Catalytic activity of dispersed CuO phases towards nitrogen oxides (N2O, NO, and NO2)

A systematic reactivity study of N₂O, NO, and NO₂ on highly dispersed CuO phases over modified silica supports (SiO₂–Al₂O₃, SiO₂–TiO₂, and SiO₂–ZrO₂) has been performed. Different reaction paths for the nitrogen oxide species abatement were studied: from direct decomposition (N₂O) to selective reductions by hydrocarbons (N₂O, NO, and NO₂) and oxidation (NO to NO₂). The oxygen concentration, temperature, and contact time, were varied within suitable ranges in order to investigate the activity and in particular the selectivity in the different reactions studied. The support deeply influenced the catalytic properties of the active copper phase. The most acidic supports, SiO₂–Al₂O₃ and SiO₂–ZrO₂, led to a better activity and selectivity of CuO for the reactions of N₂O, NO, and NO₂ reductions and N₂O decomposition than SiO₂–TiO₂. The catalytic results are discussed in terms of actual turnover frequencies starting from the knowledge of the copper dispersion values.     

Adsorption and antibacterial effect of copper-exchanged montmorillonite on Escherichia coli K88

Calcium montmorillonite (Ca-MMT), sodium montmorillonite (Na-MMT) and acid-activated montmorillonite (AAM), and their Cu²⁺-exchanged montmorillonites (Cu-MMT), Cu*Ca-MMT, Cu*Na-MMT and Cu*AAM, were used to study the antibacterial activity on Escherichia coli K₈₈. AAM, Na-MMT and Ca-MMT showed some ability to reduce bacterial plate counts by 37.4%, 13.4% and 14.2%, respectively. Exchanging the montmorillonite with Cu²⁺ enhanced the antibacterial activity. The Cu*AAM, Cu*Na-MMT and Cu*Ca-MMT reduced the bacterial plate counts by 98.6%, 97.5% and 95.6%. Attempts were made to study the desorption of Cu²⁺ by washing with sterile physiological saline solution for 24 h. The washing solutions did not show a significant reduction of the bacterial counts, while the washed Cu-MMT retained their full antibacterial activity. Results from time-depending studies showed that the reduction of the bacterial counts by Cu-MMT increased during 24 h. The ranking of antibacterial activity of the three Cu-MMT was as Cu*AAM > Cu*Na-MMT > Cu*Ca-MMT. E. coli thrived optimally in a pH range from 5 to 7. Beyond this range, the bacterial counts decreased as the pH reduced the viability of the bacteria. The ranking of antibacterial activity of Cu-MMT was not affected by pH. The mechanism by which bacterial counts are reduced may involve the enhanced affinity of Cu-MMT for E. coli K₈₈ and the antibacterial activity of Cu²⁺.     

Changes in the Peeled Surfaces of Copper Thin Films Deposited on Polyimide Substrates After Heat Treatment

Peel strength between a copper (Cu) thin film and a polyimide (pyromellitic dianhydride-oxydianiline, or PMDA-ODA) substrate is reduced by heat treatment at 150°C in air. In this work, we investigated the peel strength, the morphology of the interface between Cu films and polyimide substrates using optical microscopy and electron microscopy, and chemical change of the interface using Auger electron spectroscopy (AES) and micro X-ray photoelectron spectroscopy (XPS). The analysis showed that CuO “lumps” were present on the peeled surface of PMDA-ODA after heat treatment at 150°C in air. The peeled surfaces of other polyimide substrates were also analyzed: biphenyl dianhydride-para phenylene diamine (BPDA-PDA) and biphenyl dianhydride-oxydianiline (BPDA-ODA). CuO lumps were present on the peeled surface of BPDA-ODA after the heat treatment, but not that of BPDA-PDA. Compared with the adhesion strength for the Cu thin film, the adhesion strength was high for the Cu/PMDA-ODA and Cu/BPDA-ODA laminates, but the adhesion strength was very low for the Cu/BPDA-PDA laminate. This low strength is the reason that CuO lumps were not detected on the peeled surface of the BPDA-PDA substrate. These CuO lumps were related to the adhesion degradation of the Cu/polyimide laminates after the heat treatment.     

