Papers by Keyword: Palladium

Abstract: Pd is one of the most promising catalysts for carbon dioxide electroreduction (CO₂RR) to formate (HCOO-). However, the lack of understanding of the active phase remains remains obscure with the role of different crystal facets in the formation of formic acid. Herein, Pd nanocubes and nanooctahedra particles with Pd (100) and (111) facets were, respectively, prepared. Compared with ordinary Pd nanoparticles and Pd octahedra, Pd nanocubes exhibited the most excellent electrocatalytic performance of carbon dioxide reduction, achieving a Faraday efficiency of 96% for formate production at a low applied potential of-0.20 V (vs RHE) in 0.5 M KHCO₃. At the same time, first-principles theoretical calculations also showed that the Pd (100) surface is more conducive to the conversion of CO₂ to HCOO* intermediates, thereby promoting the formation of formic acid. This result indicates that the Pd (100) crystal plane is more conducive to the reduction of CO₂ to formate. This research has important guiding significance for exploring the efficient reduction of carbon dioxide to formic acid catalyst.

Abstract: Features of creation of porous nanostructured oxides of transition materials on an example of niobium are considered. It has been experimentally shown that variation in anodizing modes makes it possible to obtain non-porous and porous amorphous anodic oxide films (AOF) and films of the crystalline type. It is determined that the process of AOF formation on niobium, as well as its structure and properties depend on such parameters as the type of electrolyte, anodizing voltage, activator concentration, the duration of the process. It is confirmed that the presence of an activator in the electrolyte is a necessary and decisive factor in the process of forming a nanostructured anode oxide layer. To obtain a nanostructured surface of niobium oxide, a necessary condition is the introduction of fluoride into the electrolyte, but also an important task is to determine the type of compound with which F^– ions are introduced into the electrolyte. It has been experimentally determined that the optimal solution for the rapid growth of porous crystalline oxide is a solution consisting of a background electrolyte in the form of 1M H₂SO₄ with the addition of a fluoride ion activator in the form of 0.5M NaF. The increase in the activator accelerates the formation of the crystal structure on the surface of niobium. It is shown that higher voltage and longer anodizing time leads to an increase in the size of microcones and their number on the surface of niobium. Optimal for the formation of porous crystalline oxide is a voltage of 60 V in the electrolyte 1M H₂SO₄ + 0.5M NaF for 2 hours.

Abstract: Atomic force microscopy (АFМ) and high-precision scanning electron microscopy methods were used to study the surface of diffusion filter-membranes of alloy Pd₉₃Y₇. The formation of alterations in structure in one of membranes was established as a result from the homogenizing annealing at 900°C for 1 hours. It was found that the reversible doping of the membrane alloy with hydrogen caused the dispersion of the diffusion filter-membranes’ surface structure. Differences in changes by the surface structure are determined during the hydrogenation in directional and non-directional flow of hydrogen.

Abstract: The paper studies the activity of 1 % palladium catalysts containing rare earth oxides (REOs) and alumina as a carrier in the hydrogenation of nitro compounds exemplified by nitrobenzene and o-nitro anisole. Under the liquid-phase hydrogenation conditions, these catalytic systems provide high selectivity of the process and a quantitative yield. It has been found that the partial replacement of Al₂O₃ with REO allows increasing the hydrogenation rate by 5–6 times, as compared with the reference catalyst and by 1.2–1.7 times as compared with the individual carrier. The oxide mixtures (REO and Al₂O₃) containing 20–40 % REO allow reaching the same hydrogenation rate with that over an REO-containing 1 % Pd catalyst.

Abstract: The electronic and magnetic properties of palladium hydrogen are investigated using first-principles spin-polarized density functional theory. By studying the magnetic moments and electronic structures of hydrogen atoms diffusing in face-centered cubic structure of transition metal Pd, we found that the results of magnetic moments are exactly the same in the two direct octahedral interstitial site-octahedral interstitial site diffusion paths-i.e. the magnetic moments are the largest in the octahedral interstitial site, and the magnetic moments are the lowest in saddle point positions. We also studied on the density of states of some special points, with the result that the density of states near the Fermi level is mainly contributed by 4d electrons of Pd and the change of magnetic moments with the cell volume in the unit cell of transition metal Pd with a hydrogen atom.

