EXAFS study on Pd–Pt catalyst supported on USY zeolite

Local structure around Pd and Pt in the bimetallic Pd–Pt catalysts supported on ultra stable Y (USY) zeolite (SiO₂/Al₂O₃=680) was investigated by an extended X-ray absorption fine structure (EXAFS) method during oxidation, reduction, and sulfidation. The Pt L III-edge EXAFS spectra showed that a new bond that was significantly different from Pt–Pt to Pt–Pd metallic bonds was formed in the bimetallic Pd–Pt (4:1) reduced catalysts supported on USY zeolite. This new bond may reflect the ionic properties of Pt through the Pt–Pd interaction. Furthermore this new bond survived sulfidation indicating that the bond has a cationic property and sulfur-tolerance property. The Pt–Pd ionic interaction in these catalysts allows some of the Pd metal to survive as metallic phase. The existence of this metallic phase under sulfidation condition may result in high activity of Pd–Pt (4:1) catalyst supported on USY zeolite in the aromatics hydrogenation.     

Electrolyte solutions in liquid ammonia—IX. Electrodeposition and electrodissolution of metals from their salts

Anodic dissolution and cathodic deposition of 20 transition metals in acidic solutions in liquid ammonia has been surveyed. The early transition metal elements Ti, Zr, V Nb, Mo and W form high oxidation-state insoluble amido complexes during anodic oxidation. Soluble ammines of normal metal oxidation states are produced with Cr(III), Mn(II), Fe(II), Co(III), Ni(II), Cu(II), Ag(I), Zn(II), Cd(II) and Hg(II) (Mn dissolves spontaneously). The metals Ru, Pd, Pt and Au only dissolve slightly after prolonged electrolysis. Anodic enrichment of Au in its alloys is unlike that in aqueous solution; in ammonia both Cu and Ag can be simultaneously depleted from a 9 carat gold alloy. Cathodic reduction of metal-bearing solutions follows wide variations of behaviour. Fe and Ru ammines reduce to amido-complexes with concomittant hydrogen evolution, but Cr is not reduced. Solutions of Mn, Co, Ni, Pd, Pt, Ag, Au, Zn, Cd and Hg give metallic cathode deposits under differing conditions. Electrodeposition is potential dependent for Ni, Cu and Ag; metal plate at low potentials, and powders at high potentials. The two different products are the result of reduction of species with different degrees of solvation.     

Electrodeposition behavior of nickel and nickel-zinc alloys from the zinc chloride-1-ethyl-3-methylimidazolium chloride low temperature molten salt

The electrodeposition of nickel and nickel-zinc alloys was investigated at polycrystalline tungsten electrode in the zinc chloride-1-ethyl-3-methylimidazolium chloride molten salt. Although nickel(II) chloride dissolved easily into the pure chloride-rich 1-ethyl-3-methylimidazolium chloride ionic melt, metallic nickel could not be obtained by electrochemical reduction of this solution. The addition of zinc chloride to this solution shifted the reduction of nickel(II) to more positive potential making the electrodeposition of nickel possible. The electrodeposition of nickel, however, requires an overpotential driven nucleation process. Dense and compact nickel deposits with good adherence could be prepared by controlling the deposition potential. X-ray powder diffraction measurements indicated the presence of crystalline nickel deposits. Non-anomalous electrodeposition of nickel-zinc alloys was achieved through the underpotential deposition of zinc on the deposited nickel at a potential more negative than that of the deposition of nickel. X-ray powder diffraction and energy-dispersive spectrometry measurements of the electrodeposits indicated that the composition and the phase types of the nickel-zinc alloys are dependent on the deposition potential. For the Ni-Zn alloy deposits prepared by underpotential deposition of Zn on Ni, the Zn content in the Ni-Zn was always less than 50 atom%.     

New insight in the solid state characteristics, in the possible intermediates and on the reactivity of Pd–Cu and Pd–Sn catalysts, used in denitratation of drinking water

Bimetallic palladium-based supported catalysts were tested in the liquid phase hydrogenation of nitrates. They were characterised by XPS, CO chemisorption, TPD–TPR and DRIFT. The effect of the preparation method, the support, the precursors, the relative amount of active metals and their role in the formation of intermediates and products are tentatively discussed. The catalytic activity and the formation of intermediate nitrite depend on the Pd–Cu ratio. Catalysts presenting a Pd/Cu atomic ratio >1 display the highest activity and the lowest intermediate nitrite than those presenting a Pd/Cu atomic ratio <1. Sol–gel method gives catalysts with a high activity and a low nitrite formation. The Pd–Cu-based catalyst supported on zirconia is more active and selective in N₂ compared to the corresponding Pd–Sn catalyst. An enrichment of the surface by Pd is responsible for a low intermediate nitrite formation and high selectivity in N₂. The reduction of NO is activated on Pd–Cu catalysts, contrary to Pd–Sn catalysts. Sn promotes the formation of ammonia.     

