-ligated method. The catalysts were characterized by means of XRD, IR, BET, XPS and SEM. The catalytic activity for the simultaneous removal of soot and nitrogen oxides was evaluated by a technique of the temperature-programmed oxidation reaction. In the LaCoO₃ catalyst, the partial substitution of La³⁺ at A-site by alkali metal K⁺ enhanced the catalytic activity for the oxidation of soot particle and reduction of NO _x . The La_0.70K_0.30CoO₃ oxides are good candidate catalysts for the simultaneous removal of soot particle and NO _x . The combustion temperatures for soot particles over the La_0.70K_0.30CoO₃ catalyst are in the range from 289 to 461 °C, the selectivity of CO₂ is 98.4% and the conversion of NO to N₂ is 34.6% under loose contact conditions. The possible reasons that can lead to the activity enhancement for the K-substitution samples compared to the unsubstituted sample (LaCoO₃) were given. The particle size has a large effect on its catalytic performance for the simultaneous removal of diesel soot and nitrogen oxides.     

Influence of reactant type on the Sr incorporation grade and structural characteristics of Ba1−xSrxTiO3 (x=0−1) grown by sol–gel-hydrothermal synthesis

The influence of barium and strontium starting reactants used in different mole ratios, BaCl₂ and Ba(OH)₂, SrCl₂ and Sr(OH)₂, on the chemical and structural properties of Ba_1?xSr_xTiO₃ (x=0?1) (BST) nanoparticles prepared via sol–gel-hydrothermal synthesis in an oxygen atmosphere is discussed. The effect of the type of reactant on the relative amount of Sr incorporated in BST compound was also analysed. The synthesised BST nanoparticles showed differences in their structural and chemical characteristics, which were attributed to the presence of Cl^? or OH^? anions during the synthesis of the compound. The structure, morphology and oxidation state of the samples were studied by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy, respectively. In addition, theoretical calculations using cluster models were carried out to understand the possible phases formed of BST, the effect of the Sr incorporation and the possible presence of oxygen vacancies inside the BST structure.     

Dielectric and Magnetic properties of (1 − x)BiFeO3–xBa0.8Sr0.2TiO3 ceramics

The polycrystalline samples of (1 ? x)BiFeO₃–xBa_0.8Sr_0.2TiO₃ (x = 0, 0.1, 0.2, 0.25, 0.3, 0.4 and x = 1) were prepared by the conventional solid state reaction method. The effect of substitution in BiFeO₃ by Ba_0.8Sr_0.2TiO₃ on the structural, dielectric and magnetic properties was investigated. X-ray diffraction study showed that these compounds crystallized at room temperature in the rhombohedral distorted perovskite structure for x ≤ 0.3 and in cubic one for x = 0.4. As Ba_0.8Sr_0.2TiO₃ content increases, the dielectric permittivity increases. This work suggests also that the Ba_0.8Sr_0.2TiO₃ substitution can enhance the magnetic response at room temperature. A remanent magnetization M_r and a coercive magnetic field H_C of about 0.971 emu/g and 2.616 kOe, respectively were obtained in specimen with composition x = 0.1 at room temperature.     

Effect of A-Site Ionic Radius on the Structure and Microwave Dielectric Characteristics of Sr1+xSm1−xAl1−xTixO4 Ceramics

SrSmAlO₄ microwave dielectric ceramics were modified by Sr/Ti cosubstitution for Sm/Al. The effects of radius difference of A-site ions on the microwave dielectric characteristics were investigated together with the structure. Sr_1+xSm_1−xAl_1−xTi_xO₄ (x=0, 0.05, 0.10, and 0.15) ceramics were prepared by a solid-state reaction approach. X-ray diffraction studies revealed a single-phase K₂NiF₄-type solid solution with corresponding peaks shifting to lower 2θ as x increased. Minor inhomogeneous grain morphology for x=0.05 and a trace amount of second phases for x=0.10, 0.15 were detected by backscattered-electron microscopy and energy-dispersive X-ray analysis. With increasing Sr/Ti cosubstitution, the dielectric constant ɛ_r increased from 18.4 to 20.4, and the temperature coefficient of resonant frequency τ_f was adjusted from −1.8 to 7.4 ppm/°C almost linearly. However, the Q×f value decreased from 74,500 GHz at x=0–53,000 GHz at x=0.15. The internal stresses caused by the decreased tolerance factor and the large ionic radii difference between Sr²⁺ and Sm³⁺ should be the predominant reasons for such a decrease in the Q×f value. The high-resolution transmission electron microscopic results revealed an increase in the lattice distortion with increasing Sr/Ti cosubstitution, and subsequently supported the above conclusion upon the increased internal stresses.     

