Characterization and hydrogenation of methyl oleate over Ru/TiO2, Ru–Sn/TiO2 catalysts

The hydrogenation of methyl oleate over 2%Ru/TiO₂, 4.7%Sn/TiO₂ and 2%Ru–4.7%Sn–TiO₂ catalysts was studied. The catalysts were prepared by the impregnation method. The characterization techniques used were: (i) specific surface area (B.E.T. method); (ii) pore volume and mean pore diameter; (iii) thermogravimetric analysis (TGA); (iv) temperature programed reduction (TPR); (v) X-ray diffraction (DRX); and (vi) scanning electron microscopy (SEM). The results indicate that the presence of tin increases the difficulty of the ruthenium reduction, evidencing a possible metal–metal interaction. However, tin addition to the TiO₂ and the catalysts calcinations did not significantly influence the values obtained for the surface area and mean pore diameter. The DRX analyses showed that the catalysts have a crystalline structure, mostly in the anatase form. The metal-support interaction occurred probably due to the formation of RuTi of Ru/TiO₂ catalyst. In Ru–Sn/TiO₂ catalyst, the metal–metal interaction occurs between ruthenium and tin, resulting in Ru₃Sn₇. The catalysts reaction revealed that tin addition in ruthenium affects the activity of catalyst considerably in the hydrogenation of methyl oleate reaction. However, the activity decrease is accompanied by a considerable increase of alcohols yield, in particular of unsaturated alcohols.     

Composition dependence of the glass transition temperatures of PdNiP and PtNiP glasses

Thermal properties of glassy PdNiP and PtNiP alloys have been measured as a function of the concentration of transition metals. The glass transiion temperature, T_g, of these alloys glasses exhibits a negative linear deviation with transition metal content - which is in contrast to the increasing T_g of binary glassy alloys with increasing metalloids.It is suggested that the suppression of the glass transition temperature of these glassy alloys may be attributed to the excess configurational entropy of disorder associated with a mixture of hard spheres differing in radius. In contrast, the increasing T_g of binary glassy alloys with the metalloid content may be associated with the short-range order resulting from strong interactions between metal and metalloid atoms.     

Preparation and characterization of nickel based catalysts on silica,alumina and titania obtained by sol–gel method

This work reports the investigation of the characteristics of catalysts produced by the sol gel process. Our analysis focuses on the properties related to heterogeneous catalysis, such as methane steam reforming, dry reforming, hydrogenation of organic compositions. Alumina, silica and titania based materials doped with Ni were synthesized. The characterization techniques used were: temperature programmed reduction, thermogravimetric analysis, specific surface area and X-ray powder diffraction. The specific surface area values obey the following sequence: Ni–SiO₂ > Ni–Al₂O₃ > Ni–TiO₂. The temperature programmed reduction indicated that in the Ni–SiO₂ sample, the nickel oxide is present in two different forms on the surface; the Ni–Al₂O₃ material presented one peak at high temperature, suggesting the presence of a nickel aluminate form. However, Ni–TiO₂ did not present reduction peaks. The thermogravimetric analysis, which was performed under inert atmosphere, showed the decomposition of the organic residues adsorbed on surface. The X-ray powder diffraction patterns of calcined materials showed two crystalline forms for TiO₂ in Ni–TiO₂ rutile and anatase. In Ni–Al₂O₃, crystalline areas composed of α-Al₂O₃, γ-Al₂O₃ and NiO were observed and finally for Ni–SiO₂, amorphous areas and NiO were found.     

Temperature dependence of self-diffusion coefficient in several liquid metals

The temperature-dependent self-diffusion coefficient D(T) in liquid metals between the melting temperature T_m and boiling point T_b is modeled in terms of the relationship among D, liquid viscosity η, and liquid–vapor surface tension γ_lv. The model predictions for D(T) correspond to available experimental and molecular dynamics (MD) simulations results for liquid alkali metals Li, Na, Rb and Cs, semi-metal Al, transition and noble metals Ni, Cu, Ag and Au.     

