Pd Coverage Research Articles

Experimental study on spheroidal morphology of palladium coated copper wire with different palladium layer thickness

Palladium (Pd) coated copper (PCC) wire is an emerging bonding wire that has been widely researched. In this paper, the effects of electronic flame-off (EFO) current and EFO time on the free air ball (FAB) morphology of four PCC wires with Pd layer thicknesses of 60, 80, 100, and 120 nm, respectively, are first investigated. The larger the EFO current or the longer the EFO time, the larger the FAB diameter. The EFO time or EFO current setting is either too high or too low to form a FAB with good morphology. Taking the ratio of FAB diameter to wire diameter as 2 as the standard, the EFO current of 48 mA and the EFO time of 700 μs are selected as the optimal EFO parameter combination. Under this parameter combination, the symmetry, roundness, and surface smoothness of the FAB of the four PCC wires are all at a better level. It is found that the FAB surface Pd coverage of PCC wire with 120 nm Pd layer thickness is higher through the corrosion test. The Pd transfer law on the FAB at different EFO times under optimal EFO current is also studied. The results show that with the prolongation of the EFO time, the Pd on the FAB surface is gradually transferred from the neck to the middle and lower parts. This study can provide technical reference for the selection of Pd layer thickness and EFO parameters of PCC wire.

Plasmon-enhanced electrocatalytic ethanol oxidation over Au@Pd nanostars

Hybrid noble-metal nanostructures, which integrate plasmonic characteristics and electrocatalytic performance, have garnered significant interest recently. In this study, Au@Pd nanostars were synthesized and employed as an advanced electrocatalyst for the ethanol oxidation reaction (EOR), which suffers from the kinetic limitations of the anodic half-reaction of direct ethanol fuel cells. Leveraging the superior surface plasmon resonance (SPR) property of Au nanostars, the synthesized Au@Pd nanostars exhibited superior plasmon-enhanced EOR activity of 4191.63 A g−1 under laser illumination, noting a 9.40-fold increase compared to dark conditions (445.99 A g−1). The influences of Pd loading and laser power on EOR activity were explored. The impact of Pd loading on EOR activity demonstrates a volcano-shaped correlation, where optimal Pd coverage enhances catalysis but excessive amounts dampen SPR performance, crucial for maximizing EOR activity. Within a specified range, EOR activity linearly increases with laser power due to its influence on SPR performance. Mechanistic investigation suggests the critical roles of photothermal effect and hot carriers’ separation in boosting EOR kinetics. The repeated experiments show little difference, ensuring the accuracy and reproducibility of the reported activity of Au@Pd nanostars for EOR. During the long-term stability estimation, the Au@Pd nanostars display the best durability over three electrocatalysts. Overall, our findings highlight the potential of plasmon-enhanced catalysis in advancing the performance of electrocatalysts for EOR and other conventional electrocatalytic reactions.

Pharmacokinetic analysis of OMO-103 in patient tissues with advanced solid tumors.

