Hydrolysis Of Metal Alkoxides Research Articles

Amorphous nanosheets constructed nickel cobalt hydroxysulfide hollow spheres as cathode materials for hybrid supercapacitors

Tailoring architecture and multi-composition of electrode materials via a facile and cost-effective strategy are highly favorable to optimize physiochemical properties for developing energy storage devices. Herein, hierarchical nickel cobalt hydroxysulfide hollow spheres decorated with amorphous nanosheets and dual-ligands (denoted as NiCo-DHS) are synthesized through hydrolysis of self-templating metal alkoxides, followed by room-temperature anionic exchange process. The resultant dual-ligands hydroxysulfide possesses weak metallicity, reduced band gap and enhanced conductivity owing to the electronic regulation of the formed M−OH/S bonds. Additionally, the nanosheet-constructed amorphous structure contributes to accelerating ions diffusion and enlarging specific surface area, further exposing more active sites to enrich redox reactions. Benefiting from the compositional and structural superiorities, the optimized NiCo-DHS-12 electrode presents desirable electrochemical performance, including high specific capacity of 973.6 C g−1 (1 A g−1) and stable durability over 8000 cycles with a small capacity loss of 7.4 % at 10 A g−1. Moreover, the hybrid device assembled with NiCo-DHS-12 and porous activated carbon delivers an energy density of 65.91 Wh kg−1 at a power density of 0.89 kW kg−1 and considerable cycling stability. These encouraging results demonstrate a simple and reliable approach in constructing high-performance electrode materials for advanced supercapacitors in potential.

En route from metal alkoxides to metal oxides: metal oxo/alkoxo clusters

Molecular metal oxo or oxo/alkoxo clusters, MwOx(OH/OR)y(L/X)z (L or X = organic ligands), can often be isolated upon (partial) hydrolysis of metal alkoxides. Investigation of such clusters leads to a better understanding of the basic processes of sol–gel chemistry. The ligands not only stabilize the cluster core but also influence to some extent the cluster structures. They can easily change their position on the cluster surface, thus adapting to changing cluster geometries, and can be exchanged under certain conditions. A close inspection of titanium oxo/alkoxo cluster structures, taken as an informative example, shows that Ti3O units (with or without organic ligands) are the basic building blocks. Clusters with higher nuclearities appear to be predominantly formed by cluster–cluster or by cluster–monomer condensations. Ligand substitution or condensation reactions within a cluster unit are also possible.Instead of extended metal oxide networks, metal oxo/alkoxo clusters may be formed upon hydrolysis of metal alkoxides.

Highly Enhanced Catalytic Stability of Copper by the Synergistic Effect of Porous Hierarchy and Alloying for Selective Hydrogenation Reaction

Supported copper has a great potential for replacing the commercial palladium-based catalysts in the field of selective alkynes/alkadienes hydrogenation due to its excellent alkene selectivity and relatively high activity. However, fatally, it has a low catalytic stability owing to the rapid oligomerization of alkenes on the copper surface. In this study, 2.5 wt% Cu catalysts with various Cu:Zn ratios and supported on hierarchically porous alumina (HA) were designed and synthesized by deposition–precipitation with urea. Macropores (with diameters of 1 μm) and mesopores (with diameters of 3.5 nm) were introduced by the hydrolysis of metal alkoxides. After in situ activation at 350 °C, the catalytic stability of Cu was highly enhanced, with a limited effect on the catalytic activity and alkene selectivity. The time needed for losing 10% butadiene conversion for Cu1Zn3/HA was ~40 h, which is 20 times higher than that found for Cu/HA (~2 h), and 160 times higher than that found for Cu/bulky alumina (0.25 h). It was found that this type of enhancement in catalytic stability was mainly due to the rapid mass transportation in hierarchically porous structure (i.e., four times higher than that in bulky commercial alumina) and the well-dispersed copper active site modified by Zn, with identification by STEM–HAADF coupled with EDX. This study offers a universal way to optimize the catalytic stability of selective hydrogenation reactions.

"Traditional" Sol-Gel Chemistry as a Powerful Tool for the Preparation of Supported Metal and Metal Oxide Catalysts.

