Showing papers on "Mixed oxide published in 2016"

Formation of Prussian-Blue-Analog Nanocages via a Direct Etching Method and their Conversion into Ni–Co-Mixed Oxide for Enhanced Oxygen Evolution

Abstract: Novel Ni-Co-Prussian-blue-analog nano-cages consisting of pyramid-like walls were prepared via a facile chemical etching process with ammonia at room temperature. After annealing in air, the derived Ni-Co mixed oxide nanocages exhibit enhanced electrocatalytic activity and excellent stability toward the oxygen-evolution reaction.

Low temperature catalytic combustion of 1,2-dichlorobenzene over CeO2–TiO2 mixed oxide catalysts

Abstract: Ce 1− x Ti x O 2 mixed oxide catalysts with various Ti/Ce + Ti ratios were prepared by sol–gel way and used in catalytic combustion of 1,2-dichlorobenzene ( o -DCB). Characterization by XRD, Raman, HRTEM, XPS, H 2 -TPR, O 2 -TPD, CO 2 -TPD and NH 3 -TPD revealed that Ce 1− x Ti x O 2 catalysts were identified as the forms of fluorite, monocline and anatase. The incorporation of Ti distorted the crystal structure and thus increased greatly the acidity and the oxygen mobility at high temperature. Ce 1− x Ti x O 2 catalysts had considerable activity for o -DCB combustion. TOF obtained on the catalyst with Ti/Ce + Ti ratio of 0.1 at 275 °C reached the highest value of 0.64 μmol/min m 2 (Ti). Ti improved the stability of Ce 1− x Ti x O 2 catalysts through retarding the exchange of Cl for basic lattice oxygen and hydroxyl groups. High stability maintained at 330 °C for at least 50 h. In situ FTIR indicated that o -DCB adsorption was much stronger on Ti species than Ce species and different reaction pathways were related to different types of oxygen species existing on the surface of Ce 1− x Ti x O 2 catalysts.

A novel W-doped Ni-Mg mixed oxide catalyst for CO2 methanation

Abstract: Novel Ni-W-Mg mixed oxide catalysts (NiWMgOx) were prepared by homogeneous precipitation and attempted for the methanation of CO2 Adding W remarkably promoted the activity with improved stability, anti-CO-poisoning ability and resistance against coke formation compared to the undoped NiMgOx catalyst The superior reactivity of monodentate formate towards hydrogenation than that of bidentate formate species was identified by DRIFTS analysis and the formation of more active monodentate formate species was indisputably facilitated by W additives, leading to the greatly enhanced catalytic activity H-2-TPR and CO2-TPD characterization showed that doping W increased the number of stable CO2 adsorption sites and helped in anchoring the Ni sites as a result of strengthened Ni-Mg interaction, both of which were responsible for the enhanced CO2 methanation activity and the improved resistance against sintering (C) 2016 Elsevier BV All rights reserved

Selective oxidation of 5-hydroxymethyl furfural over non-precious metal heterogeneous catalysts

Abstract: An alternative synthesis of 2,5-furandicarboxylic acid (FDCA) was carried out by oxidation of 5-hydroxy-2-methyl furfural (HMF) in aqueous medium. The reaction occurred in presence of non-precious metal (MnxFey) mixed oxide catalyst. The effect of various reaction parameters such as nature and amount of base, reaction temperature, oxygen pressure, catalyst composition were investigated in order to quantitatively produce FDCA. The catalytic behavior of the mixed oxide catalyst was assigned to an optimal Mn/Fe ratio of 3/1, where a mixture of Mn(III) and Mn(IV) coexists with a hematite phase. The synergetic cooperation of these phases allowed the efficient oxidation of FFCA to FDCA. The humins species formed by HMF degradation exhibited a negative effect over the catalytic activity of Mn/Fe mixed oxide, while the chlorine resulted after the pH modification had no influence upon the catalytic oxidation.

