•Mesoporous NiAl2O4/γ-Al2O3−xLa composites were prepared through one-pot method.•Ni nanoparticles were homogeneously distributed throughout γ-alumina framework.•Addition of La oxides mainly improved the medium-strength basicity.•Ni/γ-Al2O3−xLa showed high activity and long-term stability for DRM to syngas.•Addition of La oxides inhibited phase transformation of γ-Al2O3 and coke deposition.La-modified NiAl2O4/γ-Al2O3−La composites with mesoporous structures were prepared by one-pot template-free strategy and applied for dry reforming of methane (DRM) to syngas. The characterization results confirmed that these materials possessed high specific surface areas, large pore volumes and narrow pore size distributions. The reduced catalysts exhibited excellent catalytic properties as well as long-term stability for DRM reaction. Addition of La showed little influence on the catalyst structure and the mean sizes of metal Ni particles, but could enhance the medium-strength basicity and the accumulation of Ni2+ on the catalyst surface, resulting in the enhancement of intrinsic activity, the reduction of apparent activation energy, and the suppression of carbon deposition for DRM reaction. The catalyst containing 3 wt% La possessed the best catalytic performance. The characterization of spent catalysts also demonstrated that La could effectively prevent the phase transformation of γ-alumina in the DRM process.Download high-res image (295KB)Download full-size image

A series of xNiAl2O4/γ-Al2O3 composites with various Ni contents have been prepared via one-step partial hydrolysis of metal nitrate salts in the absence of surfactants and used for carbon dioxide reforming of methane. The characterization results demonstrated that the NiAl2O4/γ-Al2O3 materials possessed mesoporous structures of uniform pore sizes; and the Ni2+ ions were completely reacted with alumina to NiAl2O4 spinel in the matrices using N2 sorption, XRD, TEM, and XPS. The NiAl2O4/γ-Al2O3 materials exhibited excellent catalytic properties and superior long-term stability for carbon dioxide reforming of methane. The effects of Ni content on the intrinsic activities and the amounts of coke disposition of the xNiAl2O4/γ-Al2O3 catalysts were discussed in detail for the carbon dioxide reforming of methane. The results revealed that the Ni particle sizes did not affect the intrinsic activity of metallic Ni, but smaller Ni particles could reduce the rate of coke deposition.Mesoporous NiAl2O4/γ-Al2O3 composites prepared through one-step hydrolysis could produce metallic Ni nanoparticles homogeneously-dispersed in γ-Al2O3 frameworks upon reduction, which showed high activity and long-term stability for dry reforming of methane.Download high-res image (258KB)Download full-size image

Innovative CeO2-Y2O3-ZrO2 membrane has been successfully developed and used in the solid oxide membrane (SOM) electrolysis process for green metallic materials production. The x mol pct ceria/(8–x) mol pct yttria-costabilized zirconia (xCe(8–x)YSZ, x = 0, 1, 4, or 7) membranes have been fabricated and investigated as the membrane-based inert anodes to control the SOM electroreduction process in molten salt. The characteristics of these fabricated xCe(8–x)YSZ membranes including their corrosion resistances in molten salt and their degradation mechanisms have been systematically investigated and compared. The results show that the addition of ceria in the YSZ-based membrane can inhibit the depletion of yttrium during the SOM electrolysis, which thus makes the ceria-reinforced YSZ-based membranes possess enhanced corrosion resistances to molten salt. The ceria/yttria-costabilized zirconia membranes can also provide reasonable oxygen ion conductivity during electrolysis. Further investigation shows that the newly modified 4Ce4YSZ ceramic membrane has the potential to be used as novel inert SOM anode for the facile and sustainable production of metals/alloys/composites materials such as Si, Ti5Si3, TiC, and Ti5Si3/TiC from their metal oxides precursors in molten CaCl2.

Metal carbides (MCs) and composites including TiC, SiC, TaC, ZrC, NbC, Ti5Si3/TiC, and Nb/Nb5Si3 have been directly electrosynthesized from their stoichiometric metal oxides/carbon (MOs/C) mixture precursors by an innovative solid oxide membrane (SOM)-assisted electrochemical process. MOs/C mixture powders including TiO2/C, SiO2/C, Ta2O5/C, ZrO2/C, Nb2O5/C, TiO2/SiO2/C, Nb2O5/SiO2 were pressed to form porous pellets and then served as cathode precursors. A SOM-based anode, made from yttria-stabilized zirconia (YSZ)-based membrane, was used to control the electroreduction process. The SOM electrochemical process was performed at 1273 K (1000 °C) and 3.5 to 4.0 V in molten CaCl2. The oxygen component contained in the MOs/C precursors was gradually removed during electroreduction process, and thus, MOs/C can be directly converted into MCs and composites at the cathode. The reaction mechanism of the electroreduction process and the characteristics of the obtained MCs and composites products were systematically investigated. The results show that the electrosynthesis process typically involves compounding, electroreduction, dissolution-electrodeposition, and in situ carbonization processes. The products can be predesigned and controlled to form micro/nanostructured MCs and composites. Multicomponent multilayer composites (MMCs) have also been tried to electrosynthesize in this work. It is suggested that the SOM-assisted electroreduction process has great potential to be used for the facile and green synthesis of various MCs and composites.