e15168 Background: MYC is a pleiotropic transcription factor aberrantly expressed in up to 70% of human cancers. OMO-103 (Omomyc) is a 91-amino-acids-long polypeptide that derives from the B-HLH-LZ domain of human MYC, containing four amino acid substitutions. It is capable of forming homos and heterodimers with MYC and with MAX and blunt MYC activity by preventing its access to target DNA sequences (E-boxes) and replacing it by inactive complexes. Previous in vivo preclinical experiments showed that Omomyc blocks MYC-driven transcription and proliferation, induces apoptosis and recruitment of intratumoral immune infiltrates, significantly abrogating tumor progression and reducing tumor grading. Here, we present PK results from the first-in-human trial (NCT04808362) of OMO-103 in patients with advanced solid tumors. Methods: Patient eligibility The study included histologically or cytologically proven advanced solid tumors for which there was no curative therapy. Patients had to demonstrate measurable disease according to RECIST v.1.1 criteria as demonstrated by CT/magnetic resonance imaging and documented progression on or following the last line of therapy. Description and dose selection OMO-103 was administered by weekly I.V. infusion over 30–45 min, one treatment cycle corresponding to three infusions. Patients were treated until progression. The starting dose of 0.48 mg kg−1 was determined based on nonclinical toxicology and efficacy studies (anticipated pharmacologically active dose) and subsequent conversion to a human equivalent dose. Pharmacokinetic assays A targeted mass spectrometry (MS) assay for the absolute quantification of 4 Omomyc proteotypic peptides was developed to quantify functional OMO-103 in tumor tissue. LLOQ and linear range of the panel was determined by spiking in dilution series of recombinant OMO-103 protein into tumor tissue lysates. Finally, in the phase I trial, we used the panel for the quantification of OMO-103 in FFPE tumor biopsies from 12 patients who received i.v. injection of OMO-103. Results: MS Data show that 2 h after i.v. administration, higher concentrations of the drug are reached in the tumors compared with serum and persist there with at least one order of magnitude higher concentration than in serum 72 h after administration in preclinical models. Functional Omomyc protein could be quantified in all 12 clinical tumor biopsies from treated patients and PK results confirmed previous observations in preclinical models. where Omomyc exhibits higher tissue concentration and prolonged residency compared to plasma. Conclusions: We demonstrate the utility of targeted MS assay for precise quantification of therapeutic (mini)proteins in clinical tissue samples. Thanks to its multiplexing capability, up to 60 peptides (epitopes) can be monitored simultaneously which enables high sequence coverage and profiling of additional PD or other supporting biomarkers. Clinical trial information: NCT04808362 .

Photocatalytic activity enhancement of two-step and one-pot synthesis of Pd/ZnO nanocomposites: an experimental and DFT study.

Pd/ZnO nanocomposites were successfully synthesized by means of one and two pot synthesis and applied in the photodegradation of Rh6G. The nanocomposites were characterized by XRD, SEM, TEM, FTIR and micro-Raman spectroscopies. It was found the presence of PdZn2, PdO and agglomerated particles in the support surface for the Palladium-based nanocomposites fabricated by one-pot route; the two-step method allowed the formation of spherical Pd nanoparticles, with homogeneous distribution in the nanocomposite matrix, with an average size of 2.16nm. The results show higher photocatalytic efficiency for the samples fabricated under the two-step approach compared to the one-pot synthesis. Based on experimental results, density functional theory (DFT) calculations were carried out to understand the enhancement photocatalytic of Pd/ZnO nanocomposites. To achieve it, the ZnO (001) and (101) surfaces were built and decorated by different Pd coverages. The theoretical results indicated two different photocatalytic mechanisms. In ZnO (001) case, the electrons flowed from surface to Pd, generating the superoxide radical anion (⋅O2-). Furthermore, the density of states of the ZnO (001) surface was modified by impurity Pd-d states at proximity to the conduction states, which may work as electron acceptors states. On the other hand, we found that the electrons flow from Pd to ZnO (101) surface, inducing the formation of ⋅OH and ⋅O2- for the degradation of Rh6G. The density of states of the ZnO (101) revealed a reduction in its bandgap, due to Pd-d states localized above valence states. Hence, our theoretical results suggest that the Pd-d states may facilitate the mobility of electrons and holes in (001) and (101) surfaces, respectively, reducing the rate of charge recombination.

Pd/Co3O4(111) Interface Formation

The formation of the metal–oxide interface in the Pd/Co3O4(111) model catalyst was investigated by means of density functional theory (DFT), synchrotron radiation photoelectron spectroscopy (SRPES), and scanning tunneling microscopy (STM). The electronic metal–support interaction results in a substantial charge transfer at the interface yielding atomically dispersed Pd2+ species and partially oxidized Pdδ+ aggregates coupled with a partial reduction of Co3O4(111). Atomically dispersed Pd2+ species at the fcc site on the Co3O4(111) surface were found to be the most energetically favorable configuration. In comparison to the dispersed Pd2+ species, the formation of Pd dimers, trimers, and tetramers was found to be less favorable. The analysis of the Bader charges revealed a substantial net positive charge on Pd atoms in dimers, trimers, and tetramers which is consistent with the formation of partially oxidized Pdδ+ aggregates detected by SRPES. The analysis of the charge distribution in Co3O4(111) revealed a partial reduction of Co3+ to Co2+ cations in the first and second Co layers. According to DFT, Pdδ+ aggregates are prone to oxidation to PdO in the presence of O2 and H2O. The partially oxidized Pdδ+ and Pd4Ox aggregates form 1 to 2 monolayer thick clusters which serve as nuclei for the growth of metallic Pd0 nanoparticles. At high Pd coverage, Pd nanoparticles coalesce resulting in the growth of two-dimensional islands that densely cover the Co3O4(111) substrate.