The sol-gel method is an attractive synthetic approach in the design of advanced catalytic formulations that are based on metal and metal oxide with high degree of structural and compositional homogeneity. Nowadays, though it originated with the hydrolysis and condensation of metal alkoxides, sol-gel chemistry gathers plenty of fascinating strategies to prepare materials from solution state precursors. Low temperature chemistry, reproducibility, and high surface to volume ratios of obtained products are features that add merit to this technology. The development of different and fascinating procedure was fostered by the availability of new molecular precursors, chelating agents and templates, with the great advantage of tailoring the physico-chemical properties of the materials through the manipulation of the synthesis conditions. The aim of this review is to present an overview of the “traditional” sol-gel synthesis of tailored and multifunctional inorganic materials and their application in the main domain of heterogeneous catalysis. One of the main achievements is to stress the versatility of sol-gel preparation by highlighting its advantage over other preparation methods through some specific examples of the synthesis of catalysts.

Evaporation-induced self-assembly synthesis of nanostructured alumina-based mixed metal oxides with tailored porosity

The one-pot synthesis of nanostructured ternary mixed oxides is challenging due to the heterogeneous nature of the hydrolysis and condensation processes of all metal oxide precursors. In addition, the solvents and additives used can affect these processes too. Herein, we report the effect of different solvents (ethanol, 1- and 2-propanol, or butanol) and additives (citric acid or 1,3,5-triisopropylbenzene) used on the formation of binary and ternary alumina-based oxides, NiO-Al2O3, NiO-TiO2-Al2O3, and NiO-ZrO2-Al2O3 in the presence of triblock copolymer Pluronic P123 used as a soft template. For comparison, this study includes also mesoporous Al2O3 prepared at the same conditions. It is shown that the kinetics of hydrolysis and condensation processes of metal alkoxides, and consequently, the properties of the resulting alumina-based mixed metal oxides are controllable by varying the solvents used. The use of propanol instead of ethanol affords mixed metal oxides with improved degree of mesostructure uniformity as evidenced by narrower pore size distributions. This finding is attributed to the smaller exchange of propanol with propoxide groups in Al(OPri)3, Ti(OPri)4, and Zr(OPrn)4 which results in an enhanced stability of the formed mesophase. Furthermore, the addition of citric acid leads to smaller pore sizes without significant changes in the textural properties of metal oxides, while addition of 1,3,5-triisopropylbenzene affords oxides with enlarged pores. The mixed metal oxides studied feature large specific surface areas (310–460 m2·g−1), large pore volumes (0.5–0.75 cm3·g−1), and uniform mesopores with widths ranging from 5 to 18 nm. Solid-state kinetic studies performed by thermal analysis using both isoconversional and model fitting methods reveal the complexity of the mesophase formation. The thermal decomposition of condensed oxoalkoxide species into metal oxides is mainly diffusion-controlled and affected by the type of solvent used too. This study shows that there are tremendous opportunities in tailoring porous structures of mixed metal oxides prepared via evaporation induced self-assembly (EISA) by selecting proper solvents and additives, and thermal treatment.

Fabrication and Microstructure of Ru Core Silica Shell Structure Particles by a Reverse Micelle and Sol-Gel Processing

The Ru core SiO2 shell nano size particles have been synthesized within reverse micelle via metal alkoxide hydrolysis and condensation. The size of the particles and the thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethoxysilane (TEOS) within the micro-emulsion. The average size of synthesized Ru core SiO2 shell particles was about in the size range of 15-40 nm. The average size and distribution of the synthesized Ru core SiO2 shell particles increased and narrow with R value increased. Otherwise, the average size and distribution of the synthesized Ru core SiO2 shell particles decreased and narrow with H value increased. TEM studies of particle formation indicate that the reaction process in the complex system containing reverse micelles and TEOS is governed by a diffusion-controlled process. The effects of synthesis parameters, such as the molar ratio of water to TEOS, and the molar ratio of water to surfactant, are discussed.

Dry Reforming of Methane on Ni@SiO2 Core-Shell Nanoparticles: Influence of Core-Shell Morphology on Catalytic Performance

Ni-nanocomposite catalysts, such as Ni@SiO2, were investigated to evaluate the influence of core-shell morphology on catalytic performance in the dry reforming of methane (DRM). The Ni-nanocomposite catalysts were synthesized by a combined reverse micelle and sol-gel technique via metal alkoxide hydrolysis and condensation. For comparison, a Ni/SiO2 catalyst was also prepared by the impregnation method. The catalysts were characterized by use of XRD, N2 adsorption, H2 TPR, H2 chemisorption, TEM, and TGA. The Ni@SiO2 catalysts with a core-shell nanostructure exhibited superior catalytic activity over the catalysts prepared by impregnation of Ni on a SiO2 support in DRM. The high catalytic activity on nanocomposite catalysts in DRM is mainly attributed to the improved sintering resistance by core-shell catalyst morphology.

