Influence of modifying additives on the catalytic activity and stability of Au/Fe2O3–MO x catalysts for the WGS reaction

The activity and stability of Au/Fe₂O₃–MO_x catalysts (M = Zr, Mg, Ca, Ni, La, Cu, Zn, Al, Ba, Cr, Co, Ce, Mo, Bi, Ti, Mn) in water-gas shift reaction were investigated extensively. The WGS activity and stability of Au/Fe₂O₃ is improved significantly upon addition of ZrO₂ and to a lesser extend MgO, CaO, NiO, La₂O₃, Cr₂O₃, CuO. In contrast, Bi, Ti and Mn oxides seriously decrease the catalytic activity while additions of Zn, Al, Ba, Co, Ce and Mo oxides do not influence evidently the catalytic activity and its stability. Based on the characterization using the methods of BET-surface area and pore structure XRF, XRD, and H₂–TPR for some of as-prepared and spent samples, it could be concluded that the catalytic activity of gold catalysts supported on composite oxide of Fe₂O₃–MO_x depends not only on the dispersion of the gold particles but also on the reduction property of composite oxide supports, regardless of the fluctuation of gold loading and some change of specific surface area and pore structure due to introduction of the modifying metal oxides. The improvement of catalytic stability may be attributed to the comparative stabilization of high dispersion of gold particles and uneasily sintering of Fe₃O₄ crystallites during the catalytic operation. However, the chemical (electronic) effects exerted by the modifying addition of metal oxides on the catalytic performance of gold catalyst may not be ruled out.     

SHS of metal-oxide systems in a DC magnetic field: Part 1. TRXRD and thermal imaging studies of the Fe-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The effect of a 0.2 T external magnetic field on the heterogeneous combustion of a mixture of iron metal and oxide (Fe₂O₃) system with solid oxidizer (NaClO₄) was studied. Time-resolved X-ray diffraction (TRXRD) was used to study the kinetics of intermediate product formation and thermal imaging experiments to measure the reaction temperature and velocity. Metastable fcc iron phase formation was discovered as an intermediate predominantly in applied field reactions.     

Spark plasma assisted carbothermal reduction-nitridation synthesis of (Ti,W, Mo)(C,N)-(Ni,Co) powders

Ultrafine (Ti, W, Mo)(C, N)-(Ni, Co) cermet powders were rapidly synthesized from various metal oxides, mainly anatase-TiO₂, by spark plasma assisted carbothermal reduction-nitridation (SPCRN) at low temperature. The phase evolution of the SPCRN reaction was investigated using X-ray diffraction (XRD) and the microstructure of the product powders was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). NiO, Co₃O₄ and MoO₃ were converted to Ni, Co and Mo₂C by CR reaction at temperatures below 900 °C. WO₃ was successively transformed from W₂C to WC by CR reaction up to 1100 °C. Finally, at up to 1350 °C, (Ti, W, Mo)(C, N) formed into the sequence of TiO₂, Ti₄O₇, Ti₃O₅, Ti(O, N), Ti(C, N), (Ti, W)(C, N) and (Ti, W, Mo)(C, N). The crystal structure of (Ti, W, Mo)(C, N)-(Ni, Co) cermet powders was analyzed by the Rietveld method and transmission electron microscopy (TEM). The findings demonstrated that the pure (Ti, W, Mo)(C, N)-(Ni, Co) cermet powders with grain size of below 0.5 µm were synthesized from metal oxides by SPCRN reaction at 1400 °C for 10 min.     

