Order Of Pd Research Articles

Dechlorination of trichloroethylene in aqueous solution by noble metal-modified iron

Bimetallic particles are extremely interesting in accelerating the dechlorination of chlorinated organics. Four noble metals (Pd, Pt, Ru and Au), separately deposited onto the iron surface through a spontaneous redox process, promoted the TCE dechlorination rate, and the catalytic activity of the noble metal followed the order of Pd ≫ Ru > Pt > Au. This order was found to be dependent on the concentrations of adsorbed atomic hydrogen, indicating that the initial reaction was cathodically controlled. Little difference in the distribution of the chlorinated products for the four catalysts ( cis-DCE: 51%; 1,1-DCE: 27%; trans-DCE: 15% and VC: 7%) was observed. The chlorinated by-products accumulated in both Pt/Fe and Au/Fe (10.3% and 2.5% of the transformed TCE, respectively), but did not accumulate in Pd/Fe and Ru/Fe. Ru/Fe was further examined as an economical alternative to Pd/Fe. The 1.5% Ru/Fe was found to completely degrade TCE within 80 min. Considering the expense, the yield of chlorinated products and the lifetime of a reductive material, Ru provides a potential alternative to Pd as a catalyst in practical applications.

Skaergaardite, PdCu, a new platinum-group intermetallic mineral from the Skaergaard intrusion, Greenland

AbstractSkaergaardite, PdCu, is a new mineral discovered in the Skaergaard intrusion, Kangerdlugssuaq area, East Greenland. It occurs in a tholeitiic gabbro associated with plagioclase, clinopyroxene, orthopyroxene, ilmenite, titanian magnetite, fayalite and accessory chlorite-group minerals, ferrosaponite, a member of the annite–phlogopite series, hornblende, actinolite, epidote, calcite, ankerite, apatite and baddeleyite. The mineral is found in composite microglobules composed of bornite, chalcocite, digenite, chalcopyrite, with rare cobalt pentlandite, cobaltoan pentlandite, sphalerite, keithconnite, vasilite, zvyagintsevite, (Cu,Pd,Au) and Pt-Fe-Cu-Pd alloys, unnamed PdCu3, (Pd,Cu,Sn), Au3Cu and PdAuCu. Skaergaardite occurs as droplets, equant grains with rounded outlines, subhedral to euhedral crystals and as irregular grains that vary in size from 2 to 75 μm, averaging 22 μm. It is steel grey with a bronze tint, has a black streak, a metallic lustre and is sectile. Neither cleavage nor fracture was observed. The mineral has a micro-indentation hardness of VHN25= 257. It is isotropic, non-pleochroic and exhibits neither discernible internal reflections nor evidence of twinning. Skaergaardite varies from bright creamy white (associated with bornite and chalcopyrite) to bright white (associated with digenite and chalcocite). Reflectance values in air (and in oil) are: 58.65 (47.4) at 470 nm, 62.6 (51.1) at 546 nm, 64.1 (52.8) at 589 nm and 65.25 (53.95) at 650 nm. The average of 311 electron-microprobe analyses gives: Pd 58.94, Pt 1.12, Au 2.23, Cu 29.84, Fe 3.85, Zn 1.46, Sn 1.08, Te 0.28 and Pb 0.39, total 99.19 wt.%, corresponding to (Pd0.967Au0.020Pt0.010)Σ0.997(Cu0.820Fe0.120Zn0.039Sn0.016Te0.004Pb0.003)Σ1.002. The mineral is cubic, space group Pm3m,a= 3.0014(2) Å,V= 27.0378 Å3,Z= 1. Dcalcis 10.64 g/cm3. The six strongest lines in the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are: 2.122(100)(110), 1.5000(20)(200), 1.2254(50)(211), 0.9491(20)(310), 0.8666(10)(222), 0.8021(70)(321). The mineral has the CsCl-type structure. It is believed to be isostructural with wairauite (CoFe), synthetic CuZn (β-brass) and is structurally related to hongshiite (PtCu). Skaergaardite developed from a disordered Pd-Cu-rich metal alloy melt that had exsolved from an earlier Cu-(Fe) sulphide melt. Ordering of Pd and Cu (beginning atT≈ 600°C) results in development of the CsCl structure from a disordered face-centred cubic structure.

