ZnO–Al2O3–CeO2–Ce2O3 mixed metal oxides as a promising photocatalyst for methyl orange photocatalytic degradation

In this research article, ZnO–Al₂O₃–CeO₂–Ce₂O₃ mixed metal oxides phases were prepared by calcination of Zn–Al/Ce–CO₃ layered double hydroxides (LDH) precursors, and evaluated for the photocatalytic degradation of methyl orange (MO) as a model textile dye from aqueous solution under UV irradiation. First, Zn–Al–CO₃ and a series of Zn–Al/Ce–CO₃ with different Ce content (5, 10, 15, 20%) were synthesized through co-precipitation method at Zn/(Al+Ce) molar ratio (r) of 3, then subjected to calcination at 500 °C for 6 h. Samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray analysis and pH point of zero charge. The experimental results of the photodegradation reveal that the photocatalyst developed from Zn–Al–Ce10%-CO₃ LDH exhibits the highest photocatalytic activity, with a degradation efficiency of 99.8% after 300 min of irradiation. This performance was mainly ascribed to the presence of difference state of Ce, leading a highest separation efficiency of electrons and holes. The recycling tests suggests a much high photostability and reusability of the photocatalyst.     

Synthesis and electrochemical performance of LiNi0.475Mn0.475Al0.05O2 as cathode material for lithium-ion battery from Ni–Mn–Al–O precursor

LiNi_0.475Mn_0.475Al_0.05O₂ cathode material was prepared by solid-state reaction using Ni–Mn–Al–O solid solution as precursor. The solid solution is of spinel structure, in which nickel, manganese, and aluminum are sufficiently mixed at atomic level. Rietveld refinement of X-ray diffraction data revealed that Al doping in LiNi_0.5Mn_0.5O₂ was significantly effective to decrease the degree of Li/Ni cation mixing. XPS analysis showed that the valence states of nickel and manganese were mainly +2 and +4, respectively. LiNi_0.475Mn_0.475Al_0.05O₂ delivered a stable capacity of about 206 mAh g⁻¹ with high reversibility. High-rate capability test was also performed.     

Nontransition metal–crown ether complexes as hydroperoxide decomposition catalysts

The decomposition of tert-butyl hydroperoxide in a chlorobenzene medium in the presence of complexes of dibenzo-18-crown-6 with calcium, strontium, and barium chlorides has been studied. It has been found and kinetically proven that the decomposition of tert-butyl hydroperoxide is preceded by the formation of an intermediate hydroperoxide–catalyst complex. Kinetic and thermodynamic parameters of the complex formation have been determined.     

A comparative study of sequentially layer-deposited and co-deposited Co–Mn oxides as potential redox capacitors

Layers of cobalt and manganese oxides were co-deposited or deposited on top of each other or next to each other by potentiostatic method onto stainless steel substrate. Deposition potentials of 1 and −1 V for the anodic and cathodic depositions were employed. Specific capacitance values in the range of 38.5–78 F g⁻¹ were found with cobalt oxide on top of manganese oxide having the lowest and manganese oxide on top of cobalt oxide having the highest capacitances. The usefulness of the electrodes was characterized by cyclic voltammetry, charge–discharge cycling, and electrochemical impedance spectroscopy in 2 M NaOH electrolyte for redox supercapacitor applications. The latter presented the best charge/discharge behavior with no voltage drop due to lower ohmic resistance in prepared substrate; although the steadiest current observed in the course of voltammetry was due to the former. The evaluated double layer and specific capacitances for co-deposited sample according to the impedance studies were 1.75 and 47.5 F g⁻¹, respectively, being in good agreement with voltammetric measurements.     

Calorimetric study of spinodal decomposition in β-Cu–Al–Mn

Journal of Thermal Analysis and Calorimetry - We report data obtained from the spinodal decomposition in samples of two compositions of intermetallic Cu–Al–Mn shape memory alloys....     

Co–Cu–La catalysts for selective CO2 hydrogenation to higher hydrocarbons

Copper and lanthanum promoted cobalt catalysts for CO₂ hydrogenation to higher hydrocarbons are described. The catalysts were prepared by the self-propagating high-temperature synthesis followed by alkaline leaching. They are active in CO₂ hydrogenation at 200 °C under 10 bar pressure (CO₂ : H₂ = 1 : 3) with selectivity to C₂₊ alkanes up to 39%; no alkenes and alcohols are formed under these experimental conditions.     

