Functionalization of Polymer Surfaces Using Excimer VUV Systems and Silent Discharges. Application to Electroless Metallization

New approaches for electroless plating of nonconductive polymers or polymer-based materials are described. In this work, polyimide substrates were surface-functionalized (i) in nitrogenated (ammonia at reduced pressure) and oxygenated (air at atmospheric pressure) atmospheres under assistance of vacuum-ultraviolet (VUV) irradiation (use of a xenon silent discharge excimer source) or (ii) directly in air at atmospheric pressure using a dielectric-barrier discharge (DBD) device. After functionalization, the substrates were “activated” by dipping in a dilute acidic PdCl₂ solution or by spin-coating of a thin metal-organic film (from a solution of palladium acetate (PdAc) in chloroform). The catalytic activity of the so-deposited palladium species toward the electroless deposition of nickel was studied before and after a VUV post-irradiation (in air at atmospheric or reduced pressure) with a view to understanding better the role of the reducer (sodium hypophosphite) within the electroless bath.

This work confirms the specific interest of grafting nitrogenated functionalities onto polymer surfaces for attaching covalently the palladium-based catalyst (in particular in the case of the PdCl₂ route), forming thus strong Pd - N - C bonds at the metal/polymer interface. This results from the strong chemical affinity of palladium toward nitrogen. On the other hand, when oxygenated functionalities are surface-grafted, the conventional two-step procedure using SnCl₂ and PdCl₂ solutions can be proposed due to the strong chemical affinity of tin toward oxygen. The Ni deposits obtained under these different conditions pass the standard Scotch^®-tape test and, therefore, exhibit a good practical adhesion. For this same purpose, it is interesting to note that the DBD treatment operating in air at atmospheric pressure causes an increase of the surface roughness and, therefore, an improvement in adhesion of metallic films when their initiation is catalyzed through the PdAc route. In addition, this work demonstrates that extensive research still has to be performed to understand and improve the Ni/polymer adhesion when the PdAc route associated with a VUV irradiation is considered.     

Poly(o-toluidine) as the matrix for incorporation of palladium species from PdCl2 aqueous solutions

Reactivity of poly(o-toluidine) in the emeraldine base form (POT) and protonated with HCl (POT/HCl) in PdCl₂ aqueous solutions of various HCl concentrations has been studied. Using elemental analysis, FTIR, UV–Vis, XPS and EXAFS spectroscopies as well as XRD and SEM it has been established that POT/HCl is more reactive than POT. The course of reactions is influenced by the type of the PdCl₂ solution. Thus, protonation of POT with incorporation of palladium (II) chloro–and/or aquachloro–and/or chlorohydroxycomplexes counterions is the main process occurring in the PdCl₂ solutions of higher HCl concentration. A redox reaction resulting in the oxidation of the polymer chain with simultaneous formation of metallic palladium takes place in the PdCl₂ solution of lower HCl concentration. POT/HCl shows enhanced reducing properties with respect to POT. Lowering of the protonation level (i.e. some deprotonation) of POT/HCl has been also observed. Coordination of palladium (II) ions by nitrogen atoms of the polymer chain can be also postulated.     

Formation of Pd nanoparticles in surfactant-mesoporous silica composites and surfactant solutions

Highly dispersed palladium nanoparticles containing mesoporous silicas MCM-41 and MCM-48 were prepared by one-pot synthesis. The method consists of the simultaneous formation of CTA⁺ surfactant templating MCM-41 mesophase and CTA⁺ micelle-capped PdO, which was reduced by hydrogen to Pd metal with particle size ≈ 2 nm and was observed to stay inside the mesochannels of MCM-41 (pore size ≈ 3.8 nm) by TEM, XAS, and PXRD. During hydrothermal synthesis of Pd/MCM-48, Pd nanoparticles of average size ≈ 6–7 nm were deposited on the MCM-48 of pore size = 4 nm. The deposition is probably derived from ethanol reduction of Pd(II) complex generated from PdCl₂ precursor by hydrolysis of TEOS and C₁₂H₂₅(OCH₂CH₂)₄OH surfactant. The formation of Pd(0) from Pd(II) species in solid mesoporous silicas by hydrogen reduction was monitored by in situ XAS, and compared with the formation of Pd(0) from [PdCl₄]²⁻, [PdCl₃(H₂O)], and Pd(OH)₂ by sodium dodecyl sulfate surfactant and alcohol reduction in aqueous solutions.     