Atomic Scaled Depth Correlation to the Oxygen Reduction Reaction Performance of Single Atom Ni Alloy to the NiO2 Supported Pd Nanocrystal.

This study demonstrates the intercalation of single-atom Ni (NiSA ) substantially reduces the reaction activity of Ni oxide supported Pd nanoparticle (NiO2 /Pd) in the oxygen reduction reaction (ORR). The results indicate the transition states kinetically consolidate the adsorption energy for the chemisorbed O and OH species on the ORR activity. Notably, the NiO2 /Ni1 /Pd performs the optimum ORR behavior with the lowest barrier of 0.49eV and moderate second-step barrier of 0.30eV consequently confirming its utmost ORR performance. Through the stepwise cross-level demonstrations, a structure-Eads -ΔE correspondence for the proposed NiO2 /Nin /Pd systems is established. Most importantly, such a correspondence reveals that the electronic structure of heterogeneous catalysts can be significantly differed by the segregation of atomic clusters in different dimensions and locations. Besides, the doping-depth effect exploration of the NiSA in the NiO2 /Pd structure intrinsically elucidates that the Ni atom doping in the subsurface induces the most fruitful NiSA /PdML synergy combining the electronic and strain effects to optimize the ORR, whereas this desired synergy diminishes at high Pd coverages. Overall, the results not only rationalize the variation in the redox properties but most importantly provides a precision evaluation of the process window for optimizing the configuration and composition of bimetallic catalysts in practical experiments.

Electroreductive coupling of benzaldehyde by balancing the formation and dimerization of the ketyl intermediate

Electroreductive coupling of biomass-derived benzaldehyde offers a sustainable approach to producing value-added hydrobenzoin. The low efficiency of the reaction mainly ascribes to the mismatch of initial formation and subsequent dimerization of ketyl intermediates (Ph-CH = O → Ph-C·-OH → Ph-C(OH)-C(OH)-Ph). This paper describes a strategy to balance the active sites for the generation and dimerization of ketyl intermediates by constructing bimetallic Pd/Cu electrocatalysts with tunable surface coverage of Pd. A Faradaic efficiency of 63.2% and a hydrobenzoin production rate of up to 1.27 mmol mg−1 h−1 (0.43 mmol cm−2 h−1) are achieved at −0.40 V vs. reversible hydrogen electrode. Experimental results and theoretical calculations reveal that Pd promotes the generation of the ketyl intermediate, and Cu enhances their dimerization. Moreover, the balance between these two sites facilitates the coupling of benzaldehyde towards hydrobenzoin. This work offers a rational strategy to design efficient electrocatalysts for complex reactions through the optimization of specified active sites for different reaction steps.

Stability of Pd Islands on Ag(111) and Au(111)

Scanning tunneling microscopy was used to compare the evolution with time and annealing temperature of the structure of Pd islands formed after room-temperature (RT) deposition of Pd on Ag(111) and Au(111). Although silver and gold share many properties, their clean (111) surfaces have distinctly different structures, and this leads to distinctly different behavior following Pd deposition. On Ag(111), large Pd islands form and become capped by Ag atoms with the simultaneous formation of vacancy pits on the Ag(111) surface. On Au(111), smaller Pd islands form for comparable Pd coverages. In contrast to Ag(111), much less capping of Pd by Au atoms occurs on the Au(111) surface at RT and no vacancy pits were observed. Upon annealing to 340 K, 98% of the Pd islands were capped by Ag atoms on Ag(111), whereas less than 4% of Pd islands on Au(111) were covered by surface Au atoms, but again without forming vacancy pits. Upon further annealing to 470 K, Pd diffuses into the subsurface of both Ag(111) and Au(111). The contrasting behavior is attributed to the herringbone reconstruction on Au(111), which provides sites with higher binding energies for Pd atoms, whereas such sites are not present on Ag(111).

