In situ STM study of nanosized Ru and Os islands spontaneously deposited on Pt(1 1 1) and Au(1 1 1) electrodes

We provide an overview of structure and reactivity of selected bimetallic single crystal electrodes obtained by the method of spontaneous deposition. The surfaces that are described and compared are the following: Au(1 1 1)/Ru, Pt(1 1 1)/Ru and Pt(1 1 1)/Os. Detailed morphological information is presented and the significance of this work in current and further study of nanoisland covered surfaces in the catalytic and spectroscopic perspective is highlighted. All surfaces were investigated by in situ STM and by electroanalytical techniques. The results confirm our previous data that nanosized Ru islands are formed with specific and distinctive structural features, and that the Ru growth pattern is different for Au(1 1 1) and Pt(1 1 1). For Au(1 1 1), Ru is preferentially deposited on steps, while a random and relatively sparse distribution of Ru islands is observed on terraces. In contrast, for Ru deposited on Pt(1 1 1), a homogeneous deposition over all the Pt(1 1 1) surface was found. Os is also deposited homogeneously, and at a much higher rate than Ru, and even within a single deposition it forms a large proportion of multilayer islands. On Au(1 1 1), the Ru islands on both steps and terraces reach the saturation coverage within a short deposition time, and the Ru islands grow to multilayer heights and assume hexagonal shapes. On Pt(1 1 1), the Ru saturation coverage is reached relatively fast, but when a single deposition is applied, Ru nanoislands of mainly monoatomic height are formed, with the Ru coverage not exceeding 0.2 ML. For Ru deposits on Pt(1 1 1), we demonstrate that larger and multilayer islands obtained in two consecutive depositions can be reduced in size--both in height and width--by oxidizing the Ru islands and then by reducing them back to a metallic state. A clear increase in the Ru island dispersion is then obtained. However, methanol oxidation chronoamperometry shows that the surface with such a higher dispersion is less active to methanol oxidation than the initial surface. A preliminary interpretation of this effect is provided. Finally, we studied CO stripping reaction on Pt(1 1 1)/Ru, Au(1 1 1)/Ru and on Pt(1 1 1)/Os. We relate CO oxidation differences observed between Pt(1 1 1)/Ru and Pt(1 1 1)/Os to the difference in the oxophilicity of the two admetals. In turn, the difference in the CO stripping reaction on Pt(1 1 1)/Ru and Au(1 1 1)/Ru with respect to the Ru islands is linked to the effect of the substrate on the bond strength and/or adlayer structure of CO and OH_ads species.     

Effect of Ni doping on the structural and magnetic properties of FePt nanoparticles

A serial of FePtNi nanoparticles were investigated on their crystal structure and magnetic properties. The FePtNi nanoparticles were synthesized simultaneously by the reduction of iron (III) acetylacetonate, platinum (II) acetylacetonate and nickel (II) acetylacetonate with 1,2-hexadecanediol as the reducing agent. The X-ray diffraction patterns indicate that the addition of 8, 12, 17 at% Ni in FePt nanoparticles suppressed the transformation of the particles from disorder face-centered cubic to order face-centered tetragonal L1₀-phase under annealing treatment. However, further increasing Ni contents to 21 at%, the nanoparticle transformed to L1₂ phase. Doping of Ni into the FePt compound system may decrease coercivity and crystal anisotropy energy. A maximum coercivity of 7 KOe at room temperature was obtained for (Fe₅₂Pt₄₈)₉₂Ni₈ nanoparticles after annealing at 600 °C for 30 min.     