Controlled Synthesis of Hollow Co–Mo Mixed Oxide Nanostructures and Their Electrocatalytic and Lithium Storage Properties

Abstract: Hollow mixed metal oxides have received much attention owing to their great performance for wide potential applications. Here, we have successfully prepared hollow Co–Mo mixed oxide nanostructures with controlled structure and compositions, including hollow Co3O4/CoMoO4 heterostructures and ball-in-ball CoMoO4 nanospheres. Uniform CoMo-hybrid precursors are prepared through one-pot solvothermal method and then transformed into hollow structures after thermal treatment. Importantly, this strategy can be used to prepare other ternary Mo-based oxides. In view of the unique heterostructure with hollow structure, the Co3O4/CoMoO4 heterostructures exhibit much better electrocatalytic activity for the oxygen evolution reaction than CoMoO4. Moreover, the as-synthesized carbon-coated Co3O4/CoMoO4 nanospheres show excellent lithium storage properties. Our result described here provides a method to fabricate other mixed metal oxides with complicated structure.

Cascade catalytic transfer hydrogenation–cyclization of ethyl levulinate to γ-valerolactone with Al–Zr mixed oxides

Abstract: A series of Al–Zr mixed oxides with different molar ratios were prepared by co-precipitation method and utilized to catalyze conversion of ethyl levulinate (EL) to γ -valerolactone (GVL). Those as-prepared catalysts were characterized by XRD, SEM, N 2 adsorption–desorption, XPS, TG, NH 3 -TPD, CO 2 -TPD and pyridine-IR. The introduction of Al into ZrO 2 was demonstrated to enlarge surface areas, as well as increase the number of acid and base sites that were catalytically active for transfer hydrogenation. Effects of Al–Zr molar ratio, calcination temperature, reaction temperature and time, catalyst dosage, and alcohols used as hydrogen donors on the catalytic performance were investigated. A high GVL yield of 83.2% at EL conversion of 95.5% could be achieved at 220 °C in 4 h over Al 7 Zr 3 -300 using 2-propanol as hydrogen donor and solvent. Poisoning experiments verified that acid–base sites played a synergic role in producing GVL from EL. Moreover, the Al–Zr mixed oxide catalyst was able to be reused for several times with a slight loss in its catalytic activity.

An effective Mn-Co mixed oxide catalyst for the solvent-free selective oxidation of cyclohexane with molecular oxygen

Abstract: Mn-Co mixed oxide (MnaCobOx) catalysts were prepared by the precipitation method, and the effect of Mn/Co (atom) on their structural and catalytic performance for the solvent-free selective oxidation of cyclohexane with oxygen was investigated. The results showed that the atomic ratio of Mn/Co would affect the phase constitution, surface area, surface Mn valence states and the reducibility of the MnaCobOx catalysts. When the atomic ratio of Mn/Co in the catalyst is 0.6, the Mn2Co3Ox catalyst behaved with excellent catalytic activity and stability, which should be attributed to its high specific surface area and the high atomic ratios of (Mn4+ + Mn3+)/Mn and Co3+/Co on its surface. The effects of the preparation conditions for the Mn2Co3Ox catalyst and the reaction conditions on the selective oxidation of cyclohexane over the Mn2Co3Ox catalyst was tested. Under the reaction conditions of 0.5 MPa O2 and 140 °C for 4 h, 10.4% conversion of cyclohexane and 62.0% selectivity to a mixture of cyclohexanone and cyclohexanol (KA oil) were achieved. After this Mn2Co3Ox catalyst was repeatedly used 10 times, the cyclohexane conversion and the selectivity to KA oil had hardly changed.