Particle Size and Shape Effects in Electrochemical Environments: Pd Particles Supported on Ordered Co3O4(111) and Highly Oriented Pyrolytic Graphite

Particle size and shape effects control the oxidation behavior of nanostructured electrocatalysts. We investigated the oxidation state of Pd nanoparticles supported on Ar+-sputtered highly oriented pyrolytic graphite (HOPG) and well-ordered Co3O4(111) films on Ir(100) as a function of electrode potential by means of synchrotron radiation photoelectron spectroscopy coupled with an ex situ emersion electrochemical (EC) cell. Scanning tunneling microscopy revealed the growth of hemispherical and flat Pd nanoparticles on Ar+-sputtered HOPG and Co3O4(111), respectively. The oxidation state of Pd nanoparticles is controlled by electronic metal support interaction (EMSI) associated with charge transfer at the interface. We found that the Pd nanoparticles are largely metallic on HOPG and partially oxidized on Co3O4(111). Specifically, we detected the formation of partially oxidized Pdδ+ aggregates in combination with atomically dispersed Pd2+ species. The latter species dominate at small Pd coverage and form the metal/oxide interface at high Pd coverage. Immersion into an alkaline electrolyte (pH 10, phosphate buffer) at potentials between 0.5 and 1.1 VRHE has no significant effect for Pd/Co3O4(111) but yields traces of surface Pd oxide at 0.9 and 1.1 VRHE for Pd/HOPG. Formation of PdO was observed at 1.3 and 1.5 VRHE. Quantitative analysis suggests nearly one monolayer and nearly two monolayers of PdO on the surfaces of the Pd nanoparticles supported on HOPG and Co3O4(111) at 1.5 VRHE, respectively. The differences in the oxidation behavior reveal the decisive role of the EMSI in the stability of the metal/oxide interfaces in an EC environment.

Pd-WO3 chemiresistive sensor with reinforced self-assembly for hydrogen detection at room temperature

Semiconducting metal oxides and metal catalysts have been widely used for gas sensors with high precision and reliability. In this study, we report a Pd-WO3 based chemiresistive sensor that can detect hydrogen at the ppm level at room temperature with a remarkably high response and selectivity. The colloidal solutions with Pd and WO3 nanoparticles were spray-deposited with controlled charge states of the droplets. The self-assembly of Pd nanoparticles (positive surface charge) and WO3 nanoparticles (negative surface charge) was reinforced with the positively charged droplets, producing Pd-WO3 nanoparticles with 1.68 times higher surface coverage of Pd on WO3 and a higher uniformity compared to those produced with neutral droplets. The optimized Pd-WO3 sensor fabricated by the positively charged droplets exhibits a 160 times higher response and 3.51 times faster response for 100 ppm of hydrogen than sensors fabricated by the neutral droplets, detecting hydrogen concentrations as low as 1 ppm with excellent cyclic stability, selectivity, and reproducibility.

Room Temperature Migration of Ag Atoms to Cover Pd Islands on Ag(111)

The structures of Pd islands at three different Pd coverages (0.028, 0.064, and 0.150 monolayer (ML)) on Ag(111) were studied at room temperature with scanning tunneling microscopy (STM). While previous studies have shown that the structure and composition of Pd islands on Ag(111) change at elevated temperatures, we found that Ag atoms migrate to cover the Pd islands even at room temperature. These Ag atoms occupy sites in the middle of the islands, and second layer growth begins at these sites. The migration of Ag atoms leads to the formation of vacancy islands in the Ag(111) terraces. Upon annealing to 340 K, the majority of the Pd islands are encapsulated by Ag atoms to form an Ag/Pd/Ag(111) structure. However, upon further annealing the composition of some islands at a Pd coverage of 0.150 ML changed to Ag/Ag/Pd/Ag(111).