Synthesis of Cu–Cr diketo,sublimable, eutectic composite complex,rod crystals from LDH as suitable MOCVD precursor of CuCr2O4 catalysts upon ceramic preforms for N2O decomposition

Metal-acteylacetonates are important sublimable metal-organic precursors for metal-oxide thin film formation over solid preforms by MOCVD (Metal Organic Chemical Vapour Deposition) technique. Mixed-metal-acetylacetonates (MMAA) are suitable starting materials for mixed metal nano-oxidic thin film formation through such facile routes. Layered Double Hydroxides (LDH) of suitable metal ion combination can perform as appropriate starting base for neutralisation by enol form of 2,4-pentanedione or acteylacetonate tautomer ligands to obtain such MMAA. In this paper synthesis of composite crystals of Cu(II)/Cr(III) acetylacetonates (CCAA) is reported by the reaction of Cu–Cr-LDH with acetylacetone. The products were characterized by various different techniques. The surface area and pore volume analysis of the crystals showed the formation of nanopores in the compound. TEM analysis confirmed that the inner core of the nanoporous crystals of Cu(acac)₂ was covered by coating of poorly crystallised Cr(acac)₃ and they together form the composite crystals, and they together form the composite crystals. Due to eutectic mixture formation the melting point of CCAA lies in between the melting points of individual components Cu(acac)₂ and Cr(acac)₃ and shows sublimability, a property important for the formation of MOCVD films. The composite was used for CuCr₂O₄ spinel mixed oxide films formation over solid ceramic honeycomb monolithic substrates. Application prospects of the route in the field of catalysis is high as it can directly combine the benefits of mixed metal oxide catalysis and structured supports without the involvement of a third component. In this work the performance of such a catalytic device has been tested for low temperature decomposition of high Global Warming Potential (GWP) gas N₂O to N₂ and O₂.     

Nickel Supported on Alkaline Earth Metal–Doped γ-Al2O3–La2O3 as Catalysts for Dry Reforming of Methane

Russian Journal of Applied Chemistry - Nickel catalysts supported on γ–Al2O3 doped with La2O3 and alkaline earth oxides (MgO, CaO, and SrO) were investigated in the dry reforming of...     

Application of mechanochemical activation for synthesis of uranium–lanthanoid mixed oxides

The applicability of mechanochemistry to produce uranium–lanthanoid mixed oxides is presented. Phase homogeneous uranium–cerium solid solutions of the type Ce _x U_1−x O₂ (x = 0.3 ÷ 0.95) and polyphase systems containing La _y U_1−y O_2+x (y = 0.12) were prepared by mechanochemical activation in air of sol–gel produced precursors. The possibility for synthesis of urania–lanthania solid solution by mechanochemical interaction of La₂O₃ with sol–gel produced U (IV,VI) oxide is established. The crystal structures of the obtained oxides before and after the mechanochemical treatment are analysed by the use of X-ray diffraction method. The size of the crystallites (8–16 nm), lattice parameters, crystallite strains and densities of the oxides are calculated by BRASS program for Rietveld calculation.     

Synthesis and characterization of mesoporous Mn–Ni oxides for supercapacitors

Mesoporous Mn–Ni oxides with the chemical compositions of Mn_1-x Ni _x O _δ (x = 0, 0.2, and 0.4) were prepared by a solid-state reaction route, using manganese sulfate, nickel chloride, and potassium hydroxide as starting materials. The obtained Mn–Ni oxides, mainly consisting of the phases of α- and γ-MnO₂, presented irregular mesoporous agglomerates built from ultra-fine particles. Specific surface area of Mn_1–x Ni _x O _δ was 42.8, 59.6, and 84.5 m² g⁻¹ for x = 0, 0.2, and 0.4, respectively. Electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge/discharge in 6 mol L⁻¹ KOH electrolyte. Specific capacitances of Mn_1-x Ni _x O _δ were 343, 528, and 411 F g⁻¹ at a scan rate of 2 mV s⁻¹ for x = 0, 0.2, and 0.4, respectively, and decreased to 157, 183, and 130 F g⁻¹ with increasing scan rate to 100 mV s⁻¹, respectively. After 500 cycles at a current density of 1.24 A g⁻¹, the symmetrical Mn_1–x Ni _x O _δ capacitors delivered specific capacitances of 160, 250, and 132 F g⁻¹ for x = 0, 0.2, and 0.4, respectively, retaining about 82%, 89%, and 75% of their respective initial capacitances. The Mn_0.8Ni_0.2O _δ material showed better supercapacitive performance, which was promising for supercapacitor applications.     