Cu–Zn alloy films have been electrodeposited directly from their oxide precursors in choline chloride (ChCl)/urea-based deep eutectic solvent (DES). The reaction mechanism and the influence of the cathodic potential on the characteristics of the Cu–Zn alloy films are studied. Cyclic voltammetry and energy dispersive spectroscopy analyses reveal that the reduction of Cu(II) species relatively more preferentially occurs in comparison with the reduction of Zn(II) species, and Cu–Zn codeposition process can be controlled in the DES. Chronoamperometric investigation further confirms that the electrodeposition of Cu–Zn alloy on a Fe electrode follows the three-dimensional instantaneous nucleation-growth process. The micro/nanostructured Cu–Zn alloy films with different phase compositions can be facilely produced by controlling the cathodic potential. The obtained Cu–Zn alloy films typically exhibit enhanced corrosion resistances in 3 wt% NaCl aqueous solution. It is suggested that Cu–Zn alloy films can be sustainably electrodeposited from their abundant and inexpensive oxide precursors in DES.Micro/nanostructured Cu−Zn alloy films have been electrodeposited directly from CuO and ZnO precursors in deep eutectic solvent (DES), the electrochemical reaction mechanism and the nucleation-growth process of Cu−Zn alloy in the DES are investigated.

In this work, CO2-tolerant Ce0.8Gd0.2O2δ–Pr0.6Sr0.4Co0.5Fe0.5−xNbxO3−δ (CG–PSCF0.5−xNx; x=0–0.125) dual-phase dense oxygen permeation membranes were successfully developed. The crystal structure, microstructure, oxygen permeability, rate-determining step and CO2 tolerance were systematically investigated. The experimental results showed that the increase in CG content improved oxygen permeability and CO2 tolerance. Thermogravimetry–differential-scanning-calorimetry analysis, X-ray photoelectron spectra and oxygen permeation tests indicated that the increase in Nb content caused a slight decrease in oxygen permeability, while the long-term CO2 resistance can be improved significantly. According to the adopted permeation model, the weight ratio and thickness affect the oxygen permeability and permeation resistance distribution. By examining the distribution of three permeation resistances, we identified the rate-determining step and then optimized the weight ratio of the two phases, as well exploring the effects of thickness on oxygen permeability. All these experiments confirm that CG–PSCF0.5−xNx dual-phase membranes have great CO2 tolerance and potential application in oxy-fuel combustion.

A series of novel cobalt-free dense oxygen-permeable membranes of the type with Pr0.6Sr0.4Fe1-xNbxO3-δ (PSFNx, x = 0–0.1) were synthesized. Subsequently, the effects of Nb-doping on the microstructure, oxygen permeability, and stability of PSFNx were studied under a pure He or CO2 atmosphere. The structure of the material did not change in either atmospheres and its stability of the material was enhanced as the level of Nb-doping increased. For the sample with x = 0 and 0.075, carbonates and sulfates were present on the sweep side of the PSF membrane, but no impurities were detected on the sweep side of the PSFN0.075. In addition, the oxygen-permeation performance exhibited almost no attenuation when the Nb-doping content were 0.075. As revealed by X-ray photoelectron spectroscopy, the CO2 resistance of the material was enhanced by reducing the basicity of PSFNx, which was induced by the substitution of Fe with Nb.

One-pot synthesized mesoporous NiAl2O4/γ-Al2O3 and NiAl2O4/MOx (M = La, Ce, Ca, Mg)–γ-Al2O3 nanocomposites with excellent textural properties were employed for the dry reforming of methane (DRM). NiAl2O4/La2O3/γ-Al2O3-imp prepared via a traditional impregnation method was used for comparison. The promotion effect of modifiers on the physicochemical properties and catalytic performance of the catalysts was systematically investigated. Characterization and evaluation results indicated that the modified catalysts showed higher activities and better coking-resistance than Ni/γ-Al2O3, and Ni/La2O3–γ-Al2O3 was found to be the most effective one. All the catalysts with or without modifiers presented similar Ni particle sizes due to the enhanced metal–support interaction derived from the reduction of the NiAl2O4 precursor. However, more medium-strength basic sites on the catalyst surface were obtained by adding promoters, which could facilitate the adsorption/activation of CO2 and the gasification of amorphous carbon, improving the catalytic properties and accelerating the coke elimination rate. Additionally, the incorporation of promoters also prevented the phase transformation of γ-alumina.

One-pot synthesized mesoporous NiAl2O4/γ-Al2O3 and NiAl2O4/MOx (M = La, Ce, Ca, Mg)–γ-Al2O3 nanocomposites with excellent textural properties were employed for the dry reforming of methane (DRM). NiAl2O4/La2O3/γ-Al2O3-imp prepared via a traditional impregnation method was used for comparison. The promotion effect of modifiers on the physicochemical properties and catalytic performance of the catalysts was systematically investigated. Characterization and evaluation results indicated that the modified catalysts showed higher activities and better coking-resistance than Ni/γ-Al2O3, and Ni/La2O3–γ-Al2O3 was found to be the most effective one. All the catalysts with or without modifiers presented similar Ni particle sizes due to the enhanced metal–support interaction derived from the reduction of the NiAl2O4 precursor. However, more medium-strength basic sites on the catalyst surface were obtained by adding promoters, which could facilitate the adsorption/activation of CO2 and the gasification of amorphous carbon, improving the catalytic properties and accelerating the coke elimination rate. Additionally, the incorporation of promoters also prevented the phase transformation of γ-alumina.