Pd/Au Thin Film: Design, Fabrication and Characterization for Their Biosensing Applications

Biosensors are typically based on the chemical/biological reactions of the analytes or the interactions/binding of the analytes with biological recognition elements to quantitatively measure the analytes with sufficient sensitivity and selectivity. In recent decades, biosensor research has experienced a revolution due to their significant potential impact on a broad range of applications including health care, the environment, food safety etc. However, in order for biosensors to provide quantitative information about an analyte/es for real world applications, the more crucial need is the robust chemical and biointerfaces that allow highly sensitive and selective detection of bioanalytes in a miniaturized and low-cost platform such as point of care diagnostics. Additionally, real-time and continuous-use biosensors are essential for in vivo sensing to reflect the dynamic concentrations of an analyte in vivo. Compared to other chemical sensors (e.g., optical or solid state-based sensors), electrochemical biosensors possess an impressive capacity to achieve the analytical requirements of high sensitivity and selectivity as well as continuous monitoring of analytes within a small footprint, are constructed with low-cost materials and fabrication techniques, and are controlled by compact low-power microelectronic circuits. However, there are some challenges associated with real-time electrochemical including: 1) some bioanalytes are typically at very low concentrations with co-present of many high concentration interference species; 2) the bioanalytes are not redox active or if they are redox active, they have high oxidation or reduction potentials that could result in side-reactions and electrolyte decomposition. These challenges necessitate the need for the development of new robust electrocatalysts and electrochemical sensing mechanisms.Rather than relying on the analytes own redox reactions for detection, our recent work shows that a bimetallic Pd/Au thin film can be used to sensitively and selectively detect hydrogen peroxide and 3-nitrotyrosine based on the unique surface electrochemistry of palladium hydride (PdHx), palladium oxides (PdOx) and palladium hydrous oxide in the presence of these analytes. The Pd/Au thin film was fabricated using underpotential deposition (UPD) of copper followed by redox replacement of the copper by palladium on the gold surface in palladium solution at open circuit potential. Our preliminary work found that the quantities of hydrogen and oxygen incorporated to from PdHx and PdOx depends on the Pd thickness, the surface coverage of Pd vs. Au, the trace amount of copper that remained, the morphology of Pd, the adsorbate from the electrolytes, and the gold substrate properties. In this work, we systematically investigate the electrochemical properties of Pd/Au thin film electrodes using this fabrication method at various conditions to understand the parameters that impact Pd/Au thin film properties in order to further optimize the fabrication methods. We studied Pd/Au thin film thickness and electrolytes effects (0.5 M sulfuric acid, 0.1 M phosphate buffer solution with three different pH, etc.) on the resulting Pd/Au film properties. Also, the electrode electrochemical properties particularly PdHx and PdOx redox processes at various conditions (such as various electrochemical potential windows, scan rate) were thoroughly studied and characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy and electrochemical quartz Crystal microbalance. The results indicate that dominant phosphate anions at different pH greatly influence PdHx and PdOx redox properties, as do different potential windows and scan rate. Furthermore, the electrode reproducibility at the same experimental conditions were investigated. Since the Au substrate electrode areas vary in these experiments, surface oxide reduction charge method was used to calibrate the electrode areas for Pd/Au electrodes.Finally, the Pd/Au electrode fabricated at optimum conditions were tested for biosensing of most common neurotransmitters: dopamine (DA), gamma aminobutyric acid (GABA), and acetylcholine (Ach) using in situ electrochemical and quartz crystal microbalance (EQCM) techniques at phosphate buffer solution (pH=7.4). Our results show that the difference in the potential dependent adsorption of these bioanalytes at catalytic Pd/Au surface depends on their chemical and physical properties which can be used to sensitively and selectively detect these analytes in real-time with multimodal EQCM methods. From the QCM signal, a high sensitivity of 3, 0.2 and 0.13 ng.nM-1 for detection of DA, Ach, and GABA, respectively, broad detection range of 1–10000nM, and low detection limit up to 1nM was obtained. Besides, the CV results show that the corresponding PdOx reduction and PdHx oxidation current peaks decrease with increase in analyte concentrations as expected. Additionally, the Pd/Au thin film demonstrated good stability (up to 7 days), reproducibility, reusability (ca. 70% after extensive use) and selectivity and showed promising results for sensing these neurotransmitters simultaneously.The Pd/Au thin film electrochemistry-based method reported in this work is a powerful method allowing the synergistic integrating of two different metallic catalysts, into a surface structure on nanoscale. Thus, its unique surface electrochemistry opens up new opportunities to develop useful electrocatalytic materials and innovative biosensing methods for highly sensitive and selective detection of a broad range of bioanalytes based on the surface chemistry and electrochemistry of noble metal electrode catalysts.