Formation of Insulating Oxide Films with Hydrolysis Reactions of Alkoxide Precursors in Supercritical Fluid CO2: Chemistry, Morphology, Characterization and Film Thickness

ABSTRACTInsulating silicon dioxide (SiO2) films can be produced by hydrolysis of metal alkoxide tetraethylorthosilicate (TEOS) in the presence of an acid catalyst in supercritical fluid CO2 (sc-CO2). In this study, SiO2 films are formed on different substrates using TEOS as a source of silicon, and acetic acid (HAc) as a catalyst. Water required for the hydrolysis reaction is from in situ generation of esterification and condensation reactions involving HAc and the alcohol produced. The acid catalyzed deposition reaction actually starts at room temperature but produces decent films in sc-CO2 at moderately high temperatures (e.g. 50 °C). Supercritical fluid CO2 is known to have near zero surface tension and provides an ideal medium for fabrication of SiO2 films. Formation of SiO2 films via hydrolysis reaction in sc-CO2 is more rapid compared to the traditional hydrolysis reaction at room temperature. In general, metal alkoxide hydrolysis reactions carried out in a closed sc-CO2 system is not affected by moisture in air compared with traditional open-air hydrolysis systems. Using sc-CO2 as a reaction medium can eliminate undesirable organic solvents utilized in traditional alkoxide hydrolysis reactions.X-ray diffraction (XRD) and electron diffraction (ED) measurements demonstrated that the SiO2 films produced are amorphous. Energy dispersive spectroscopy (EDS), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) spectroscopy show elemental compositions of the films formed on the substrate surfaces to be SiO2. Film thickness formation by controlling the amount of the catalyst is discussed.

Synthesis and characterization Au doped TiO2film for photocatalytic function

Au doped <TEX>$TiO_2$</TEX> nanoparticles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. Au doped <TEX>$TiO_2$</TEX> was coated with glass substrate. The size of the particles and thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reaction of TTIP within the micro-emulsion. The average size of synthesized Au doped <TEX>$TiO_2$</TEX> nanoparticle was about in the size range of 15 to 25 nm and the Au particles formed mainly the range of 2 to 10 nm in diameter. The effect of synthesis parameters, such as the molar ratio of water to TTIP and the molar ratio of water to surfactant, are discussed. The synthesized nanopaticles were coated on glass substrate by a spin coating process. The thickness of thin film was about 80 nm. The degradation of MB on a <TEX>$TiO_2$</TEX> thin film was enhanced over 20 % efficiency by the incorporation of Au.

Preparation of Silica Microspheres Coated by Nano-ZrO&lt;sub&gt;2&lt;/sub&gt;

Silica microspheres coated by nanoZrO2 were prepared by the sol-gel process using butoxidesolution (TBOZ) as precursor. The nanomicrospheres were formed via hydrolysis and condension reaction of metal alkoxides with the hydroxyl (-OH) of silica microspheres by form Zr-O-Si bonds. The samples were characterized by X-ray diffraction, FT-IR and SEM. Presence of the FT-IR bands with frequencies ranging from 800 to 900 cm-1 can be assigned to SiO vibration, and to ZrOSi stretching vibration. XRD analysis shows obviously the characteristic diffraction peaks of tetragonal (T-ZrO2) in the sample by heat-treatment at 400°C. The SEM image showed that the surface layers of silica microspheres were coated by nanoparticles.

Synthesis and characterization of erbium-doped SiO2 nanoparticles fabricated by using reverse micelle and sol-gel processing

Erbium-doped SiO2 nanoparticles have been synthesized using a reverse micelle technique combined with metal-alkoxide hydrolysis and condensation. The sizes and the morphologies of the erbium-doped SiO2 nanoparticles could be changed by varying the molar ratio of water to surfactant. The sizes and the morphologies of the erbium-doped SiO2 nanoparticles were examined by using a transmission electron microscope. The average size of synthesized erbium-doped SiO2 nanoparticles was approximately 20–25 nm and that of the erbium particles was 3–5 nm. The effects of the synthesis parameters, such as the molar ratio of water to surfactant, are discussed.

