Synthesis of active supported gold catalysts for CO oxidation and light alkane activation.

The preparation of gold catalysts supported on different metal oxides such as ZnO and Fe2O3, using two coprecipitation methods is investigated to determine important factors, such as selection of support material and preparation method, and preparation parameters, such as preparation temperature, pH, and ageing process. These factors control the synthesis of high activity catalysts for the oxidation of carbon monoxide at ambient temperature. The two preparation methods differ in the manner in which the pH is controlled during coprecipitation, either constant pH throughout or variable pH in which the pH is raised from an initial low value to a defined end point. Non- calcined Au/ZnO catalysts prepared using both methods are very sensitive to pH and ageing time. Catalysts prepared at higher pH give lower activity. However, all catalysts require a short indication period during which the oxidation activity increases. In contrast, the calcined catalysts are not sensitive to preparation conditions. Non-calcined Au/Fe203 catalysts exhibit high activity when prepared at pH > 5. Active calcined Au/Fe2O3 catalysts can be prepared when the pH is controlled at pH 6-7, 8, whereas calcined catalysts prepared using the variable pH method are inactive. The study demonstrates the immense sensitivity of catalyst preparation methods on the performance. Catalysts exhibited excellent catalytic activity and stability compared with the pure supports, ZnO and Fe2O3, and the best preparation temperature was 80 C. Use of temperatures > 80 C led to inactive catalysts. The deposition-precipitation (DP) method was also employed using four different supports in this study (ZnO, Fe2O3, MgO, and MnO2). A comparison between these catalysts was taken rather than an investigation of the effect of the preparation parameters on catalysts prepared by DP method because they have been well studied previously. Several characterization techniques including AAS, BET surface area, XRD, TPR, and XPS, were utilised to investigate the physical and chemical properties of the prepared supported gold catalysts. Characterization results were combined with catalytic results for the low temperature CO oxidation reaction of catalysts in order to study the aforementioned factors that can affect either the properties of catalysts or their activities. Subsequently, several experiments at high GHSV were conducted to study the catalytic activities of these catalysts in-depth and to correlate data with alkane activation reactions. CH4 activation reaction using supported gold catalysts at light temperatures and the effect of the preparation parameters, types of supports on catalysts activities were investigated. The Au/Fe2O3 catalyst prepared by coprecipitation method B at pH 8 showed the highest catalytic activity for CO oxidation and CH4 activation reactions. The most active catalysts were also evaluated for C2H6 and C3H8 activation at low temperature. After this, a comparison between CO oxidation and alkane activation over supported gold catalysts was undertaken to investigate the relationship between the behaviour of supported gold catalysts for these two types of reactions. Activation energies and pre-exponential factors of many catalysts were calculated based on the Arrhenius equation either for CO oxidation or for alkane activation. The preparation of gold catalysts supported on different metal oxides such as ZnO and Fe2O3, using two coprecipitation methods is investigated to determine the important factors that control the synthesis of high activity catalysts for the oxidation of carbon monoxide at ambient temperature. (Abstract shortened by UMI.

Oxidation of ethane to ethylene and acetic acid by MoVNbO catalysts

The influence of niobium on the physicochemical properties of the Mo-V-O system and on its catalytic properties in the oxidation of ethane to ethylene and acetic acid is examined. Solids based on MoV0.4Ox and MoV0.4Nb0.12Oy composition and calcined at 350 or 400°C were studied by X-ray diffraction, and by laser Raman and X-ray photoelectron spectroscopies. Their reactivity during reduction and reoxidation was examined by in situ XRD and by XPS after pre-treatment. Their stability in air was evaluated by means of Raman spectroscopy during laser heating of particles. Niobium is responsible for both stabilization and nanosize of MoO3 and (VNbMo)5O14 crystals. The high global selectivity to ethylene and acetic acid (90-96 mol%) is related to the presence of both phases while higher activity is owed to nanoparticles. The model already proposed by Merzouki et al. (Stud. Surf. Sci. Catal., 72 (1992) 81) suggesting that MoVNbO catalysts could be made up from (VNbMo)5O14-type microdomains embedded in MoO3 matrix seems still topica

MoVO-based catalysts for the oxidation of ethane to ethylene and acetic acid. Influence of niobium and/or palladium on physicochemical and catalytic properties.