ELECTROLESS PLATING OF GLASS AND SILICON SUBSTRATES THROUGH SURFACE PRETREATMENTS INVOLVING PLASMA-POLYMERIZATION AND GRAFTING PROCESSES

Electroless plating of nickel (or copper) was carried out on glass (or silicon) substrates that were previously surface modified by using plasma-polymerization and grafting processes, and then activated by immersion in a simple acidic PdCl₂ solution. Three pretreatments based on the deposition of plasma-polymerized thin films (PACVD process) on O₂ plasma-cleaned substrates were investigated. They include film deposition of (1) amorphous hydrogenated carbon (a-C:H) grown from CH₄, whose surface is subsequently plasma-functionalized in NH₃ or N₂; (2) amorphous hydrogenated carbon nitride (a-CN_x:H) grown from CH₄/NH₃ or CH₄/N₂ mixtures; and (3) amorphous hydrogenated carbon nitride grown from volatile organic precursors (allylamine, acetonitrile).

In the three cases, X-ray photoelectron spectroscopy (XPS) results show that chemisorption of the catalyst occurs on the nitrogen-containing functionalities created by plasma polymerization and grafting and thus that the electroless deposition is possible. Differences were observed depending on the nature and thickness of the plasma-polymerized thin films, as well as on the nature and concentration of the nitrogen-containing functionalities present or grafted at the surface. Practical adhesion of Ni films was investigated using a Scotch® tape test. Ni films up to 3 or 4 μm in thickness were shown to pass this test successfully, i.e., without causing any metal detachment.     

Methane conversion to C2 hydrocarbons and hydrogen in atmospheric non-thermal plasmas generated by different electric discharge techniques

Methane conversion to C₂ hydrocarbons and hydrogen has been investigated in a needle-to-plate reactor by pulsed streamer and pulsed spark discharges and in a wire-to-cylinder dielectric barrier discharge (DBD) reactor by pulsed DC DBD and AC DBD at atmospheric pressure and ambient temperature. In the former two electric discharge processes, acetylene is the dominating C₂ products. Pulsed spark discharges gives the highest acetylene yield (54%) and H₂ yield (51%) with 69% of methane conversion in a pure methane system and at 10 SCCM of flow rate and 12 W of discharge power. In the two DBD processes, ethane is the major C₂ products and pulsed DC DBD provides the highest ethane yield. Of the four electric discharge techniques, ethylene yield is less than 2%. Energy costs for methane conversion, acetylene or ethane (for DBD processes) formation, and H₂ formation increase with methane conversion percentage, and were found to be: in pulsed spark discharges (methane conversion 18–69%), 14–25, 35–65 and 10–17 eV/molecule; in pulsed streamer discharges (methane conversion 19–41%), 17–21, 38–59, and 12–19 eV/molecule; in pulsed DBD (methane conversion 6–13%), 38–57, 137–227 and 47–75 eV/molecule; in AC DBD (methane conversion 5–8%), 116–175, 446–637, and 151–205 eV/molecule, respectively. The immersion of the γ-Al₂O₃ pellets in the pulsed streamer discharges, or in the pulsed DC DBD, or in the AC DBD has a positive effect on increasing methane conversion and C₂ yield.     

Catalytic dechlorination of 1-chlorooctadecane in supercritical carbon dioxide

Palladium catalyzed hydrodechlorination of 1-chlorooctadecane in supercritical carbon dioxide (SC–CO₂) was performed and compared to dechlorination in isopropanol at atmospheric pressure (liquid isopropanol). The reaction utilized isopropanol as a hydrogen donor and its rate in SC–CO₂ was significantly faster than in isopropanol at atmospheric pressure. The dechlorination yield in liquid isopropanol was increased by addition of NaOH, while the presence of either NaOH or triethylamine in SC–CO₂ lowered the dechlorination yield significantly. Experimental parameters such as pressure, temperature, and the concentrations of reagents (isopropanol and palladium) in the absence of base were optimized in SC–CO₂ to obtain complete dechlorination. Kinetic studies of the reaction were then performed to deduce the reaction mechanism. The apparent activation energies of the reaction were 43±5 kJ mol⁻¹ in SC–CO₂ and 35±3 kJ mol⁻¹ in liquid isopropanol. The rate determining step of the reaction was deduced to be adsorption of 1-chlorooctadecane on the palladium surface.     