A study on the optical and electrical properties of direct-patternable ZnO films incorporated various contents of Pt nanoparticles

Platinum nanoparticles were synthesized by the methanol reduction method, and their size was controlled to 3 nm on average using PVP [poly(N-vinyl-2-pyrrolidon)] as a protecting unit. Various contents of Pt nanoparticles were incorporated into ZnO solutions which were synthesized by a sol-gel process. ZnO films with Pt nanoparticles of various content were annealed at 500 °C and 600 °C for 1 h. The crystallinity increased with the annealing temperature and also slightly with the content of Pt nanoparticles. The sheet resistance of ZnO films decreased with the incorporation of Pt nanoparticles, however the decreasing behavior was not maintained with increasing content of Pt nanoparticles. A shift of valence band maximum energy of ZnO film with Pt nanoparticles to higher energy was also observed due to electron transfer from Pt nanoparticles to ZnO film. The optical transmittance was 88 ± 2% in the visible region for all the ZnO films. Well-defined 60 μm wide direct-patterned ZnO films containing Pt nanoparticles of 0.5 atomic percent could be formed without using dry etching process.     

Nanofibers and nanoplatelets of MoO3 via an electrospinning technique

Polyvinyl alcohol (PVA)/ammonium molybdate composite fibers were prepared by using sol-gel processing and electrospinning technique. After calcinations of the above precursor fibers at 500 °C, MoO₃ nanofibers with a diameter of 100-150 nm were successfully obtained. MoO₃ nanoplatelets and submicron platelets were prepared by further calcinations of the MoO₃ nanofibers at 600 and 700 °C. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). A possible growth mechanism for the MoO₃ nanofibers and nanoplatelets was suggested.     

NiO+YSZ anode substrate for screen-printing fabrication of YSZ electrolyte film in solid oxide fuel cell

Anode substrate has a great effect on screen-printing fabrication of yttria-stabilized zirconia (YSZ) electrolyte film and cell performance. In this work, NiO+YSZ anode substrate was prepared by a conventional ceramic sintering method, on which dense YSZ electrolyte film was successfully fabricated by screen-printing method. Microstructure of the anode substrate and cell performance were investigated. The optimal amount of addition of starch to the anode substrate was 20 wt%. The optimal temperature for pre-sintering of NiO powder was 800 °C. A single cell with the NiO powder pre-sintered at 800 °C exhibited the highest power density of 0.95 W cm⁻² at 700 °C.     

Preparation and characterization of CuZnAl catalysts by citrate gel process

CuZnAl catalysts with different Cu loading (1-23 wt%) and a Zn:Al atomic ratio nearly constant (Zn:Al≅0.6), were prepared by the citrate sol-gel method and characterized by different techniques such as TG, BET, TPR, XRD and FTIR. The final structure obtained was strongly influenced by the calcination temperature and metal precursor composition. XRD and quantitative Rietveld revealed Zn and Al species were mainly incorporated into the normal spinel matrix and copper predominantly forms CuO. The formation of a ZnAl₂O₄ spinel was favored by increasing Cu amounts and/or by increasing calcination temperature (from 500° to 700 °C). The spinel phase of the catalysts calcined at 700 °C, had a good thermal stability and it was preserved after TPR measurements. Under hydrogen atmosphere Cu²⁺ was fully reduced to Cu⁰. Although the composition and the calcination temperature have a strong influence on the phase nature in CuZnAl catalysts, the reducibility of Cu species changes in a non significant way.     

A nanogravimmetric investigation of the charging processes on ruthenium oxide thin films and their effect on methanol oxidation

The charging processes and methanol oxidation that occur during the oxidation-reduction cycles in a ruthenium oxide thin film electrode (deposited by the sol-gel method on Pt covered quartz crystals) were investigated by using cyclic voltammetry, chronoamperometry and electrochemical quartz crystal nanobalance techniques. The ruthenium oxide rutile phase structure was determined by X-ray diffraction analysis. The results obtained during the charging of rutile ruthenium oxide films indicate that in the anodic sweep the transition from Ru(II) to Ru(VI) occurs followed by proton de-intercalation. In the cathodic sweep, electron injection occurs followed by proton intercalation, leading to Ru(II). The proton intercalation/de-intercalation processes can be inferred from the mass/charge relationship which gives a slope close to 1 g mol⁻¹ (multiplied by the Faraday constant) corresponding to the molar mass of hydrogen. From the chronoamperometric measurements, charge and mass saturation of the RuO₂ thin films was observed (440 ng cm⁻²) during the charging processes, which is related to the total number of active sites in these films. Using the electrochemical quartz crystal nanobalance technique to study the methanol oxidation reaction at these films was possible to demonstrate that bulk oxidation occurs without the formation of strongly adsorbed intermediates such as CO_ads, demonstrating that Pt electrodes modified by ruthenium oxide particles can be promising catalysts for the methanol oxidation as already shown in the literature.     