Synthesis of Fe/SiO2 Core-Shell Nanoparticles by a Reverse Micelle and Sol-Gel Processes

Fe/<TEX>$SiO_2$</TEX> core-shell type composite nanoparticles have been synthesized using a reverse micelle process combined with metal alkoxide hydrolysis and condensation. Nano-sized <TEX>$SiO_2$</TEX> composite particles with a core-shell structure were prepared by arrested precipitation of Fe clusters in reverse micelles, followed by hydrolysis and condensation of organometallic precursors in micro-emulsion matrices. Microstructural and chemical analyses of Fe/<TEX>$SiO_2$</TEX> core-shell type composite nanoparticles were carried out by TEM and EDS. The size of the particles and the thickness of the coating could be controlled by manipulating the relative rates of the hydrolysis and condensation reaction of TEOS within the micro-emulsion. The water/surfactant molar ratio influenced the Fe particle distribution of the core-shell composite particles, and the distribution of Fe particles was broadened as R increased. The particle size of Fe increased linearly with increasing <TEX>$FeNO_3$</TEX> solution concentration. The average size of the cluster was found to depend on the micelle size, the nature of the solvent, and the concentration of the reagent. The average size of synthesized Fe/<TEX>$SiO_2$</TEX> core-shell type composite nanoparticles was in a range of 10-30 nm and Fe particles were 1.5-7 nm in size. The effects of synthesis parameters, such as the molar ratio of water to TEOS and the molar ratio of water to surfactant, are discussed.

Synthesis and Characterization of Sn Doped SiO&lt;sub&gt;2&lt;/sub&gt; by Reverse Micelle and Sol-Gel Process

Sn doped SiO2nanoparticles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. The size of the particles and the thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) within the micro-emulsion. The properties of the Sn doped SiO2nanoparticles were studied as a function of various processing parameters such as R and H value. The average size of synthesized Sn doped SiO2nanoparticles was about in the size range of 20-40 nm and core particle (Sn) 1-5 nm. The Sn doped SiO2nanoparticles were characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM).

Carbon–Nb0.07Ti0.93O2 composite supported Pt–Pd electrocatalysts for PEM fuel cell oxygen reduction reaction

Carbon–Nb0.07Ti0.93O2 (C67wt%–(Nb0.07Ti0.93O2)33wt%) composite support for Pt0.55Pd0.45 alloy catalysts was prepared by hydrolysis of metal alkoxides in the presence of carbon. Physical characterization by XRD, EDX, BET, TEM and TGA showed that the Nb0.07Ti0.93O2 was well distributed on the carbon particle surface with an average particle size of 15nm, and this support has a high surface area of 176m2/g and a similar porosity to that of carbon used to prepare this composite support. Pt0.55Pd0.45 alloy nanoparticles were deposited on the composite support to form a Pt0.55Pd0.45/C67wt%–(Nb0.07Ti0.93O2)33wt% catalyst, which shows a higher catalytic activity toward ORR than those of monometallic counterpart Pt/C67wt%–(Nb0.07Ti0.93O2)33wt%, Pt0.55Pd0.45/C, and Pt0.55Pd0.45/Nb0.07Ti0.93O2. Pt0.55Pd0.45/C67wt%–(Nb0.07Ti0.93O2)33wt% showed higher stability than Pt0.55Pd0.45/C, and similar to the commercially available Pt/C catalyst.

Structure and Catalytic Properties of Pd/10Al2O3·2B2O3. Effect of Preparation Routes and Additives

Abstract The synthesis route of 10Al2O3·2B2O3 (10A2B) and effect of additives were studied to use this compound as a thermally stable support material for Pd catalysts. The preparation by reverse coprecipitation was found to have a beneficial effect on the BET surface area of 10A2B and thus Pd metal dispersion, compared to other preparation routes via solid-state reaction and hydrolysis of metal alkoxides. The addition of 3 wt % BaO suppressed the sintering of 10A2B and Pd during thermal aging at 900 °C in a stream of air containing 10% H2O. Although direct interactions between Pd and the support material were not detected by EXAFS, the catalytic performance for NO–CO–C3H6–O2–H2O reactions under modulated air-to-fuel ratio (A/F) conditions was strongly influenced by the Ba additive. The activity for NO and C3H6 in a rich region (A/F &amp;lt; 14.6) was especially enhanced in the presence of Ba because of accelerated elemental reactions including NO–CO and NO–C3H6. In situ FT-IR of CO suggested that the Pd electronic state changed by electrostatic effect of Ba additives would activate NO and weaken the self-poisoning effect of C3H6.