Acceptor Doping and Oxygen Vacancy Migration in Layered Perovskite NdBaInO4-Based Mixed Conductors

Abstract: The Ca2+ and Ba2+ solubility on Nd3+ sites in new layered perovskite NdBaInO4 mixed oxide ionic and hole conductor and their effect on the oxide ion conductivity of NdBaInO4 were investigated. Among the alkaline earth metal cations Ca2+, Sr2+, and Ba2+, Ca2+ was shown to be the optimum acceptor–dopant for Nd3+ in NdBaInO4 showing the largest substitution for Nd3+ up to 20% and leading to oxide ion conductivities ∼3 × 10–4–1.3 × 10–3 s/cm within 600–800 °C on Nd0.8Ca0.2BaInO3.9 composition, exceeding the most-conducting Nd0.9Sr0.1BaInO3.95 in the Sr-doped NdBaInO4. Energetics of defect formation and oxygen vacancy migration in NdBaInO4 were computed through the atomistic static-lattice simulation. The solution energies of Ca2+/Sr2+/Ba2+ on the Nd3+ site in NdBaInO4 for creating the oxygen vacancies confirm the predominance of Ca2+ on the substitution for Nd3+ and enhancement of the oxygen vacancy conductivity over the larger Sr2+ and Ba2+. The electronic defect formation energies indicate that the p-type c...

Catalytic Response and Stability of Nickel/Alumina for the Hydrogenation of 5-Hydroxymethylfurfural in Water

Abstract: The catalytic response of Ni on Al2O3 obtained from Ni-Al layered double hydroxides was studied for the liquid-phase hydrogenation of hydroxymethyl furfural to tetrahydrofuran-2,5-diyldimethanol (THFDM) in water. The successive calcination and reduction of the precursors caused the removal of interlayer hydroxyl and carbonate groups and the reduction of Ni(2+) to Ni(0). Four reduced mixed oxide catalysts were obtained, consisting of different amount of Ni metal contents (47-68 wt%) on an Al-rich amorphous component. The catalytic activity was linked to Ni content whereas selectivity was mainly affected by reaction temperature. THFDM was formed in a stepwise manner at low temperature (353 K) whereas 3-hydroxymethyl cyclopentanone was generated at higher temperature. Coke formation caused deactivation; however, the catalytic activity can be regenerated using heat treatment. The results establish Ni on Al2O3 as a promising catalyst for the production of THFDM in water.

A highly effective catalyst of Sm-Mn mixed oxide for the selective catalytic reduction of NOx with ammonia: Effect of the calcination temperature

Abstract: For low temperature selective catalytic reduction (SCR) of NOx with ammonia, the highly effective Sm-Mn mixed oxide (Sm-Mn-O, the molar ratio Sm/Mn is 0.1) catalysts was developed. The effect of the calcination temperature on the structure, physicochemical and catalytic properties of the Sm-Mn-O catalysts was investigated in detail. The results showed that the Sm-Mn-O catalyst calcined at 450 °C exhibited the highest activity, and after been calcined at >550 °C its catalytic activity markedly decreased. With an increase in the calcination temperature, its surface area firstly increased and then decreased, and the poorly crystallized MnO 2 in Sm-Mn-O was transformed to highly crystalized Mn 2 O 3 phase. These changes influenced the adsorption ability of the Sm-Mn-O catalyst for NH 3 or NO + O 2 . After calcination at >550 °C, the contents of Mn 4+ and adsorbed oxygen (O S ) on the surface of Sm-Mn-O decreased obviously, resulting in the decrease in its catalytic properties for the NO oxidation and transformation of bridged nitrite to active intermediate of bidentate nitrate. Conversely, its catalytic activity for NH 3 oxidation was enhanced after being calcined at high temperature. These adverse factors cause the decrease in the SCR activities of Sm-Mn-O calcined at >550 °C.

One-step synthesis of magnetic iron–aluminum oxide/graphene oxide nanoparticles as a selective adsorbent for fluoride removal from aqueous solution