Experimental and theoretical study on enhanced electrical properties of nickel-substituted La0.5Sr0.5CoO3−δ ceramics

The effect of Ni substitution on the thermal behavior, crystal structure, densification, and electrical properties of La_0.5Sr_0.5Co_1–yNi_yO_3-δ (y = 0.00–0.08) (LSCN) ceramics was discussed based on experimental measurements and theoretical calculations to search for a ruthenium–free and lead–free conductive oxide for thick film resistors. Ceramics were synthesized by the solid–state reaction, and calculations were performed with first–principle density functional theory (DFT). Results showed that the replacement of Ni ion to Co ion could help decrease the densification temperature and enhance the densification level and improve the conductivity of LSCN. Theoretical calculations, including the crystal structure, bond population, total energy, and density of states (DOS), supported the experimental results well. The maximum conductivity of 3155 S/cm was achieved as y = 0.04 was sintered at 1200 °C, and the peak temperature coefficient of resistance (TCR) of 2405.7 ppm/°C occurred at y = 0.06.     

Aqueous Solution Preparation,Structure, and Magnetic Properties of Nano-Granular ZnxFe3?xO4 Ferrite Films

This paper reports a simple and novel process for preparing nano-granular Zn_xFe_3−xO₄ ferrite films (0 ≤ x ≤ 0.99) on Ag-coated glass substrates in DMAB-Fe(NO₃)₃-Zn(NO₃)₂ solutions. The deposition process may be applied in preparing other cations-doped spinel ferrite films. The Zn content x in the Zn _x Fe_3−x O₄ films depends linearly on the Zn²⁺ ion concentration ranging from 0.0 to 1.0 mM in the aqueous solutions. With x increasing from 0 to 0.99, the lattice constant increases from 0.8399 to 0.8464 nm; and the microstructure of the films changes from the non-uniform nano-granules to the fine and uniform nano-granules of 50–60 nm in size. The saturation magnetization of the films first increases from 75 emu/g to the maximum 108 emu/g with x increasing from 0 to 0.33 and then decreases monotonously to 5 emu/g with x increasing from 0.33 to 0.99. Meanwhile, the coercive force decreases monotonously from 116 to 13 Oe.     

Influence of deposition parameters on the dielectric properties of rf magnetron sputtered Ba(ZrxTi1−x)O3 thin films

Ba(Zr_xTi_1−x)O₃ (BZ_xT_1−x in short) thin films have been deposited on Pt/Ti/SiO₂/Si substrates by radio frequency magnetron sputtering and their dielectric properties have been characterized as a function of sputtering parameters. The BZ_xT_1−x thin films are amorphous when sputtered at rf power (R_p)=100 W and substrate temperature (S_T)=300 °C. The crystalline phase of the BZ_xT_1−x thin films appears when the substrate temperature increases from 300 to 400 and 500 °C, respectively, and the films have a high degree of (100) preferred orientation. The dielectric constant decreases with increasing measurement temperature, irrespective of the rf power and Zr content of the BZ_xT_1−x thin films. The BZ_0.3T_0.7 thin films have a low dielectric loss tangent irrespective of the sputtering parameters. The dielectric constant of the BZ_0.3T_0.7 thin film increases with increasing Zr·(Zr+Ti)⁻¹ ratio and deposition temperature but decreases with increasing working pressure. Besides, the dielectric constant suddenly increases from 244.0 to 284.1 when the rf power increases from 100 to 130 W, then it decreases from 284.1 to 270.0 when the rf power increases from 130 to 160 W. The dielectric constant also suddenly increases from 164.1 to 281.5 when the sputtering gas contains O₂ from 0 to 10%, but its variation is insignificant when the sputtering gas contains O₂ from 10 to 20%.     

Role of gallium ion on the conducting properties of La0.7(Ba,Sr)0.3Mn1−xGaxO3 (x=0.0, 0.1 and 0.2) perovskite

The transport properties of Ga-doped La_0.7(Ba, Sr)_0.3Mn_1−xGa_xO₃ (x=0.0, 0.1 and 0.2) perovskite materials were investigated by admittance spectroscopy over a wide range of temperatures and frequencies. The electronic conduction was found to be dominated by thermally activated hopping and to depend strongly on Ga-content. Results have shown samples with x=0.0 and 0.1 exhibit a metallic behavior at low temperature and a semiconducting one at high temperature. The temperature (T_MI) of the metal–insulator transition was found to be about 180 and 120 K for samples with x=0.0 and 0.1, respectively. Ga doping leads to a depletion in the number of hopping electrons, which suppresses metallicity and pushes the system in semiconductor side. Besides, the activation energy (E_a) deduced from the variation of conductance as a function of temperature, was found to increase from 89 to 165 meV when x increased from 0.0 to 0.2. This increase can be explained by the decrease of charge carriers with increasing Ga-content.     

Influence of sintering temperature on energy storage properties of BaTiO3–(Sr1−1.5xBix) TiO3 ceramics

The effect of sintering temperature on microstructure, dielectric properties and energy storage properties of BaTiO₃–(Sr_1?1.5xBi_x)TiO₃ (x = 0.09) (BT–SBT) ceramics was investigated. The sintering temperature has pronounced influence on the grain size, shrinkage, and dielectric properties of the BT–SBT ceramics. With increasing sintering temperature, the dielectric constant increases largely. However, the increasing tendency of the dielectric breakdown strength (BDS) is less noticeable but become more evident with the consideration of Weibull modulus. For the BT-SBT ceramics, the unreleased energy density decreases and the electric field stability of the energy storage efficiency enhances with the increase of sintering temperature.     