Advanced nanostructure Ti0.7In0.3O2 support enhances electron transfer to Pt: Used as high performance catalyst for oxygen reduction reaction

ABSTRACT

The slow rate of the oxygen reduction reaction (ORR) and the instability of Pt based catalysts are two of the most important issues which must be solved in order to make proton exchange membrane fuel cells (PEMFCs) a reality. Here, we present a new approach by exploring robust non-carbon Ti_0.7In_0.3O₂ used as a novel functionalised co-catalytic support for Pt. This approach is based on the novel nanostructure Ti_0.7In_0.3O₂ support with “electronic transfer mechanism” from Ti_0.7In_0.3O₂ to Pt that can modify surface electronic structure of Pt, owing to a shift in the d-band centre of the surface Pt atoms. The 20 wt% Pt/Ti_0.7In_0.3O₂ catalyst shows high activity than that of that of the commercial 20 wt% Pt/C (E-TEK). Our data suggest this enhancement is a result of both the electronic structure change of Pt upon its synergistic interaction with Ti_0.7In_0.3O₂ and the inherent structural and chemical stability and the corrosion-resistance of the Ti_0.7In_0.3O₂ in acidic and oxidative environments.     

Nickel-alumina composite aerogel catalysts with a high nickel load: a novel fast sol-gel synthesis procedure and screening of catalytic properties

Nickel-alumina composite aerogels with large nickel loading were synthesized using a novel complexing agent-assisted sol-gel procedure to obtain materials displaying very large and open internal surface area, easily accessible for large molecules and demonstrating excellent catalytic properties. They were tested in the following reactions: (i) hydrogenation of propene and 1-butene, (ii) methanization of carbon dioxide, (iii) isometization of 1-butene, (iv) dehydrogenation of cyclohexane, (v) conversion of equimolar mixture of CO and NO to CO₂ and N₂. Full conversions and 100% selectivities were obtained in reactions (i), (ii), (iv) and (v) and an equilibrium composition in reaction (iii). These catalysts showed no pyrophoric activity on exposing to air even at Ni content as large as 50 wt%.     

Quenched-in excess volume and structural relaxation in Ni- and FeNi based metallic glasses

The amount of quenched-in excess volume (ΔV_R) in various Ni- and FeNi based metallic glasses, which is defined by the volume change due to the structural relaxation, was estimated from measurements of length changes caused by isochronal annealing. It was found that the values of ΔV_R depend greatly on the kind of transition metals (Fe, Ni) and metalloids (Si, B, P) and their ratios (Fe/Ni, Si/B). In non-magnetic Ni-based metallic glasses, almost a linear relationship was observed between the changes in volume and electrical resistivity during the low temperature annealing below around 275°C. Furthermore, a large ΔV_R was observed in the metallic glasses which have a large thermal expansion coefficient such as Ni₇₅Si_12.5B_12.5 or which exhibit a well-defined glass transition such as Fe₂₇Ni₅₃P₁₄B₆, as a general trend. These results indicate that the amount of quenched-in excess volume is very sensitive to the local atomic arrangement and is attributed mainly to the distribution in bond lengths, angles and coordination numbers in the short range structure and the difference in packing of basic structural units between as-quenched and relaxed glassy states.     

Characterization of Pr2O3 Added Metals/GaAs Schottky Diodes using X-ray Photoelectron Spectroscopy

In this research, the surface chemical structures of Pr₂O₃ doped Liquid Phase Epitaxy (LPE) layers were investigated by X-ray Photoelectron Spectroscopy (XPS). The bonding energies of these grown surfaces are studied under various adding conditions. The comparisons of these surface chemical structures were used to explain the evolutions of the grown surfaces with their effects on the Schottky barrier height. Because the surface states are lowered and the Fermi level is not pinned, these metals(Au, Ag, Ni, Pt)/GaAs Schottky structures all show an improved diode performance by adding Pr₂O₃. The resulting barrier height and ideality factor, as estimated by the current-voltage measurement, can be as high as 0.94+-0.02 eV and as unitary as 1.03+-0.01, respectively.     