Electrodeposition of PtZn in a Lewis acidic ZnCl2-1-ethyl-3-methylimidazolium chloride ionic liquid

The electrodeposition of PtZn from a Lewis acidic 40-60 mol% zinc chloride-1-ethyl-3-methylimidazolium chloride ionic liquid containing PtCl₂ was investigated at polycrystalline tungsten substrates at 90 °C. Cyclic voltammetric data indicates that Pt(II) was reduced at a potential slightly more positive than Zn(II) was. The Pt-Zn electrodeposits exhibited multiple anodic stripping waves. The Zn-dominant deposits were stripped at a potential less positive than that of the Pt-dominant deposits. Energy-dispersive spectroscopy and scanning electron microscopy data indicated that the composition and morphology of the electrodeposited Pt-Zn alloys were affected by the deposition potential and the Pt(II) concentration in the plating solution. The electrodeposition of Zn at a Pt substrate also produced surface Pt-Zn alloys. The Pt of the electrochemically prepared Pt-Zn alloys was easier to oxidize than the bulk Pt substrate.     

铜铝双金属复合离子液体的电化学行为及电沉积铜机理

铜铝双金属复合离子液体是新型碳四烷基化技术所用的绿色催化剂,电化学处理是回收工业应用过程外排复合离子液体中金属铜的有效途径之一,为此需要深入研究其电化学行为和电沉积铜机理。循环伏安研究发现,铜铝双金属复合离子液体在Pt盘电极、W盘电极和玻碳电极上的还原过程均包括铜的欠电势沉积、Cu(Ⅰ)的还原和铜的超电势沉积,氧化过程均包括Cu→Cu(Ⅰ)、Cu(Ⅰ)→Cu(Ⅱ)。计时安培研究表明,铜的成核方式为三维瞬时成核。长周期实验结果显示Cu(Ⅰ)的浓度随着时间下降的趋势变缓,表明电沉积铜速率逐步下降。电沉积电势对沉积产物的形貌影响较大,-2.60 V下的产物形貌更平整致密。XRD结果表明在-1.20~-2.60 V电势下阴极电沉积只生成金属铜。     

铜铝双金属复合离子液体的电化学行为及电沉积铜机理

铜铝双金属复合离子液体是新型碳四烷基化技术所用的绿色催化剂,电化学处理是回收工业应用过程外排复合离子液体中金属铜的有效途径之一,为此需要深入研究其电化学行为和电沉积铜机理。循环伏安研究发现,铜铝双金属复合离子液体在Pt盘电极、W盘电极和玻碳电极上的还原过程均包括铜的欠电势沉积、Cu(Ⅰ)的还原和铜的超电势沉积,氧化过程均包括Cu→Cu(Ⅰ)、Cu(Ⅰ)→Cu(Ⅱ)。计时安培研究表明,铜的成核方式为三维瞬时成核。长周期实验结果显示Cu(Ⅰ)的浓度随着时间下降的趋势变缓,表明电沉积铜速率逐步下降。电沉积电势对沉积产物的形貌影响较大,-2.60 V下的产物形貌更平整致密。XRD结果表明在-1.20~-2.60 V电势下阴极电沉积只生成金属铜。     

Monte Carlo simulation of hydrogen absorption in palladium and palladium–silver alloys

A modified Monte Carlo (MC) simulation was performed to investigate the hydrogen absorption behavior in Pd and Pd–Ag alloys of the composition Pd_xAg_1−x (x=0.7–0.8) under H₂ pressure (0.1 MPa) at different temperatures. The present method employed can consider the dissociative adsorption of hydrogen molecule and the subsequent absorption of hydrogen atom by formalizing the relationship between the pressure of hydrogen molecule and hydrogen atom. The potential parameters were determined to reproduce the solution enthalpy of hydrogen in pure metals. The results are in good agreement with experimental findings as well as previous theoretical studies. We confirmed that our method is useful to simulate the absorption of hydrogen in metals and alloys.     

