Co-deposition Of Pd Research Articles

CO2 hydrogenation to methanol on intermetallic PdGa and PdIn catalysts and the effect of Zn co-deposition

The behaviour of Pd deposited on Ga2O3 and In2O3 by CVI is compared for the hydrogenation of CO2 to methanol. Ga2O3 alone is inactive, but In2O3 has good conversion, and selectivity as high as 89 % to CH3OH. The addition of Pd to the catalysts had relatively little effect for In2O3, but in contrast, the addition of Pd to Ga2O3, has a very big effect, inducing high activity and selectivity to methanol. Both oxides form Pd intermetallics - Pd2In3 and Pd2Ga. However, for the In catalysts there is also a thick (∼3 nm) overlayer of the oxide, while for the Ga catalyst there was no such overlayer. Hence this is why addition of Pd to the Indium catalysts has relatively little effect on performance compared with Ga. Furthermore, the effect of Pd and Zn co-deposition on Ga₂O₃ and In₂O₃ was investigated, as well as the effect of the support morphology. Upon co-deposition of Pd and Zn, and after reduction, the Pd2In3 catalyst remains phase stable, whereas the Pd2Ga alloy is replaced by PdZn, and is improved in methanol yield.

Codeposition of Palladium and Gold on Nickel Wire Electrodes via Galvanic Replacement Reactions for Ethanol Oxidation

Codeposition of Pd and Au on a Ni wire was explored using a simple treatment of Ni wire electrodes in aqueous solutions containing both K2PdCl4 and HAuCl4, and the electrochemical properties of the...

Codeposition of Pd and Pb and electrocatalytic properties of their composite

A mixed electrolytic deposit (e.d.) PdPb with 33 ± 4 at.% Pb is obtained on the gold electrode from 5 mM PdCl2 + 0.7 mM Pb(ClO4)2 + 0.1 M HClO4 under potentiostatic conditions in the region of lead underpotential deposition (+100 mV vs. RHE). The deposit is characterized by SEM, EDX, XPS, CVA and ICP- AES methods before and after polarization measurements. The problem of thermodynamic instability of the deposit is discussed. It is shown that cycling of the potential of e.d. PdPb in the interval of 0.1–1.25 V results in preferential dissolution of Pb; however, no dense Pd shell is formed. The codeposition of Pb with Pd increases the degree of dispersion and the defectiveness of the deposit. The possible reasons for the lower specific activity of e.d. PdPb in formic acid oxidation reaction (FAOR) as compared with e.d. Pd are considered. The high solubility of Pd from e.d. PdPb as compared with e.d. Pd is observed. The latter effect cannot be explained by only the increased surface area of the Pd component; it is assumed that the defectiveness of the deposit structure is also responsible for this effect.

Effect of the Co-deposition of Pd and Pt on $$\hbox {TiO}_{2}$$ TiO 2 Photoactivity

$$\hbox {TiO}_{2}$$ was obtained by a simple sol–gel synthesis and subsequently modified by the addition of Pt and/or Pd particles on the surface by photodeposition. These photocatalysts were characterised by X-ray diffraction analysis, UV–Vis diffuse reflectance spectra, Brunauer–Emmett–Teller measurements, Fourier transform infrared spectroscopy, transmission electron microscopy, electron dispersive spectroscopy and X-ray photoelectron spectroscopy. Their photocatalytic activity was studied by following the degradation, mineralisation and detoxification of solutions of phenol, propanil and methylene blue. For comparison purposes, different commercial $$\hbox {TiO}_{2}$$ catalysts were also tested: Kronos vlp7000, Millenium PC100, Aeroxide P90 and Aeroxide P25. This latter catalyst was also modified with Pt and/or Pd. The degradation kinetics of all the pollutants in aqueous solutions satisfactorily followed the pseudo-first order according to the Langmuir–Hinshelwood model in conditions of low concentration values. It was found that the simultaneous photodeposition of Pt and Pd contributed to enhancing photoactivity more than the individual deposition of either Pt or Pd.

Pd Nanoparticle Formation in Ionic Liquid Thin Films Monitored by in situ Vibrational Spectroscopy.

