Zr Pd Research Articles

Composition dependence of phase transformation and shape memory effect of Ti-Zr-Pd-Pt high temperature shape memory alloys

Ti-Zr-Pd-Pt alloys have been considered as potential candidates for high-temperature shape memory alloys (HT-SMAs). In this study, nine alloys were prepared to investigate the effect of multi-component alloying on the phase transformation and shape memory effect. The structural phase diagram of martensite in Ti–Zr–Pd–Pt quaternary alloys was firstly systematically investigated to provide insights and predictions for further research. The phase transformation is divided into three groups: typical martensitic transformation (MT) area, supercooling-controlled phase transformation area and diffusion-assisted phase transformation area. The martensite structure changes from B19 to B33 with the addition of Zr over 25 %. The contribution of Pt contents to raising the martensitic transformation temperature (MTT) became less pronounced with increasing Zr contents. As for shape recovery, over 87 % shape recovery was obtained even under 300 MPa in Ti-10Zr-Pd-Pt alloys, among which Ti-10Zr-15Pt-35Pd presents the highest recovery ratio of over 97 %.

Isotermal section at 870 K of Zr–Pd–Ga phase diagram in the range 45–75 ат. % Ga

Isotermal section at 870 K of Zr–Pd–Ga phase diagram in the range 45–75 ат. % Ga

The critical role of Zr in controlling the activity of Pd/Beta on the hydrogenation of phenol to cyclohexanone

The promoting effect of zirconium addition on Pd/Beta catalysts has been investigated in the selective hydrogenation of phenol to cyclohexanone in the aqueous phase. The activity of the catalyst in the reaction was greatly improved by introducing Zr atoms into the framework of H-Beta zeolite. An important synergy between the Zr species and Pd, affecting the Pd dispersion state on the support, has been observed. The modification of the support with Zr4+ improves the Lewis/Brønsted acid ratio of the catalyst, suppressing the further transformation of cyclohexanone. The kinetics of Pd/Zr-Beta catalyst showed high selectivity to cyclohexanone. The catalytic results showed that the Pd/Zr-Beta had the best catalytic performance at the desired temperature of 80 °C for 5 h.

Microstructure, surface properties, and CO oxidation properties of oxidized Zr2Pd alloy glass

Pd-dispersed composite catalysts were derived from amorphous Zr2Pd-based alloys; Zr65Pd35, Zr65Pd30Pt5, and Zr60Pd35Ce5 by heat treatment at 800 °C in air, and their CO oxidation reactivities were studied. The results of the X-ray diffraction (XRD) analysis indicated that the PdO phase mainly formed in the oxidized Zr65Pd35, and the metallic Pd phase formed in the oxidized Zr65Pd30Pt5 and Zr60Pd35Ce5. The scanning electron microscopic (SEM) images showed that the size of the Pd (PdO) particles increases by the addition of Pt or Ce into Zr–Pd metallic glass. The light-off CO oxidation reactivity and the frequency factor of oxidized Zr65Pd35 were higher than the others. This result was consistent with the amount of adsorbed CO, corresponding to the specific surface area of Pd phase. The CO oxidation reactivity was influenced not only by the morphology and the microstructure but also by the chemical state. Raman spectra and X-ray photoelectron spectra (XPS) indicated the existence of active oxygen species on the surface of Pd (PdO) particles in these catalysts. Thus, a novel type oxidation catalyst was achieved on the Pd-based materials by developing from amorphous alloy precursors and characterized by various methods.

Thermodynamic assessment of the Pd–Zr system

Abstract The Pd–Zr system has been critically assessed by means of the CALPHAD technique. The solution phases (liquid, body-centered cubic (Zr), face-centered cubic (Pd) and hexagonal close-packed (Zr)) were modeled with the Redlich – Kister equation. The intermetallic compounds Pd3Zr and γPdZr, which have a homogeneity range, were treated as the formulae (Pd, Zr)3(Pd, Zr) and (Pd, Va)(Pd, Zr) by a two-sublattice model with Pd and Zr or Pd and vacancies, denoted Va, on the first sublattice, Pd and Zr on the second one, respectively. Both compounds Pd2Zr and PdZr2 having a tetragonal MoSi2-type structure were treated as one phase with the formula PdZr(Pd, Zr) by a three-sublattice model with Pd on the first sublattice, Zr on the second, and Pd and Zr on the third one, respectively. The others were treated as stoichiometric compounds. A set of self-consistent thermodynamic parameters of the Pd–Zr system was obtained.