Electrodeposition of palladium-indium from 1-ethyl-3-methylimidazolium chloride tetrafluoroborate ionic liquid

Voltammetry at a glassy carbon electrode was used to study the electrochemical co-deposition of Pd-In from a chloride-rich 1-ethyl-3-methylimidazolium chloride/tetrafluoroborate air-stable room temperature ionic liquid at 120 °C. Deposition of Pd alone occurs prior to the overpotential deposition (OPD) of bulk In. However, underpotential deposition (UPD) of In on the deposited Pd was observed at the potential same as the deposition of Pd. The UPD of In on Pd was, however, limited by a slow charge transfer rate. Samples of Pd-In alloy coatings were prepared on nickel substrates and characterized by energy dispersive spectroscope (EDS), scanning electron microscope (SEM) and X-ray powder diffraction (XRD). The electrodeposited alloy composition was relatively independent on the deposition potential within the In UPD range. At more negative potentials where the OPD of Pd-In has reached mass-transport limited region, the alloy composition corresponds to the Pd(II)/In(III) composition in the plating bath. The Pd-In alloy coatings obtained by direct deposition of Pd and UPD of In on the deposited Pd appeared to be superior to the Pd-In alloys that were obtained via the co-deposition of Pd and bulk In at OPD potentials.     

Extraction–electrodeposition (EX–EL) process for the recovery of palladium from high-level liquid waste

Extraction–electrodeposition (EX–EL) process has been developed for the quantitative recovery of palladium from nitric acid medium and fast reactor-simulated high-level liquid waste (FR-S-HLLW). The process exploits some characteristic properties of room temperature ionic liquid, tri-n-octylmethylammonium nitrate (TOMAN), for quantitative and favorable recovery of palladium. Extraction of palladium (II) from FR-S-HLLW and nitric acid medium by a solution of 0.5 M TOMAN in chloroform has been studied in detail. More than 60% of palladium was extracted in a single contact of equal volumes of organic and aqueous phases and nearly five contacts were required for quantitative extraction. The electrochemical behavior of palladium (II) present in the organic phase was investigated at stainless steel electrode by cyclic voltammetry. A surge in cathodic current occurring at a potential of –0.5 V (vs. Pd) was due to the reduction of palladium (II) to palladium (0). The kinetics of electrodeposition was followed by the UV–VIS absorption spectrum of palladium present in organic phase and under the given conditions nearly 20 and 35 h were required for the quantitative deposition of palladium from organic phase, which was obtained after extraction of palladium from 4 M nitric acid and FR-S-HLLW, respectively. Decontamination of palladium from other fission products during extraction and electrodeposition was studied and the results are reported in this article.     

Electrodeposition of nanocrystalline copper thin films from 1-ethyl-3-methylimidazolium ethylsulphate ionic liquid

Copper thin films are increasingly important as interconnectors for the creation of smaller and better performing integrated circuits and electrodeposition from ionic liquid-based electrolytes could provide a greener fabrication method for these films. The electrodeposition of copper from copper(I) and copper(II) salt solutions in a low cost, widely available ionic liquid, 1-ethyl-3-methylimidazolium ethylsulphate, was studied using a range of different deposition potentials and temperatures. Three different electrolytes containing ~0.1 M of copper(I) chloride(CuCl), copper(II) chloride (CuCl₂) and copper(II) sulphate (CuSO₄) were used. Under similar deposition conditions, the films obtained from CuCl and CuSO₄-based electrolytes presented better continuity than films obtained from CuCl₂-based electrolyte. Continuous films with a homogeneous structure were obtained by electrodeposition from CuCl and CuSO₄-based solutions at a constant potential of ?1.8 V and a temperature of 35 °C. Under similar deposition parameters, the films deposited from CuCl₂-based electrolyte presented the largest particle size, while those deposited from copper(I) chloride and CuSO₄-based solutions presented finer microstructures. X-ray diffraction analysis and energy dispersive X-ray spectroscopy showed that the deposits were crystalline and consisted mainly of copper, with traces of oxygen and sulphur resulting from residues of the ionic liquid. The films presented a nanocrystalline microstructure consisting of particles about 25 nm, aggregated in clusters.     