Amorphous Ni59Nb40PtxM1−x (M = Ru, Sn) electrocatalysts for oxygen reduction reaction

The oxygen reduction reaction, ORR, on amorphous Ni₅₉Nb₄₀Pt₁, Ni₅₉Nb₄₀Pt_0.6Ru_0.4 and Ni₅₉Nb₄₀Pt_0.6Sn_0.4 electrocatalysts was analyzed by electrochemical techniques such as cyclic voltammetry, CV; rotating disk, RDE, and ring-disk electrodes, RRDE, in a 0.5 M H₂SO₄ solution. The reduced amount of platinum and the incorporation of transition metals in the amorphous catalysts were found to have significant effect on the kinetic parameters of the cathodic reaction. The kinetics study (RRDE) performed on the amorphous catalysts showed a high activity towards the ORR, preferentially proceeding via multi-electron (4e^?) charge transfer pathway toward water formation, with less than 2.8% H₂O₂ in the region of PEMFC applications. The performance on Ni₅₉Nb₄₀Pt₁ was different, which may be related to changes in the electrode surface enrichment of one or two of the amorphous alloy constituents. The performance towards the cathodic reaction allows to envisage that incorporation of small amounts of Pt in the catalyst, may lead to the fabrication of good amorphous electrocatalytic materials with possible applications as cathode electrodes in polymer electrolyte fuel cells.     

A facile approach towards synthesis,characterization, single crystal structure,and DFT study of 5-bromosalicylalcohol

5-Bromosalicylalcohol was prepared by the interaction of NaBH₄ and 5-bromosalicylaldehyde. The use of sodium borohydride makes the reaction easy, facile, economic and does not require any toxic catalyst. The compound is characterized by FTIR, ¹H NMR, ¹³C NMR, TEM and ESI-mass spectra. Crystal structure is determined by single crystal X-ray analysis. Quantum mechanical calculations of geometries, energies and thermodynamic parameters are carried out using density functional theory (DFT/B3LYP) method with 6-311G(d,p) basis set. The optimized geometrical parameters obtained by B3LYP method show good agreement with experimental data.     

Synthesis and Size-Selective Application of Palladium Metal Particles Intercalated in Mesopore-Size Controlled Smectite

Abstract

Mesoporous smectite-type materials (SM) were synthesized with a hydrothermal method from water glass, magnesium chloride and alkyl ammonium salt. The mesopore diameter of SM was controlled from 30 to 130 Å by changing the reaction temperature, pH and the template materials during hydrothermal treatment. Palladium metal particles were intercalated in the mesopores of SM with an ion-exchanging of [Pd(NH₃)₄Cl₂] on them and hydrogen reduction treatment. The size-selective hydrogenation of butadiene-acrylonitrile rubbers (NBR) in carbon tetrachloride was studied using palladium loaded smectite catalysts (Pd-SM). The reaction was controlled by the sizes of mesopore of Pd-SM, which determine the diffusion of polymer molecules onto the dispersed palladium particles within the pores.     

X-ray heating chamber investigations of reforming Pt-Al2O3 catalysts

Model catalysts with increased Pt content and commercial catalysts have been tested in an X-ray heating chamber at different temperatures and in various fluids (O₂, N₂, N₂/H₂ and Ar) at atmospheric pressure. In an air atmosphere and at temperatures between ambient and approx. 850 K, the Pt crystallites are subjected to superficial oxidation, sintering starts at approx. 850 K. In a hydrogen atmosphere, an increase in temperature at first results in the formation of crystalline Pt particles having a degree of crystallinity of 100% (error range 5%). Depending on the kind of sample and beginning at approx. 700 K, a Pt hydride phase which is stable in H₂ only and has a lattice constant of a = 3.875 Å is formed later on. Furthermore, conclusions for the evaluation and interpretation of X-ray measurements of catalysts are drawn.     

