Pd Phases Research Articles

Activity of bimetallic PdIn/CeO2 catalysts tuned by thermal reduction for improving methanol synthesis via CO2 hydrogenation

AbstractSynergistic Pd–In2O3 catalysts are promising candidates for producing methanol via CO2 hydrogenation, and the metal phases in them can be tuned by thermal reduction treatment affecting the catalytic activity significantly. This work presents a comprehensive investigation to gain an insight into the effect of thermal reduction temperature on the variation and interaction of Pd and In2O3 phases supported on CeO2 (viz., PdIn/CeO2) and their correlations with CO2 hydrogenation toward methanol synthesis. The findings show that Pd/In‐rich PdIn alloys and In2O3 with relatively strong interaction are key phases (by reducing the PdIn/CeO2 at 300°C) for promoting methanol formation, leading to a high selectivity to methanol at 78.9% and space–time yield (STY) of 3.6 gCH3OH gPdIn−1 h−1. A further increase in reduction temperature (from 300 to 500°C) promoted the formation of homogenized PdIn intermetallic alloys with significantly poor ability for H2 dissociation and CO2 activation, and hence poor methanol yield.

Synthesis and performance of PdAu/ITO electrocatalysts in urea oxidation reaction

PdAu electrocatalysts were prepared in different atomic compositions supported on ITO by sodium Borohydride process. XRD results show intense crystalline peaks related to ITO, which may mask the appearance of less crystalline Pd or Au phases. Transmission results indicate agglomeration of palladium and gold nanoparticles on the support, a phenomenon compatible with metal oxide supports. Cyclic voltammograms in the absence of urea display characteristics commonly observed for PdAu electrodes, with an increase in oxygenated species compared to pure Pd or Au. Voltammograms in the presence of urea showed oxidation processes and lower current values, indicating catalyst deactivation processes. PdAu 75:25 demonstrated higher power density values compared to other prepared electrocatalysts, suggesting a synergy between Pd and Au for urea oxidation reaction.

One-Pot Liquid-Phase Synthesis of Methyl Isobutyl Ketone Over Bifunctional Ion-Exchange Resins: Unravelling the Role of Resins Structure and Active Pd or Cu Phases on Sintering, Leaching and Catalytic Activity

One-Pot Liquid-Phase Synthesis of Methyl Isobutyl Ketone Over Bifunctional Ion-Exchange Resins: Unravelling the Role of Resins Structure and Active Pd or Cu Phases on Sintering, Leaching and Catalytic Activity

Catalytic combustion of light hydrocarbons over Pd − Pt/Al2O3: The hidden Pt1 active sites

Rationalizing the roles of different active phases in Pd − Pt/Al2O3 for light hydrocarbon (methane, ethane, propane, ethylene, and propylene) catalytic combustion is of central importance in producing practical air pollution abatement and power generation systems. So far, considerable efforts have been paid to understanding the microstructural evolution of Pd − Pt catalysts during high-temperature ageing, while much less is known about the key features in these catalysts at industry-related mild temperatures (e.g., ≤ 550 °C). In this article, by starting from platinum and palladium nitrates impregnated on commercially available γ-Al2O3, the microstructural evolution of Pd − Pt/Al2O3 induced by calcinations at below 550 °C in air was distinguished and further disentangled by comparison with the cases of Pt/Al2O3. Supported by electron microscopy, in situ DRIFTS, and other characterizations, we showed that the PdO nanoparticles on Pd − Pt/Al2O3 catalysts worked not only as a reactive phase for alkane combustion, but also as a “trapper” that reduced the amount of single-site Pt1 species by anchoring and aggregating them on the PdO (101) surface during calcinations. Since these Pt single atoms were highly reactive for the combustion of alkenes, Pd − Pt/Al2O3 exhibited enhanced methane/ethane/propane oxidation activity with increasing Pd contents, but were weaker ethylene and propylene oxidizers than Pt/Al2O3. Water and sulfur tolerance tests were also performed to evaluate the true practicability of the catalysts, which demonstrated the overall higher robustness of the Pd-free recipes for light hydrocarbon combustion.