The influence of palladium on the hydrogenation of acetylene on Ag(111).

We have used reflection absorption infrared spectroscopy (RAIRS) and temperature programmed reaction (TPR) to study the selective hydrogenation of acetylene on both a clean Ag(111) surface and on a Pd/Ag(111) single-atom-alloy surface. The partial hydrogenation of acetylene to ethylene is an important catalytic process that is often carried out using PdAg alloys. It is challenging to study the reaction with ultrahigh vacuum techniques because H2 does not dissociate on Ag(111), and while H2 will dissociate at Pd sites, H-atom spillover from Pd to Ag sites does not generally occur. We bypassed the H2 dissociation step by exposing the surfaces to atomic hydrogen generated by the hot filament of an ion gauge. We find that hydrogen atoms react with acetylene to produce adsorbed ethylene at 85 K, the lowest temperature studied. This is revealed by the appearance of a RAIRS peak at 950 cm-1 due to the out-of-plane wagging mode of adsorbed ethylene when acetylene is exposed to a surface on which H atoms are pre-adsorbed. The formation of both ethylene and ethane are detected with TPR, but no acetylene coupling products, such as benzene, were found. From quantitative analysis of the TPR results, the percent conversion and selectivities to ethylene and ethane were determined. Low coverages of Pd enhance the conversion but do so mainly by increasing ethane formation.

Catalytic Reactions on Pd-Au Bimetallic Model Catalysts.

ConspectusThe enhanced catalytic activity of Pd-Au catalysts originates from ensemble effects related to the local composition of Pd and Au. The study of Pd-Au planar model catalysts in an ultrahigh vacuum (UHV) environment allows the observation of molecular level catalytic reactions between the Pd-Au surface and target molecules. Recently, there has been progress in understanding the behavior of simple molecules (H2, O2, CO, etc.) employing UHV surface science techniques, the results of which can be applied not only to heterogeneous catalysis but also to electro- and photochemical catalysis.Employing UHV methods in the investigation of Pd-Au model catalysts has shown that single Pd atoms can dissociatively adsorb H2 molecules. The recombinative desorption temperature of H2 varies with Pd ensemble size, which allows the use of H2 as a probe molecule for quantifying surface composition. In particular, H2 desorption from Pd-Au interface sites (or small Pd ensembles) is observed from 150-300 K, which is between the H2 desorption temperature from pure Au (∼110 K) and Pd (∼350 K) surfaces. When the Pd ensembles are large enough to form Pd(111)-like islands, H2 desorption occurs from 300-400 K, as with pure Pd surfaces. The different H2 desorption behavior, which depends on Pd ensemble size, has also been applied to the analysis of dehydrogenation mechanisms for potential liquid storage mediums for H2, namely formic acid and ethanol. In both cases, the Pd-Au interface is the main reaction site for generating H2 from formic acid and ethanol with less overall decomposition of the two molecules (compared to pure Pd).The chemistry behind O2 activation has also been informed through the control of Pd ensembles on a gold model catalyst for acetaldehyde and ethanol oxidation reactions under UHV conditions. O2 molecules molecularly adsorbed on continuous Pd clusters can be dissociated into O adatoms above 180 K. This O2 activation process is improved by coadsorbed H2O molecules. It is also possible to directly (through a precursor mechanism) introduce O adatoms on the Pd-Au surface by exposure to O2 at 300 K. The quantity of dissociatively adsorbed O adatoms is proportional to the Pd coverage. However, the O adatoms are more reactive on a less Pd covered surface, especially at the Pd-Au interface sites, which can initiate CO oxidation at temperatures as low as 140 K. Acetaldehyde molecules can be selectively oxidized to acetic acid on the Pd-Au surface with O adatoms, in which the selectivity toward acetic acid originates from preventing the decarboxylation of acetate species. Moreover, the O adatoms on the Pd-Au surface accelerate ethanol dehydrogenation, which causes the increase in acetaldehyde production. Hydrogen is continuously abstracted from the formed acetaldehyde and remaining ethanol molecules, and they ultimately combine as ethyl acetate on the Pd-Au surface.Using Pd-Au model catalysts under UHV conditions allows the discovery of molecular level mechanistic details regarding the catalytic behavior of H and O adatoms with other molecules. We also expect that these findings will be applicable regarding other chemistry on Pd-Au catalysts.