Abstract: A novel magnetic adsorbent consisting of iron–aluminum oxide nanoparticles anchored on graphene oxide (IAO/GO) was prepared through a simple one-step co-precipitation method for fluoride removal from aqueous solution. Through this one-step method, this study simplified the operation processes to realize the magnetic composite of a binary iron–aluminum mixed oxide and graphene oxide (GO). By combining the advantages of GO and IAO, IAO/GO exhibits high adsorption capacity, good acid–alkali stability, super paramagnetism and good selectivity for fluoride. With magnetic properties, the adsorbent could easily be collected from aqueous solution using an external magnetic field. The physicochemical properties of IAO/GO were characterized through N2 adsorption/desorption, XRD, TEM, XPS, FT-IR, and AGM. Several main factors, such as dosage, initial solution pH, contact time, initial fluoride concentration, and co-existing anions, were investigated. Kinetic data revealed that the adsorption process followed a pseudo-second-order model. Fluoride sorption onto the adsorbents fitted well with the Langmuir model. The maximum sorption capacity calculated from the Langmuir model was 64.72 mg g−1 for IAO/GO. Effective fluoride removal occurred in a wide pH range from 3 to 9. IAO/GO showed good selectivity for fluoride when anions existed except for HPO42−. According to the sorption studies, electrostatic attraction, anion exchange, and inner-sphere complexation were the most likely mechanisms for fluoride sorption. Overall, based on the above-mentioned merits, the IAO/GO prepared in this study could be applied widely for fluoride removal in natural water environments.

Synergistic effect of bimetallic Au-Pd supported on ceria-zirconia mixed oxide catalysts for selective oxidation of glycerol

Abstract: A series of bimetallic Au-Pd catalysts supported on Ce 0.62 Zr 0.38 O 2 mixed oxide has been synthesized using a simultaneous deposition-precipitation method. Different Au:Pd ratios were obtained maintaining Au loadings constant and varying Pd content. Elemental analysis, X-ray diffraction, N 2 physisorption , X-ray photoelectron spectroscopy, scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) and X-ray energy dispersive spectroscopy (XEDS) techniques have been employed to characterize these catalysts. The catalytic activities for selective oxidation of glycerol over these bimetallic catalysts have been evaluated, a synergistic effect being observed. Thus, the bimetallic Au-Pd catalyst with the lowest Pd content was the one exhibiting the highest catalytic activity among all the prepared catalysts. Oxidation at 700 °C of the bimetallic 2.2AuPd/Ce 0.62 Zr 0.38 O 2 catalyst led to an increase of the catalytic activity for the selective oxidation of glycerol, which seemed to be due to the formation of a larger fraction of bimetallic Au-Pd alloy-type nanoparticles after oxidation at higher temperatures.

Atomic Layer Deposition of Al2O3-Ga2O3 Alloy Coatings for Li[Ni0.5Mn0.3Co0.2]O2 Cathode to Improve Rate Performance in Li-Ion Battery.

Abstract: Metal oxide coatings can improve the electrochemical stability of cathodes and hence, their cycle-life in rechargeable batteries. However, such coatings often impose an additional electrical and ionic transport resistance to cathode surfaces leading to poor charge–discharge capacity at high C-rates. Here, a mixed oxide (Al2O3)1–x(Ga2O3)x alloy coating, prepared via atomic layer deposition (ALD), on Li[Ni0.5Mn0.3Co0.2]O2 (NMC) cathodes is developed that has increased electron conductivity and demonstrated an improved rate performance in comparison to uncoated NMC. A “co-pulsing” ALD technique was used which allows intimate and controlled ternary mixing of deposited film to obtain nanometer-thick mixed oxide coatings. Co-pulsing allows for independent control over film composition and thickness in contrast to separate sequential pulsing of the metal sources. (Al2O3)1–x(Ga2O3)x alloy coatings were demonstrated to improve the cycle life of the battery. Cycle tests show that increasing Al-content in alloy coat...