The chemoselective reduction of nitroarenes is an important transformation for the production of arylamines, which are the primary intermediates in the synthesis of pharmaceuticals, agrochemicals and dyes. Heterogeneous non-noble metal nickel-molybdenum oxide catalysts supported on ordered mesoporous silica SBA-15 (Ni-MoO3/CN@SBA-15) were prepared for the first time by treating SBA-15-supported nickel-molybdenum oxide materials with 1,10-phenanthroline, and exhibited unprecedented catalytic activity and chemoselectivity for the reduction of various substituted nitroarenes to the corresponding aromatic amines in ethanol with hydrazine hydrate as a hydrogen donor under mild conditions owing to the synergistic effect of metal Ni and MoO3 species, affording excellent yields of >99% within very short reaction periods (≤60 min). The Ni-MoO3/CN@SBA-15 catalysts were highly stable and could easily be recovered by simple filtration or by an external magnetic field for at least ten recycling reactions without any observable loss of catalytic performance or leaching of metal components.

The chemoselective reduction of nitroarenes is an important transformation for the production of arylamines, which are the primary intermediates in the synthesis of pharmaceuticals, agrochemicals and dyes. Heterogeneous non-noble metal nickel-molybdenum oxide catalysts supported on ordered mesoporous silica SBA-15 (Ni-MoO3/CN@SBA-15) were prepared for the first time by treating SBA-15-supported nickel-molybdenum oxide materials with 1,10-phenanthroline, and exhibited unprecedented catalytic activity and chemoselectivity for the reduction of various substituted nitroarenes to the corresponding aromatic amines in ethanol with hydrazine hydrate as a hydrogen donor under mild conditions owing to the synergistic effect of metal Ni and MoO3 species, affording excellent yields of >99% within very short reaction periods (≤60 min). The Ni-MoO3/CN@SBA-15 catalysts were highly stable and could easily be recovered by simple filtration or by an external magnetic field for at least ten recycling reactions without any observable loss of catalytic performance or leaching of metal components.

Mesoporous γ-alumina-supported Ni–Mg oxides (xNiO–MgO/γ-MA) with various mass percentage contents of nickel (x = 0, 5, 10, 15, 18 and 21) were prepared through one-pot hydrolysis of metal nitrate salts without surfactants. The influences of nickel content on the catalyst structure, surface properties, interaction between Ni species and the support, reducibility of Ni2+ ions and Ni particle dispersion were investigated in detail using XRD, N2 sorption, TEM, XPS, CO2-TPD, H2-TPR, hydrogen chemisorption and TG techniques. The xNiO–MgO/γ-MA materials showed wormhole-like mesoporous structures with large surface areas and narrow pore size distributions. The dominant NiO species were homogeneously dispersed and had an attenuated interaction with the support with the increase in Ni content, producing uniform Ni nanoparticles throughout γ-alumina frameworks after H2 reduction. The Ni particle sizes decreased with increasing Ni content and showed a minimum at 18 wt%, likely due to Ni crystallite growth by Ostwald ripening rather than by migration of Ni nanoparticles. The reduced xNi–MgO/γ-MA catalysts were investigated for their catalytic behaviors in pre-reforming of liquefied petroleum gas. The results demonstrated that the Ni surface areas were mainly responsible for their catalytic activities; smaller Ni nanoparticles promoted steam reforming of hydrocarbons, methanation of carbon oxides and water gas shift reaction, but inhibited hydrocracking of hydrocarbons and lowered the rate of coke deposition, improving the catalytic activity and stability.

A series of CO2-tolerant dual-phase dense oxygen permeable membranes of stoichiometry Ce0.8Gd0.2O2−δ–Ba0.95La0.05Fe1–xNbxO3−δ (CG–BLF1–xNx, x = 0, 0.025, 0.05, 0.10, and 0.15) were designed and prepared by the sol–gel method. Their stability regarding phase composition and structure, oxygen permeability, and CO2-tolerant property were investigated by X-ray diffraction (XRD), thermogravimetry and differential scanning calorimetry (TG-DSC), and temperature-programmed desorption of oxygen (O2-TPD). Results of the materials characterization showed excellent chemical compatibility between CG and BLF1–xNx without the formation of any impurity phase after sintering at 1200 °C in air. The oxygen-permeation experiments showed that with increasing niobium content, the oxygen permeability of the CG–BLF1–xNx membranes decreased slightly, but the compositional and structural stability in CO2 atmosphere improved significantly. The 60 wt % CG–40 wt % BLF0.9N0.1 membrane showed simultaneously good oxygen permeability and excellent CO2 tolerance, and the oxygen-permeation flux reached 0.195 mL·cm–2·min–1 in pure CO2 atmosphere at 925 °C using a 1.0 mm thick membrane. This work demonstrates that CG–BLF1–xNx dual-phase membranes have great application potential for separating oxygen from highly concentrated CO2 atmosphere.Keywords: CO2 tolerance; Dual-phase membrane; Oxygen permeation; Stability;

