Pd Oxide Research Articles

Boosting methane catalytic combustion by confining PdO-Pd interfaces in zeolite nanosheets

Supported Pd/zeolite is a potential candidate for catalytic methane combustion. However, improving the catalytic lifespan of Pd/zeolite catalysts remains a challenge. Herein, we developed zeolite sheet-confined PdO-Pd interface sites for highly efficient methane combustion. CH4 conversion remained at ∼ 99.5 % throughout a 150-hour test at 360 °C for a Pd-Pt/HMCM-22 nanosheet catalyst. In comparison, the highest deactivation rate was observed for the Pd-Pt/Silicalite-1 catalyst. The fresh and spent samples were characterised using X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), demonstrating that the zeolite nanosheet-confined PdO-Pd interface sites possessed exceptional structural stability and thermal sintering resistance for Pd-Pt/HMCM-22. The poor catalytic stability of Pd-Pt/Silicalite-1 was related to the sintering of the Pd/Pt species and the oxidation of metallic Pd.

Controllable Fabrication of Hg–Pd–PdO Heterostructures as Efficient Peroxidase Mimics for Carcinoembryonic Antigen Detection

The growth of oxides on the surface of noble metals and the introduction of alloys are effective methods to enhance the catalytic activity of noble metals. However, the fabrication of noble metal oxides always involves harsh experimental conditions and the oxidation degree could not be controlled. Herein, a simple, fast, and controlled Pd oxidation method by mixing Hg2+ and Pd nanosheets (PdNSs) under mild conditions to form PdxHgy(PdO)z (PHOs) was reported, which consists of the Pd–Hg alloy and PdO. The density functional theory (DFT) calculation and experiment results proved that the Hg atom incorporation promotes the nearby Pd–Pd bond breaking, initiating a cascade of PdO generation. More precisely, 1 Hg atom incorporation induced ∼8 Pd atom oxidation, ensuring that the oxidation degree of Pd could be easily controlled by adjusting the ratio of Hg2+ and PdNS. As a peroxidase-mimicking nanozyme, the PHO affinity for its substrate could be 21.7- and 123.6-fold greater than that of the PdNS and the natural peroxidase (HRP), respectively. For the colorimetric immunoassay of carcinoembryonic antigen (CEA) detection, PHO has an ultralow detection limit of 1.33 pg mL–1, which is ∼8.6 and ∼282 times lower than that of the PdNS and the natural HRP, respectively.

Effect of palladium chemical states on CO2 photocatalytic reduction over g-C3N4: Distinct role of single-atomic state in boosting CH4 production

Cocatalyst decoration has been recognized as an effective strategy in photocatalysis, yet the critical role of sing-atomic state on CO2 photocatalytic reduction, distinguished from the oxide and elemental states, remains a mystery hitherto. Herein, single-atom Pd (Pd-SA), Pd oxides (PdOx), and Pd nanoparticles (Pd-NP), were homogeneously anchored on g-C3N4 (CN) to investigate their CO2 reduction behaviors under visible-light irradiation. Performance tests showed Pd species decoration improved the CH4 production of CN, with Pd/CN-SA exhibiting the optimum yields (2.25 μmol g–1), markedly higher than that of PdOx/CN (1.08 μmol g–1) and Pd/CN-NP (0.44 μmol g–1). After comprehensive mechanism analysis with various characterization techniques, in-situ DRIFT spectra and DFT calculations, it was found that the conducive activation of CO2, negative conduction band potentials, and excellent •H utilization efficiency, collaboratively contributed to the superior CH4 production of Pd/CN-SA. Despite the larger electron density of Pd/CN-NP and PdOx/CN, the moderate reduction ability of their photogenerated electrons restricted the further reduction of adsorbed CO2 species and CO intermediate, limiting the enhancement of CO2 reduction activity. Furthermore, the CH4 evolutions of Pd/CN-NP and PdOx/CN were also limited by the poor •H supply and inferior •H utilization efficiency, respectively. It is expected that the effect of chemical states, especially the critical role of single-atomic state, revealed in this work can inspire the rational design of more advanced photocatalysts for CO2 reduction.