Formation and properties of high entropy oxides in Co-Cr-Fe-Mg-Mn-Ni-O system: Novel (Cr,Fe,Mg,Mn,Ni)3O4 and (Co,Cr,Fe,Mg,Mn)3O4 high entropy spinels

Possibility of formation of quinary and senary equimolar high entropy oxides from the Co-Cr-Fe-Mg-Mn-Ni-O system is presented. Different proposed compositions are synthesized using the solid-state reaction route at high temperatures (900−1100 °C) and quenched to room temperature. Phase composition of the samples is studied, showing tendency toward formation of two main phases: rock salt-structured Fm-3 m and spinel-structured Fd-3 m. It is documented that the annealing temperature has a profound effect on stability of both structures, and at 1100 °C usually the highest content of Fm-3 m phase is usually observed. Three different oxides, namely, (Co,Cr,Fe,Mn,Ni)₃O₄, (Co,Cr,Fe,Mg,Mn)₃O₄ and (Cr,Fe,Mg,Mn,Ni)₃O₄ are obtained as single-phase materials, which structure can be described as the high entropy Fd-3 m spinel one. The latter two compounds have not been previously reported in the literature. Activated character of the electrical conductivity dependence on temperature is observed, with relatively high total conductivity at high temperatures and corresponding high absolute values of Seebeck coefficient.     

On the development of metallic inert anode for molten CaCl2–CaO System

Some fundamental aspects related to inert anode development in molten CaCl₂–CaO were investigated based on thermodynamic analysis, electrochemistry of metals and solubility of oxide measurements. The Gibbs free energy change of several key anodic reactions including electro-stripping of metals, electro-formation of metallic oxides, electro-dissolution of metallic oxides as well as oxygen and chlorine evolution was calculated and documented, for the first time, as a reference to develop metallic inert anode in chloride based melts. The anodic behaviors of typical metals (Ni, Fe, Co, Mo, Cu, Ag, and Pt) in the melt were investigated. The results confirmed the thermodynamic stability order of metals in the melts and revealed that surface oxide formation can increase the stability of the electrodes in CaO containing melt. Furthermore, solubility of several oxides (NiO, Fe₂O₃, Cr₂O₃, Co₃O₄, NiFe₂O₄) in pure CaCl₂ or CaCl₂–CaO melts was measured to evaluate the stability of oxide coating or a cermet inert anode in the melt. It was found that the solubility of NiO decreased with increasing CaO concentration, while that of Fe₂O₃ increased. Ni coated with NiO film had much higher stability during anodic polarization.     

Preparation and formation mechanism of Cr-free spinel-structured high entropy oxide (MnFeCoNiCu)3O4

In this work, two Cr-free high entropy oxides (HEOs), an equimolar (MnFeCoNiCu)₃O₄ and a non-equimolar (Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄ have been synthesized by a solid-state reaction method. The reaction sequence and electrical conductivity were also studied for these two HEOs. It is demonstrated that a rock-salt phase containing a solid solution of NiO and CuO appears in the synthesizing process of (MnFeCoNiCu)₃O₄, which is ascribed to the incomplete solubilization of rock-salt phase in the spinel phase. For (Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄, a single spinel phase (Fd-3m) is obtained at 750 °C, which is much lower than that of the (MnFeCoNiCu)₃O₄ sample. Furthermore, Mn, Fe, Co, Ni elements exist in the chemical states of +2 and + 3, and Cu exists in Cu²⁺ state. The electrical conductivity of (Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄ is approximately 15.77 S cm^-1 at 800 °C, which is nearly three times higher than that of the (MnFeCoNiCu)₃O₄ sample.     

Effects of O2 on aqueous SO2 leaching of Co,Cu and Ni from discard smelter slag

In the leaching of non‐ferrous smelter slag with a dissolved gas mixture of SO₂ and O₂, the behaviour of Co, Cu, Ni, Zn and Fe was studied in a 1‐L batch reactor. The parameters investigated include P_SO2, P_O2, temperature, particle size and pH. Co, Zn and Fe behaved similarly while Ni and Cu displayed distinguishable characters. The addition of O₂ prevented the precipitation of Cu after dissolution, and increased acidity of the leaching solution. The increase in acid strength resulted in an increase in the extraction of Co, Zn and Fe. The effect of acidity on Cu and Ni extraction was however much weaker. The combination of SO₂ and O₂ was found to be a more effective oxidant of Fe(II) to Fe(III) than O₂ alone. Simultaneous extraction of valuable metals and removal of Fe could be achieved by leaching at pH of 3 to 4. Maximum selectivities obtained for Co, Ni and Cu over Fe were 300, 2000 and 4000, respectively.     