•B-site doping has a great influence on the performance of BaCo0.7Fe0.2M0.1O3 − δ.•The highest oxygen permeation flux of 14.65 ml min− 1 cm− 2 was achieved in this work.•The high-temperature phase change of the BCFZ was observed by TG-DSC.The perovskite-type oxygen-transporting membranes of BaCo0.7Fe0.2M0.1O3 − δ (M = Ta, Nb, Zr) were prepared by solid state reaction methods and used for producing hydrogen from coke oven gas (COG). The structural stability of the membranes was characterized systematically using XRD, H2-TPR, O2-TPD, TG–DSC, and SEM-EDXS. Meanwhile, the oxygen permeation flux of the membranes was measured at different temperatures under He or CO2 containing atmosphere. It can be concluded that the Ta-substituting BaCo0.7Fe0.2M0.1O3 − δ is a promising candidate of the membrane materials for producing hydrogen through the catalytic partial oxidation of COG.

•Mesoporous γ-alumina supported Ni–Mg oxides were prepared through one-pot route.•Influence of reduction temperature on γ-Al2O3 supported Ni–Mg oxides was studied.•Ni nanoparticles were uniformly dispersed in mesoporous γ-Al2O3 framework.•Formation of larger Ni particles was due to crystallite growth by Ostwald ripening.•NiO species unreduced promoted hydrocarbon reforming and carbon deposition.Mesoporous γ-alumina supported Ni–Mg oxides (NiO–MgO/γ-MA) with narrow pore size distributions were prepared via one-pot template-free route for pre-reforming of liquefied petroleum gas (LPG). Influences of reduction temperature on catalyst structures and surface properties, reduction degree of Ni2+, surface areas and sizes of Ni particles formed, and catalytic properties were systematically investigated. After reduction, mesoporous γ-MA structure was still retained and Ni nanoparticles were homogeneously distributed in support framework. The Ni particle sizes decreased with reduction temperature and exhibited a minimum at 600 °C, due to Ni crystallite growth by Ostwald ripening. The results revealed that the reduction temperatures strongly influenced reduction degree of Ni2+ species and Ni crystallite sizes, resulting in the variations in activity, stability and resistance to coke deposition of Ni–MgO/γ-MA catalysts. NiO species unreduced at lower reduction temperature not only benefited hydrocracking of LPG, but also promoted coke deposition over Ni–MgO/γ-MA catalysts.

In this paper, the thermodynamics of the reduction of ilmenite using multiple gases (H2/CO) was calculated. It is found that the metallization rate of 20.1 %–98.8 %, H2 consumption rate of 43.0 %–99.1 %, and carbon deposition amount of 5.7 × 10−7 − 0.49 mol can be obtained based on the conditions of hydrogen volume fraction of 10 %–90 % and temperature of 450–1200 °C. Experimental study was also carried out using synthetic ilmenite as initial materials and reduced in a static bed reactor at 1100 °C. The metallization rate reaches 97 % when the multiple gas (70 % H2/10 % CO/20 % Ar) flow rate is 120 ml·min−1. A thermogravimetric analyzer was used to measure the variation of sample weight caused by the deposition of solid carbon. The amount of carbon deposited during experiments reaches its maximum while the original hydrogen volume content is 20 %. The experimental results are well consistent with the thermodynamic analysis.

Low temperature electrochemical reduction of iron(III) oxide to iron in a strongly alkaline solution has been systematically investigated in this article. The facile electrochemical process was carried out in 50 to 70 wt pct aqueous NaOH solution at 383 K (110 °C) and 1.7 V. The preformed spherical Fe2O3 pellets with porous structures were used directly as precursors for the electrolytic production of iron. The influences of the experimental parameters on the electroreduction process and the characteristics of the iron products as well as the reaction mechanisms were investigated. The results show that the precursor’s pre-sintering process and the concentration of NaOH aqueous electrolyte have significant influences on the electroreduction process. The electroreduction-generated spherical metallic iron layer comprising dendritic iron crystals is first formed on the surface of Fe2O3 pellet precursor and then extends gradually into the pellet’s interior along the radial direction. The electroreduction process is confirmed to be a typical shrinking-core reaction process. The direct solid state electroreduction mechanism and the dissolution-electrodeposition mechanism coexist in the electrochemical process. The experimental observations suggest that the dissolution-electrodeposition mechanism appears to be the dominant mechanism under the experimental conditions employed in this study. This facile process may open a new green electricity-based route for the production of dendritic iron crystals from iron(III) oxide in alkaline media.