Ionic liquids (ILs) are flexible reaction media and solvents for the synthesis of metal nanoparticles (NPs). Here, we describe a new preparation method for metallic NPs in nanometer thick films of ultraclean ILs in an ultrahigh vacuum (UHV) environment. CO-covered Pd NPs are formed by simultaneous and by sequential physical vapor deposition (PVD) of the IL and the metal in the presence of low partial pressures of CO. The film thickness and the particle size can be controlled by the deposition parameters. We followed the formation of the NPs and their thermal behavior by time-resolved IR reflection absorption spectroscopy (TP-IRAS) and by temperature-programmed IRAS (TR-IRAS). Codeposition of Pd and [C1C2Im][OTf] in CO at 100 K leads to the growth of homogeneous multilayer films of CO-covered Pd aggregates in an IL matrix. The size of these NPs can be controlled by the metal fraction in the co-deposit. With increasing metal fraction, the size of the Pd NPs also increases. At very low metal content, small Pd carbonyl-like species are formed, which bind CO in on-top geometry only. Upon annealing, the [OTf](-) anion coadsorbs at the NP surface and partially displaces CO. Co-adsorption of CO and IL is indicated by a strong red-shift of the CO stretching bands. While the weakly bound on-top CO is mainly replaced below the melting transition of the IL, coadsorbate shells with bridge-bonded CO and IL are stable well above the melting point. Larger three-dimensional Pd NPs can be prepared by PVD of Pd onto a solid [C1C2Im][OTf] film at 100 K. Upon annealing, on-top CO desorbs from these NPs below 200 K. Upon melting of the IL film, the CO-covered Pd NPs immerse into the IL and again form a stable coadsorbate shell that consists of bridge-bonded CO and the IL.

Preparation of PdCu Decorated Screen Printed Carbon Electrodes for Non-Enzymatic Hydrogen Peroxide Sensors

In the last couple of years, Pd and its alloys gained considerable interest for non-enzymatic hydrogen peroxide (H2O2) and glucose sensing applications. Although Pd shows lower catalytic activity than Pt, its eco-friendly nature and low cost make it a promising catalyst material for many applications ranging from fuel cells to biosensors. Great effort has been devoted to improve the catalytic activity of Pd using various methods such as preparation of Pd nanostructures with different morphologies and alloy formation with transitional metals. In this work, Pd and PdCu alloys with varying compositions were deposited via a simple electrodeposition method on screen printed carbon electrodes (SPCEs) to fabricate non-enzymatic H2O2 sensors. Our results showed that co-deposition of Pd and Cu improved the electrochemical activity of the prepared electrodes significantly compared to pure Pd decorated SPCEs. The highest electrochemical activity was obtained from PdCu electrodes with (7:3) molar ratio. The sensitivity of this electrode to H2O2 was found to be -390.5 µA mM-1 cm-2 at the working potential of -300 mV (vs. Ag/AgCI). In addition, the electrodes showed a wide linear range of 0.5-6 mM and a low detection limit (0.3 µM).

Effect of co-deposition of LaFeO3 on the catalytic properties of Pd on Al2O3 support for CO–O2 and NO–CO reactions

Pd/LaFeO3/Al2O3 catalysts were prepared by co-deposition of Pd and LaFeO3 perovskite oxides in the intrapores of Al2O3 by the incipient wetness method. Pd and LaFeO3 perovskite oxides were highly dispersed on Al2O3 in the inside pore. H2-TPR studies revealed that the oxidation state, dispersion and redox properties of Pd were affected by the presence of LaFeO3 with close proximity. The Pd and LaFeO3 co-deposited Al2O3 catalysts exhibited much higher activity for CO oxidation and NO–CO reaction than Pd/Al2O3 catalysts.

Formation and characterization of Pd, Pt and Pd-Pt alloy films on polyimide by catalyst-enhanced chemical vapor deposition

Platinum, palladium and their alloy films on polyimide were formed by catalyst-enhanced chemical vapor deposition (CVD) in the carrier gas (N2, O2) at 220–300 °C under reduced pressure and normal pressure. The deposition of palladium complexes [ Pd((η3-allyl)(hfac) and Pd(hfac)2] gives pure palladium film, while the deposition of platinum needs the enhancement of palladium complex by mixing precursor platinum complex Pt(COD)Me2 and palladium complex in the same chamber. The co-deposition of Pd and Pt metals was used for the deposition of alloy films. During the CVD of palladium-platinum alloy, the Pd/Pt atomic ratios vary under different co-deposition conditions. These metal films were characterized by XPS and SEM, and show a good adhesive property.