Abstract: The electrical and optical properties of nanomaterials depend on their structural form. As an effort to develop an advanced nanomaterial, zinc oxide (ZnO) is interesting to synthesis for many applications such as active material for solar cells and biosensors. This paper provides the role of palladium and plasmonic materials in growing ZnO nanostructure, with a focus on its structural analysis. Nanomaterial ZnO was grown by seed-mediated hydrothermal method with layering by plasmonic materials, i.e. gold (Au) and platinum (Ag). X-ray diffraction analysis shows the presence of three dominant peak angles, i.e 34.43^o, 36.32^o, and 47.49^o corresponding to crystal orientation of (002), (101) and (102), respectively. Palladium (Pd) treatment plus layering by plasmonic materials give a higher size of the nanostructure, but their electric band gaps are decreasing slightly. These findings also supported by high absorbance in UV-vis spectra. Gold layering on the nanomaterial gives a more significant role than platinum which indicated by higher size in diameter and higher absorption of UV-Vis spectra. The average size of pristine ZnO, ZnO:Pd, ZnO:Pd:Ag, and ZnO:Pd:Ag are 44.13, 45.99, 45.28, and 44.81 nm, respectively.

Abstract: Results of the development of a method for immobilizing nanosized palladium into an electrochemically synthesized polyaniline (PAn) electrically conductive porous matrix to create a sensitive element of an ignition sensor are presented. Two methods of manufacturing a sensitive element in the form of an electrode are investigated. The first method consists in the co-precipitation of polyaniline and palladium on a graphitized butyl rubber substrate in a mode of cycling of potential. It was shown that this method can be used to obtain a volume-porous electrode in which palladium nanoparticles are embedded in a polyaniline matrix. The second method involves the deposition of palladium on a polyaniline film formed on graphitized butyl rubber. It was shown that micron-sized island palladium conglomerates on the surface of a polyaniline film can be obtained by this method. The conclusions made are confirmed by physical research methods and the results of scanning electron microscopy. Investigations of the electrocatalytic properties of the electrode in the sensor model showed that with a change in the H₂ concentration formed upon ignition, occurs change in the hydrogen concentration on the surface of metal-catalyst (Pd) and a linear change in the current of electrochemical reaction. Comparison of a composite volume-porous polyaniline electrode with embedded palladium showed its superior efficiency compared to a compact palladium electrode and an electrode in which palladium is deposited on the surface of a polyaniline film. The possibility of using an electrochemical detector based on polyaniline with immobilized palladium nanoparticles for a gas amperometric sensor of low hydrogen concentrations and a fire hazard detector is shown.

Abstract: The paper is devoted to the study of the influence of surface modification by catalysts on the gas sensitivity of a gas sensor. The sample for the study is a gas sensor crystal with dimensions of 1 × 1 mm², manufactured using microelectronic technology. Its design is represented by a film heater, two sensitive elements (SE) based on tin dioxide with the addition of 1 % at. Si (film thickness = 250 nm, the size of the SE area is 200 x 320 μm²) and contacts for the sensitive layer in the form of an interdigital platinum structure with a distance between contacts of 10 μm. It is established that doping increases the gas sensitivity and lowers the operating temperature.

Abstract: This article represents the results of studies of the drawing thin wire from the alloy Pd-5Ni process. The studies used the software developed by the authors using the methods of calculating the drawing process and the computer model implemented in the DEFORM 3D software package. By way of calculation, a drawing route was determined, including 14 transitions, and the efforts of deforming the metal were found when producing wire with a diameter of 0.075. For this mode of deformation processing using the DEFORM 3D software package, we simulated the drawing process and established the temperature and stress distribution over the volume of the workpiece. The simulation results confirmed that the calculated safety factor for drawing is in the range of 2.85-3.43, which ensures a stable process of deformation of the metal without breaks and, as a consequence, an increase in productivity and yield of the suitable metal. Experimental studies have confirmed the adequacy of the developed model, so it can be used to analyze the process of drawing wire from other precious metal alloys. The results of the research are recommended to improve the production technology of thin wire from the alloy Pd-5Ni for the manufacture of catalytic gripping grids.

Abstract: The microstructure of the palladium modified and non-modified aluminide coatings was examined by the EDS and the positron annihilation spectroscopy methods. Both coatings have a double layer structure: β-NiAl phase or β-(Ni,Pd)Al phase on the top and the interdiffusion zones with the chromium and molybdenum rich phases in the β-NiAl or or β-(Ni,Pd)Al phase below. Palladium, that forms the β-(Ni,Pd)Al phase and substitutes for nickel atoms causes the increase of the positron lifetime value due to the increase in the number of open volume defects in the lattice which are jogs or vacancies on dislocation lines.