Ti5Si3 silicide has been extracted directly from complex multicomponent Ti/Si-containing metal oxide compounds by electro-deoxidation in molten calcium chloride using an inert solid oxide oxygen-ion-conducting membrane (SOM) based anode. Studies on the microstructure evolution and electrochemical extraction mechanism show that the formation of Ti5Si3 and the removal of impurity elements happened simultaneously during the electro-deoxidation process. It is found that the electro-deoxidation generated Ti5Si3 micro-particles typically possess a smooth surface, which could contribute to create a continuous anti-oxidation surface layer with excellent high-temperature oxidation resistance property. Consideration is also given to the parameters of electrolysis and the electrochemical characteristics including chemical and/or electrochemical reactions during the electro-deoxidation process, and then a relevant kinetic model is proposed.

•A series of noble metals (Ru, Pd, Ag) modified Ni/La2O3–ZrO2 catalysts were synthesized by sol–gel method.•The highest CH4 conversion of 96.0% and H2 selectivity of 94.6% were obtained in this work.•The type of carbonaceous species was investigated by H2-TPH.•The scheme of surface reaction of CHx species with CO2 and H2 on the catalysts was proposed.•The bimetallic catalysts prepared in this work have excellent resistance to carbon deposition.A series of noble metal (Ru, Pd, Ag) doped Ni catalysts supported on La2O3–ZrO2 mixed oxide were prepared using the sol–gel method and evaluated for use in dry reforming of coke oven gas (COG). The catalysts were investigated by means of N2 adsorption–desorption, XRD, H2-TPR, TPH, TEM and TG–DSC. TPH analysis revealed that two carbonaceous species formed on the used catalysts and that the low-temperature carbon species was sufficiently active for the reforming reaction. TEM observations indicated that highly dispersed and small metal particles were formed, suppressing coke deposition and improving catalytic performance. The test results indicated that the addition of trace amounts of noble metals effectively promotes catalytic activity. The 0.1Ru–10Ni/8LZ catalyst showed the highest performance among the bimetallic catalysts, because of the strong synergetic effect between Ru and Ni via the formation of a Ru–Ni alloy, which will be promising catalysts in the catalytic dry reforming of COG.

•A series of Ni/La2O3–ZrO2 catalysts were synthesized by sol–gel method.•The catalysts prepared in this work have excellent resistance to carbon deposition.•Effects of Ni content on the performances of the catalysts were studied in detail.•The reducibility of the Ni/La2O3–ZrO2 catalysts was investigated by H2-TPR.•The highest CH4 conversion of 95.2% and H2 selectivity of 94.3% were achieved in this work.Syngas production by CO2 reforming of coke oven gas (COG) was studied in a fixed-bed reactor over Ni/La2O3–ZrO2 catalysts. The catalysts were prepared by sol–gel technique and tested by XRF, BET, XRD, H2-TPR, TEM and TG–DSC. The influence of nickel loadings and calcination temperature of the catalysts on reforming reaction was measured. The characterization results revealed that all of the catalysts present excellent resistance to coking. The catalyst with appropriate nickel content and calcination temperature has better dispersion of active metal and higher conversion. It is found that the Ni/La2O3–ZrO2 catalyst with 10 wt% nickel loading provides the best catalytic activity with the conversions of CH4 and CO2 both more than 95% at 800 °C under the atmospheric pressure. The Ni/La2O3–ZrO2 catalysts show excellent catalytic performance and anti-carbon property, which will be of great prospects for catalytic CO2 reforming of COG in the future.

Quantitative oxidation of benzylic alcohols to aldehydes catalyzed by P123-stabilized Pd nanoclusters was first developed in acidic aqueous solution with air at near ambient temperature. The Pd nanocluster colloidal system showed high conversion rates for aerobic oxidation of benzylic alcohols and could easily be recovered by a simple process for multiple recycling reactions without significant loss of activity.Keywords: aerobic oxidation; benzylic alcohol; colloid; nanocluster; Pd

Direct electrochemical extraction of Ti5Si3 from pressed cathode pellets comprising of powdered Ti/Si-containing metal oxide compounds was investigated by using molten salt electro-deoxidation technology. Three groups of mixtures including TiO2 mixed with SiO2, Ti-bearing blast furnace slag (TBFS) mixed with TiO2, and TBFS mixed with high-titanium slag (HTS) were prepared at the same stoichiometric ratio (Ti: Si = 5: 3) corresponding to the target composition of Ti5Si3, and used as the starting materials in this experiment, respectively. The pressed porous cylindrical pellet of the Ti/Si-containing compounds served as a cathode, and two different anode systems, i.e., the inert solid oxide oxygen-ion-conducting membrane (SOM) based anode system and graphite-based anode system were used contrastively. The electrochemical experiment was carried out at 900–1050°C and 3.0–4.0 V in molten CaCl2 electrolyte. The results show that the oxide components were electro-deoxidized effectively and Ti5Si3 could be directly extracted from these complex Ti/Si-containing metal oxide compounds.