Reduction of chloroacetone over silica-supported noble metal catalysts

The reduction of chloroacetone over silica-supported noble metal catalysts yielded the hydrodechlorinated (acetone), the hydrogenated (1-chloro-2-propanol), and the hydrodechlorinated–hydrogenated (2-propanol) products at different selectivities depending on the catalyst used. Pd/SiO2 catalyzed the single-step hydrodechlorination preferentially to give acetone selectively. Pt/SiO2 promoted the hydrogenation into 1-chloro-2-propanol concurrently and the consecutive hydrogenation of acetone into 2-propanol as well. Over Rh/SiO2, acetone was transformed to 1-chloro-2-propanol through the addition of hydrogen chloride. The hydrodechlorination activity of noble metals followed the order of Pd > Pt ⪢ Rh > Ru.The high selectivity of Pd/SiO2 toward acetone was not influenced by Pd dispersion. The selectivity of Pt/SiO2 changed largely with Pt dispersion and the hydrogenation of carbonyl group was promoted preferentially over the catalysts with low Pt dispersion.

Reductive dechlorination of TCE by zero valent bimetals

Six zero valent bimetal combinations were tested for trichloroethene (TCE) dechlorination. Palladium, nickel, and copper were coated at 500 mg kg‐1 or less onto zero valent iron, producing Pd/Fe, Ni/Fe, and Cu/Fe bimetals, and zinc, producing Pd/Zn, Ni/Zn, and Cu/Zn bimetals. The order of reactivity of the six bimetals and two metals based on surface area normalized pseudo first order rate constants was observed to be: Pd/Fe >Pd/Zn > Ni/Fe > Cu/Fe > Ni/Zn > Cu/Zn > Fe > Zn. Thus, in general, 1) iron metal and bimetals exhibit faster reaction rates than the corresponding zinc reductants, 2) bimetals exhibit faster reaction rates than pure metals, and 3) metal coating enhance reactivity in the order of Pd > Ni > Cu. Chlorinated intermediate products were observed in small amounts for Fe only. In all cases, the chloride balance, calculated from TCE and chloride concentrations, ranged from 90 to 111%. The results are discussed in terms of the effects of bimetal combinations on catalytic dechlorination, prevention of nonreactive film and metal corrosion.

Atomic Concentration Wave in Pt–Ti and Pd–Ti Alloys

The atomic short range order of Pd–Ti and Pt–Ti alloys with a Ti concentration of about 10 at.% was studied by neutron diffraction. Temperature-independent diffuse satellite peaks were observed at ...

Size Effects of PVP−Pd Nanoparticles on the Catalytic Suzuki Reactions in Aqueous Solution

A series of poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized Pd nanoparticles with varying particle size are prepared by using the stepwise growth reaction. The effect of Pd particle size on the Suzuki reaction between phenylboronic acid and iodobenzene is investigated by the use of four Pd catalysts with mean particle sizes of 3.0, 3.9, 5.2, and 6.6 nm, respectively. The catalytic activity of the Pd nanoparticles expressed in terms of the initial turnover frequency (moles of the biphenyl product per mole of total surface Pd atoms per min) is found to be in the order of Pd (3.9 nm) > Pd (3.0 nm) ≈ Pd (5.2 nm) > Pd (6.6 nm), indicating that surface Pd atoms do not all have the same reactivity in this reaction. The general trend of increased catalytic activity with the decrease in the particle size suggests that the low-coordination number vertex and edge atoms on the particle surface are active sites for the Suzuki reaction. The lower catalytic activity for the smallest Pd nanoparticles might be due to stronge...