Evaluation of Microstructure, Mechanical and Thermal Properties of Ti–Zr–Pd–Cu and Ti–Zr–Pd–Cu–Bi Nanoglass Thin Films

Evaluation of Microstructure, Mechanical and Thermal Properties of Ti–Zr–Pd–Cu and Ti–Zr–Pd–Cu–Bi Nanoglass Thin Films

Towards a reliable assessment of charging effects during surface analysis: Accurate spectral shapes of ZrO2 and Pd/ZrO2 via X-ray Photoelectron Spectroscopy

X-ray Photoelectron Spectroscopy of large bandgap or insulating material surfaces relies on an effective mechanism that compensates for the emission (loss) of electrons by maintaining the material surface at a steady-state uniform potential. While a steady-state may be attained by utilizing an active compensation, such as low power electron emitting filament, there is the possibility that the surface potential is not uniform over the area analyzed, leading to peak shifts and incorrect spectral interpretation. In this work, a spectral data processing method based on mapping the ZrO2 and Pd/ZrO2 surfaces utilizing photoemission peak binding energy is proposed, which provides information about the response of specific material surfaces to charge compensation. Spectromicroscopy of ZrO2 and Pd/ZrO2 surfaces without spatial information is used to monitor the efficacy of charge compensation. Exploiting counts distributed over many bins require the use of procedures and algorithms essential to practical mapping peak positions. Iterative singular value decomposition is therefore introduced and utilized as a means of efficiently delivering spatially resolved spectra from which binding energy for peaks is computed. The concepts developed in this work result in robust and accurate peak models of ZrO2 and Pd/ZrO2 that can be applied in XPS analysis of not only ZrO2 but other large bandgap or insulating material surfaces. Supporting arguments for a peak model representing signal from Zr 3p and Pd 3d are developed within this work are presented.

Tris(Butadiene) Compounds versus Butadiene Oligomerization in Second-Row Transition Metal Chemistry: Effects of Increased Ligand Fields.

The geometries, energetics, and preferred spin states of the second-row transition metal tris(butadiene) complexes (C4H6)3M (M = Zr–Pd) and their isomers, including the experimentally known very stable molybdenum derivative (C4H6)3Mo, have been examined by density functional theory. Such low-energy structures are found to have low-spin singlet and doublet spin states in contrast to the corresponding derivatives of the first-row transition metals. The three butadiene ligands in the lowest-energy (C4H6)3M structures of the late second-row transition metals couple to form a C12H18 ligand that binds to the central metal atom as a hexahapto ligand for M = Pd but as an octahapto ligand for M = Rh and Ru. However, the lowest-energy (C4H6)3M structures of the early transition metals have three separate tetrahapto butadiene ligands for M = Zr, Nb, and Mo or two tetrahapto butadiene ligands and one dihapto butadiene ligand for M = Tc. The low energy of the experimentally known singlet (C4H6)3Mo structure contrasts with the very high energy of its experimentally unknown singlet chromium (C4H6)3Cr analog relative to quintet (C12H18)Cr isomers with an open-chain C12H18 ligand.

Controlled Hydrodeoxygenation of Biobased Ketones and Aldehydes over an Alloyed Pd–Zr Catalyst under Mild Conditions

The substitution of green hydrogen donors for replacing high-pressure H2 to achieve biomass derived ketone and aldehyde hydrodeoxygenation (HDO) under mild conditions has attracted widespread atten...

Increasing Complexity Approach to the Fundamental Surface and Interface Chemistry on SOFC Anode Materials.