Dielectric properties and diffuse phase transition behavior of CuO-doped lead-free Ba(ZrxTi1−x)O3 ceramics

CuO-doped lead-free Ba(Zr_0.2Ti_0.8)O₃ (BZT20) ceramics were prepared through a solid state processing technique, and the effects of CuO on microstructure, dielectric properties and diffuse phase transition behavior were investigated. The average grain sizes were increased by CuO doping. The temperature and frequency dependences of the dielectric constant revealed that CuO-doped BZT20 ceramics exhibited broad diffuse phase transition behavior. The dielectric constant increased with increasing CuO concentration. The value of T_m and degree of diffusion (γ) changed regularly in the studied compositional ranges. The BZT20 samples with 1.0 mol% CuO doping, sintered at 1310 °C, showed excellent dielectric property and lower diffusivity with ε_m=21,371 and γ=1.87. These results can be explained by the disordered distribution of Cu ions in the B sites and the weakened bonding force with oxygen ions in Cu substituted BZT20 structure.     

Influence of drying conditions and plasticizer-to-binder ratio on the water-based tape casting of La0.6Sr0.4Co0.2Fe0.8O3−δ

Tape casting is a flexible technique for manufacturing scalable ceramic sheets. This study fabricated La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF6428) tapes using water-based tape casting. A high molecular weight plasticizer, polyethylene glycol 4000, was chosen to balance flexibility and mechanical strength. Adjusting the plasticizer-to-binder ratio (R-value) and increasing relative humidity during drying led to crack-free and flawless green tapes of 330 µm. The uniform polymer matrix improved homogeneity and consistency as well. An applicable suspension formulation was developed for the water-based fabrication of LSCF tapes for continuous production.     

Preparation and properties of (Ba0·7Sr0·3)TiO3 powders and thin films using precursor solutions formed from alkoxide-hydroxide

(Ba_0·7Sr_0·3)TiO₃ powders and thin films were prepared using alkoxide-hydroxide route. Solutions of Ba and Sr hydroxides dissolved in methanol were reacted with Ti-isopropoxide under conditions of stirring at room temperature for 15 h, and then dried under reduced pressure at ≦40°C to prepare precursors of (Ba_0·7Sr_0·3)TiO₃ powder. The amorphous precursors were hydrolyzed at 100°C by introducing nitrogen gas containing water vapor. The hydrolyzed products were crystalline nanosize powders of (Ba_0·7Sr_0·3)TiO₃. As-hydrolyzed (Ba_0·7Sr_0·3)TiO₃ powders showed a good crystallinity with cubic phase. (Ba_0·7Sr_0·3)TiO₃ thin films were also successfully prepared at 650°C on Pt/Ti/SiO₂/Si substrates from precursor solutions obtained by the reaction of alkoxide with hydroxides. The (Ba_0·7Sr_0·3)TiO₃ thin films exhibited the microstructure with fine grains as small as 20–60 nm. The dielectric constants of the thin films ranged from 600 to 800 at room temperature.     

The Influence of Copper–Copper Interaction on the Structure and Applications of a Metal–Organic Framework Based on Cyanide and 3-Chloropyridine

The structure of the new metal–organic framework, [(CuCN)₂·(3-Clpy)], 1, was characterized by IR, UV–visible, TGA and X-ray single crystal analysis. The structure of 1 consists of CuCN building blocks, which are connected by CN group to form two different chains; one puckered chain with TP-3 geometry around Cu(1) and a linear Cu(2)(CN)₂ chain. The two kinds of chains are bonded by cuprophilic interactions creating a 3D-network. The network structure of 1 is further close-backed by π–π stacking and hydrogen bonds. The electronic absorption and emission spectra as well as the thermodynamic parameters from TGA of the MOF 1 are discussed. MOF 1 was used as an effective heterogeneous catalyst for the oxidative discoloration of methylene blue dye by dilute solution of hydrogen peroxide as the oxidant. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was used to determine the in vitro antitumor activity of MOF 1 on human breast cancer cell line, MCF7.     

Conductivity and electrochemical performance of (Ba0.5Sr0.5)0.8La0.2CoO3−δ cathode for intermediate-temperature solid oxide fuel cell

This study reports the successful preparation of a single-phase cubic (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ perovskite by the citrate–EDTA complexing method. Its crystal structure, thermogravimetry, coefficient of thermal expansion, electric conductivity, and electrochemical performance were investigated to determine its suitability as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Its coefficient of thermal expansion shows abnormal expansion at 300 °C, which is associated with the loss of lattice oxygen. The maximum conductivity of a (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ electrode is 689 S/cm at 300 °C. Above 300 °C, the electronic conductivity of (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ decreases due to the formation of oxygen vacancies. The charge-transfer resistance and gas phase diffusion resistance of a (Ba_0.5Sr_0.5)_0.8La_0.2CoO_3?δ–Ce_0.8Sm_0.2O_1.9 composite cathode are 0.045 Ω cm² and 0.28 Ω cm², respectively, at 750 °C.