Tuning Pd species via electronic metal-support interaction for methane combustion

Utilizing catalytic combustion to convert methane (CH4) into CO2 and H2O stands as one of the most effective approaches for mitigating unburnt CH4 emissions from natural gas engines. Supported Pd catalysts have been extensively researched for their role in low-temperature CH4 combustion, with their catalytic activity greatly influenced by metal-support interactions. Surface interaction Pd phases, as a special type of Pd species originating from metal-support interactions on supported Pd catalysts, show controversial catalytic performance in CH4 combustion. Moreover, the impact of electronic metal-support interactions (EMSI, which refers to metal-support interactions associated with electron transfer) remains unclear. Hence, we opted for Ce-Zr solid solutions with different Ce:Zr molar ratios as supports and synthesized a range of supported Pd catalysts with varying EMSI intensities. Characterization revealed that as the oxygen vacancy concentration on the support increased, electron transfer weakened, leading to a higher Pd-O-Ce content, resulting in a lower CH4 activation barrier and better catalytic performance. This study offers a promising approach for regulating EMSI and active Pd species on supported catalysts in practical applications.

Electrochemical Promotion of Bimetallic Palladium‐Cobalt Nano‐Catalysts for Complete Methane Oxidation

AbstractThe catalytic activity and electrochemical promotion of catalysis (EPOC) of the bimetallic Pd−Co nanoparticles (10 nm) deposited on yttria‐stabilized zirconia were investigated for complete methane oxidation. The reaction was conducted under open‐circuit and under polarization in a temperature range of 320–400 °C in reducing, stoichiometric, and oxidizing conditions. The catalytic activity of the catalyst nanoparticles increased to 40 % upon positive polarization in all gaseous compositions. A comparison of three reaction conditions revealed that the highest reaction rate increase (enhancement ratio, ρ=1.4) occurs under reducing conditions. The reaction rate increased upon anodic polarization, resulting in non‐Faradaic electrochemical modification of catalytic activity (Λ≫1) in reducing and oxidizing conditions and Faradaic or electrochemical enhancement (Λ<1) in stoichiometric reaction condition. This work demonstrates that the formation of different Pd and Co oxide phases can be accurately controlled by electrochemical stimuli and, in reducing conditions, result in pseudo‐capacitor behaviour.

Structure characterization of aged automobile exhaust catalysts using electron probe microanalysis

BackgroundDriven by emission regulations, the technology of emission control catalysts has been under increasing need for development. Understanding the deactivation mechanism of aged or spent automobile exhaust catalysts is the key to extending their service lifetime. However, the lack of comprehensive microstructural characterization results in an incomplete understanding of their physicochemical properties. Deactivation mechanism of automobile exhaust catalysts is a considerably complex phenomenon, it can be classified into three groups based on its origin: thermal sintering, chemical poisoning and mechanical deactivation. ResultsIn this study, an aged high-mileage automobile exhaust catalyst with Pd and Rh active phases supported on a cerium zirconium oxide doped alumina coating on cordierite was analysed; six consecutive monolithic blocks along the inlet to the outlet of the aged catalyst were extracted, and the corresponding metallographic samples were fabricated using the vacuum impregnation resin method. The purpose of this study was to accurately characterize the different regions of the monolith via electron probe microanalysis and to infer potential causes of catalyst deactivation. Two major causes of deactivation were found: (1) aggregation and alloying of precious-metal particles caused by thermal sintering and (2) chemical poisoning caused by sulphur and phosphorus. Other mechanisms, such as mechanical degradation, which mainly manifests as the loss or wear of the washed coating, were also found to be involved in deactivation. Additionally, the catalytic activity tests showed a considerable decrease in the aged catalyst. The poison concentration trends in the washcoat indicated that P is detrimental to CO oxidation, while S accumulation affects propane oxidation. SignificanceThis analysis method can be of substantial practical significance in developing advanced washcoat materials. Meanwhile, it has great potential in the washcoat analysis of honeycomb-shaped monolithic catalyst, such as natural gas catalyst, diesel vehicle oxidation catalyst and other honeycomb catalysts applied in chemical industry.

How and when do Pt- and Pd-semimetal minerals crystallize from saturated sulfide liquids?