Electrocatalytic performance of bimetallic platinum–ruthenium nanoclusters supported on graphite nanofibers

In this work, graphite nanofibers (GNFs) as a catalysts supports were impregnated with Pt and Ru precursor compounds to investigate the effect of various Pt–Ru compositions on the catalytic activity of direct methanol fuel cells (DMFCs). The particle sizes and morphological structures of the catalysts were analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical oxidation of the prepared catalysts was investigated by cyclic voltammetry (CV) measurement. Inductive coupled plasma-mass spectrometer (ICP-MS) analysis showed that the metallic ratio in the catalysts was very near to expectations. Cyclic voltammetry showed that the catalysts were electro catalytically active in the methanol oxidation. Among the prepared catalysts, the Pt₅₀Ru₅₀ catalysts exhibited the best electrocatalytic performance. It was concluded that catalytic activity is dependent on the alloy compositions of the catalysts, and that Ru metal has a positive effect on CO poisoning of Pt metal for methanol oxidation.     

Preparation of nano-sized platinum metal catalyst using photo-assisted deposition method on mesoporous silica including single-site photocatalyst

Pt particles in a uniform dispersion were successfully synthesized on single-site photocatalyst (Ti-containing mesoporous silica (Ti-HMS)) under UV-light irradiation by a photo-assisted deposition (PAD) method. Using an aqueous solution of H₂PtCl₆ as a precursor, the nano-sized Pt metal particles were deposited directly on the photo-excited tetrahedrally coordinated titanium oxide moieties within the framework of mesoporous silica (PAD-Pt/Ti-HMS). The Pt catalysts were characterized by means of XRD, Pt L_III-edge XAFS, CO adsorption, and TEM analysis. It was demonstrated that Pt particles had mean diameter of 4 nm in a narrow size distribution. Meanwhile, Pt particles loaded by a conventional impregnation method (imp-Pt/Ti-HMS) showed a wide size distribution ranging from 2 to 30 nm. The PAD-Pt/Ti-HMS catalyst was more active in the CO oxidation than the conventional impregnated imp-Pt/Ti-HMS catalyst. It is suggested that the PAD method using single-site photocatalyst is a useful and unique technique to prepare fine and uniform Pt nanoparticles.     

Visible luminescence of Al2O3 nanoparticles embedded in silica glass host matrix

This paper deals with the sol-gel elaboration and defects photoluminescence (PL) examination of Al₂O₃ nanocrystallites (size ∼30 nm) confined in glass based on silica aerogel. Aluminium oxide aerogels were synthesized using esterification reaction for hydrolysis of the precursor and supercritical conditions of ethyl alcohol for drying. The obtained nanopowder was incorporated in SiO₂ host matrix. After heating under natural atmosphere at 1150 °C for 2 h, the composite Al₂O₃/SiO₂ (AS) exhibited a strong PL bands at 400-600 and 700-900 nm in 78-300 K temperature range. PL excitation (PLE) measurements show different origins of the emission. It was suggested that OH-related radiative centres and non-bridging oxygen hole centres (NBOHCs) were responsible for the bands at 400-600 and 700-900 nm, respectively.     