Ti5Si3/TiC composites have been electrosynthesized directly in molten CaCl2 electrolyte from pressed cathode pellets comprising powdered mixture of TiO2, SiO2 and C. This electrochemical experiment was carried out at 900 °C, 3.1 V and 1000 °C, 4.0 V using a graphite-based anode and an inert-oxygen-ion-conducting membrane-based anode, respectively. The membrane-based anode electrolysis system exhibits a higher current efficiency and reduction rate than the graphite-base anode electrolysis system. During the electro-deoxidation process, the oxide component was electro-deoxidized effectively and Ti5Si3/TiC powder was produced as the final product in the cathode. It is suggested that the reaction procedure involves compounding and electro-deoxidation processes simultaneously. Our work suggests that the solid-oxide oxygen-ion-conducting membrane-based anode electro-deoxidation process, so called the SOM process, is a promising low energy costs and environmentally friendly electrochemical method for the production of carbide-containing alloys, for instance, Ti5Si3/TiC composites.Highlights► Ti5Si3/TiC composite was directly electrosynthesized from their oxides/C precursors. ► The reaction mechanism of the electro-deoxidation process is proposed. ► Solid oxide oxygen-ion-conducting membrane (SOM) was used as a membrane-based anode. ► The SOM process is a novel method for production of carbide-containing composites.

The direct electrochemical extraction of Ti-Fe alloys from natural ilmenite (FeTiO3) in molten CaCl2 is reported in this article. The sintered porous pellet of natural ilmenite acted as the cathode of the electrochemical system, and the carbon-saturated liquid tin contained in a solid-oxide oxygen-ion-conducting membrane (SOM) tube served as the anode of the electrolytic cell. The electrochemical process was carried out at 3.8 V, under 1223 K and 1273 K (950 °C and 1000 °C). Oxygen was ionized continuously from the cathode and discharged at the anode; solid porous Ti-Fe alloys were obtained at the cathode. The electro-deoxidation procedure of the ilmenite was characterized by analyzing partially electro-deoxidized samples taken periodically throughout the electro-deoxidation process. The findings of this study are as follows: (1) The electro-deoxidation process followed these steps: Fe2TiO5 → FeTiO3 → Fe2TiO4 → Fe, Ti (and/or Ti-Fe alloys); and TiO2 → CaTiO3 → Ti; and (2) two types of particle growth pattern are observed in the experiments. The first pattern is characterized with particle fusion and second pattern is interconnection of particles to form porous structure. A microhole oxygen-ion-migration model is suggested based on the experimental evidence.

The reduction of ilmenite concentrate by hydrogen gas was investigated in the temperature range of 500 to 1200°C. The microstructure and phase transition of the reduction products were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical microscopy (OM). It was found that the weight loss and iron metallization rate increased with the increase of reduction temperature and reaction time. The iron metallization rate could reach 87.5% when the sample was reduced at 1150°C for 80 min. The final phase constituents mainly consist of Fe, M3O5 solid solution phase (M=Mg, Ti, and Fe), and few titanium oxide. Microstructure analysis shows that the surfaces of the reduction products have many holes and cracks and the reactions take place from the exterior of the grain to its interior. The kinetics of reduction indicates that the rate-controlling step is diffusion process control with the activation energy of 89 kJ·mol−1.

The dense ceramic membranes BaCo0.7Fe0.2Nb0.1O3−δ (BCFN) combined with GdBaCo2–xFexO5+δ (0 ≤ x ≤ 2.0) surface modification layers was investigated for hydrogen production by partial oxidation reforming of coke oven gas (COG). As oxygen permeation of BCFN membrane is controlled by the rate surface exchange kinetics, the GdBaCo2–xFexO5+δ materials improve the oxygen permeation flux of the BCFN membrane by 20–44% under helium atmosphere at 750 °C. The maximum oxygen permeation flux reached 14.4 mL min–1 cm–2 in the GdBaCoFeO5+δ coated BCFN membrane reactor at 850 °C, and a CH4 conversion of 94.9%, a H2 selectivity of 88.9%, and a CO selectivity of 99.6% have been achieved. The GdBaCo2–xFexO5+δ coating materials possess uniform porous structure, fast oxygen desorption rate and good compatibility with the membrane, which showed a potential application for the surface modification of the membrane reactor.Keywords: coke oven gas; hydrogen production; oxygen-permeation membrane; partial oxidation; surface-coating;

Titanium silicide (Ti5Si3) has been extracted directly from complex Ti-bearing compounds by electro-deoxidation. A pressed cylindrical pellet of the multi-component compounds acted as a cathode, and carbon-saturated liquid metal contained in a solid-oxide oxygen-ion-conducting membrane (SOM) tube served as an anode. This electrochemical process was carried out in a molten CaCl2 system at 950–1050 °C and 3.5–4.0 V. The parameters of electrolysis and the electrolytic characteristics were investigated, and the morphology and phase composition of the final products were examined. Ti5Si3 was directly extracted from Ti-bearing compounds. Electrolysis time, applied potential, and electrolysis temperature are the dominant factors that affect the characteristics of the final products. The mechanisms of the extraction of Ti5Si3 and the removal of metallic elements (Ca, Mg, and Al) are suggested based on our experimental results and theoretical analysis. The optimal conditions of the electrolysis are a temperature of ∼1050 °C and a potential of 3.5–4.0 V, which result in rapid reduction and good product morphology. The excellent oxidation resistance of the extracted Ti5Si3 is confirmed.Highlights► Ti5Si3 has been successfully extracted from multi-component Ti-bearing compounds. ► The multi-step mechanism of the electrochemical extraction process is proposed. ► The excellent oxidation resistance property of the obtained Ti5Si3 is confirmed.