Platinum and Pd-arsenides, antimonides, tellurides, bismuthinides, and sulfides are the major hosts of Pt and Pd in magmatic and hydrothermal Cu-Ni-sulfide ores. Textural relationships among such minerals in nature often provide contradictory messages about the mechanism and timing of their formation. To know how and when Pt and Pd mineral phases crystallize from sulfide-saturated liquids and how their compositions and textures evolve during cooling, we undertook controlled cooling experiments in evacuated silica tubes. A Cu-Ni-Fe sulfide mixture, similar in composition to the average Merensky Reef sulfide magma, was charged (in a 9:1 wt.% proportion) with one of the PtAs2, PtTe2, PtSb2, PtBi2, PdAs2, PdTe2, PdSb, and PdBi2 compounds, heated to 1,100°C, and slowly cooled (15°C/day) to room temperature. The run products were sampled at 950°C, 750°C, and 25°C by quenching the silica tubes in water. The results show that Pt formed stable phases with As, Te, and Sb above 950°C and with Bi and S below 750°C. The Pt phases were found mostly in the decomposed intermediate solid solution (ISS), and all the phases survived to 25°C with no compositional changes. At 950°C, Pd formed arsenide, telluride, and antimonide immiscible melts that coexisted with monosulfide solid solution (MSS) and sulfide melt. The composition of the Pd-semimetal melt droplets changed during cooling by equilibration with the host sulfide. Palladium mineral phases formed at temperatures below 750°C directly from the immiscible semimetal-rich melts where they kept the rounded shapes of the melt droplets. Ni-sulfarsenides preceded the formation of Pd arsenides. No Ni tellurides, antimonides, or bismuthinides formed in any of the systems, implying that their formation requires higher semimetal/Pt + Pd ratios. The decomposition of MSS and ISS to base metal sulfides led to significant textural changes in Pt and Pd mineral grains. The compositions of Pt and Pd phases are inherited from the magmatic stage, and their textures are low-temperature (<450°C) features.

Giant honeybees (Apis dorsata) trade off defensiveness against periodic mass flight activity.

The giant honeybee Apis dorsata (Fabricius, 1793) is an evolutionarily ancient species that builds its nests in the open. The nest consists of a single honeycomb covered with the bee curtain which are several layers of worker bees that remain almost motionless with their heads up and abdomens down on the nest surface, except for the mouth area, the hub between inner- and outer-nest activities. A colony may change this semi-quiescence several times a day, depending on its reproductive state and ambient temperature, to enter the state of mass flight activity (MFA), in which nest organisation is restructured and defense ability is likely to be suppressed (predicted by the mass-flight-suspend-defensiveness hypothesis). For this study, three episode of MFA (mfa1-3) of a selected experimental nest were analysed in a case study with sequences of >60 000 images at 50 Hz, each comprise a short pre-MFA session, the MFA and the post-MFA phase of further 10 min. To test colony defensiveness under normative conditions, a dummy wasp was cyclically presented with a standardised motion programme (Pd) with intervening sessions without such a presentation (nPd). Motion activity at five selected surveillance zones (sz1-5) on the nest were analysed. In contrast to mfa1,2, in mfa3 the experimental regime started with the cyclic presentation of the dummy wasp only after the MFA had subsided. As a result, the MFA intensity in mfa3 was significantly lower than in mfa1-2, suggesting that a colony is able to perceive external threats during the MFA. Characteristic ripples appear in the motion profiles, which can be interpreted as a start signal for the transition to MFA. Because they are strongest in the mouth zone and shift to higher frequencies on their way to the nest periphery, it can be concluded that MFA starts earlier in the mouth zone than in the peripheral zones, also suggesting that the mouth zone is a control centre for the scheduling of MFA. In Pd phases of pre- and postMFA, the histogram-based motion spectra are biphasic, suggesting two cohorts in the process, one remaining at quiescence and the other involved in shimmering. Under MFA, nPd and Pd spectra were typically Gaussian, suggesting that the nest mates with a uniform workload shifted to higher motion activity. At the end of the MFA, the spectra shift back to the lower motion activities and the Pd spectra form a biphasic again. This happens a few minutes earlier in the peripheral zones than in the mouth zone. Using time profiles of the skewness of the Pd motion spectra, the mass-flight-suspend-defensiveness hypothesis is confirmed, whereby the inhibition of defense ability was found to increase progressively during the MFA. These sawtooth-like time profiles of skewness during MFA show that defense capability is recovered again quite quickly at the end of MFA. Finally, with the help of the Pd motion spectra, clear indications can be obtained that the giant honeybees engage in a decision in the sense of a tradeoff between MFA and collective defensiveness, especially in the regions in the periphery to the mouth zone.