Decoration of Ni/C with Small Amounts of Pd and Au for Allyl Alcohol Oxidation

The decoration of the surface of Ni nanoparticles supported on carbon black with Pd and Au and the electrooxidation of allyl alcohol on the Au/Pd/Ni/C catalysts in alkaline solution have been investigated. The decoration of Ni/C is performed by the electrochemical deposition of a small amount of Pd and then Au on Ni/C, and the Aux/Pdy/Ni100/C catalysts with the (x+y):100 atomic ratios of less then 4.5 (0.2 < x < 1.2 and 0.6 < y < 3.1) are prepared. Characterizations of Au/Pd/Ni/C reveal a uniform dispersion of the metal nanoparticles on carbon black and a low coverage of Au and Pd on the Ni nanoparticle surface. Au/Pd/Ni/C behaves more similar to Pd/C than Au/C in allyl alcohol oxidation, and the catalytic activity of Au/Pd/Ni/C depends on the amounts of Pd and Au, with Au0.9/Pd2.2/Ni100/C exhibiting the highest activity. Besides Pd and Au, the Ni nanoparticles also play important roles in the activity of Au/Pd/Ni/C, although Ni itself has no catalytic activity. The lack of any one of Pd, Au and Ni leads to low catalytic activity, indicating the synergy among the three metals. The result is helpful for preparing ternary electrocatalysts by the surface decoration.

Oxophilicity Drives Oxygen Transfer at a Palladium–Silver Interface for Increased CO Oxidation Activity

A single-layer AgOx phase grown on Ag(111) efficiently transfers oxygen to Pd domains at room temperature, rendering the Pd-decorated surface highly reactive toward CO oxidation. Oxygen transfer from AgOx to Pd and the surface reactivity toward CO were investigated as a function of the Pd coverage using X-ray photoelectron spectroscopy, surface infrared spectroscopy of adsorbed CO, temperature-programmed reaction spectroscopy, and density functional theory (DFT) calculations. Our results show that all of the oxygen from the AgOx layer (∼0.375 monolayer) migrates to the surface of Pd during formation of a nearly complete Pd bilayer at 300 K and that the oxygen coverages generated on Pd increase as the Pd cluster size decreases, reaching values that exceed the oxygen concentration in the AgOx layer by as much as a factor of 2. Experimental measurements and DFT calculations show that preferential binding of oxygen on the edges of the Pd clusters enhances the oxygen coverage on Pd clusters of decreasing size and produces a heterogeneous spatial distribution of oxygen. CO adsorbs in high coverages at 100 K by binding on both the terraces and O-rich edges of the Pd clusters. During subsequent heating, oxidation of the adsorbed CO consumes nearly all of the oxygen that transferred from AgOx to the Pd domains; in contrast, the pure AgOx layer exhibits limited reactivity toward CO adsorbed at 100 K. These results demonstrate that differences in oxophilicity drive facile oxygen transfer from Ag to the edges of Pd nanoclusters and thereby give rise to an efficient pathway for CO oxidation on bimetallic PdAg surfaces. The cooperation between the Pd and Ag domains results in near-interfacial chemistry that may be broadly important in catalysis by bimetallic alloys.