The influence of niobium and/or palladium in MoV0.4Ox on both solid state chemistry and catalytic properties in the oxidation of ethane to acetic acid and ethylene is examined. Catalysts without molybdenum (VNb031Pd3e-4Ox) are also studied for comparison. The structural properties of the precursors and of the catalysts obtained by calcination of precursors at 350 and 400°C are studied by X-ray diffraction, and by laser Raman and X-ray photoelectron spectroscopies. These properties depend on the presence or absence of niobium, and to a lesser extent, of palladium. Nb-free precursors and catalysts are heterogeneous mixtures of crystalline oxides, among which hexagonal and orthorhombic MoO3. The presence of Pd favors the instability of both precursors and catalysts. The catalysts are poorly active (conversion < 4%), but they are mainly selective to acetic acid (SAA max = 61-73 mol%) and to COx (SCOx max = 30-72 mol%). The Nb-containing precursors without or with Pd are more stable, and the catalysts are made up of nanocrystalline particles of V,Nb-doped Mo5O14 and of VxMo1 xO3 x/2. They are active (conversion < 15%) and very selective to ethylene and acetic acid (Stot = 90-96 mol%). The surface being enriched with vanadium in most cases, the discussion deals with the relative role of Nb and Pd and their possible location in the identified oxides. Because no M1 and/or M2 oxides could be identified, synergistic effects between nanocrystals of (VMoNb)5O14 and VxMo1-xO3-0.5x are proposed to account for the high catalytic performance of the multicomponent MoVNb(Pd)oxides

Optical absorption of Zn(V,Al)O thin films studied by spectroscopic ellipsometry from 1 to 6 eV

Aerogel nanoparticles prepared with various Al concentrations were used as a target for the deposition of (V,Al) co-doped ZnO films by rf-magnetron sputtering on glass substrates. The influence of Al content on the structural and the optical properties of the Zn(V,Al)O films was investigated by X-ray diffraction and spectroscopic ellipsometry (SE). It is found that all films exhibit one high intensity (0 0 2) peak, indicating that they have c-axis preferred orientation due to self-texturing mechanism. SE measurements, used to determine the complex pseudo dielectric functions, were carried out at room temperature in the 1–6 eV photon energy region. The excitonic edge of the fundamental band gap (E0) transition in the imaginary part of the dielectric function of the Zn(V,Al)O films is observed around 3.5 eV and shows a dependence on the Al content. The E0 absorption edge of the Zn0.9−x V0.1AlxO alloys shows a blueshift from that of pure ZnO, reaching 389 meV for x = 0.02. This blueshift is interpreted by the Burstein-Moss effect. By analyzing the dielectric function, reduced effective mass m* of the Zn0.9−x V0.1AlxO alloy is extracted and shows good agreement with literature values

MoV-based catalysts in ethane oxidation to acetic acid: Influence of additives on redox chemistry

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MoV-based catalysts in ethane oxidation to acetic acid: Influence of additives on redox chemistry

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Green material: ecological importance of imperative and sensitive chemi-sensor based on Ag/Ag2O3/ZnO composite nanorods

In this report, we illustrate a simple, easy, and low-temperature growth of Ag/Ag(2)O(3)/ZnO composite nanorods with high purity and crystallinity. The composite nanorods were structurally characterized by field emission scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy which confirmed that synthesized product have rod-like morphology having an average cross section of approximately 300 nm. Nanorods are made of silver, silver oxide, and zinc oxide and are optically active having absorption band at 375 nm. The composite nanorods exhibited high sensitivity (1.5823 μA.cm(−2).mM(−1)) and lower limit of detection (0.5 μM) when applied for the recognition of phenyl hydrazine utilizing I-V technique. Thus, Ag/Ag(2)O(3)/ZnO composite nanorods can be utilized as a redox mediator for the development of highly proficient phenyl hydrazine sensor

Highly conductive and flexible fiber for textile electronics obtained by extremely low-temperature atomic layer deposition of Pt

Thermal atomic layer deposition (ALD) of metal has generally been achieved at high temperatures of around 300 degrees C or at relatively low temperatures with highly reactive counter reactants, including plasma radicals and O-3, which can induce severe damage to substrates. Here, the growth of metallic Pt layers by ALD at a low temperature of 80 degrees C is achieved by using [(1,2,5,6-eta)-1,5-hexadiene]-dimethyl-platinum(II) (HDMP) and O-2 as the Pt precursor and counter reactant, respectively. ALD results in the successful growth of continuous Pt layers at the low temperature without any reactive reactants owing to the low activation energy of the HDMP precursor for surface reactions. Because of the high reactivity of the precursor, the growth of a pure Pt layer is achieved on various thermally weak substrates, leading to the fabrication of high-performance conductive cotton fibers by ALD. A capacitive-type textile pressure sensor is successfully demonstrated by stacking elastomeric rubber-coated conductive cotton fibers perpendicularly and integrating them onto a fabric with a 7 x 8 array configuration to identify the features of the applied pressure, which can be effectively utilized as a new platform for future wearable and textile electronics