Synthesis of Pd-Cu/TPPCu electrocatalyst for direct ethanol fuel cell applications

In this study, the electro-oxidation reaction of ethanol over Pd–Cu supported on Cu porphyrin (TPPCu) was investigated. The catalyst was synthesized using the microwave-assisted polyol method and physicochemically characterized by XRD, XPS, SEM, EDS, TEM, EDAX, UV–Vis, FTIR, and RBS. A Cu-enriched catalyst with Cu3Pd, Pd,Cu, and TPPCu phases was identified using XRD and XPS. However, according to the RBS results, the catalytic surface was enriched with Pd, indicating that the interaction between TPPCu and Pd–Cu allowed the presence of Pd on the surface, thus enhancing the catalytic response of the material. This synthesis prevented the deprotonation of porphyrin on the electrocatalyst, as confirmed by XPS analysis. Electrochemical studies based on cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the response of the catalyst to variations in the scan rate and increasing ethanol concentration. The electrochemical response of PdCu/TPPCu improved with an increasing number of cycles, indicating improved mass transport, thus improving its electrochemical response and tolerance to CO contamination. This catalyst exhibited a high electroactive surface area of 49.4 m2/g, which could be related to the presence of TPPCu as a support. The behavior of the catalyst on the anode of a fuel cell fed with ethanol, bioethanol, and bioethanol residues was evaluated.Graphical

Prevalence of pituitary dysfunction after aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis

BackgroundPituitary dysfunction (PD) is a common complication after aneurysmal subarachnoid hemorrhage (aSAH). The prevalence of PD varies widely at a global level and no recent meta-analysis is available. Therefore, the aim of our systematic review and meta-analysis was to summarize the updated estimates of worldwide prevalence of PD after aSAH.MethodsScopus, Embase, Web of Science, and PubMed databases were used to comprehensively search the appropriate literature and a random-effects meta-analysis on the results of the available studies was performed. The heterogeneity in the prevalence estimates was evaluated by subgroup analysis in terms of types of PD, and acute and chronic phases of aSAH. The onset of PD within 6 months after aSAH was considered as acute, while that after 6 months was considered as chronic.ResultsTwenty-seven studies with 1848 patients were included in this analysis. The pooled prevalence of PD in the acute phase was 49.6% (95% CI, 32.4-66.8%), and 30.4% (95% CI, 21.4-39.4%) in the chronic phase. Among the hormonal deficiencies, growth hormone dysfunction was the most prevalent in the acute phase, being 36.0% (95% CI, 21.0-51.0%), while hypoadrenalism was the most prevalent in the chronic phase, being 21.0% (95% CI, 12.0-29.0%). Among the six World Health Organization regions, the South-East Asia Region has the highest prevalence of PD in the acute phase (81.0%, 95%CI, 77.0-86.0%, P < 0.001), while the European Region had the highest prevalence of PD in the chronic phase (33.0%, 95%CI, 24.0-43.0%, P < 0.001). Moreover, single pituitary hormonal dysfunction occurred more frequently than the multiple one, regardless of acute or chronic phase.ConclusionsAlmost half (49.6%) of the included patients with aSAH developed PD complication in the acute phase, while 30.4% of the patients developed them in the chronic phase. Although prevalence varies globally, the high healthcare burden, morbidity and mortality require greater awareness among clinicians.

PdxNiy/TiO2 Electrocatalysts for Converting Methane to Methanol in An Electrolytic Polymeric Reactor—Fuel Cell Type (PER-FC)

PdxNiy/TiO2 bimetallic electrocatalysts were used in fuel cell polymeric electrolyte reactors (PER-FC) to convert methane into methanol through the partial oxidation of methane promoted by the activation of water at room temperature. X-ray diffraction measurements showed the presence of Pd and Ni phases and TiO2 anatase phase. TEM images revealed mean particle sizes larger than those reported for PdNi materials supported, indicating that TiO2 promotes particle aggregation on its surface. Information on the surface structure of electrocatalysts obtained by Raman spectra indicated the presence or formation of NiO. The PER-FC tests showed the highest power density for the electrocatalyst with the lowest amount of nickel Pd80Ni20/TiO2 (0.58 mW cm−2). The quantification of methanol through the eluents collected from the reactor showed higher concentrations of methanol produced, revealing that the use of TiO2 as a support also increased the reaction rate.