ConspectusIn this Account, we demonstrate an increasing complexity approach to gain insight into the principal aspects of the surface and interface chemistry and catalysis of solid oxide fuel cell (SOFC) anode and electrolyte materials based on selected oxide, intermetallic, and metal–oxide systems at different levels of material complexity, as well as into the fundamental microkinetic reaction steps and intermediates at catalytically active surface and interface sites. To dismantle the complexity, we highlight our deconstructing step-by-step approach, which allows one to deduce synergistic properties of complex composite materials from the individual surface catalytic properties of the single constituents, representing the lowest complexity level: pure oxides and pure metallic materials. Upon mixing and doping the latter, directly leading to formation of intermetallic compounds/alloys in the case of metals and oxygen ion conductors/mixed ionic and electronic conductors for oxides, a second complexity level is reached. Finally, the introduction of an (inter)metall(ic)–(mixed) oxide interface leads to the third complexity level. A shell-like model featuring three levels of complexity with the unveiled surface and interface chemistry at its core evolves. As the shift to increased complexity decreases the number of different materials, the interconnections between the studied materials become more convoluted, but the resulting picture of surface chemistry becomes clearer. The materials featured in our investigations are all either already used technologically important or prospective components of SOFCs (such as yttria-stabilized zirconia, perovskites, or Ni–Cu alloys) or their basic constituents (e.g., ZrO2), or they are formed by reactions of other compounds (for instance, pyrochlores are thought to be formed at the YSZ/perovskite phase boundary). We elaborate three representative case studies based on ZrO2, Y2O3, and Y-doped ZrO2 in detail from all three complexity levels. By interconnection of results, we are able to derive common principles of the influence of surface and interface chemistry on the catalytic operation of SOFC anode materials. In situ measurements of the reactivity of water and carbon surface species on ZrO2- and Y2O3-based materials represent levels 1 and 2. The highest degree of complexity at level 3 is exemplified by combined surface science and catalytic studies of metal–oxide systems, oxidatively derived from intermetallic Cu–Zr and Pd–Zr compounds and featuring a large number of phases and interfaces. We show that only by appreciating insight into the basic building blocks of the catalyst materials at lower levels, a full understanding of the catalytic operation of the most complex materials at the highest level is possible.

The Influence of Magnetron Sputtering Conditions on the Structure of Zr–Pd Coatings

Using the method of DC magnetron sputtering, nonstructured amorphous metal coatings of Zr75Pd25 composition were obtained with an average deposition rate of 1.3 nm/s at a substrate temperature of 40°C, while crystalline coatings were formed at a higher substrate temperature. A crystalline coating with equilibrium phase composition was obtained at 350°C. Coatings deposited at intermediate temperatures contained predominantly a PdZr phase, in contrast to the equilibrium PdZr2 phase. The surface roughness of amorphous coatings was on a level of 0.2–0.5 nm, which was about ten times lower than the mean roughness of crystalline coatings with the same composition.

Microdomain atomic structure of Zr50Pd40Al10 metallic glasses and its formation mechanism

Zr-based Zr50Pd40Al10 metallic glasses has not only crystalline phases of about 5 nm in diameter but also amorphous phases. In this work, the radial distribution functions (RDFs) of amorphous structure of Zr50Pd40Al10 metallic glasses were firstly measured by electron diffraction, and then Reverse Monte Carlo (RMC) optimization accompanied by density functional theory (DFT) calculations. The amorphous structure has not only short-range order but also good medium-range order. In the RDFs of its amorphous structure, the first and the second peaks are located at 2.96 Å and 4.79 Å, respectively. Partial radical distribution functions (PRDFs) show that the contributions of the first and the second nearest-neighbor distances of various atom pairs to the G(r) peak values, and the first nearest-neighbor distances of Pd–Zr and Zr–Zr atom pairs are the sources of main G(r) peak values between 2 Å and 6 Å. The competition mechanism for generating the Pd25Zr55Al20 amorphous phase and the intermetallic crystalline phase Pd11Zr9 is associated with the differences of atomic radius, the proportion, and the melting point of different atoms, as well as the heat of mixing between atoms, leading to an equilibrium state of the two phases. Accordingly, a composite system with intertwined nanocrystals and amorphous phases is in turn formed, and improves the stability of the material.