Electrochemical Properties of TiO2 Electrode Prepared by Various Methods

Abstract Thin transparent TiO2 layers were created on the conductive ITO glass by means of the templated sol-gel technique and by the subsequent calcination at 450° C. The sol-gel method using molecular templating is based on a chemical process utilizing hydrolysis and polycondesation of metal alkoxides in the core of reverse micelles which allows a production of uniform particles in layers. The sol-gel method was chosen by reason of the sol-gel layers electrodes are transparent and possess very stabile surface. For the preparation of the thin sol-gel TiO 2 films, numerous deposition techniques were applied. This contribution is focused on the study of structural and photo-electrochemical properties of the sol-gel nanostructured layers deposited by two various techniques (a dip-coating and an inkjet printing). The sol's viscosity, concentration, solvent volatility, speed of pulling etc. may influence the final structural properties of layers, such as film thickness, nanoparticles size and surface morphology. The surface properties were determined by XRD, Raman, SEM, AFM and UV-Vis analyses. Photo-induced electrochemical properties were measured by potentiodynamic methods in the three-compartment electrochemical cell. This Pyrex cell contained supporting electrolyte (0.1 M Na2SO4) and the TiO2/ITO electrode was used as a working electrode. As an UV source the polychromatic mercury lamp was employed and the wavelength of the incident light was focused by an interference filter on 365 nm.

Effect of acid concentration on pore size in polymer-templated mesoporous alumina

Ordered mesoporous alumina and alumina-titania composites can be prepared in a facile and reproducible manner by mixing metal precursors, acid, solvent and polymer template in one-pot and performing evaporation induced self assembly followed by removal of the template. Structural characteristics, particularly pore size, of these materials can be tailored by controlling the acid concentration in the synthesis mixture. The optimal range for alumina materials with a large range of pore widths (4.0–10.5 nm), high surface areas (up to 467 m2 g−1) and significant pore volumes (up to 0.74 cm3 g−1) was found to be within the range of 1.2 and 3.0 moles of nitric acid per mole of metal. For well ordered, thermally stable titania-alumina samples the range over which nitric acid concentration produces high surface area (431 m2 g−1), large pore volume (0.79 cm3 g−1) and significant pore widths (up to 15.5 nm) is 1.2 to 3.0 moles of nitric acid to metal. The effect of acid concentration on the pore width is likely due to the combination of a salt-like effect from the increased concentration of H+ and NO3− ions, the effect of increased water concentration in the synthesis mixture and the direct relationship between the metal alkoxide hydrolysis rate and acid concentration.

ChemInform Abstract: A Novel Oxygen-Centered Hexanuclear Molybdenum Alkoxide Cluster, Mo6O( OEt)18.

The sol-gel approach, viz. hydrolysis of metal alkoxides and subsequent processing of the precipitated hydroxides or hydrous oxides, has become an important method for synthesis of oxide ceramics. Using this approach, the authors have recently attempted to isolate reduced molybdenum oxides by hydrolysis of appropriate molybdenum alkoxides. At present, further efforts are underway to develop rational syntheses of compounds of this type and to elucidate their spectroscopic and chemical properties.

ChemInform Abstract: Emulsion Precipitation of Yttria-Stabilized Zirconia for Plasma Spray Coatings.

This paper reports on chemically uniform, high-purity, yttria-stabilized zirconia (YSZ) powders prepared by emulsion hydrolysis of metal alkoxides, acetates, and mixtures of alkoxides and acetates. Both the morphology and particle size of the powders can be controlled by varying the hydrolysis conditions. Spherical or granular powders with particle sizes ranging from submicrometer to a few hundred micrometers were obtained. X-ray diffraction and EDX results showed that yttria was evenly distributed throughout the zirconia particles. The crystalline phase of the powders after calcination at 800{degrees}C was 100% nontransformable tetragonal. The powders were successfully sprayed by a plasma coating technique on stainless steel coupons, and the coatings were evaluated.

ChemInform Abstract: Chemical Processing and Microwave Characteristics of (Zr,Sn)TiO4 Microwave Dielectrics.

Monosized spherical particles of (Zr, Sn)TiO4 with an average diameter of about 0.3 μm were synthesized by the controlled hydrolysis of metal alkoxides. The as-prepared, amorphous, particles were compacted without any sintering aid, crystallized, and then sintered at 1600°C for 3 h into bodies with >96.0% of theoretical density. The dense sintered bodies of (Zr0.80Sn0.20)TiO4 showed good microwave characteristics; ɛr= 40.0, Q= 5000, and τt= 3 ppm/°C at 10 GHz. The dielectric constant was remarkably dependent upon the relative densities of the sintered bodies and the change of the lattice parameters, while Q value was mainly affected by the oxygen deficiency. An increase of the dielectric constant with the substitution of Sn4+ in ZrTiO4 was attributable to the enhancement of ionic polarization with the increase of the c-axis length.