Photographic production of metal nano-particles for fuel cell electrodes

A photographic Pt printing process has been used to prepare catalysts for fuel cell applications. Ferric oxalate was used as a UV sensitizer, absorbing UV energy and converting Fe 3+ to Fe 2+, which then reduces metal catalyst ions, such as Pt or Pd ions to metals in the presence of a developer, such as ammonium citrate. Transmission electron microscope (TEM) and scanning electron microscope (SEM) studies revealed that Pt particles smaller than 5 nm were formed, however, the particles tended to aggregate and form clusters up to 300 nm. A deposition efficiency of 16% was obtained when Pt was printed on Nafion membranes. The catalytic performance of the photo-printed Pt was evaluated using a single H 2 fuel cell. The mass-specific electrochemical area of the catalyst, H 2 crossover rate through the Pt-printed membrane and the membrane resistance were measured. At 60 °C, a peak power density of 75 mW cm −2 was obtained with a MEA consisting of photo-printed Pt (0.12 mg cm −2) on a Nafion membrane as the catalyst. Cyclic voltammetry measurements in solutions containing methanol or formic acid showed that a mass-specific methanol oxidation current of 197 mA mg −1 Pt could be achieved and that the co-deposition of Pd with Pt lowered the formic acid oxidation potential in addition to reducing the formation of the “poisonous” intermediate CO ads.

Surface alloying of Pd and Cu on Ru(0 0 0 1)

Codeposition of Pd and Cu on Ru(0001) with total coverages varying from submonolayer to nm thickness has been carried out at temperatures of 300 and 550 K. The effects of heating the overlayers up to 1250 K were studied. Besides the characterization of the overlayer composition as a function of temperature and observation of possible ordering, a series of questions is addressed. This includes conditions for alloying, possible effects related to dimensionality (2- or 3-dimensions), and the significance of the order of deposition. Photoelectron spectroscopy (PES) based on application of synchrotron radiation and the Mg Kα X-rays (XPS) was used to obtain information on the electronic structure of the bimetallic overlayers via the Ru 3d, Pd 3d core levels (PES) and Cu 2p core levels (XPS). Furthermore, the valence band (VB) electron energy distribution curves (EDC's) were measured at a photon energy of 40 eV which is the Cooper minimum of Cu 3d electrons. LEED was used to establish the order of the overlayers.The main findings of the bimetallic studies are that (i) the deposited Cux and Pd1−x for 0⩽x⩽1 with a total coverage of 1 ML, are distributed in one layer with temperature dependent intermixing, (ii) the valence bands are very characteristic with the Cu 3d band separated from the Pd 4d band and alloying gives rise to new features with binding energies (BE's) between these bands, (iii) the Cu 2p core level shifts (CLS) are correlated linearly with the composition of the films in 2- and 3-dimensions, an effect which is attributed to the different coordination numbers between Pd and Cu in the different dimensions, (iv) the structure of the overlayers depends only slightly on the order of deposition of the two coadsorbates for T>660 K and (v) (1×1) LEED patterns are obtained for 1 ML Cu+2 ML Pd at room temperature and for 2 ML Cu+2 ML Pd after annealing at 660 K indicating, in combination with the pronounced hybridization of Cu 3d and Pd 4d orbitals, formation of a surface alloy.

Scanning tunneling microscope and atomic force microscope study of epitaxially grown palladium crystallites on graphite

Scanning tunneling microscope (STM) and atomic force microscope (AFM) have been applied to the study of an epitaxial growth of Pd on graphite. Pd deposited at 450 °C nucleates to crystallize and grow epitaxially along the [111] direction. The STM images of the topmost layer of the (111) face exhibited a long periodic structure with a periodic distance of about 2.7 nm. Codeposition of Pd and Cu on graphite at 550 °C created clear images of the atomic arrangement together with the periodic structure. The periodic length was found to exactly correspond to a distance of 10 atoms. Auger measurements of each crystallite showed that its surface layer mostly contains Pd atoms although almost equal amount of Pd and Cu was deposited. The AFM observations also showed images with similar periodicity to those from the STM. On the basis of the STM and the AFM results, the possibility of the reconstruction of the surface is discussed.

ChemInform Abstract: Electrocatalytic Activities of Some Codeposited Binary Noble Metal Surfaces Over Carbon Substrates for Anodic Oxidation of Methanol in Alkaline Medium. Part 2. Palladium‐Noble Metal Codeposits.

AbstractBinary metal surfaces are generated by codeposition of Pd with other noble metals, viz.