Elastic strain effects on the catalytic response of Pt and Pd thin films deposited on Pd–Zr metallic glass

Abstract

Nanoporous PdZr surface alloy as highly active non–platinum electrocatalyst toward oxygen reduction reaction with unique structure stability and methanol–tolerance

Nanoporous (NP) PdZr alloy with controllable bimetallic ratio is successfully fabricated by a simple dealloying method. By leaching out the more reactive Al from PdZrAl precursor alloy, NP–PdZr alloy with smaller ligament size was generated, characterized by the nanoscaled interconnected network skeleton and hollow channels extending in all three dimensions. Upon voltammetric scan in acid solution, the dissolution of surface Zr atoms generates the highly active Pd–Zr surface alloy with a nearly pure Pd surface and Pd–Zr alloy core. The NP–Pd80Zr20 surface alloy exhibits markedly enhanced specific and mass activities as well as higher catalytic stability toward oxygen reduction reaction (ORR) compared with NP–Pd and the state–of–the–art Pt/C catalysts. In addition, the NP–Pd80Zr20 surface alloy shows a better selectivity for ORR than methanol in the 0.1 M HClO4 and 0.1 M methanol mixed solution. X–ray photoelectron spectroscopy and density functional theory calculations both demonstrate that the weakened Pd–O bond and improved ORR performances in turn depend on the downshifted d–band center of Pd due to the alloying Pd with Zr (20 at.%). The as–made NP–PdZr alloy holds prospective applications as a cathode electrocatalyst in fuel–cell–related technologies with the advantages of superior overall ORR performances, unique structure stability, and easy preparation.

XPS valence band studies of nanocrystalline Zr Pd alloy thin films

Abstract The Pd Zr alloy thin films were prepared onto oxidised Si(100) substrates in the temperature range of 295 K up to 700 K using computer-controlled UHV magnetron co-sputtering. The chemical composition and the cleanness of all layers were checked in-situ, immediately after deposition, transferring the samples to an UHV (4 × 10− 11 mbar) analysis chamber equipped with X-ray Photoelectron Spectroscopy (XPS). Structural studies showed that the samples deposited at 295 K are nanocrystalline with average grain size D ~ 5 nm. Thin films deposited at about 700 K are polycrystalline with D ~ 100 nm. XPS results showed that the position of the valence band measured for the polycrystalline ZrPd2 alloy thin film are in good agreement with ab initio (GGA + U) calculations. On the other hand, the XPS valence bands of the nanocrystalline ZrPd2 thin films are considerably broader compared to those measured for the polycrystalline samples. The different microstructures observed in polycrystalline and nanocrystalline alloy thin films lead to significant modifications of their electronic structure.

Enhanced photocatalytic activity of TiO2 activated by doping Zr and modifying Pd

The photocatalytic activity of 4-CP degradation is apparently enhanced by doping Zr and modifying Pd in TiO2 (TiO2–Zr–Pd) under visible light irradiation.

Chemical vapor deposition-prepared sub-nanometer Zr clusters on Pd surfaces: promotion of methane dry reforming.

An inverse Pd-Zr model catalyst was prepared by chemical vapor deposition (CVD) using zirconium-t-butoxide (ZTB) as an organometallic precursor. Pd-Zr interaction was then investigated with focus on the correlation of reforming performance with the oxidation state of Zr. As test reactions, dry reforming of methane (DRM) and methanol steam reforming (MSR) were chosen. Depending on treatments, either ZrOxHy or ZrO2 overlayers or Zr as sub-nanometer clusters could be obtained. Following the adsorption of ZTB on Pd(111), a partially hydroxylated Zr4+-containing layer was formed, which can be reduced to metallic Zr by thermal annealing in ultrahigh vacuum, leading to redox-active Zr0 sub-nanometer clusters. Complementary density functional theoretical (DFT) calculations showed that a single layer of ZrO2 on Pd(111) can be more easily reduced toward the metallic state than a double- and triple layer. Also, the initial and resulting layer compositions greatly depend on gas environment. The lower the water background partial pressure, the faster and more complete the reduction of Zr4+ species to Zr0 on Pd takes place. Under methanol steam reforming conditions, water activation by hydroxylation of Zr occurs. In excess of methanol, strong coking is induced by the Pd/ZrOxHy interface. In contrast, dry reforming of methane is effectively promoted if these initially metallic Zr species are present in the pre-catalyst, leading to a Pd/ZrOxHy phase boundary by oxidative activation under reaction conditions. These reaction-induced active sites for DRM are stable with respect to carbon blocking or coking. In essence, Zr doping of Pd opens specific CO2 activation channels, which are absent on pure metallic Pd.