The electrodeposition of Mn and Zn-Mn alloys from the room-temperature tri-1-butylmethylammonium bis((trifluoromethane)sulfonyl)imide ionic liquid

Zinc, manganese and zinc-manganese alloys were electrodeposited from the hydrophobic room-temperature ionic liquid, tri-1-butylmethylammonium bis((trifluoromethane)sulfonyl)imide. Zn(II) and Mn(II) species needed to produce these alloys were introduced into the ionic liquid by the anodic dissolution of the respective metallic electrodes. The diffusion coefficients of the dissolved Zn(II) and Mn(II) species are not constant, but decrease with the increasing concentrations of these ions, suggesting the formation of aggregated species at higher concentrations. Coatings containing Zn, Mn or Zn-Mn can be obtained by controlled-potential electrolysis. The current efficiencies of Mn electrodeposition in this ionic liquid approach 100%, which is a high improvement comparing to the results obtained in aqueous solution (20-70%). The Mn/Zn ratio of these alloys depended almost completely on Mn(II)/Zn(II) concentration ratio in the ionic liquid. The Zn-Mn alloy deposits obtained in this study were compact, adherent, and exhibited an amorphous structure. The surface morphology of these deposits depended on the Mn/Zn ratio. The addition of Mn up to about 50 a/o improves the corrosion resistance of Zn. However, the addition of Mn beyond this amount decreases the corrosion resistance of the Zn-Mn alloy.     

Abatement of volatile organic compounds: oxidation of ethanal over niobium oxide-supported palladium-based catalysts

Niobium-supported palladium-based catalysts (Pd, Pd–Cu and Pd–Au) were employed in the oxidation of ethanal. The catalysts were prepared according to original methods by either multi-steps (anchoring of complexes, calcination and reduction) or one-step (photoassisted reduction) procedures. The oxidation of ethanal was carried out in gas phase in a dynamic-differential reactor at 300 °C at atmospheric pressure. The activity/selectivity of the catalysts depend on (i) the catalyst preparation; (ii) the presence of a second metal. Addition of Au or Cu decreases the catalysts deactivation and the best performance in total oxidation was obtained with Pd–Au/Nb₂O₅ prepared by photoassisted reduction. As shown by in situ IR spectroscopy of adsorbed CO, this peculiarity may be ascribed to Au→Pd electron donation, which prevents the surface oxidation of palladium particles.     

Catalytic denitrification of water with palladium-based catalysts supported on activated carbons

The performance of carbon-supported, Pd bimetallic catalysts for nitrate reduction has been investigated. Pd–In and Pd–Sn catalysts have been tested for a range of nitrate concentration up to 1000 ppm in acidic and close to neutral pH. Pd–Cu was also studied at pH 5 for reference. Nitrate reduction was inhibited strongly by nitrite and moderately by sulphate. Activated carbon catalysts are shown to display an activity similar to metal oxide supported catalysts.     

Effect of synthetic reducing agents on morphology and ORR activity of carbon-supported nano-Pd–Co alloy electrocatalysts

Three different reducing agents, ethylene glycol (EG), formaldehyde (HCHO), and sodium borohydrate (NaBH₄), were used in the synthesis of carbon-supported Pd–Co catalysts (Pd–Co/C–EG, Pd–Co/C–HCHO, and Pd–Co/C–NaBH₄, respectively). The differences among these three catalysts in morphology and electrocatalytic activity for oxygen reduction reaction (ORR) were observed and characterized using X-ray diffraction, energy dispersive X-ray analysis, transmission electron microscope, Fourier transform infrared spectra, surface cyclic voltametry, and rotating disk electrode technique. It was observed that by using a mild reducing agent such as EG, well-controlled and homogenous nucleation and growth could be achieved during the catalyst synthesis. With respect to the morphology and ORR activity of synthesized catalysts, the order of preferred reducing agents was found to be EG > NaBH₄ > HCHO. In order to improve activity and stability, the catalysts were heat-treated at temperatures ranging from 300 °C to 700 °C. It was found that for all three Pd–Co/C catalysts, a temperature of 300 °C gave the best catalyst morphology and ORR activity. The investigation in ORR kinetics catalyzed by these three catalysts revealed that all three could catalyze a four-electron reduction of oxygen to produce water. The average Tafel slope of the catalyzed ORR was found to be 70 mV/dec, suggesting that the determining step in the mechanism is a one-electron transfer process. In an effort to validate the theoretical explanation, the ORR activity as a function of particle size, Pd lattice constant, and Pd–Pd bond distance of the three Pd–Co/C catalysts was also investigated. In addition, in the case of EG as reducing agent the impregnation–reduction method employed in this work was simplified, because the need for a stabilizing agent usage was removed and water was used as the solvent.     