High-entropy oxide phases with magnetoplumbite structure

Sintering of oxides and carbonates at 1400 °C gives crystalline high-entropy single phase products with a BaFe₁₂O₁₉ (magnetoplumbite) structure containing 5 doping elements at high concentration level: Ba(Fe₆Ti_1·2Co_1·2In_1.2Ga_1.2Cr_1.2)O₁₉. The complete list of explored substitutions includes K, Ca, Sr, Pb, La, Bi, Al, Ga, In, Ti, V, Cr, Mn, Co, and Ni. Loading to the batch more than 5 dopants or introduction of NiO, or V₂O₅ initiates formation of second phases like spinels or vanadates. Bi₂O₃ and K₂O are too volatile at sintering temperature and were evaporated from the samples.Due to large ionic radius, the In³⁺ cation is likely to be incorporated not only on Fe³⁺ sites, but also on Ba²⁺ sites, that follow from resulting crystal composition. The smallest di-valent and tri-valent cations, Sr²⁺ and Al³⁺, are found to preferably concentrate together in the same magnetoplumbite phase crystals within one sample.According to elemental analysis of selected hexagonal crystals in the investigated 8 doped samples the most prospective compositions for obtaining high-entropy single phase with magnetoplumbite structure can be formulated as (Ca,Sr,Ba,Pb,La)Fe_x(Al,Ga,In,Ti,Cr,Mn,Co)_12-xO₁₉ where x = 1.5–6.     

In situ TEM investigations of reactions of Ni, Fe and Fe-Ni alloy particles and their oxides with amorphous carbon

Ni, Fe and Ni-Fe alloy particles were vapour deposited on thin films of amorphous carbon (a-C) inside a specially equipped transmission electron microscope, and reactions with the substrate were observed at elevated temperatures. The influence of oxidation of the particles was also investigated. In contrast to Ni, which was found in earlier work to graphitise the carbon at above 600 °C without bulk carbide being involved, pure Fe reacted with the a-C support at about 500 °C to Fe₃C, which graphitised the carbon similar to Ni, starting at about 600 °C. No carbide was formed from oxidised Fe particles. FeO decomposes above 500 °C, higher oxides (Fe₃O₄, Fe₂O₃) only above 750 °C. The remaining Fe particles graphitised the carbon support directly. Alloy particles with composition Ni80:Fe20 (permalloy) graphitised a-C in the same way as pure Ni, without any phase separation. Annealing of a mixed phase of finely dispersed Ni-Fe-oxide or deposition of Ni-Fe under oxygen at above 300 °C resulted in nucleation of three-dimensional crystallites of virtually pure Ni, which graphitised the carbon, while the remaining phase of small particles was converted to inactive Ni-ferrite, NiFe₂O₄.     

An attempt to produce NiFe2O4 powder from electrodeposited Fe–Ni alloy powders by subsequent recrystallization in air

The electrodeposition of the Fe–Ni powders from citrate-ammonium chloride containing electrolytes for different Ni/Fe ions concentration ratios at pH 4.0 was investigated by the polarization measurements. The morphology, chemical composition, and phase composition of the obtained powders were investigated using SEM, EDS, and XRD analysis. EDS analysis of as-deposited alloy powders confirmed anomalous co-deposition of Fe and Ni. A common characteristic for all as-deposited powder samples was the presence of cone-shaped cavities and nodules on the big agglomerates of the order of 200–400 μm. After annealing in air at 400, 600, and 700 °C for 3 h, all alloy powders oxidized forming NiO, NiFe₂O₄, and Fe₂O₃ phases in different proportions depending on the original powder composition. The NiFe₂O₄ phase was found to be dominant in the sample with the highest percentage of Fe after annealing at 600 °C.     