Pd oxide nanoparticles enhanced biomass driven N-doped carbon for hydrogen evolution reaction

The development of an efficient and stable hydrogen evolution reaction (HER) electrocatalyst is essential for industrial water splitting. Here, we used waste durian shells, cheap urea and palladium acetate to synthesize PdO supported nitrogen-doped biomass based carbon nanomaterials. The prepared Pd-N-CDS electrocatalyzed the hydrogen evolution reaction in 0.5 M H2SO4, and the overpotential recorded was 143 mV at 10 mA cm−2. In particular, the potential applied at a current density of 10 mA cm−2 obtained excellent stability using the chronoamperometry. In addition, the Pd oxide nanoparticles covered by the thin carbon layer cooperate to catalyze HER through the radiated electronic effect.

High-efficiency palladium/halloysite nanotubes catalyst for toluene catalytic oxidation: Characterization, performance and reaction mechanism

In this study, the halloysite treated with nitric acid was designed as a functionalized support material for favoring surface availability and dispersion of nanometric palladium (Pd) nanoparticles. The prepared supported catalysts were characterized by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and O2 temperature-programmed desorption (O2-TPD). The catalytic performance and reaction mechanism of toluene oxidation were evaluated and proposed. Scanning and transmission electron microscopy images showed that 4–5 nm diameter Pd nanoparticles were uniformly dispersed on the external and edge surfaces of the A-Hal nanotubes and no obvious aggregations observed. The Pd nanoparticles were mainly present in the zero-valent state. The ratio of metallic Pd to Pd oxide species and adsorbed (Oads) to lattice (Olatt) presented a maximum value of 2.54 and 23.0, respectively, when the Pd loading was 0.5%. The prepared support catalysts exhibited a satisfactory catalytic performance and cycling stability for toluene conversion. Among the analyzed samples, the 0.5% Pd/A-Hal catalyst exhibited the highest catalytic activity for toluene oxidation, stability, and water resistance. Toluene conversions of 50% and 90% were obtained at 167 and 185 °C, respectively. In situ diffuse reflection Fourier transform spectroscopy measurements confirmed the intermediates generated during toluene oxidation and revealed that toluene oxidation occurred via the benzyl alcohol → benzaldehyde → benzoic acid → maleic anhydride reaction pathway over the obtained catalysts. These results were attributed to the high content of metal Pd species, abundant Oads species, and low-temperature reducibility. These results indicate that Hal support catalysts are promising materials for application in environmental protection.

C-H functionalization of quinoline N-oxides catalyzed by Pd(II) complexes: a computational study.

Pd(II) catalysts, particularly the acetate salt in acetic acid, tended to favor regioselective C-H activation of quinoline N-oxides (QOs) at the C2 position. However, Pd(II)Cl2 was shown to catalyze their C-H activation at C8 and, in the presence of water, C8-H activation was accompanied by the formation of 2-quinolinones. The aim of the DFT study described in this work was to shed light on the complete mechanism of these competing catalytic reactions, when PdCl2 reacts with QO and benzaldehyde in dichloroethane. C-H activation of QO was the first step of the reaction and involved either a metallacycle, with a CQO-Pd(II) σ-bond and a C(8)-H-Pd(II) agostic bond, or an η3-QO complex, with three carbon atoms of the heteroring of QO binding PdCl2. The first situation led to the unusual C8 activation and the second to C2 activation. The σ-metallacycle undergoes C8-H activation and the energy of the TOF determining the transition state to form the product is ∼17 kcal mol-1, while for the reaction through the π-metallacycle (C2-H activation) the corresponding energy is higher (∼29 kcal mol-1) and thus is not competitive under the same conditions. The reaction proceeding through the σ-complex, activating the C8 position, is preferred, in agreement with experimental results. Both reactions involve oxidation of Pd(II) to Pd(IV) and the catalyst is regenerated. When small amounts of water are added to the reaction mixture, C8-H activation (acylation) results from the same σ-metallacycle with the same barrier, but the simultaneous formation of 2-quinolinones is more complicated. It starts with OH- attack at the C2 position, and is followed by the migration of two hydrogen atoms, and the final reductive elimination step ends with Pd(0). The higher barriers for the migration and reoxidation of Pd(0) are associated with the more demanding reaction conditions. The different reactivity of Pd(II)(OAc)2 under analogous conditions is clarified, as it is only capable of forming the above mentioned π-complex and thus of activating the C2 position of QO. This catalyst can preferentially activate the C8-H bond under rather different conditions, including in particular acetic acid medium, as shown by other authors.