Formation of intermetallic PdIn nanoparticles: influence of surfactants on nanoparticle atomic structure.

Bimetallic nanoparticles have been extensively studied as electrocatalysts due to their superior catalytic activity and selectivity compared to their monometallic counterparts. The properties of bimetallic materials depend on the ordering of the metals in the structure, and to tailor-make materials for specific applications, it is important to be able to control the atomic structure of the materials during synthesis. Here, we study the formation of bimetallic palladium indium nanoparticles to understand how the synthesis parameters and additives used influence the atomic structure of the obtained product. Specifically, we investigate a colloidal synthesis, where oleylamine was used as the main solvent while the effect of two surfactants, oleic acid (OA) and trioctylphosphine (TOP) was studied. We found that without TOP included in the synthesis, a Pd-rich intermetallic phase with the Pd3In structure initially formed, which transformed into large NPs of the CsCl-structured PdIn phase. When TOP was included, the syntheses yielded both In2O3 and Pd3In. In situ X-ray total scattering with Pair Distribution Function analysis was used to study the formation process of PdIn bimetallic NPs. Our results highlight how seemingly subtle changes to material synthesis methods can have a large influence on the product atomic structure.

Deactivation Mechanism of Palladium Catalysts for Ethanol\t\t\tConversion to Butanol

A Pd/Al2O3 catalyst (Pd = 0.1 wt\t\t\t\t\t%) for ethanol conversion to butanol deactivates within 10 h of service, despite\t\t\t\t\tits high initial activity at 275°C. Probable deactivation mechanisms were\t\t\t\t\texplored, including poisoning of\t\t\t\t\t\tPd/Al2O3 due to adsorption of\t\t\t\t\tby-products on Pd, sintering of Pd phases, leaching of Pd from the catalyst,\t\t\t\t\tchanges in the Pd electronic state, changes in the catalyst’s porous structure,\t\t\t\t\tand blockage of Al2O3 active\t\t\t\t\tsites. The Pd/Al2O3 deactivation\t\t\t\t\twas found to be mainly caused by CO molecules that evolved during side\t\t\t\t\treactions. These molecules can either block Pd active sites due to the formation\t\t\t\t\tof strong Pd–CO complexes, or enter a CO disproportionation reaction to form\t\t\t\t\tcarbon deposits on Pd phases. The knowledge gained from this study can be used\t\t\t\t\tfor the targeted modification of\t\t\t\t\t\tPd/Al2O3 and the creation of\t\t\t\t\tselective systems operating stably in the presence of by-products.

Mineralogical and geochemical constraints on the origin of the Sohland-Rožany Ni-Cu-(PGE) sulfide mineralization (Lausitz Block, Bohemian Massif, Germany/Czech Republic)