The titanium silicide intermetallics have been directly prepared from the mixture of titanium oxide (TiO2) and silicon oxide (SiO2) powder by using the solid-oxygen-ion-conducting membrane (SOM) electrolysis process. The electrochemical process was carried out in a molten flux CaCl2 at 950 °C with a potential of 3.5–4.0 V. The effects of the stoichiometry of the initial mixture on the electrolysis characteristics and the final product compositions were investigated. It has been found that the molar ratio of TiO2:SiO2 dominates the composition of final products. A single-phase silicide Ti5Si3 intermetallic was obtained when the TiO2:SiO2 molar ratio is 5:3; the TiSi was identified as the dominant phase with a minor amount of TiSi2 at TiO2:SiO2 molar ratio 1:1; three silicide phases, Ti5Si4, Ti5Si3 and TiSi, were found coexisting in the final product produced from TiO2–SiO2 mixture of molar ratio 5:4; the product of electrolysis consisted of the compound Ti5Si3 and the pure metal Ti as TiO2:SiO2 molar ratio equals to 3:1; and two silicide phases, TiSi and TiSi2, are formed as TiO2:SiO2 molar ratio equals to 1:2. The preliminary experimental results suggest that the electro-deoxidization process is fast and the current efficiency reached 75%.

A novel SOM process was used to prepare CeNi5 and LaxCe1−xNi5 hydrogen storage alloys directly from their mixed oxides. The electrolytic reduction was carried out in molten CaCl2 system at 1000 °C. The reduction mechanism was investigated by analyzing the chemical compositions and the phase constitutions of the intermediate products of electrolysis. The results suggested that the reduction of NiO–CeO2 may take place in two steps: first, NiO was reduced into Ni and CeO2 reacted with CaCl2 to form CeOCl, then Ni reacted with CeOCl leading to the formation of CeNi5. It was found that the reduction rate increased while decreasing the pressure load of the mixed oxide pellets. Furthermore, CeNi5 could not be produced if the pressure load was lower than 10 MPa. It was also found that the pellets of NiO–CeO2 could be completely reduced to CeNi5 alloy by the SOM process, which was greatly excelled than FFC process. The successful preparation of LaxCe1−xNi5 (x = 0–1) alloy reported here suggests that the SOM process may be promising for the industrial application of producing such alloys.

•Mesoporous γ-alumina supported Ni–Mg oxides were prepared through one-pot route.•Metal Ni nanoparticles were homogeneously distributed throughout γ-alumina framework.•Addition of MgO improved basicity of catalyst surface and lowered Ni particle sizes.•Supported Ni–MgO catalysts possessed excellent activity and stability for steam reforming of liquefied petroleum gas.•High stability and coke resistance ability were attributed to smaller Ni nanoparticles and stable support structures.Mesoporous γ-alumina (γ-MA)-supported Ni–MgO catalysts were first prepared through one-pot hydrolysis of inorganic salts without surfactants and used for the prereformation of liquefied petroleum gas (LPG). The influence of MgO addition on catalyst structure, surface characteristics, distribution of Ni species, and reducibility of Ni2+ ions was investigated in detail. The prepared Ni–MgO/γ-MA catalysts possessed wormhole-like mesoporous structures with large surface areas, narrow pore size distributions, and metallic Ni nanoparticles f homogeneously dispersed in γ-MA frameworks. The results showed that MgO could improve catalyst surface basicity and lower metallic Ni particle sizes, resulting in significant enhancements in the activity, stability, and resistance to coke deposition for the prereformation of LPG. Comparative investigation of the prereformation of LPG over Ni–MgO/Al2O3 catalysts obtained by different routes revealed that the high stability and coke resistance ability were mainly due to the formation of smaller metallic Ni nanoparticles and stable support structures.Graphical abstractDownload high-res image (134KB)Download full-size image

Ba0.9R0.1Co0.7Fe0.225Ta0.075O3-δ (BRCFT, R = Ca, La or Sr) membranes were synthesized by a solid-state reaction. Metal cation Ca2+, La3+ or Sr2+ doping on A-site partially substituted Ba2+ in BaCo0.7Fe0.225Ta0.075O3-δ oxides, and its subsequent effects on phase structure stability, oxygen permeability and oxygen desorption were systematically investigated by XRD, TG-DSC, H2-TPR, O2-TPD techniques and oxygen permeation experiments. The partial substitution with Ca2+, La3+ or Sr2+, whose ionic radii are smaller than that of Ba2+, succeeded in stabilizing the cubic perovskite structure without formation of impurity phases, as revealed by XRD analysis. Oxygen-involving experiments showed that BRCFT with A-site fully occupied by Ba2+ exhibited good oxygen permeation flux under He flow, reaching about 2.3 mL·min−1 ·cm−2 at 900 °C with 1 mm thickness. Of all the membranes, BLCFT membrane showed better chemical stability in CO2, owing to the reduction in alkalinity of the mixed conductor oxide by La doping. In addition, we also found the stability of the perovskite structure under reducing atmospheres was strengthened by increasing the size of A-site cation (Ba2+>La3+>Sr2+>Ca2+).The A-site fully occupied by Ba2+ makes the membranes display very high oxygen permeability, 2.3 mL·min−1 ·cm−2 at 900 °C with 1.0 mm thickness.Download full-size image