Effects of surface treatments on the electrical and the microstructural changes of Pd contact on p-type GaN

We investigated the effects of surface treatments by aqua regia and (NH4)2Sx on the electrical and the microstructural changes of Pd contact on p-type GaN during annealing. The formation of a surface oxide was suppressed by the (NH4)2Sx treatment, and S-Ga and S-N bonds with binding energy of 162.1 eV and 163.6eV were formed, degrading the structural ordering of Pd. After 300°C annealing, the contact resistivity in the aqua regia-treated sample increased significantly. This could be attributed to the outdiffusion of N atoms leaving N vacancies below the contact, as confirmed by the increase of the Pd (111) plane spacing probably due to the dissolution of N atoms in Pd interstitial sites. Meanwhile, the contact resistivity in the (NH4)2Sx-treated sample was not degraded and no change was observed in the Pd (111) plane spacing. These results suggest that S-Ga and S-N bonds formed on (NH4)2Sx-treated GaN could act as a diffusion barrier for the outdiffusion of N atoms. The contact resistivity for the aqua regia-treated sample decreased again, probably due to the outdiffusion of Ga as well as N atoms at 500°C.

Surface and interface studies with ASPIC

Magnetic properties at surfaces and interfaces have been investigated performing Perturbed Angular Correlation (PAC) measurements in the UHV chamber ASPIC (Apparatus for Surface Physics and Interfaces at CERN) using different PAC probes. The results are: (i) determination of magnetic hyperfine fields of Se on Fe, Co, Ni which are explained by a theoretical study on the magnetic hyperfine fields of 4sp-elements in adatom position on Ni and Fe;(ii) static magnetic hyperfine fields in ultrathin Pd on Ni(0 0 1) which indicate an induced magnetic order in Pd;(iii) the observation of induced fluctuating magnetic interactions in Pd when thick Pd is in contact with Ni. Monolayer-resolved measurements of the magnetic hyperfine fields in magnetized Pd are in accordance with theoretical predictions of the layer dependence of the induced magnetic moments in Pd.

A Study of the Dynamics of Pd Oxidation and PdO Reduction by H2and CH4

Palladium is one of the most active catalysts for the catalytic combustion of methane. Since Pd is oxidized during methane combustion to PdO and PdO is required for high activity, it is of interest to understand the dynamics of Pd oxidation and the structure of the oxide formed as well as the dynamics of PdO reduction by H2and CH4. In the present study isothermal and temperature-programmed oxidation and reduction were used to probe the dynamics of the oxidation and reduction of zirconia-supported Pd. During uptake in oxygen, a monolayer of oxide is generated immediately, and upon further oxidation, the oxide forms a shell around a core of metal with thicknesses that increase with the oxidation temperature. The initial oxide is amorphous and subsequently transforms to crystalline PdO. The dynamics of Pd oxidation suggest that oxidation follows the Cabrera–Mott theory. Reduction of PdO by H2occurs in a shellwise manner, consistent with a shrinking core mechanism, while reduction in CH4occurs via an autocatalytic, nucleation mechanism. In the latter case, small particles of Pd must first be formed on which CH4can dissociate. The fragments (H and CHx(x=3–1)) diffuse to the metal–oxide boundary where reduction of the oxide occurs. Consistent with this picture, the kinetics of PdO reduction are first order in Pd initially, but then they become zero order in Pd.

Short range order in Pd 2− xCo xTiSn alloys

The influence of the local environment on the magnetic properties in Pd 2− x Co x TiSn alloys are studied. The total magnetic moment in Pd 2− x Co x TiSn increases with the increase of Co concentration. We observe the magnetic phase transition from the paramagnetic to the ferromagnetic states for x > 0.5. The spin polarised LMTO calculations have shown that PdCoTiSn alloy is ferromagnetic with the magnetic moment on cobalt atom m Co = 1.07 μ B.