The Sohland-Rožany Ni-Cu-(PGE) sulfide mineralization is hosted by a small gabbroic dike that is one of several Ni-Cu sulfide-bearing gabbroic intrusions in the northern Bohemian Massif. The intrusions are associated with a Middle Devonian to Early Carboniferous mafic–ultramafic plumbing system that emplaced within Cadomian granodiorites of the Lausitz Block. The Sohland-Rožany dike comprises varitextured olivine- and hornblende-bearing gabbro and hornblende gabbro which originated from differently fractionated magma batches. Fractionation likely took place in deeper parts of the magmatic systems, e.g. within staging magma chambers. Mineralogical features like Ti-rich primary brown hornblende and diopsidic clinopyroxene as well as overall enriched incompatible element contents suggest moderate alkaline basaltic parental magmas with relatively high volatile contents.The magmatic sulfide mineralization is exclusively hosted by the olivine- and hornblende-bearing gabbro and include disseminated, net-textured and massive sulfides. The ore types are predominated by pyrrhotite-pentlandite-chalcopyrite assemblages accompanied by secondary violarite and pyrite as well as by accessory Pt, Pd, Au and Ag phases. The disseminated and net-textured sulfides have highly variable modal proportions of base-metal sulfides with pyrrhotite-dominated beside chalcopyrite-dominated aggregates on the hand specimen scale. The platinum-group mineral (PGM) assemblage includes Pd-Pt-Ni-bearing bismuthotellurides of the melonite–merenskyite and michenerite–testibiopalladite solid solution series as well as sperrylite. The sulfide ores feature predominantly elevated Ni and highly variable Cu and Pt, Pd and Au tenors (3.5–6.4 wt.% Ni, 0.1–16.6 wt.% Cu, 80–3080 ppb Pt, 50–5320 ppb Pd and 20–3770 ppb Au). The magmatic sulfides are locally characterized by a late-stage hydrothermal overprint where sulfides were replaced by hydrous secondary phases (e.g. actinolite–tremolite and chlorite). A significant redistribution of the PGE due to hydrothermal alteration is unlikely as the majority of PGM show a close spatial association to the base-metal sulfides.Textures and chemical compositions of the sulfides suggest that repeated magma batches eroded already fractionated sulfide pools and entrained early crystalized cumulates of monosulfide solid solution (MSS) together with variable fractionated sulfide melts. Sulfide saturation in the Sohland-Rožany magmas was locally controlled by assimilation of the granodioritic wall-rock in the course of thermomechanical erosion. This process was amplified by high mica contents of the granodiorites. Sulfur isotope signatures (–2.0 to –1.2‰ VCDT) and the S-poor nature of the hosting granodiorites exclude a significant contribution of S from the country rocks.

Phase Transition and Electronic Structures of All-d-Metal Heusler-Type X2MnTi Compounds (X = Pd, Pt, Ag, Au, Cu, and Ni).

In this work, we investigated the phase transition and electronic structures of some newly designed all-d-metal Heusler compounds, X2MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni), by means of the first principles. The competition between the XA and L21 structures of these materials was studied, and we found that X2MnTi favors to feature the L21-type structure, which is consistent with the well-known site-preference rule (SPR). Under the L21 structure, we have studied the most stable magnetic state of these materials, and we found that the ferromagnetic state is the most stable due to its lower energy. Through tetragonal deformation, we found that the L21 structure is no longer the most stable structure, and a more stable tetragonal L10 structure appeared. That is, under the tetragonal strain, the material enjoys a tetragonal phase transformation (i.e., from cubic L21 to tetragonal L10 structure). This mechanism of L21-L10 structure transition is discussed in detail based on the calculated density of states. Moreover, we found that the energy difference between the most stable phases of L10 and L21, defined as ΔEM (ΔEM = ECubic-ETetragonal), can be adjusted by the uniform strain. Finally, the phonon spectra of all tetragonal X2MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni) phases are exhibited, which provides a powerful evidence for the stability of the tetragonal L10 state. We hope that our research can provide a theoretical guidance for future experimental investigations.

Synthesis of binary metal oxide-doped Co3O4 nanoparticles by organic template and investigation of its structural, optical and electrochemical properties

Over the past decade, electrochemical devices have significantly improved due to advanced fabrication and synthesis of nano-electrode materials. However, the cost-effective and -efficient fabrication of nanomaterials is still challengeable. In this regard, we have used bio-organic compounds of E. cognata as fuel to synthesize and functionalize the Co3O4 nanoparticles and then incorporated NiO–PdO–Pd following the hydrothermal route. X-ray diffraction revealed Co3O4:NiO–PdO–Pd phases with crystallite size of 21 nm while spherical-shaped nanoparticles are observed by scanning electron microscope. The X-ray photoelectron spectroscopy revealed the presences of organic-functional groups of E. cognata on the surface of synthesized nanomaterial. The as-synthesized Co3O4:NiO–PdO–Pd nanomaterial is investigated as supercapacitor electrode material. In 3 M KOH the Co3O4:NiO–PdO–Pd nanomaterial exhibits a specific capacitance of 217.4 F/g. The Co3O4:NiO–PdO–Pd was reach up to 142.91 F/g at 10 mV/s while 115.15 F/g of capacitance is achieved by GCD data. Moreover, excellent conductivity is revealed by lower internal Ohmic resistance of 0.71 Ω which corresponds to the efficient transport of charges, and promotes the electrolyte diffusion. These results indicate that Co3O4:NiO–PdO–Pd nanomaterial can be a potential electrode for supercapacitor application.