Tuning size and coverage of Pd nanoparticles using atomic layer deposition

The morphology evolution of supported palladium nanoparticles (Pd NPs) during plasma-enhanced atomic layer deposition using palladium hexafluoroacetylacetonate (Pd(hfac)2) as precursor was investigated using in situ and ex situ X-ray fluorescence (XRF) and grazing incidence small angle X-ray scattering (GISAXS), as well as ex situ scanning electron microscopy (SEM). The initial areal density of Pd NPs increases through adding cycles of the three-step process using Pd(hfac)2, H2 plasma and trimethylaluminum (TMA) prior to the standard Pd(hfac)2 + H2 plasma process. The participation of an O2 plasma exposure as additional co-reactant before or after the H2 plasma step also plays a role in the nucleation density and particle coalescence, affecting also the shape of the deposited particles. Based on the gathered knowledge, a synthetic approach that enables precise control of the Pd nanoparticle dimensions and coverage is developed.

Selective Hydrogenation of Acrolein on a Pd/Ag(111) Single-Atom Alloy Surface

The hydrogenation of acrolein on the Ag(111) and Pd/Ag(111) single-atom alloy (SAA) surfaces was studied using temperature-programmed reaction spectroscopy. On Ag(111), the percent conversion of acrolein increased with increasing atomic hydrogen coverage. At an acrolein coverage of 0.17 ML followed by a low exposure to atomic hydrogen, the highest selectivity to 2-propenol was reached at 19%. However, increasing the acrolein coverage caused the selectivity to 2-propenol to decrease and the selectivity to propanal to increase to a maximum of 92%. In all cases, increasing atomic hydrogen exposure decreased the selectivity to 2-propenol. The selectivity to 1-propanol was constant at only 1%. Activity and conversion on the Ag(111) and Pd/Ag(111) SAA surfaces were compared for Pd coverages of 0.2, 0.5, and 0.9%. With increasing Pd coverage, the percent conversion increased while the selectivity to 2-propenol decreased. The selectivity toward 1-propanol only increased from 1 to 3% for the 0.9% Pd/Ag(111) SAA surface.

A monolayer of Pd on ZrC(0 0 1) speeds up O2 dissociation: An ab initio study

We propose the Pd monolayer (ML) on ZrC(001) surface as an effective catalyst for the dissociation of oxygen by density functional theory calculations. We find that the coverage of Pd has a conspicuous impact on the adsorption and dissociation of O2. The strong interaction between the Pd atoms and the ZrC(001) support enhances the reactivity and stability of the electrocatalyst. By comparing the binding energies of Pd-Pd and Pd-C, we conclude that the Pd adatoms do not aggregate to form a cluster and prefer to form a monolayer when the coverage is low. With a monolayer of coverage, the C sites are fully saturated by adsorbed Pd atoms, which prevent the oxidation of the ZrC(001) surface. The dissociation activity of O2 on PdML/ZrC(001) is predicted to be a rival of or even surpass Pt(111). In addition, the high mobility of the dissociated oxygen atoms on PdML/ZrC(001) also benefits the later reaction step for ORR.

Degradation mechanism of a Pd/Ta composite membrane: Catalytic surface fouling with inter-diffusion

Composite metallic membranes comprising Pd coated on group 5 elements such as V, Nb, and Ta are actively explored as a promising material for hydrogen permeable membrane. However, such composite membranes are known to suffer from performance degradations owing to excessive surface fouling due to inter-diffusion between Pd and group 5 elements at high temperatures. In this study, mechanically stable Pd/Ta composite membranes are fabricated, and their H2 permeation flux degradation rates and mechanism of membrane degradation are investigated. Fabricated membranes had full coverage of Pd on Ta surface, with less than 5 wt% of impurities. H2 permeation rates of Pd/Ta membrane samples with different Pd and Ta thicknesses are evaluated at temperatures from 450 °C to 650 °C for a prolonged period of 20–100 h. Over the tested period, degradation in H2 permeation rate was 5% or higher, with temperature being a dominant factor. SEM, TEM, and XRD analyses of the surface and cross-sectional morphology, compositions, and crystallinity reveal that the main degradation mechanism of the composite membrane is the inter-diffusion between Pd and Ta leading to the formation of intermetallic compounds as well as morphology change of the catalytic layer. By evaluating the exponential factor in Sievert’s equation over the degradation period, it was found that the diffusion mechanism does not change over time, confirming that the bulk diffusion mechanism is affected by the inter-diffusion. H2 flux degradation was less prominent at lower temperatures with thicker Pd catalytic layers.