A study of structural, compositional and optical properties of spray-deposited non-stoichiometric (Zn,Fe)S thin films

Non-stoichiometric ternary chalcogenides (Zn,Fe)S were prepared in the film form by pyrolytic spray deposition technique, using air/nitrogen as the carrier gas. The precursor solution comprised of ZnCl₂, FeCl₂ and thiourea. The depositions were carried out under optimum conditions of experimental parameters viz. carrier gas (air/nitrogen) flow rate, concentration of precursor constituents, nozzle substrate distance and temperature of quartz substrate. The deposited thin films were later sintered in argon at 1073 K for 120 min.The structural, compositional and optical properties of the sintered thin films were studied. X-ray diffraction studies of the thin films indicated the presence of (Zn,Fe)S solid solution with prominent cubic sphalerite phase while surface morphology as determined by scanning electron microscopy (SEM) revealed a granular structure.The chemical composition of the resulting thin films as analyzed by energy dispersive X-ray analysis (EDAX) reflected the composition of the precursor solutions from which the depositions were carried out with Fe at% values ranging from 0.4 up to 33.SEM micrographs of thin films reveal that the grain sizes of the thin films prepared using air as carrier gas and N₂ as carrier gas are in the vicinity of 300 and 150 nm, respectively.The diffuse transmittance measurements for thin films, as a function of wavelength reveal the dependence of direct optical band gap on Fe content and type of phase.     

Synthesis and characterization of room-temperature ferromagnetism in Fe- and Ni-co-doped In2O3

Observation of room-temperature ferromagnetism in Fe- and Ni-co-doped In₂O₃ samples (In_0.9Fe_0.1−xNi_x)₂O₃ (0?x?0.1) prepared by citric acid sol-gel auto-igniting method is reported. All of the samples with intermediate x values are ferromagnetic at room-temperature. The highest saturation magnetization (0.453 μ_B/Fe+Ni ions) moment is reached in the sample with x=0.04. The highest solubility of Fe and Ni ions in the In₂O₃ lattice is around 10 and 4 at%, respectively. The 10 at% Fe-doped sample is found to be weakly ferromagnetic, while the 10 at% Ni-doped sample is paramagnetic. Extensive structure including Extended X-ray absorption fine structure (EXAFS), magnetic and magneto-transport including Hall effects studies on the samples indicate the observed ferromagnetism is intrinsic rather than from the secondary impurity phases.     

Thermal treatment effects on the Ru/CeO2 catalysts performance for partial hydrogenation of benzene

The aim of this work is to study the effect of the preparation conditions of Ru/CeO₂ catalyst (calcination temperature and/or reduction) over the performance in the partial hydrogenation of benzene reaction in the presence of TiCl₃. The catalysts were prepared through chlorinated precursors by incipient wetness impregnation method. The reaction occurred in three-phase reactional medium in presence of water at 373 K and 5.0 MPa. Temperature programmed reduction (TPR) profiles of calcinated catalysts indicate the presence of oxidated ruthenium. X-ray photoelectron spectroscopy (XPS) analysis confirms this supposition, showing that the ruthenium appears in the form of RuO₂ for the sample calcinated at 673 K, while for the reduced solid at 773 K, the Ru appears in the metallic state. However, the calcination step followed or not by reduction, strongly hinders the catalytic performance. In its turn, the direct reduction leads to a more active Ru/CeO₂ catalysts, as well as higher cyclohexene yields throughout all the reaction.     