Comparison of Pd and Pd4S based catalysts for partial hydrogenation of external and internal butynes

The partial hydrogenation of but-1-yne and but-2-yne was studied with a view to probing the difference between external and internal alkynes. Catalysts with Pd and Pd4S active phases were prepared on a carbon nanofiber support. Over the simple Pd catalyst over-hydrogenation was common which restricted alkene selectivity greatly – 25–35% depending on temperature. In contrast, the Pd4S active phase offered exceptional alkene selectivity (maximum of 92–93% alkene selectivity for both the external and internal alkyne). DFT calculations were subsequently used to rationalise this difference in product selectivity – sulfur appears to change the geometry of the active site in Pd4S and create a surface which favours alkene desorption relative to over-hydrogenation. This work further emphases the potential of palladium sulfide phases as an alternative to purely metallic palladium catalysts for partial alkyne hydrogenation.

Physical Operating Principles of Palladium–Barium Cathodes of Microwave Devices

High-resolution X-ray diffraction method (XRD) is used to determine sizes and crystallographic orientation of the nanocrystallites of the Pd and Pd5Ba phases in palladium–barium cathode. Electron spectroscopy for chemical analysis (ESCA) is used to study Ba and Pd chemical states in cathode material and determine the phase composition including dissolved microimpurities in the phases. The comparison of the XRD and ESCA data makes it possible to reveal effects related to the formation of the BaO crystallites in the cathode material, which are responsible for the emission properties. Electron-energy loss spectroscopy is used to determine the concentration of oxygen vacancies in the BaO crystallites that are formed in the cathode material due to activation. An original crystallite model of the working palladium–barium cathodes that is based on the results of this work may serve as an alternative to the known film model and makes it possible to optimize technology of cathode fabrication and activation.

Copper Electrodeposition from a Deep Eutectic Solvent, Used for Nitrates Reduction

This research work studied Cu electrodeposition over a glassy carbon electrode (GC) using deep eutectic solventes (DESs) instead of conventional aqueous media to subsequently assess the electrodeposit catalytic properties during nitrates reduction. These are nitrogen’s most reduced form, typically present in residual waters from chemical industries, from human consumption and from agriculture, which represent a significant contamination problem; they are not at all easy to eliminate through conventional methods used in water treatment plants, because they can reach potable water sources provoking in humans the incidence of severe illnesses, like cancer among others. It has been shown, that catalysts based in Pd, Pt and Cu metal phases reduce the nitrate ions, where the Cu ones have been studied because of their attractive catalytic properties. There are various forms of synthesizing the Cu catalysts, where electrodeposition leads to better control of Cu nucleation and growth. Cu electrocristalization was carried out from DES to compare the influence of the medium over the nucleation and growth mechanism. The eutectic mixtures used were prepared from choline chloride as the ionic species while the hydrogen bond donnors were urea and ethylene glycol. Both the DES were prepared in a 1:2 molar ratio, taking particular care to establish the influence of the resulting liquid at the early stages of electrodeposition, which was studied from Cu (II) solutions. It was shown that its electrodeposition takes place through a separte stage during which Cu (II) reduces first to Cu (I). All media studied led to demonstrate that electrodeposition follows a nucleation and 3D diffusion controlled growth. The Cu (II) diffusion coefficient, the A (nucleation frequence) and N0 (number density of active sites) parameters were estimated from potentiostatic plots using the Heerman and Tarallo model. The nitrates reduction at different concentrations was studied via differential pulse voltammetry to determine analytical parameters, like sensibility, detection and quantification limits. The Cu-modified glassy carbon electrodes and a Cu bar served to reduce the nitrates, immersed in 100 mM NaCl supporting electrolyte at pH=1.4 set with HClO4 analytical grade, adding different KNO3 concentraciones. It was shown that in acid medium the nitrates ion can be quantified reliably. Figure 1