Kinetics of the selective catalytic reduction of NO by NH3 on a Cu-faujasite catalyst

The kinetics of the selective catalytic reduction (SCR) of NO by NH₃ in the presence of O₂ has been studied on a 5.5% Cu-faujasite (Cu-FAU) catalyst. Cu-FAU was composed of cationic and oxocationic Cu species. The SCR was studied in a gas phase-flowing reactor operating at atmospheric pressure. The reaction conditions explored were: 458<T_R<513 K, 2503 (ppm) < 4000, 12 (%) < 4. The kinetic orders were 0.8–1 with respect to NO, 0.5–1 with respect to O₂, and essentially 0 with respect to NH₃. Based on these kinetic partial orders of reactions and elementary chemistry, a wide variety of mechanisms were explored, and different rate laws were derived. The best fit between the measured and calculated rates for the SCR of NO by NH₃ was obtained with a rate law derived from a redox Mars and van Krevelen mechanism. The catalytic cycle is described by a sequence of three reactions: (i) Cu^I is oxidized by O₂ to “Cu^II-oxo”, (ii) “Cu^II-oxo” reacts with NO to yield “Cu^II-N_xO_y”, and (iii) finally “Cu^II-N_xO_y” is reduced by NH₃ to give N₂, H₂O, and the regeneration of Cu^I (closing of the catalytic cycle). The rate constants of the three steps have been determined at 458, 483, and 513 K. It is shown that Cu^I or “Cu^II-oxo” species constitute the rate-determining active center.     

Hydrogenation of 3,4-epoxy-1-butene over Cu–Pd/SiO2 catalysts prepared by electroless deposition

Electroless deposition has been used to prepare Cu–Pd/SiO₂ bimetallic catalysts wherein initial Cu coverages are limited only to the pre-existing Pd surface. Cu loading on the Pd surface can be systematically varied by modification of deposition kinetic parameters. In this case deposition time was used as the kinetic variable for the preparation of a series of Cu–Pd catalysts. These materials have been characterized using atomic absorption, CO chemisorption, and FT-IR (adsorption of CO), and then evaluated for the hydrogenation of 3,4-epoxy-1-butene, a functionalized olefin having many potential reaction pathways. Catalyst performance and characterization results suggest that Cu is not distributed in a monodisperse manner on the Pd surface, indicating the existence of autocatalytic deposition of Cu on Cu sites. The FT-IR results suggest that although CO adsorption on all sites is suppressed by Cu addition, initial Cu deposition occurs more readily on certain sites. The bimetallic Cu–Pd sites that are formed exhibit unusually high activity for EpB conversion and formation of unsaturated alcohols and aldehydes. This bimetallic effect on catalyst activity and selectivity is best explained, not by the existence of either ligand or ensemble effects, but rather by the bifunctional nature of the Cu–Pd sites present on the surface of these catalysts.     

Electrodeposition of copper on Ru(0 0 0 1) in sulfuric acid solution: Growth kinetics and nucleation behavior

The electrodeposition of Cu on Ru(0 0 0 1) from 0.1 M CuSO₄/0.5 M H₂SO₄ solution has been studied by cyclic voltammetry, current-time transient measurements, and by in situ electrochemical atomic force microscopy (EC-AFM). Cyclic voltammetry measurements show that the as-prepared Ru(0 0 0 1) electrode exhibits a UPD peak, while EC-AFM data indicate a broadly terraced surface with step heights of atomic dimensions. Kinetic data show that the electrodeposition/nucleation process is not well described by 3D or 2D nucleation models. The EC-AFM data show that at potentials near the OPD/UPD threshold, Cu crystallites exhibit pronounced growth anisotropy, with lateral dimensions greatly exceeding vertical dimensions. AFM data also show that deposition at more cathodic potentials result in smaller crystallites.     