Influence of Ti and Fe doping on the structural and electrochemical performance of LiCo0.6Ni0.4O2 cathode materials for Li-ion batteries

The combination of lithium cobalt oxide (LCO) and lithium nickel oxide (LNO) property for Li-ion batteries (LIB) brings a very promising cathode material, LiCo_1?xNi_xO₂ with a high specific reversible capacity and good cycling behaviour. Nonetheless, high toxic Co content and an instability of Li⁺/Ni²⁺ interaction in LiCo_1?xNi_xO₂ crystal structure paved the way for some modification for the development of this potential material. In this research, the self-propagating combustion method is used to reduce 40% Co content of LCO by replacing it with 40% Ni content resulting in cathode material with the stoichiometry of LiCo_0.6Ni_0.4O₂ (LCN). To improve the stability of the LiCo_0.6Ni_0.4O₂ structure, 5% of Ti and Fe was substituted at the Co site of the LCN material. The effect of these different cation substitutions (Ti⁴⁺ and Fe³⁺) on the structural and electrochemical performance of layered LiCo_0.6Ni_0.4O₂ cathode materials was investigated. Rietveld refinement revealed that Fe doped material has the longest atomic distance Li–O in the structure that allow better Li⁺ diffusion during intercalation/deintercalation to give an excellent electrochemical performance (138 mAhg^?1). After 50th cycle, it is found that the discharge cycling for Ti and Fe substituted materials were improved by more than 5% compared to pristine material. Both Ti and Fe doped materials were also having less than 13% of capacity fading indicates that the substitution of some Co with Ti and Fe are stable and can retain their electrochemical properties.     

Removal of metal ions from electrochemical decontamination solution using organic acids

Applicability of the organic acids and cyclodextrin (CD) for the removal of Fe, Co and Ni from the spent electro-decontamination solution was investigated. Oxalic acid showed the highest removal efficiency: 90% for 0.89 M Fe and 95% for 0.0089 M Co and Ni, respectively. The metal–oxalate precipitates were characterized by differential scanning calorimetry/thermogravimetry analysis (DSC/TGA), Fourier transform infrared (FTIR) and X-ray fluorescence (XRF). After thermal decomposition at >300°C, the metal–oxalate precipitates were transformed into metal oxides (Fe₂O₃, FeO, CoO and NiO) and pure metals (Co and Ni). The results imply that organic acids have a high potential for the removal of heavy metals from electro-decontamination solutions.     

Mechanism of MxOy nanoparticles/CNTs for catalytic carbonization of polyethylene and application to flame retardancy

Three kinds of metal oxide nanoparticles (Fe₃O₄, Co₃O₄, and Ni₂O₃) are produced on carbon nanotubes (CNTs). The synergistic effects rendered by the CNTs and metal oxide nanoparticles on carbonization of polyethylene (PE) are studied and applications to flame retardancy of PE are investigated systematically. The CNT‐Ni₂O₃ delivers the best performance and the mechanism pertaining to the enhanced flame retardancy is proposed and discussed. It is found that under the same conditions, the carbonization rate can be a factor to influence the flame retardancy performance. Among Fe, Co, and Ni, Ni has the fastest carbonation rate, which leads to the best flame retardancy performance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45233.     

Flame synthesis of carbon nanotubes and few-layer graphene on metal-oxide spinel powders

Multi-walled and single-walled carbon nanotubes (CNTs) and few-layer graphene (FLG) are grown directly on spinel powders using flame synthesis. CNT and FLG growth occurs via the decomposition of flame-generated carbon precursors (e.g., CO, C₂H₂, and CH₄) over nanoparticles (i.e., Ni, Co, Fe, and Cu) reduced from the solid oxide. The growth of CNTs is investigated on NiAl₂O₄, CoAl₂O_4, and ZnFe₂O₄, using counterflow diffusion flame and multiple inverse-diffusion flames (m-IDFs), while the growth of FLG is investigated on CuFe₂O₄ using m-IDFs. As shown by analytical electron microscopy techniques, Raman spectroscopy, and X-ray diffraction, substrate temperature and spinel composition play critical roles in the growth of both CNTs and FLG.     