Physico–chemical properties of CdO–Al2O3 catalysts. I – Structural characteristics

Alumina gels AN6 and AN7 were prepared by precipitation with NaOH from hydrated aluminum sulfate at pH 6 and 7, respectively. A third alumina gel AA7 was similarly prepared, but by precipitation with 30% ammonia. Pure cadmia C8 and C9 were precipitated from cadmium sulfate at pH 8 and 9 using NaOH. Five mechanically mixed gels ACM (1:0.25), ACM (1:0.5), ACM (1:1), ACM (0.5:1) and ACM (0.25:1) were prepared by thoroughly mixing the appropriate molar ratios of AN7 and C8. Also, five coprecipitated gels ACC (1:0.25), ACC (1:0.5), ACC (1:1), ACC (0.5:1) and ACC (0.25:1) were coprecipitated by dropping simultaneously the appropriate volumes of 1 M aluminum sulfate, 1 M cadmium sulfate and 3 M NaOH. Calcination products at 400, 500, 600, 800 and 1000 °C were obtained from each preparation.TG–DTA patterns of uncalcined samples were analyzed and the XRD of all 1000 °C-products and some selected samples calcined at 400–800 °C were investigated. The thermal behaviors of pure and mixed gels depend on the precipitating agent, pH of precipitation, chemical composition and method of preparation. Generally, calcination at temperatures below 800 °C gave poorly crystalline phases. Well crystalline phases are obtained at 800 and 1000 °C. For pure alumina γ-Al₂O₃ was shown as 400 °C-calcination product that transforms into the δ form around 900 °C and later to θ-Al₂O₃ as a major phase and α-Al₂O₃ as a minor phase at 1000 °C. CdO was shown by 500 °C-calcined cadmia gel that showed color changes with rise of calcination temperature. The most stable black cadmium oxide phase (Monteponite) is obtained upon calcination at 1000 °C. Thousand degree celsius- calcined mixed oxides showed θ-Al₂O₃, α-Al₂O₃, CdAl₂O₄ and monteponite which dominate depending on the chemical composition.     

Vanadium/cobalt oxides–anchored flexible carbon nanofibers with tunable magnetism as recoverable peroxidase-like catalysts

High-efficiency peroxidase-like catalysts that can be easily recycled are desperately needed for the rapid and accurate detection of H₂O₂. Herein, a novel flexible membrane composed of vanadium/cobalt oxides–anchored carbon (VCoO/C) nanofibers has been purposely designed and fabricated by electrospinning and subsequent carbonization, where there are processing temperature-dependent morphology, composition, and versatile properties. As the carbonization temperature increases from 600°C to 900°C, the saturation magnetization of the as-prepared VCoO/C nanofibers rises gradually. When treated at 750°C under Ar protection, the resultant VCoO/C-750 nanofibers yield superior peroxidase-like catalytic activity toward H₂O₂ with a low limit of detection of 0.44 μM (signal-to-noise ratio = 3). The combination of magnetic behavior and flexibility enables the effective recovery of catalysts. It is believed that our results will open a new avenue for the controlled preparation of flexible nanofiber materials, which are endowed with multiple functions.     

Bimetallic Co–Pd alloy nanoparticles as magnetically recoverable catalysts for the aerobic oxidation of alcohols in water

Co–Pd bimetallic alloy nanoparticle catalysts were prepared from CoCl₂, Pd(OAc)₂ and several capping agents with Li(C₂H₅)₃BH. The nanoparticle catalysts were applied to the aerobic oxidation of a variety of alcohols in water to give the corresponding carbonyl products. The catalyst was magnetically recovered and reused for further oxidation. The nanoparticle catalysts were characterized with TEM, ICP, and XPS analyses.     

Recent developments in Pt–Co catalysts for proton-exchange membrane fuel cells

Development of Pt-based oxygen reduction reaction catalysts with high efficiency and high durability is central to the application of proton-exchange membrane fuel cell systems. Pt–Co bimetallic catalysts have drawn extensive attention owing to their capability of delivering high performance and long lifetime for fuel cell applications including light-duty and heavy-duty vehicles. However, further improvements in durability and performance are needed to meet market requirements. To fully exploit the potential of Pt–Co catalysts, new insights into the relationship between catalyst properties and fuel cell performance and durability are needed, and more effective methods to tailor the features of Pt–Co catalysts need to be developed. This review provides a summary and perspective on recent efforts, including work on customizing the Pt shell and Pt:Co ratio, tailoring the crystal structure, and improving carbon support properties, with a particular emphasis on mechanisms leading to enhancement of mass activity, power density, and durability in membrane electrode assembly testing.     

Comparative study of Co/TiO<Subscript>2</Subscript>, Co–Mn/TiO<Subscript>2</Subscript> and Co–Mn/Ti–Ce catalysts for oxidation of elemental mercury in flue gas