Phase stability, elastic properties and martensitic transformation temperature of Zr50Pd50–xRux alloys from first-principles calculations

The phase stability, elastic properties and martensitic transformation temperature of Zr50Pd50–xRux (x = 0, 6.25, 12.5, 18.75) alloys have been investigated by first-principles calculations based on density functional theory. The formation energy results show that the alloying Ru tends to occupy the Pd site in ZrPd alloy. The lattice constants of the austenite phases decrease with increasing Ru content, which is in accordance with the experimental results. According to the calculations of total energy difference between the austenite and martensite phases, the martensitic transformation temperature of Zr50Pd50–xRux (x = 0, 6.25, 12.5, 18.75) alloys decreases with increasing Ru content. From the formation energy and electronic structure, the increase of the Ru content in Zr50Pd50–xRux alloys can further stabilize the austenite phases but decrease the stability of the martensite phases at the same time. The B/G ratios of the Zr50Pd50–xRux alloys indicate that all the Zr50Pd50–xRux alloys are ductile. Moreover, the lower martensitic transformation temperature can be attributed to the stronger Zr–Ru hybridization interaction as compared to the Zr–Pd one.

Hydrogenation of 1-octene over skeletal Pd catalysts prepared from Pd–Zr amorphous alloys and the effect of Ni addition

The skeletal Pd catalysts were prepared from Pd–Zr alloys which possess amorphous or crystalline state. The hydrogenation of 1-octene to octane over skeletal Pd catalysts proceeded efficiently while Pd–Zr alloy was inactive. The skeletal Pd prepared from amorphous alloy showed higher catalytic activities despite the smaller surface area compared to that prepared from the corresponding crystalline alloy. These catalytic activities were attributed to the number of surface-exposed Pd of skeletal Pd which was strongly affected by the atomic arrangement of the precursor. Moreover, we investigated the effect of Ni addition to the P–Zr alloy as the third metal. Skeletal Pd with 16at% Ni showed an excellent selectivity while keeping as high catalytic activity as skeletal Pd.

Modeling grain growth kinetics of binary substitutional alloys by the thermodynamic extremal principle

The thermodynamics and kinetics fundaments of grain growth in binary substitutional alloys were analyzed using the thermodynamic extremal principle. Applying the regular solution approximation, a new equation for solute segregation at steady-state diffusion is proposed, which suggests reduced solute segregation as the grain boundary (GB) solute concentration increases, differently from previous models [Acta Mater 2009;57(5):1466, Acta Mater 2012;60:4833, Scripta Mater 2010;63:989] that adopt constant segregation enthalpy. Furthermore, a self-consistent consideration has been carried out to account for the coupled changes in GB energy and GB mobility as a result of solute segregation. On this basis, the quantitative relation is evaluated between the thermodynamic and kinetic effects of solute segregation to determine the dominant role in retarding and even suppressing grain growth, by comparison of the dimensionless GB energy (i.e., the GB energy of alloy over that of pure solvent) and the dimensionless effective GB mobility (i.e., the effective GB mobility over that of pure solvent): the kinetic effect prevails if the dimensionless effective GB mobility is smaller than the dimensionless GB energy, and vice versa. The present model is adopted to describe well the experimental results for Fe–P alloys, and nanocrystalline Ni–P and Pd–Zr alloys.