Surface State Changes of Pd Three-Way Catalysts under Dynamic Lean/Rich Perturbation Compared with Static Condition

In three-way catalytic converters, momentary perturbations of the exhaust gas composition between fuel-rich (reducing) and fuel-lean (oxidizing) conditions near the stoichiometric point affect the catalyst surface and the conversion efficiencies of NOx, CO, and hydrocarbons. However, the specific changes in the surface state of the catalyst under such dynamic conditions have not been elucidated in detail. In this study, in situ diffuse reflectance spectroscopy (DRS) was applied to monitor real-time changes in the surface state of Pd-based catalysts occurring under rich/lean perturbation at intervals of 2 s. The Pd oxidation state was found to fluctuate in synchronism with this perturbation, but its oscillation amplitude was much smaller when supported on CeO2–ZrO2 (CZ) than on Al2O3. Because this buffering effect of CZ due to its oxygen scavenging function mitigates the gradual oxidation of active metallic Pd to less-active Pd oxide, higher reaction rates were achieved especially for NOx and CO under the dynamic perturbation atmosphere. Furthermore, the Pd–CZ interface quickly supplied active oxygen species to prevent coke deposition originating from the decomposition of adsorbed hydrocarbon, which was unavoidable on Pd/Al2O3 under stoichiometric and fuel-rich conditions. This study demonstrates that in situ DRS provides a simple and useful tool for the direct observation of surface state changes under the real reaction atmosphere at the laboratory level. The information obtained is of great use for understanding the role of CZ in transient and unsteady-state catalytic processes and bridging a gap between real on-board TWC performances and laboratory tests.

A Versatile Approach to Electrochemical In Situ Ambient-Pressure X-ray Photoelectron Spectroscopy: Application to a Complex Model Catalyst.

We present a new technique for investigating complex model electrocatalysts by means of electrochemical in situ ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). Using a specially designed miniature capillary device, we prepared a three-electrode electrochemical cell in a thin-layer configuration and analyzed the active electrode/electrolyte interface by using "tender" X-ray synchrotron radiation. We demonstrate the potential of this versatile method by investigating a complex model electrocatalyst. Specifically, we monitored the oxidation state of Pd nanoparticles supported on an ordered Co3O4(111) film on Ir(100) in an alkaline electrolyte under potential control. We found that the Pd oxide formed in the in situ experiment differs drastically from the one observed in an ex situ emersion experiment at similar potential. We attribute these differences to the decomposition of a labile palladium oxide/hydroxide species after emersion. Our experiment demonstrates the potential of our approach and the importance of electrochemical in situ AP-XPS for studying complex electrocatalytic interfaces.

Engineering the microenvironment of Pd nanoparticles on porous MnOx matrix to improve catalytic toluene combustion