The Co–Mn/Ti–Ce catalyst prepared by sol–gel and impregnation method was evaluated for catalytic oxidation of Hg⁰ in the simulated flue gas compared with Co/TiO₂ and Co–Mn/TiO₂. The results showed that Co–Mn/Ti–Ce catalyst exhibited higher catalytic activity (around 93% Hg⁰ removal efficiency in the temperature of 150 °C with 6% O₂, 400 ppm NO, 200 ppm SO₂ and 3% H₂O) than Co/TiO₂ and Co–Mn/TiO₂. Based on the characterization results of N₂ adsorption–desorption, XRD, UV–Vis, XPS, H₂-TPR and Hg-TPD, it could be concluded that the lower band gap, better reducibility and mercury adsorption capability and the presence of Co³⁺/Co²⁺, Mn⁴⁺/Mn³⁺ and Ce⁴⁺/Ce³⁺ redox couples as well as surface oxygen species contributed to the excellent Hg⁰ oxidation removal performance. In addition, well dispersion of active components and a synergetic effect among Co, Mn and Ce species might improve the activity further. A Mars–Maessen mechanism is thought to be involved in the Hg⁰ oxidation. The lattice oxygen derived from MnO _x or CoO _x would react with adsorbed Hg⁰ to form HgO and the consumption of lattice oxygen could be replenished by O₂. For Co–Mn/Ti–Ce, MnO _x?1 could be alternatively reoxidized by the lattice oxygen derived from adjacent CoO _x and CeO _x which is beneficial to the Hg⁰ oxidation.     

Heterogeneous bimetallic Au–Co nanoparticles as new efficient catalysts for the three-component coupling reactions of amines,alkynes and CH2Cl2

Research on Chemical Intermediates - Propargylamines are key intermediates for the synthesis of many biologically active molecules. A new synthesis of propargylamines via a three component-coupling...     

Catalytic oxidation of NO over Mn–Co–Ce–Ox catalysts: effect of reaction conditions

Manganese–cobalt–cerium oxide (Mn–Co–Ce–Ox) catalysts were synthesized by the co-precipitation method and tested for activity in low-temperature catalytic oxidation of NO in the presence of excess O₂. With the best Mn–Co–Ce mixed-oxide catalyst, approximately 80 % NO conversion was achieved at 150 °C and a space velocity of 35,000 h^?1. The effect of reaction conditions (reaction temperature, volume fractions of NO and O₂, gas hourly space velocity (GHSV), and catalyst stability) was investigated. The optimum reaction temperature was 150 °C. Increasing the O₂ content above 3 % results in almost no improvement of NO oxidation. This catalyst enables highly effective removal of NO within a wide range of GHSV. Furthermore, the stability of the Me–Co–Ce–Ox catalyst was excellent; no noticeable decrease of NO conversion was observed in 40 h.     

Highly dispersed Mn2O3−Co3O4 nanostructures on carbon matrix as heterogeneous Fenton-like catalyst

This work reports the synthesis of various carbon (Vulcan XC-72 R) supported metal oxide nanostructures, such as Mn₂O₃, Co₃O₄ and Mn₂O₃−Co₃O₄ as heterogeneous Fenton-like catalysts for the degradation of organic dye pollutants, namely Rhodamine B (RB) and Congo Red (CR) in wastewater. The activity results showed that the bimetallic Mn₂O₃−Co₃O₄/C catalyst exhibits much higher activity than the monometallic Mn₂O₃/C and Co₃O₄/C catalysts for the degradation of both RB and CR pollutants, due to the synergistic properties induced by the Mn−Co and/or Mn (Co)−support interactions. The degradation efficiency of RB and CR was considerably increased with an increase of reaction temperature from 25 to 45°C. Importantly, the bimetallic Mn₂O₃−Co₃O₄/C catalyst could maintain its catalytic activity up to five successive cycles, revealing its catalytic durability for wastewater purification. The structure–activity correlations demonstrated a probable mechanism for the degradation of organic dye pollutants in wastewater, involving •OH radical as well as Mn²⁺/Mn³⁺ or Co²⁺/Co³⁺ redox couple of the Mn₂O₃−Co₃O₄/C catalyst.     

Preparation of highly active and reusable heterogeneous Al2O3–Pd catalysts by the sol–gel method using bayberry tannin as stabilizer

A novel heterogeneous Al₂O₃–Pd catalyst has been prepared by the sol–gel method; bayberry tannin (BT) was used as stabilizer to prevent the migration and aggregation of Pd species during calcination. According to N₂ adsorption/desorption determination, Al₂O₃–Pd has a mesoporous structure and its specific area is as high as 336.5 m²/g. Transmission electron microscopy observation indicated that the size of the Pd particles was greatly reduced by the presence of BT. On the basis of X-ray photoelectron spectra analysis, it was found that the most of Pd nanoparticles were dispersed in the pores, implying that BT can prevent migration of Pd particles from the pores to the outer surface of Al₂O₃ during calcination. For comparison, Al₂O₃–Pd^* was prepared by the sol–gel method but without use of BT. In the hydrogenation of acrylic acid, Al₂O₃–Pd had high catalytic activity and excellent reusability compared with commercial and traditionally prepared heterogeneous Pd catalysts. The turnover number of Al₂O₃–Pd is as high as 11,328.0 mol/mol after recycling seven times, which is much higher than that of a commercial Pd–C catalyst (8048.0 mol/mol).