Thermal and spectroscopic study of dialkyl [ α-(4-benzeneazoanilino)- N-benzyl] phosphates and their palladium (II) halide complexes

The mode of thermal decomposition of diethyl and dibutyl esters of [ α-(4-benzeneazoanilino)- N-benzyl] phosphonic acid and their palladium (II) dihalide adducts, Pd(L) 2X 2 (L = organophosphorous ligand; X = Cl, Br), as well as cyclopalladated complexes, [Pd(L-H)Cl] 2, have been investigated by thermal (TG, DTA) and spectroscopic (IR, FAB-mass) analyses. Thermal decomposition of the complexes takes place through a multistep process, the first step being a dehalogenation along with deesterification, followed by a complex pyrolysis that leads to a mixture of Pd and P 2O 5. All complexes are anhydrous, and on the basis of their initial decomposition temperatures, the thermal stability follows the order of Pd(L) 2Cl 2 < Pd(L) 2Br 2 < [Pd(L-H)Cl] 2. The mass spectrometric data indicate differences in the gas-phase fragmentation pathways between the two types of metal complex and a scheme for their thermal decomposition is proposed. In the adducts the main fragmentation routes consist off sequential losses of HCl giving arise to the mono- and bis-orthometallated species. The primary decomposition step in the cyclometallated complexes is shown to be the loss of Cl. In both derivatives these processes are in competition with the loss of the phosphate ester group.

The growth of metastable bcc Cu(001) and lattice expanded Pd(001) and magnetic coupling in Fe/Cu/Fe and Fe/Pd/Fe trilayers

Bcc Cu(001) and laterally stretched Pd(001) can be grown epitaxially on Fe(001) and vice versa. FMR and BLS studies were carried out on Fe/Cu/Fe, Fe/Pd/Fe trilayers and Fe/Pd, Pd/Fe, Fe/Cu and Cu/Fe bilayers. The exchange coupling in bcc Cu was found to exhibit a behavior similar to bcc Cr but with a somewhat longer range of the antiferromagnetic interaction. 4 ML Pd couples Fe layers strongly ferromagnetically and is most likely ferromagnetically ordered. One additional Pd atomic layer destroys the long range order in Pd, but the Pd layer possesses fluctuating moments which are partly magnetized by the adjacent Fe layers. The exchange coupling in thick Pd interlayers ( > 8 ML) is weakly dependent on temperature and originated from a different mechanism.

The (α + β) hydrogen miscibility gaps in hydrogenated palladium-rich Pd-Y(Gd)-Ag ternary alloys

This work has been concerned with a study of palladium-rich Pd-Y(Gd)-Ag ternary alloys as possible diffusion membranes for hydrogen purification; these are expected to be stronger and more permeable to hydrogen than the commercially used membranes made from Pd-Ag alloys. As a preliminary to the hydrogen permeability study, the alloying behaviour of the ternary alloys and the extent of (α + β) hydrogen miscibility gaps in hydrogenated alloys were investigated. The metallographic examination and X-ray studies of annealed Pd 100 − x − y (Y(Gd)) x Ag y alloys with a silver content y(of 5–24 at.%) and x (at.%), the value of the content of yttrium and/or gadolinium, together satisfying the condition y + 3 x ⩽ 24 ( i.e. up to the valence electron concentration e a = 0.24 ) indicate that every one of these alloys forms as a single α-Pd phase; neither long-range order nor intermetallic compounds were observed. However, electron diffraction and electrical resistance measurements on Pd 95 − x Gd x Ag 5 with x = 6.3 gave faint indications of short-range order in Pd 7(Gd, Ag). It was found that the (α + β) hydrogen miscibility gaps in the hydrogenated alloys with any given silver content decrease gradually as the content of yttrium and/or gadolinium increases, and the critical compositions for the disappearance of the miscibility gaps are approximately isoelectronic with an electron-to-atom ratio e a of 0.24 for all the Pd 100 − x − y (Y(Gd)) x Ag y alloys.