Tuning the microenvironment of noble-based catalyst is a key issue for improved catalytic performance. Here, the porous MnOx enclosed Pd nanoparticles were successfully fabricated by template-free method, that was based on an acid-etching strategy using Pd-doped manganite perovskite (e.g., LaPd0.1Mn0.9O3) as precursor. The performance of prepared Pd/MnOx catalyst is beyond the performance of acid-treated MnO2 and traditional Pd/MnO2 catalyst, showing a T90 of 200 °C under a space velocity of 60,000 mL/(g.h). The superior performance should be attributed to the exposure of Pd active sites, the large surface area, abundant oxygen vacancies and the synergistic effect between Pd and MnOx support. XPS spectra demonstrated that the change of Pd oxidation state was well associated with catalytic activity, and the mixed Pd0/Pdn+ species were benefit for improved activity. On the basis of in-situ XRD and TG results, it was revealed that the thermal deactivation was caused mainly by the structural change of MnOx other than the Pd oxidation state. And the structural stability could be strengthened by the thermal treatment at high temperature (e.g., 500 °C), and remained a robust performance over the long-term stability test.

Influence of Pd and Rare Earth Metals Oxides (Ce, La) as Modifying Additives in the Co,Ni-Oxide Catalyst Compositions on the Process of Methane Oxidation

Influence of Pd and Rare Earth Metals Oxides (Ce, La) as Modifying Additives in the Co,Ni-Oxide Catalyst Compositions on the Process of Methane Oxidation

Experimental and Theoretical Studies of Pd Cation Reduction and Oxidation During NO Adsorption on and Desorption from Pd/H–CHA

Passive NOx adsorbers (PNAs) have been proposed for trapping NOx present in automotive exhaust during the period of cold start during which the three-way convertor is not yet hot enough to be effective for NOx reduction. Pd-exchanged chabazite (Pd/H–CHA) is a good candidate for passive NOx adsorption due to its ability to store NO and retain it to high temperatures (>473 K). Previous research suggests that NO adsorbs on both Pd2+ and Pd+ cations and that NO desorption from Pd2+ cations occurs at lower temperatures than from Pd+ cations. Since experimental evidence shows that Pd exchanges into CHA exclusively as Pd2+, it is not clear how these cations are reduced to Pd+. In this study we show through experiments and theoretical analysis that Pd+ cations can form via two processes, each of which involves water adsorbed on Brønsted-acid sites of the zeolite. The first of these processes is 1.5 NO + Pd2+Z–Z– + 0.5 (H2O)H+Z– → (NO)Pd+Z–H+Z– + 0.5 NO2 + 0.5 H+Z–. Experiments confirm that the ratio of the NO2 formed upon NO adsorption to the NO desorbing from Pd+ at elevated temperatures corresponds to 0.5. Pd2+ can also be reduced via the reaction 1.5 CO + Pd2+Z–Z– + 0.5 (H2O)H+Z– → (CO)Pd+Z–H+Z– + 0.5 CO2 + 0.5 H+Z–. Upon subsequent adsorption of NO, NO fully displaces CO from Pd+ to form (NO)Pd+Z–H+Z–. In this case, the amount of CO2 formed upon CO adsorption is 0.5 of the NO desorbing at elevated temperatures from Pd+. Gibbs free energy calculations for the above processes at various potential ion-exchange sites in the CHA framework indicate that these reactions are thermodynamically feasible. We also find that Pd+ is not formed in the absence of adsorbed water and is readily reoxidized to Pd2+ by trace amounts of O2.

Biological Evaluation and Antioxidant Studies of Nio, Pdo and Pt Nanoparticles Synthesized from a New Schiff Base Complexes

This research included the preparation of Ni, Pd oxide and Pt metal nanoparticles derived from Schiff base (E)-2-(((2,5-dichlorophenyl)imino)methyl)-4-methyl phenol octahedral from Ni(II) complex and square planar from Pd(II) and Pt(II) complexes using pulsed laser ablation immersed in deionized water. The optical properties of the prepared NiO, PdO, and Pt nanoparticles were investigated using UV-Visible spectra and FTIR spectrophotometer. The shape and structure were analyzed by Transmission Electron Microscope (TEM) and the X-ray Diffraction Instrument XRD. By using the Scherrer equation, the results showed Ni, Pd, and Pt nanos with average particle sizes of 28.53nm, 20.47nm, and 22.30nm. The biological activity of the nanocomposites was tested against two types of Escherichia coli, Staphylococcus aureus bacteria, and one type of fungus, such as candida Albicans, using antibiotics (Ceftriaxone and metronidazole), showing promising results and the DPPH radical scanning activity is a standard test in studies of antioxidant activity for them.