Pt immobilization on TiO2‐embedded carbon nanofibers using photodeposition

Currently, the use of fuel cell electrodes containing Pt catalysts has been limited due to technological problems in this system, primarily the system's high cost. The improvement of Pt catalyst use has been achieved by changes in the Pt immobilization method. In this study, we have studied Pt immobilization on carbon nanofiber composites using the photodeposition method. First, we prepared the carbon nanofibers, which were homogeneously embedded TiO₂ using the electrospinning technology. These TiO₂‐embedded carbon nanofiber composites (TiO₂/CNFs) were then immersed in a Pt precursor solution and irradiated with UV light. The obtained Pt‐deposited TiO₂/CNFs contained Pt that was immobilized on the carbon nanofibers, and the Pt particle size was 2‐5 nm. The XPS spectra showed that the amount of Pt increased with an increasing UV irradiation time. The current densities and total charge also increased with an increase in the UV irradiation time, possibly due to an increase of active specific area by finely dispersed Pt nanoparticles. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Alloying effect on the viscous flow in metallic glasses

The temperature dependence of viscosities near the glass transition is measured from the rates of thermal transformation for metallic glasses PtNiP, PdNiP, NiPBA1 and (Fe, Co)PBA1. Alloying among metallic elements which lowers the glass transition temperature T_g lowers the ideal glass transition temperature T₀, but raises the residual configurational entropy S_g and the activation energies for “diffusive” rearrangement, $\text{Δμ}{}^1$, of the alloying glasses, while compositional ordering associated with the addition of metalloids raises the T_g and T₀ and lowers the S_g and $\text{Δμ}{}^1$. Results are correlated to the atomic ordering and stability of the glasses. The extracted free volume and the critical diffusive volume are much smaller, by a factor of 4, for metallic glasses than for many other glasses.     

Zu Fragen der Legierungsbildung bei Bimetallkatalysatoren

Problems of alloying and surface composition of bimetallic catalysts and some results of investigations on alloying in Ni–Cu-η-Al₂O₃ catalysts are discussed.     

The effect of transition M metals on the two-stage enthalpy relaxation behavior of (FeM)83P17 amorphous alloys

The anneal-induced relaxation behavior for (FeM)₈₃P₁₇ (M  Cr, Mo, Mn, Co or Ni) amorphous alloys was examined calorimetrically with the aim to clarify the effect of M substitution on the two-stage relaxation previously found by the present authors. Upon heating the sample annealed at temperatures below T_g, a reversible endothermic reaction (enthalpy relaxation) occurs above T_a. The changes in ΔC_p,endo and with T_a show two distinguishable stages only for The FeMoP alloy which exhibits glass transition; a low-temperature peak at a temperature that is lower by about 180 K than T_g and a high-temperature one just below T_g. However, any indication of the high-temperature peak is not detected for the other alloys which crystallize before T_g. From the data of ΔC_p,endo, ΔH_σ,endo and activation energy for the low-temperature peak which has been thought to generate by relaxation of metal atoms, the first-stage relaxation was concluded to become difficult in the order of Ni < Co < Mn < Cr < V < Mo, i.e., with the decrease in the group number of the periodic table. The change in the first-stage enthalpy relaxation behavior with the substitution of Fe by M is interpreted to originate from the change in the mobility (i.e., relaxation time) of metal atoms through the change in the bonding force among the constituent elements.     

Synthetic nanodiamonds (SNDs) containing bimetallic Ni(Co)–Fe composites: preparation,characterization and catalytic performance in the reaction of CO2 methanation