Infrared spectroscopy on size-controlled synthesized Pt-based nano-catalysts

Pt, Ru and Pt/Ru nano-particles, synthesized in ethylene glycol solutions, are studied using infrared (IR) spectroscopy and high resolution transmission electron microscopy (HRTEM). The synthesis method allows the control of the mono- and bi-metallic catalyst particle sizes between 1 and 5.5 nm. The IR spectra of CO adsorbed (CO_ads) on the Pt, Ru and bi-metallic Pt/Ru colloids are recorded as a function of the particle size. The stretching frequency of CO_ads depends on the particle size and composition. Strong IR bands due to the stretching vibration of CO_ads are observed between 2010 and 2050 cm⁻¹ for the Pt nano-particles, while two IR bands between 2030 and 2060 cm⁻¹ for linear bonded CO_ads, and at lower wavenumbers between 1950 and 1980 cm⁻¹ for bridged bonded CO_ads, are found for the Ru particles. The IR spectra for the Pt/Ru nano-sized catalyst particles show complex behaviour. For the larger particles (>2 ± 0.5 nm), two IR bands representative of CO_ads on Ru and Pt-Ru alloy phases, are observed in the range of 1970-2050 cm⁻¹. A decrease in the particle size results in the appearance of a third band at ∼2020 cm⁻¹, indicative of CO_ads on Pt. The relative intensity of the band for CO_ads on the Pt-Ru alloy vs. the Pt phase decreases with decreasing particle size. These results suggest that Ru is partially dissolved in the Pt lattice for the larger Pt/Ru nano-particles and that a separate Ru phase is also present. A Pt-Ru alloy and Ru phase is observed for all Pt/Ru particles prepared in this work. However, a decrease in particle size results in a decrease of the number of Pt and Ru atoms in the Pt-Ru alloy phase, as they are increasingly present as single Pt and Ru phases.     

Preparation and characterization of a layered transparent luminescent thin film of silica-CTAB-Tb(acac)3 composite with mesostructure

A layered luminescent mesostructured thin film of silica-CTAB-Tb(acac)₃ composite has been synthesized by a dip-coating process through an in situ sol-gel method. The terbium (Tb³⁺) ion and β-diketone organic ligand acetylacetone (acac) were introduced into the precursor solution, respectively. The as-synthesized composite film was transparent, colorless and possessed a layered structure. After the composite film was dried at 50 °C for a few minutes Tb(acac)₃ complex was synthesized in the mesostructured thin film, which can be indicated by the luminescence of the composite film under the UV lamp. The properties of the samples were characterized by XRD, absorption, Fourier transform infrared spectroscopy, and luminescent spectra.     

Formic acid decomposition on palladium-coated Pt(1 1 0)

Pt/Pd anode catalysts for direct formic acid polymer electrolyte membrane fuel cells outperform both Pt and Pd in steady-state electrooxidation trials. Temperature-programmed desorption (TPD) experiments in ultra-high vacuum (UHV) were performed with 1 L formic acid on clean Pt(1 1 0), 0.6 monolayers Pd/Pt(1 1 0), and multilayer Pd/Pt(1 1 0) to gain a better understanding of the effect of Pd additions to a Pt catalyst. Both dehydration and dehydrogenation of formic acid occur on all three surfaces. As Pd coverage increases, the activation barrier for formate decomposition to CO₂ decreases, but the effect does not explain the unusual activity of Pt/Pd in the electrochemical environment.     

Preparation of nanocomposite PbO·CuO/CNTs via microemulsion process and its catalysis on thermal decomposition of RDX

Mixture of carbon black, copper and lead was used as catalyst of high-content RDX-composite-modified double base propellant. To enhance the catalytic effect and improve the flaring performance, metal oxide deposited on carbon nanotubes (CNTs) are replaced with afore-mentioned catalyst. A new type of nano-combustion catalyst is synthesized with microemulsion process. In present work, ternary diagram was adopted to analyze the essential factors which affect microemulsion, including temperature, surfactant or cosurfactant and concentration of solution in order to find the best technical parameters and thus to control the core formation and growth of oxides on the nano-template. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) are applied to characterize the products. Through observation of microstructures and analysis of crystal structure, it is confirmed that nano-oxides are deposited on the surface of carbon nanotubes. Its particle size is below 50 nm. According to propellant components, a certain amount of combustion catalyst and RDX will be mixed. PbO·CuO/CNTs can catalyze thermal decomposition of RDX by thermal analysis. The results show that the new catalysts obviously accelerate the decomposition of RDX, and the peak temperature of decomposition reduce by 14.1 °C. The catalytic effect of nano-catalyst is better than original catalyst.     