Layered Pd oxide on PdSn nanowires for boosting direct H2O2 synthesis

Hydrogen peroxide (H2O2) has the wide range of applications in industry and living life. However, the development of the efficient heterogeneous catalyst in the direct H2O2 synthesis (DHS) from H2 and O2 remains a formidable challenge because of the low H2O2 producibility. Herein, we develop a two-step approach to prepare PdSn nanowire catalysts, which comprises Pd oxide layered on PdSn nanowires (PdL/PdSn-NW). The PdL/PdSn-NW displays superior reactivity in the DHS at zero Celcius, presenting the H2O2 producibility of 528 mol kgcat−1·h−1 and H2O2 selectivity of >95%. A layer of Pd oxide on the PdSn nanowire generates bi-coordinated Pd, leading to the different adsorption behaviors of O2, H2 and H2O2 on the PdL/PdSn-NW. Furthermore, the weak adsorption of H2O2 on the PdL/PdSn-NW contributes to the low activation energy and high H2O2 producibility. This surface engineering approach, depositing metal layer on metal nanowires, provides a new insight in the rational designing of efficient catalyst for DHS.

Effect of Support and Pd Cluster Size on Catalytic Methane Partial Oxidation to Dimethyl Ether Using a NO/O2Shuttle

The partial oxidation of methane to dimethyl ether (DME) was studied on palladium supported on SiO2, SiO2-ZrO2, and ZrO2 at 225–375 °C and 0.1 MPa using either O2 or a mixture of NO and O2 as the oxidants. The NO + O2 mixture was more reactive than the O2 toward methane, probably due to the formation of active surface nitrate species. The formation of DME on the catalysts was influenced by the support, with the Pd/ZrO2 catalyst producing DME and the Pd/SiO2 catalyst producing only CO2, irrespective of the oxidant used. The Pd/SiZrO2 catalyst formed DME only when O2 alone was used as the oxidant. For the reaction with NO + O2, in situ Fourier transform infrared (FTIR) measurements showed that the partial oxidation activity on Pd/ZrO2 was related to its ability to form surface-bridged nitrate species, likely due to the presence of basic sites. However, an inhibitory effect of basicity on CH4 turnover frequency (TOF) was attributed to surface nitrate-induced structural modification deduced from X-ray absorption fine structure spectroscopy measurements. For the reaction with only O2, the formation of DME over Pd/ZrO2 and Pd/SiZrO2 was attributed to the reported ability of ZrO2 to retain methoxy intermediates. Furthermore, a weak structural effect on the TOF observed with O2 was attributed to competing effects of decreasing activity for C-H activation and increasing resistance to Pd oxidation with increasing particle size.

Investigation of the evolution of Pd-Pt supported on ceria for dry and wet methane oxidation

Efficiently treating methane emissions in transportation remains a challenge. Here, we investigate palladium and platinum mono- and bimetallic ceria-supported catalysts synthesized by mechanical milling and by traditional impregnation for methane total oxidation under dry and wet conditions, reproducing those present in the exhaust of natural gas vehicles. By applying a toolkit of in situ synchrotron techniques (X-ray diffraction, X-ray absorption and ambient pressure photoelectron spectroscopies), together with transmission electron microscopy, we show that the synthesis method greatly influences the interaction and structure at the nanoscale. Our results reveal that the components of milled catalysts have a higher ability to transform metallic Pd into Pd oxide species strongly interacting with the support, and achieve a modulated PdO/Pd ratio than traditionally-synthesized catalysts. We demonstrate that the unique structures attained by milling are key for the catalytic activity and correlate with higher methane conversion and longer stability in the wet feed.