Electrochemical codeposition of copper and manganese from room-temperature N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid

The voltammetric behavior of N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid (BMP-TFSI) containing Cu(I), Mn(II), or mixtures of Cu(I) and Mn(II) as well as the electrodeposition of copper-manganese alloy coatings (Cu-Mn alloy coatings) was studied at 323 K. The Cu(I) and Mn(II) species required to prepare these coatings were introduced into the BMP-TFSI by anodic dissolution of the relevant metallic electrodes. Electrodeposits of Cu, Mn, and Cu-Mn with various contents of Mn can be obtained by controlled-potential electrolysis. It was found that the compositions and surface morphology of the electrodeposited Cu-Mn alloy coatings depend on the deposition potentials and the concentration ratio of [Cu(I)]/[Mn(II)] in BMP-TFSI. The Cu-Mn alloy coatings obtained in this study were compact and adherent. They did not show any significant X-ray diffraction signal that could be assigned to the crystalline structures of Cu, Mn, or Cu-Mn alloys. In the aqueous solution containing 0.1 M NaCl, the Cu-Mn alloy coatings demonstrated passive behavior—no continuous oxidation was observed. However, a significant oxidation current was observed at the electrodes deposited with Cu or Mn.     

Effect of pH in a sol–gel synthesis on the physicochemical properties of Pd–alumina three-way catalyst

The effect of pH during sol–gel synthesis on the structural and physicochemical properties of a Pd–Al₂O₃ three-way catalyst (TWC) prepared by the sol–gel method was investigated by using BET, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and solid state ²⁷Al MAS NMR. The Pd–Al₂O₃ catalyst prepared at pH=10 (Pd–Al₂O₃–B) showed a high activity in three-way catalytic reaction, a high dispersion of Pd, and large surface area and pore volume. A basic condition (pH=10) in the sol–gel process was essential for the preparation of highly dispersed palladium clusters on alumina gel. The formation of highly stable palladium oxide species in Pd–Al₂O₃–B that were not completely reduced at 423 K was ascribed to the strong interaction between Pd and oxygen in alumina texture, resulting in the formation of –Al–O–Pd bond.     

Liquid-phase hydrogenation of maleic anhydride over Pd–Sn/SiO2

Pd and Pd–Sn supported on SiO₂ and active carbon were prepared and tested as catalysts in the hydrogenation of maleic anhydride. Particularly Pd–Sn/SiO₂ was active and selective in the hydrogenation of maleic anhydride to γ-butyrolactone, and showed a resistance to the deactivation. The results of XPS and CO adsorption evidenced that the catalytic performance of Pd–Sn/SiO₂ was related to the modification of electronic configuration of Pd due to the effective interaction between Pd and Sn.     

Zn–Sn electrodeposition from deep eutectic solvents containing EDTA,HEDTA, and Idranal VII

The use of deep eutectic solvents for metal electrodeposition has become an area of interest in the recent years. In this study, ethaline, propeline, and reline were used as solvents for the electrodeposition of Sn–Zn alloys. Ethaline, propeline, and reline displayed identical voltammetric profiles for the reduction of Zn(II) and Sn(II). Further studies were carried out in ethaline which is the liquid with lowest viscosity. To improve physical and morphological properties of the Sn–Zn deposits, additives were added to the ionic liquid solution. In this study, the addition of three chelators (EDTA, HEDTA, and Idranal VII) and their effects on the voltammetric behavior of zinc and tin and the resultant morphology was described. The structure and composition of the Zn–Sn deposit was largely affected by the additives with the largest effect being obtained in the presence of Idranal VII.     

Electrodeposition of Ni-W-B amorphous alloys

Partial polarization curves at the glassy carbon rotating disc electrode have been used to study the electrodeposition of Ni and Ni-W alloy from citrate-containing solution. For deposition of Ni-W alloys, the partial polarization curves indicate diffusion control for nickel reduction and stoichiometric limitation for tungsten deposition by the composition of the alloy. Plating experiments show that current efficiency of the electrodeposition and composition of the resulting alloy depend on the parameters of the electrolysis. The best conditions for electrodeposition of the alloy Ni-W-B are current density of 45–50 mA cm^–2, temperature of 60–70 °C, Ni(II) concentration of 20–25 mm, and pH 8.5. Pulsed galvanostatic plating at 1 Hz increased slightly the current efficiency. The concentration of Ni(II) in the solution can be self-regulated by using a nickel bipolar electrode in the cathode compartment.