Nickel Oxide Based Supported Catalysts for the In-situ Reactions of Methanation and Desulfurization in the Removal of Sour Gases from Simulated Natural Gas

Supported nickel oxide based catalysts were prepared by wetness impregnation method for the in-situ reactions of H₂S desulfurization and CO₂ methanation from ambient temperature up to 300 °C. Fe/Co/Ni (10:30:60)–Al₂O₃ and Pr/Co/Ni (5:35:60)–Al₂O₃ catalysts were revealed as the most potential catalysts, which yielded 2.9% and 6.1% of CH₄ at reaction temperature of 300 °C, respectively. From XPS, Ni₂O₃ and Fe₃O₄ were suggested as the surface active components on the Fe/Co/Ni (10:30:60)–Al₂O₃ catalyst, while Ni₂O₃ and Co₃O₄ on the Pr/Co/Ni (5:35:60)–Al₂O₃ catalyst.     

Synthesis,optical, and magnetic properties of six-layered Aurivillius bismuth ferrititanate

This work reports on the preparation, structure, photochemical, and magnetic properties of six-layered Aurivillius bismuth ferrititanates, that is, Bi₇Ti₃Fe₃O₂₁, Bi₇(Ti₂Nb)Fe₃O_21+δ, and Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticles. The samples were prepared through the modified citrate complexation and precursor film process. The XRD Rietveld refinements were conducted to study the phase formations and crystal structure. The morphological and chemical component characteristics were investigated using SEM, TEM, and EDX analyses. Bi₇Ti₃Fe₃O₂₁, Bi₇(Ti₂Nb)Fe₃O_21+δ, and Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticles present an indirect allowed transitions with band energies of 2.04, 2.03, and 2.02 eV, respectively. The hybridized (O2p+Fet_2g+Bi6s) formed the valence band (VB) and electronic components of (Ti–3d+Fe–e_g) formed the conduction band (CB) of this six-layered Aurivillius bismuth ferrititanate. The three samples showed efficient photocatalytic degradation of Rhodamine B (RhB) dyes with the excitation wavelength λ > 420 nm. The optical absorption, photodegradation, and magnetic abilities were improved through microstructural modification on “B” site via partial substitution of Mg²⁺ and Nb⁵⁺ for Ti⁴⁺. The photocatalytic results were discussed based on the layer structure and multivalent Fe ions. Fe^3+/2+ in the perovskite slabs (Bi₅Fe₃Ti₃O₁₉)²⁻ could act as the catalytic mediators in the photocatalysis process. As a photocatalyst, Aurivillius Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticle is advantageous due to its photocatalytic and magnetically recoverable abilities.     

Chemical compatibility of proton conducting LaNbO4 electrolyte with potential oxide cathodes

The chemical and physical compatibility of the proton conducting electrolyte material LaNbO₄ with the potential partner materials LaMO₃ (MMn, Fe, Co) and La₂NiO₄ is investigated via the reaction of fine-grained powders and solid-state diffusion couples. Results show generally good chemical compatibility for LaNbO₄ with perovskite type compositions, particularly the LaFeO₃ and LaMnO₃ systems. In contrast, Ruddlesden–Popper type phases are predicted to be poor candidates for use with LaNbO₄. Investigation of the La₂O₃–NiO–Nb₂O₅ and La₂O₃–CoO–Nb₂O₅ phase diagrams finds two new perovskite-related materials of stoichiometry LaNb_1/3M_2/3O₃ (MNi, Co), and indicates coexistence of LaNbO₄ with the binary oxides NiO and CoO. Additionally, reduction of a LaNbO₄–NiO composite confirms coexistence of LaNbO₄ with Ni, and so it is concluded that doped-LaMO₃|LaNbO₄|Ni-LaNbO₄ type electrochemical cells may be manufactured via a direct co-firing route without the formation of secondary phases at inter-phase boundaries.     