Assessing the effect of O2 dithering on CH4 oxidation on Pd/Al2O3

Under periodic lean/rich operation generated by repeated O2 pulses (O2-dithering), the abatement of CH4 and NO is enhanced compared to static operation. However, it is not well understood how the dithering parameters (pulse amplitude and frequency) affect CH4 conversion, making it difficult to anticipate the impact of such pulses on the catalytic performance. Here, we show that the effect of O2-dithering on the activity of Pd/Al2O3 can be reliably assessed as a function of dithering parameters, temperature, and exhaust gas composition. Operando X-ray absorption spectroscopy was used to support the conclusions based on considerations of the Pd oxidation state. Our work relies on explicit calculations of the O2 concentration present in the reactive feed, which is based on the amount of O2 pulsed to the system and the pollutants’ conversion. Since NO contributes to the amount of oxygen available during reaction, its concentration and conversion need to be correctly evaluated.

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.

(Digital Presentation) New Trends in the Formation of Composites with Desired Functional Properties

The main requirements for anode materials can be divided into two groups: i) overall operating (satisfactory electrical conductivity, availability and reasonable cost, long service life, etc.); ii) specific, due to particular target process (high electrocatalytic activity and selectivity) [1]. The lack of universal anode material requires the creation of new approaches to managing the functional properties of the catalyst. In our opinion, the optimal strategy is to choose a base material that meets the general operational requirements, followed by the creation of an active layer on its basis in accordance with the requirements of particular target processes.The regularities of formation of composites of the TiOx-Pt and TiOx-Pt-Pd systems and their physicochemical properties were studied.Composites were obtained in two stages. First, a thin non-continuous layer of Pt or successive layers of Pt-Pd was applied to the substrate by electrodeposition. Nitrite electrolyte for platinating and phosphate palladation were used. The amount of Pt and Pd on the surface ranged from 0.1 to 2.0 mg cm-2. Then the resulting material was heat treated in an air atmosphere. The surface layers of the composites were formed due to the oxidation of the substrate and the encapsulation of platinum and palladium particles into titanium oxides during this stage. The chemical composition of the bulk and surface of the electrocatalytic coatings obtained was determined by XPS, SEM and EDAX.XPS showed that Pt exists in the metallic state, while Ti is in the form of both metal and intermetallic TixPty, with low Pt content, and in oxide form in Ti(IV) compounds on the surface of non-heat treated electrode As one can see, the coating is not uniform, and the platinum content is significantly reduced from the surface to the substrate (from 92 to 67 at.%), that indicates the local nature of the coating and confirmed by SEM data. As thermal treatment contributes to a more uniform distribution of Pt on the surface, as well as its diffusion in combination with oxygen in the coating bulk, it leads to the formation of a composite of titanium-platinum oxides.The semiconductor properties of such anodes are due to the presence of TiO2, which is an n-type semiconductor. As the temperature increases, the potentials of the flat zones and the carrier concentrations increase, which may be related to the interaction of platinum (electron donor) with TiO2. The use of titanium suboxides as a substrate and increasing the processing temperature also leads to an increase in the potential of flat zones. However, this reduces the number of carriers due to the increase in the degree of stoichiometry of titanium suboxides due to oxygen uptake. The electrodes obtained at 583 K do not correspond to the general dependence. It is likely that the new Ti-O phase formed under such conditions makes an individual contribution to the semiconductor properties of such materials.Palladation of platinum titanium does not lead to a significant change in surface morphology. Platinum, according to EDAX, is fairly evenly distributed on the surface of titanium, which is not observed for palladium. Unlike platinum, the maximum amount of palladium is observed in the protruding parts of the surface, and the minimum - in the hollows, due to the uneven distribution of current on the surface of Ti/Pt during the electrodeposition of palladium. The most noticeable change in morphology occurs at a surface Pd content of 1.0 mg cm-2. The oxygen concentration increases on the surface during heat treatment of Ti/Pt-Pd, there is oxidation of Pd, the surface becomes blue. The distribution of oxygen on the surface coincides with palladium, which indicates the formation of an oxide layer. The XRD method detected the PdO phase on the surface of heat-treated samples with a surface palladium content of 0.2 to 1.0 mg cm-2. At 2θ = 33.8°, the PdO-specific reflex is manifested, the area of which increases with increasing of surface palladium content.Thus, the use of the combined electrochemical-pyrolytic method of obtaining composite anode materials allows to create materials that differ significantly in their structural parameters, composition and physicochemical properties. The main factors influencing the properties of such materials are the nature of the substrate, the amount and nature of platinum and palladium in the surface layer, the temperature and duration of heat treatment in the air. Developed anode materials are characterized by long service life. References Walsh, F.C. Modern developments in electrodes for electrochemical technology and the role of surface finishing / F.C. Walsh // Trans. Inst. Met. Finish. – 2019. – Vol. 97(1). – P. 28-42