Hydrogen generation by ammonia decomposition using Co/MgO–La2O3 catalyst: Influence of support calcination atmosphere

Abstract: Performing calcinations of the support in different atmospheres is a vital precondition for preparation of active cobalt supported on MgO–La 2 O 3 catalyst for ammonia decomposition. This work studied the influence of support calcination conditions on basic properties, morphology and catalytic performance. The catalytic performance was evaluated in the temperature range of 300–550 °C at atmospheric pressure. The XPS results showed the surface metal concentration was increased in 5 wt% Co supported on MgLa mixed oxide catalyst (5CMLa–N 2 ) whose support was calcined in N 2 atmosphere. The TPR measurements showed strong metal support interaction in 5CMLa–N 2 catalyst. From the SEM results the formation of MgLa mixed oxide was increased in 5CMLa–N 2 catalyst. The moderate basic site density determined by CO 2 TPD results was increased in 5CMLa–N 2 catalysts compared with other catalysts. These outcomes are might be one of the reasons in enhancing activity in 5CMLa–N 2 catalysts compared to other catalysts. Hence support calcinations under N 2 being the best choice, was the one of the parameters that influenced on catalytic properties of the cobalt on MgO–La 2 O 3 system, for ammonia decomposition.

WGS and CO-PrOx reactions using gold promoted copper-ceria catalysts: “bulk CuO-CeO2 vs. CuO-CeO2/Al2O3 with low mixed oxide content”

Abstract: A copper-ceria bulk catalyst has been compared to a series of catalysts designed according to the as called “supported approach”, corresponding to the dispersion of low content mixed copper-ceria oxide on alumina matrix. The principal characteristics of both types of catalysts are contemplated and the differences in their electronic and redox properties discussed in details. As a plus, the gold metal promotion of the catalysts is also envisaged. The advantages of the systems in the CO clean up reactions, WGS and CO-PrOx are commented. While the WGS activity appears to be ruled especially by the Cu/Ce surface to volume ratio, the CO-PrOx reaction is governed by the CuO loading. Gold addition provides benefits only at the low temperature WGS regime. Very importantly, the supported systems are always superior to the bulk configuration in terms of specific activity, a key factor from the catalyst’s design perspective.

Dimethyl carbonate synthesis from carbon dioxide using ceria–zirconia catalysts prepared using a templating method: characterization, parametric optimization and chemical equilibrium modeling

Abstract: In this paper, a series of CexZr1−xO2 solid solution spheres were synthesized by exo- and endo-templating methods and tested for dimethyl carbonate (DMC) synthesis using direct conversion of CO2. The synthesized catalysts were characterized by X-ray diffraction (XRD), N2-physisorption, scanning electron microscopy (SEM), and CO2/NH3-temperature-programmed desorption (TPD). Formation of CexZr1−xO2 solid solutions with tetragonal and cubic crystal structures depending on cerium/zirconium compositions was confirmed by XRD analysis. The specific surface area of the mixed oxide decreased and the average pore diameter increased with an increase in the ceria content, with the exception of the mixed oxides with x = 0.4–0.5 i.e. Ce0.4Zr0.6O2 and Ce0.5Zr0.5O2. The basic and acidic site density of the synthesized catalysts was in the order: ZrO2 < CeO2 < Ce0.5Zr0.5O2, and the basic and acidic site density per unit area followed the same order. The best Ce0.5Zr0.5O2 catalyst was further used for the optimization of reaction conditions such as reaction time, reaction temperature, catalyst dose and reusability for DMC synthesis. Furthermore, study of chemical equilibrium modeling was done using the Peng–Robinson–Stryjek–Vera equation of state (PRSV-EoS) along with the van der Waals one-fluid reaction condition so as to calculate change of Gibbs free energy (ΔG°) and heat of reaction (ΔH°).

Spent Tea Leaf Templating of Cobalt-Based Mixed Oxide Nanocrystals for Water Oxidation.

Abstract: The facile synthesis of nanostructured cobalt oxides using spent tea leaves as a hard template is reported. Following an impregnation–calcination and template removal pathway, sheetlike structures containing nanosized crystallites of Co3O4 are obtained. Co3O4 incorporated with Cu, Ni, Fe, and Mn (M/Co = 1/8 atomic ratio) are also prepared, and the materials are thoroughly characterized using X-ray diffraction, electron microscopy, and N2 sorption. The method is applicable to several commercial tea leaves and is successfully scaled up to prepare over 7 g of Co3O4 with the same nanostructure. The oxides are then tested for electrochemical water oxidation, and Cu, Ni, and Fe incorporations show beneficial effect on the catalytic activity of Co3O4, achieving performance comparable to levels from benchmark electrocatalysts. These data suggest that tea leaf templating can be utilized as a facile and promising approach to prepare nanostructured functional catalyst.