X‐ray absorption spectroscopy study of synthetic cobalt blue pigments similar to Kangxi blue and white porcelain

A series of cobalt blue pigments, which were synthesized based on the chemical compositions of the blue pigments in Kangxi blue and white porcelain, were investigated by Co, Mn, and Fe K‐edge and L_2,3‐edge X‐ray absorption spectroscopy to determine the oxidation states and species of the elements and to discern their impact on the blue color. The results reveal that Co is bivalent and mainly located at tetrahedral sites, which is the main parameter controlling the blue color. Mn is mainly present as Mn²⁺, or Co_xZn_1‐xAl₂O₄ and Fe is mainly present as Fe³⁺. In particular, Fe³⁺ substitutes the Al in CoAl₂O₄ and occupies octahedral sites with a high Mn content. All the synthetic cobalt blue pigments can form a solid solution with various end‐members or an intermediate solution spinel. The spectroscopic determination of the oxidation states and speciation of Co, Mn, and Fe furthers understanding of the coloration of blue pigments in blue and white porcelain.     

Electrophoretic co-deposition of Mn1.5Co1.5O4, Fe2O3 and CuO: Unravelling the effect of simultaneous addition of Cu and Fe on the microstructural,thermo-mechanical and corrosion properties of in-situ modified spinel coatings for solid oxide cell interconnects

A systematic microstructural, thermo-mechanical and electrical characterization of simultaneous Fe–Cu doped Mn–Co spinel coatings processed by electrophoretic co-deposition on Crofer 22 APU is here reported and discussed. An innovative approach for the simultaneous electrophoretic deposition of three spinel precursors is designed, conceived and optimised, with the aim of outlining time- and energy-saving spinel modification routes. The effect of different levels of Cu and Fe co-doping is observed on the stability of the modified Mn–Co spinel phase, the coefficient of thermal expansion (CTE), the corrosion resistance and on the densification behaviour of the obtained coatings. Cu determines an increase of CTE, while Fe has the opposite behavior. The synergic effect of the simultaneous Fe and Cu co-doping results in an improved densification and the stabilization of the MnCo₂O₄ cubic phase. The most interesting results in terms of corrosion resistance are obtained for the Mn_1.28Co_1.28Fe_0.15Cu_0.29O₄ spinel.     

Investigation of the catalytic activity of LaBO3 (B = Ni, Co, Fe or Mn) prepared by the microwave-assisted method for hydrogen evolution in acidic medium

LaBO₃ (B = Ni, Co, Fe and Mn) were prepared by microwave-assisted citrate method. The electrocatalytic activity toward hydrogen evolution reaction (HER) was investigated. XRD characterization showed that pure perovskite crystals were indeed formed. SEM images showed that changing the type of the B-site metal ion affected the morphology of the prepared perovskites. The influence of the type of B-cation on the catalytic activity toward hydrogen evolution was studied and the order of the electrocatalytic activity was LaFeO₃ > LaCoO₃ > LaNiO₃ > LaMnO₃, that was related to the calculated values of the activation energy 51.61, 45.37, 41.15 and 55.05 kJ mol⁻¹ for LaBO₃ (B = Ni, Co, Fe and Mn), respectively. The reaction order and the reaction mechanism for all the prepared perovskites were identified. In addition, the effect of the partial substitution at the B-site in LaNi_{1 − x}Co_xO₃ was also studied. It was found that among ternary perovskites, the catalytic activity of LaNiO₃ decreased by increasing the fraction of doped-Co.