New liquid membrane technology for simultaneous extraction and stripping of copper(II) from wastewater

In this paper, a new liquid membrane technique, hollow fiber renewal liquid membrane (HFRLM), is presented, which is based on the surface renewal theory, and integrates the advantages of fiber membrane extraction, liquid film permeation and other liquid membrane processes. The results from the system of CuSO₄+D2EHPA in kerosene+HCl show that the HFRLM process is very stable. The liquid membrane is renewed constantly during the process, the direct contact of organic droplets and aqueous phase provides large mass transfer area. These effects can significantly reduce the mass transfer resistance in the lumen side. Then the mixture of feed phase and organic phase flowing through the lumen side gives a higher mass transfer rate than that of stripping phase and organic phase, because the aqueous layer diffusion of feed phase is the rate-controlling step. The overall mass transfer coefficient increases with increasing flow rates and D2EHPA concentration in the organic phase, and with decreasing initial copper concentration in the feed phase. The overall mass transfer coefficient also increases with increasing pH in the feed phase, and reaches a maximum value at pH of 4.44, then decreases. Also, there is a favorable w/o volume ratio of 20:1 to 30:1 for this process. Compared with hollow fiber supported liquid membrane and hollow fiber membrane extraction processes, HFRLM process has a high mass transfer rate. Mathematical model for the HFRLM process based on the surface renewal theory is developed. The calculated results are in good agreement with experimental results under the conditions studied.     

Influence of ammonium salt on electrowinning of copper from ammoniacal alkaline solutions

In order to develop an energy-saving copper recycling process from wastes, electrochemical measurements were conducted in ammoniacal alkaline solutions containing Cu(I) ions and an ammonium salt of sulfate, chloride or nitrate. The results of each system were then compared. The polarization measurements suggested that the voltage required for the electrode process is lower in the chloride and nitrate systems than that in the sulfate system. The cathode current efficiency during the copper electrodeposition varied from 39 to 97% and increased with current density in the chloride and sulfate systems. In the nitrate system, the lowest cathode current efficiency of 30% was observed because of nitrate ion reduction. Based on these results, the power consumption required for the electrowinning stage of the copper recycling process was calculated. Among these three systems, the chloride system showed the lowest power consumption of 500 kWh t⁻¹ at the current density of 200 A m⁻², which is about 25% of the conventional copper electrowinning process from a copper sulfate-sulfuric acid solution.     

PLANAR COPPER PLATING AND ELECTROPOLISHING TECHNIQUES

Electrochemical mechanical deposition (ECMD) is a novel technique that has the ability to deposit planar conductive films on non planar substrate surfaces. This technique involves electrochemical deposition (ECD) while simultaneously polishing the substrate surface. Preferential deposition of the conductor into the cavities on the substrate surface may be achieved through two different mechanisms. The first mechanism is more mechanical in nature and it involves material removal from the top surface. The second mechanism is more chemical in nature, and it involves enhancing the deposition into the cavities where mechanical sweeping does not reach and reducing deposition onto surfaces that are swept. In this study we demonstrate that in an ECMD process, low-pressure mechanical sweeping of the wafer surface during copper plating can establish a differential in the activity of the organic accelerator species between the surface and the cavity regions of the substrate and thus give rise to bottom-up filling in even the lowest aspect-ratio cavities. Planar layers obtained by the ECMD technique have been successfully employed in an electrochemical polishing technique for stress-free removal of Cu.     

Adsorption of mercaptopropionic acid onto Au(1 1 1): Part II. Effect on copper electrodeposition

Copper deposition in the presence of an organic additive (3-mercaptopropionic acid, MPA) was studied by cyclic voltammetry and in situ scanning tunneling microscopy (STM) and the results are compared to those for additive-free solutions. It is shown that underpotential deposition (upd) of copper onto a fully MPA-covered electrode produces a defect-rich substrate, but the defects are blocked by the dense organic film for bulk deposition, resulting in a low number of nuclei. A grain-refining effect of MPA, however, was found, when Cu deposition was initiated shortly after addition of MPA to the solution, i.e., for a low-coverage MPA adlayer.