Hydrogen and Carbon Monoxide Production by Chemical Looping over Iron‐Aluminium Oxides

Abstract: H-2 and CO production from H2O and CO2 is investigated experimentally using a two-step chemical looping process based on the redox cycles of iron-alumina mixed oxides. The reduction of Fe3O4 in the first endothermic step is followed by the splitting of CO2 or H2O in a second exothermic step. The iron-aluminum oxides are more reactive with H2O than with CO2 in the range 650-750 degrees C. Insitu XRD shows that deactivation results from different processes: iron oxide sintering and the formation of spinel (FeAl2O4) with a lower oxygen-storage capacity. However, FeAl2O4 assumes the role of Al2O3 and mitigates the iron oxide sintering. Deactivation at 650 degrees C is governed predominantly by sintering, and the further loss of activity is caused by combined sintering and spinel formation. Spinel formation is more dominant at 750 degrees C. A mixed oxide of Fe2O3 and Al2O3 with a mass ratio of 70:30 was the most active and stable for H2O and CO2 splitting in chemical looping.

Synergic effect of Cu/Ce0.5Pr0.5O2-δ and Ce0.5Pr0.5O2-δ in soot combustion

Abstract: A series of 5%Cu/Ce0.5Pr0.5O2-δ and Ce0.5Pr0.5O2-δ mixed oxides have been prepared and combined in different ratios. The resulting catalysts have been characterized by N2 adsorption, XRD, Raman spectroscopy and H2-TPR and tested for soot combustion by means of temperature-programmed experiments. The optimum catalyst for soot combustion in NOx/O2/N2 atmosphere is the mixture containing 40% Cu/Ce0.5Pr0.5O2-δ and 60% Ce0.5Pr0.5O2-δ. This mixture is more active than a reference catalyst containing the same amount of copper distributed in the whole Ce-Pr mixed oxide support. The benefit of mixing Ce0.5Pr0.5O2-δ particles with and without copper in a single catalyst formulation is that the participation of the two soot combustion mechanisms based on active oxygen and NO2, respectively, is optimized. The particles with copper mainly promote the catalytic oxidation of NO to NO2 (the NOx-assisted mechanism) while those without copper are more effective in promoting the active oxygen mechanism. If copper is loaded homogeneously in all the Ce0.5Pr0.5O2-δ particles, the positive effect of copper improving NO2 production is offset by the lower efficiency of the active oxygen mechanism, due to a lack of active oxygen on the Ce0.5Pr0.5O2-δ support.

Nanosized spinel Cu–Mn mixed oxide catalyst prepared via solvent evaporation for liquid phase oxidation of vanillyl alcohol using air and H2O2

Abstract: A highly crystalline and spinel-structured Cu–Mn mixed oxide prepared via a solvent evaporation technique demonstrated superior catalytic activity for the oxidation of vanillyl alcohol to vanillin using different oxygen sources, air and H2O2, under optimum reaction conditions. The Cu–Mn mixed oxide catalyst contains large concentrations of structural defects (i.e. surface oxygen vacancy sites, defective oxygen species and grain boundaries) which act as active sites to enrich the transformation of vanillyl alcohol to vanillin. The atomic ratio of Cu and Mn in the metal oxides was observed to influence the catalytic performance significantly under similar reaction conditions. Moreover, reaction conditions such as time, solvent, temperature, and pressure were investigated to achieve suitable reaction parameters for the oxidation of vanillyl alcohol. For the catalytic activity, 94% conversion was measured with 99% selectivity for vanillin using H2O2 in the presence of base. Meanwhile, 91% conversion with 81% selectivity for vanillin was obtained by liquid phase aerobic oxidation in base-free conditions. The catalyst also showed high stability for three recycling redox reactions.