A series of oxygen permeable dual-phase composite oxides 60 wt% Ce0.8Gd0.2O2–δ-40 wt% LnBaCo2O5+δ (CGO-LBCO, Ln = La, Pr, Nd, Sm, Gd and Y) were synthesized through a sol-gel route and effects of the Ln3+ cations on their phase structure, oxygen permeability and chemical stability against CO2 were investigated systemically by XRD, SEM, TG-DSC and oxygen permeation experiments. XRD patterns reveal that the larger Ln3+ cations (La3+, Pr3+ and Nd3+) successfully stabilized the double-layered perovskite structure of sintered LBCO, while the smaller ones (Sm3+, Gd3+, and Y3+) resulted in the partial decomposition of LBCO with some impurities formed. CGO-PBCO yields the highest oxygen permeation flux, reaching 2.8×10−7 mol·s−1·cm−2 at 925 °C with 1 mm thickness under air/He gradient. The TG-DSC profiles in 20 mol% CO2/N2 and oxygen permeability experiments with CO2 as sweep gas show that CGO-YBCO demonstrates the best chemical stability against CO2, possibly due to its minimum basicity. The stable oxygen permeation flux of CGO-YBCO under CO2 atmosphere reveals its potential application in the oxy-fuel combustion route for CO2 capture.The time dependence of oxygen permeation fluxes through 1 mm CGO-LBCO membranes with different concentration of CO2/He mixture gases as sweep gases at 925 °C.Download full-size image

•NiO-La2O3/SiO2 materials were prepared by a one-pot sol-gel route.•Ni nanoparticles were homogeneously distributed throughout silica framework.•Ni-La2O3/SiO2 catalyst possessed high activity and long-term stability for DRM.•Ni-La2O3/SiO2 catalyst showed a H2/CO molar ratio of unity for DRM.•Addition of La significantly inhibited the reverse water-gas shift reaction (RWGS).Mesoporous silica-supported Ni–La oxides with homogeneously-dispersed NiO nanoparticles were first synthesized via one-pot sol-gel route of tetraethoxysilane, metal nitrates, and poly(ethylene glycol). Upon reduction with H2, the NiO nanoparticles were reduced to in situ generate metallic Ni particles distributed in the matrices. The obtained Ni-La2O3/SiO2 catalysts exhibited high activity and excellent stability for DRM with an almost 100% H2 selectivity or a H2/CO molar ratio of unity. The presence of La significantly inhibited the reverse water gas shift reaction, resulting in a H2/CO ratio close to unity.Download high-res image (184KB)Download full-size image

Ti5Si3 silicide has been extracted directly from complex multicomponent Ti/Si-containing metal oxide compounds by electro-deoxidation in molten calcium chloride using an inert solid oxide oxygen-ion-conducting membrane (SOM) based anode. Studies on the microstructure evolution and electrochemical extraction mechanism show that the formation of Ti5Si3 and the removal of impurity elements happened simultaneously during the electro-deoxidation process. It is found that the electro-deoxidation generated Ti5Si3 micro-particles typically possess a smooth surface, which could contribute to create a continuous anti-oxidation surface layer with excellent high-temperature oxidation resistance property. Consideration is also given to the parameters of electrolysis and the electrochemical characteristics including chemical and/or electrochemical reactions during the electro-deoxidation process, and then a relevant kinetic model is proposed.

Mesoporous γ-alumina-supported Ni–Mg oxides (xNiO–MgO/γ-MA) with various mass percentage contents of nickel (x = 0, 5, 10, 15, 18 and 21) were prepared through one-pot hydrolysis of metal nitrate salts without surfactants. The influences of nickel content on the catalyst structure, surface properties, interaction between Ni species and the support, reducibility of Ni2+ ions and Ni particle dispersion were investigated in detail using XRD, N2 sorption, TEM, XPS, CO2-TPD, H2-TPR, hydrogen chemisorption and TG techniques. The xNiO–MgO/γ-MA materials showed wormhole-like mesoporous structures with large surface areas and narrow pore size distributions. The dominant NiO species were homogeneously dispersed and had an attenuated interaction with the support with the increase in Ni content, producing uniform Ni nanoparticles throughout γ-alumina frameworks after H2 reduction. The Ni particle sizes decreased with increasing Ni content and showed a minimum at 18 wt%, likely due to Ni crystallite growth by Ostwald ripening rather than by migration of Ni nanoparticles. The reduced xNi–MgO/γ-MA catalysts were investigated for their catalytic behaviors in pre-reforming of liquefied petroleum gas. The results demonstrated that the Ni surface areas were mainly responsible for their catalytic activities; smaller Ni nanoparticles promoted steam reforming of hydrocarbons, methanation of carbon oxides and water gas shift reaction, but inhibited hydrocracking of hydrocarbons and lowered the rate of coke deposition, improving the catalytic activity and stability.