Observations of order in Pd–Y solid solutions and in Pd7Y

Observations of order in Pd–Y solid solutions and in Pd₇Y

Spin Fluctuations in Ferromagnetic Metals –Temperature Variation of Local Moment and Short Range Order

Magnetic properties of typical ferromagnetic metals are discussed on the basis of the previously-developed unified theory with the use of relatively small number of physical parameters including the longitudinal and transverse (exchange) stiffness constants for the spin fluctuation. From the analysis of existing experimental results we discuss on the temperature variation of the amplitude of local spin fluctuation (local moment) and the degree of short rang order in Pd 2 MnSn, Fe 3 Pt, CoS 2 , Fe, Co, Ni and MnSi.

Dirichlet Finite Solutions of Δu = Pu

The purpose of this paper is to give a necessary and also a sufficient condition for a Dirichlet finite harmonic function on a Riemann surface to be represented as a difference of a Dirichlet finite solution of Au=Pu (P_O) and a Dirichlet finite potential of signed measure. 1. Let P=P(z) dx dy (z=x+iy) be a nonnegative not identically zero o-Holder continuous (0<<?1) second order differential on a Riemann surface R and PD(R) be the Hilbert space of all Dirichlet finite solutions of (1) AU(Z) = P(Z)U(Z), A = 4a2./I aZa, on R with the scalar product given by mixed Dirichlet integral, i.e. (u, v)=D11(u, v)=fS11 duA*dv, not the energy integral. The study of PD(R) was begun by Royden [6]. We will use the fact shown by Nakai [2] that PD(R) forms a vector lattice under the natural order in PD(R). We also use the Glasner-Katz maximum principle [1] that the modulus of every function in PD(R) takes its maximum on the Royden harmonic boundary. The recent result of Nakai [3] that PBD(R) is dense in PD(R) will not be made use of. Let A(R) be the Royden harmonic boundary and HD(R) be the class of Dirichlet finite harmonic functions on R. (For the basic materials from the Royden compactification and the class HD(R) we refer to the monograph of Sario and Nakai [7].) One of the important problems in the theory of PD(R) which is not fully developed yet is to describe the distribution of PD(R)|A(R) in HD(R)|A(R). We will prove a theorem which contributes to this question. 2. If R is parabolic, then PD(R)= {0} (cf. Royden [6]), which case offers no interest. Therefore we assume throughout the paper that R is hyperbolic. Let M(R) be the class of all Dirichlet finite Tonelli functions on R and MA(R) the subclass of M(R) consisting of functions f with f JA(R)=O (cf. [7]). We then have the orthogonal decomposition M(R) = HD(R) + MA(R), Received by the editors May 26, 1971. AMS 1970 subject classifications. Primary 31A05, 58G99. 1 The work was sponsored by the U.S. Army Research Office-Durham, Grant DA-ARO-D-31-124-71-G20, UCLA. (e, American Mathematical Society 1972

ELECTRON SPIN RESONANCE OR Pd(I). III: The Nature of the Metal-ligand Bonds in Square Planar Complexes of Palladium(I)

Abstract ESR spectra for a variety of palladium(I) complexes produced in the powders and the frozen solutions of palladium(II) complexes by γ -ray irradiation have been interpreted in terms of the nature of the metal-ligand bonds. It has been found that the covalency for the palladium-ligand σ-bond increases in the order of Pd[sbnd]O, Pd[sbnd]Cl < Pd[sbnd]N < Pd[sbnd]S, Pd[sbnd]C, and that the nature of the metal-ligand bond in palladium(I) complexes is very similar to that in copper(II) complexes. The ratio of the magnitude of the ligand field splitting for palladium(I) complex to that for the copper(II) complex with the same ligand has been estimated from the comparison of their g values.