Electronic state of ruthenium deposited onto oxide supports: An XPS study taking into account the final state effects

The electronic state of ruthenium in the supported Ru/EO_x (EO_x = MgO, Al₂O₃ or SiO₂) catalysts prepared by with the use of Ru(OH)Cl₃ or Ru(acac)₃ (acac = acetylacetonate) and reduced with H₂ at 723 K is characterized by X-ray photoelectron spectroscopy (XPS) in the Ru 3d, Cl 2p and O 1s regions. The influence of the final state effects (the differential charging and variation of the relaxation energy) on the binding energy (BE) of Ru 3d_5/2 core level measured for supported Ru nanoparticles is estimated by comparison of the Fermi levels and the modified Auger parameters determined for the Ru/EO_x samples with the corresponding characteristics of the bulk Ru metal. It is found that the negative shift of the Ru 3d_5/2 peak which is observed in the spectrum of ruthenium deposited onto MgO (BE = 279.5-279.7 eV) with respect to that of Ru black (BE = 280.2 eV) or ruthenium supported on γ-Al₂O₃ and SiO₂ (BE = 280.4 eV) is caused not by the transfer of electron density from basic sites of MgO, as considered earlier, but by the differential charging of the supported Ru particles compared with the support surface. Correction for the differential charging value reveals that the initial state energies of ruthenium in the Ru/EO_x systems are almost identical (BE = 280.5 ± 0.1 eV) irrespectively of acid-base properties of the support, the mean size of supported Ru crystallites (within the range of 2-10 nm) and the surface Cl content. The results obtained suggest that the difference in ammonia synthesis activity between the Ru catalysts supported on MgO and on the acidic supports is accounted for by not different electronic state of ruthenium on the surface of these oxides but by some other reasons.     

LDH-intercalated d-gluconate: Generation of a new food additive-inorganic nanohybrid compound

Intercalation of d-gluconate into the interlamellae of zinc-aluminum-layered double hydroxide for the formation of a food additive-inorganic layered nanohybrid was accomplished by both direct (co-precipitation) and indirect (ion-exchange) methods. Powder X-ray diffraction (PXRD) together with CHNS and Fourier transform infrared (FTIR) analyses showed that the hybridization of d-gluconate with pure phase and good crystallinity was successfully accomplished by a direct method within ranges of pH 7.5-10, Zn to Al initial molar ratio of 2-5 and DG concentration of 0.05-0.3 M. The same nanohybrid compound was also prepared using an indirect ion-exchange method by contacting the pre-prepared LDH with 0.1 M DG for 80 min. The basal spacing of the nanohybrid synthesized by the direct method ranged between 9 and 12.0 Å while that synthesized by the indirect ion-exchange method was 14.0 Å. The crystallinity of the latter was higher than the former and it inherited the crystallinity of the precursor. This work shows that a food additive, such as d-gluconate, can be hybridized into an inorganic host for the formation of a new nanohybrid compound, which can be used to regulate the release of acidity in the food industry.     

Thin porous Ni-YSZ films as anodes for a solid oxide fuel cell

Porous Ni-YSZ (YSZ—yttria-stabilized zirconia) films were fabricated by reactive co-sputtering of a Ni and a Zr-Y target, followed by sequentially annealing in air at 900 °C and in vacuum at 800 °C. The Ni-YSZ films comprised small grains and pores that were tens of nanometers in size. The porous Ni-YSZ films were used as an anode on one side of a YSZ electrolyte disc and a La_0.7Sr_0.3MnO₃ thick film was used as a cathode on the other side of the disc to form solid oxide fuel cells (SOFCs). The voltage-current curves of the SOFCs with single- and a triple-layered porous anodes were measured in a single-chamber configuration, in a mixture of CH₄ and air (CH₄:O₂ volume ratio=2:1). The maximum power density of the SOFC using the single-layered porous Ni-YSZ thin films as the anode was 0.38 mW cm⁻², which was lower than that of 0.76 mW cm⁻², obtained using a screen-printed Ni-YSZ thick anode. The maximum power density of the SOFC with a thin anode was increased, but varied between 0.6 and 1.14 mW cm⁻² when a triple-layered porous Ni-YSZ anode was used.