Effect of Ethylene Glycol on the Dissolution of Palladium with HCl Solution Containing Oxidizing Agents and Selective Precipitation of Pd(IV) Compound

There is growing interest in the recovery of pure palladium (Pd) compound from cemented Pd from spent electroplating solutions due to increasing demand for Pd, and there is considerable motivation to develop an efficient recovery process. In conventional methods of leaching Pd metal, HCl solutions containing oxidizing agents are employed. In this work, ethylene glycol (EG) replaced water as a diluent in the HCl solution containing oxidizing agents such as H2O2, NaClO and NaClO3. Leaching of the Pd metal and the subsequent precipitation of the Pd(IV) compound was investigated. Among the three kinds of oxidizing agent, NaClO3 showed the best Pd metal leaching efficiency from a metallic mixture of Pd and Zn from HCl in EG solution. The role of EG in enhancing the leaching and precipitation is discussed in light of its interaction with other components in the solutions. To precipitate the Pd(IV) compound with NH4Cl, it is important that the dissolved Pd ion exists as Pd(IV). Therefore, NaClO3 was again added to the leaching solution to verify the oxidation of Pd(II) to Pd(IV). Extra pure ammonium hexachloropalladate ((NH4)2PdCl6) was recovered by precipitation from the leaching solution of the cemented Pd under the optimum conditions. Compared to conventional HCl systems, the present process shows some advantages, by reducing both chemical dosage and energy consumption. The results confirm a process can be developed for the recovery of the Pd(IV) compound from spent electroplating solutions containing a small amount of Pd(II).

Promoted catalytic potential in sulfides oxidation and biological screening of green Pd (II) and Co (II) complexes of salicylidene isatin hydrazone ligand

Mononucleating complexes of isatin hydrazone sodium sulfonate ligand (HLn) with palladium (II) and cobalt (II) ions: The complexes were synthesized within 1:1 and 2:1 molar ratio of HLn with Pd2+and Co2+ion in PdLn and Co (Ln)2, respectively. The catalytic reactivity of both complexes was examined in the oxidation of sulfides (diphenyl sulfide, dps, and methylphenyl sulfide, mps) using hydrogen peroxide under aerobic conditions. Oxoproducts, dipheylsufoxide, dpo, and methyl phenyl sulfoxide, mpo, are the chemoselective products with detection of large amounts of the unselective further oxidation products of dioxoproducts (dipheylsufone, dpn, and methylphenyl sulfone, mpn). The homogenous catalyst of Co (Ln)2revealed more efficient action compared to that of PdLn depending on the high electrochemical reversible potential of the central metal ion in the catalytic reaction within the electron and/or oxygen transfer system.Exploring the importance of the M2+ion in the coordinated ligand, the bio‐reactivity of HLn, PdLn, and Co (Ln)2was illustrated within some commonly well‐known bacteria and fungi strains. Additionally, they were involved as anticancer reagents against some human cancer cell lines in vitro. Both metal complexes presented high inhibited action versus the growth of the studied microorganism and cancer. The interaction effect of Pd2+and Co2+ions in their pincer complexes was tested with calf thymus DNA spectroscopically and via the viscosity changes.