Abstract

In this article, we present the preparation, characterization, and catalytic performance of bimetallic Co₉₃Fe₀₇ and Ni₈₀Fe₂₀ active mass loaded on synthetic nanodiamonds (SNDs) in the carbon dioxide (CO₂) methanation. The pristine SNDs possessing a developed specific surface are thermally stable and inert to the reaction mixture of CO₂ and dihydrogen. However, it is shown that 100% conversion of CO₂ into methane can be reached at the lower temperature than that for a massive Co₉₃Fe₀₇ or Ni₈₀Fe₂₀ catalyst when 20?wt.% of the catalyst mass was loaded on the surface of SNDs. The catalytic activity of the prepared bimetallic/SNDs composites is estimated as the minimum temperature at the maximum conversion of CO₂ at atmospheric pressure: it is 325 and 290?°C for Co₉₃Fe₀₇/SNDs and Ni₈₀Fe₂₀/SNDs, respectively. Thermal desorption studies showed that the methanation over Co-Fe/SNDs and Ni-Fe/SNDs catalysts run through the stage of CO₂ dissociation into carbon and oxygen atoms and their subsequent interaction with hydrogen to form methane and water molecules. Scanning electron microscopy studies have shown that the presence of transition metal-rich sites on the surface of the carrier contributes to the improvement of efficiency of the Ni₈₀Fe₂₀ catalyst action.     

Platinum-catalyst-assisted metalorganic vapor phase epitaxy of InN

This paper reports the first attempt of the Pt-catalyst-assisted MOVPE growth of InN. In order to enhance NH₃ decomposition at a relatively low growth temperature (～550 °C), Pt is used as a catalyst. The catalyst is installed in the NH₃ introduction tube in the MOVPE reactor and the tube is located just above the susceptor to be heated. Compared with InN films grown without the catalyst, the samples grown with Pt catalyst show improved electrical properties; a carrier concentration in the order of 10¹⁸ cm^?3 and a Hall mobility as high as 1350 cm²/Vs are obtained. The crystalline quality is also improved by employing the catalyst and a tilt fluctuation as low as 8.6 arcmin is obtained for a sample grown on a GaN/sapphire template. It is confirmed that for InN films grown at 550 °C with Pt catalyst, the electrical and crystallographic properties are also improved with increase in thickness. These results indicate that the growth at around 550 °C with the Pt catalyst is performed under the circumstances where NH₃ is effectively decomposed, whereas the deterioration of InN during growth is significantly suppressed.     

Non-crystalline mesoporous aluminosilicates catalysts: Synthesis, characterization and catalytic applications

Non-crystalline mesoporous aluminosilicate materials were synthesized using citric acid as a pore-forming agent. The amount of Al incorporated in the mesoporous framework could be controlled by adjusting the addition of citric acid. The analytical techniques of N₂ adsorption/desorption and transmission electron micrographs (TEM) had been applied to characterize the textural properties of the new mesoporous materials. ²⁷Al nuclear magnetic resonance (²⁷Al MAS NMR) and temperature-programmed desorption (NH₃-TPD) of ammonia techniques suggested that most of the Al was present in tetrahedral coordination and imparted acid sites. Tert-butylation of phenol was carried out to evaluate the catalytic activity of the novel mesoporous aluminosilicate catalysts. In addition, the influence of various reaction parameters such as reaction time, reaction temperature, and reactant ratio and weight hourly space velocity were also studied. At the reaction temperature of 418 K, phenol conversion of 92.3% and 2,4-di-tert-butyl phenol selectivity of 45.7% over the optimum novel catalyst (CA-32) were observed, which was much higher than those over the conventional mesoporous Al-MCM-41 catalyst.     

The Effect of Li on Structure of Supported Rh Particles in Zeolite

Abstract

We prepared Rh ion exchanged Y-type zeolite (RhY) and Li-doped RhY (Li/RhY) catalysts and studied the structure transformation of Rh intercalated species during CO adsorption and CO₂ hydrogenation by EXAFS and TEM. We found that Rh particles in RhY initially supported inside the zeolite cage as 1.3 nm spherical or hemispherical particles. CO exposure of the fresh RhY caused formation of atomically dispersed Rh species. After CO₂ hydrogenation and following reduction, the Rh particles aggregated to form 3.3 nm particles on the outer surface. Meanwhile, Rh particles in Li/RhY were embedded in the zeolite cages, which were narrowed by Li deposition on the wall. The size of the Rh particles was 0.8 nm in diameter. The Rh particles in Li/RhY were stable under reduction, CO adsorption, and CO₂ hydrogenation conditions. We concluded Li additive changed the stability of Rh particles in the supercage by modifying surface hydroxyl group concentration.