Effects of Sn residue on the high temperature stability of the H_2-permeable palladium membranes prepared by electroless plating on Al_2O_3 substrate after SnCl_2–PdCl_2 process: A case study

The stability of composite palladium membranes is of key importance for their application in hydrogen energy systems. Most of these membranes are prepared by electroless plating, and beforehand the substrate surface is activated by a SnCl_2–PdCl_2 process, but this process leads to a residue of Sn, which has been reported to be harmful to the membrane stability. In this work, the Pd/Al_2O_3 membranes were prepared by electroless plating after the SnCl_2–PdCl_2 process. The amount of Sn residue was adjusted by the SnCl_2 concentration, activation times and additional Sn(OH)_2coating. The surface morphology, cross-sectional structure and elemental composition were analyzed by scanning electron microscopy(SEM), metallography and energy dispersive spectroscopy(EDS), respectively. Hydrogen permeation stability of the prepared palladium membranes were tested at450–600 °C for 400 h. It was found that the higher SnCl_2 concentration and activation times enlarged the Sn residue amount and led to a lower initial selectivity but a better membrane stability. Moreover, the additional Sn(OH)_2coating on the Al_2O_3 substrate surface also greatly improved the membrane selectivity and stability.Therefore, it can be concluded that the Sn residue from the SnCl_2–PdCl_2 process cannot be a main factor for the stability of the composite palladium membranes at high temperatures.     

Plasma Chemical Modification of Polycarbonate Surfaces for Electroless Plating

The preliminary steps of the “electroless” metallization of polycarbonate are investigated by XPS. They consist of the chemisorption of a catalyst (Pd) on the surface to be metallized. The corresponding surface can be activated either by chemical etching or by reactive or non-reactive gas plasma treatment. Therefore, the surface treatment of polycarbonate determines the palladium adsorption. It is shown here that a surface carrying oxygenated functions adsorbs palladium through Sn²⁺ ions which are themselves bonded to oxygen atoms. On the other hand, a surface on which nitrogenated groups have been grafted (by NH₃ or N₂ plasma treatment) chemisorbs palladium directly on these nitrogen atoms. Reaction mechanisms are proposed in both cases and a new and simplified process for making the surfaces catalytic is proposed.     

Plasma Chemical Modification of Polycarbonate Surfaces for Electroless Plating

The preliminary steps of the “electroless” metallization of polycarbonate are investigated by XPS. They consist of the chemisorption of a catalyst (Pd) on the surface to be metallized. The corresponding surface can be activated either by chemical etching or by reactive or non-reactive gas plasma treatment. Therefore, the surface treatment of polycarbonate determines the palladium adsorption. It is shown here that a surface carrying oxygenated functions adsorbs palladium through Sn²⁺ ions which are themselves bonded to oxygen atoms. On the other hand, a surface on which nitrogenated groups have been grafted (by NH₃ or N₂ plasma treatment) chemisorbs palladium directly on these nitrogen atoms. Reaction mechanisms are proposed in both cases and a new and simplified process for making the surfaces catalytic is proposed.     

Surface organometallic chemistry on metals in water: Chemical modification of platinum catalyst surface by reaction with hydrosoluble organotin complexes: application to the selective dehydrogenation of isobutane to isobutene

Surface organo-metallic chemistry on metals can be a new route to generate supported bimetallic catalysts. According to previous works on Pt–Sn catalysts, the reaction of tetra n-butyl-tin on the reduced platinum surface leads to well-defined bimetallic catalysts which are very active and selective in the dehydrogenation of isobutane into isobutene. The presence of tin not only isolates the surface platinum atoms from each other (EXAFS) and thus prevents a fast deactivation by decreasing the processes of C–C bond cleavage but also favors the regeneration processes under air. So far the catalyst preparations were carried out either in the gas phase or in organic solution (e.g. heptane). However, in order to meet the industrial criteria of process simplicity, there is a need to carry out such catalyst preparation in water.

In this work, Pt–Sn/Al₂O₃ and Pt–Sn/SiO₂ catalysts was prepared by reacting tris n-butyl-tin hydroxide on the platinum surface, in water solution under atmospheric pressure of hydrogen. The kinetics of the reaction was followed by measuring the amount of butane evolved as a function of time. The solids obtained were characterized by CO, O₂ or H₂ chemisorption and electron microscopy (CTEM and EDAX). Clearly, the (n-Bu)₃Sn(OH) reacts selectively on the platinum surface and not with the support, with evolution of butane, leading to a bimetallic catalyst where the platinum atoms are isolated from each other by the tin atoms. Very high selectivities (>95%) and activities were obtained for the reaction of isobutane dehydrogenation into isobutene and it was concluded that surface organo-metallic chemistry on metal in water can be an alternative route to prepare well-defined supported bimetallic Pt–Sn catalysts.     

Preparation of axially non-uniform Pd catalytic monoliths by chemical vapour deposition

Metal-organic chemical vapour deposition was used to prepare palladium catalytic monoliths under atmospheric pressure. Palladium(II) acetylacetonate was utilised as the precursor and was introduced in a helium stream flowing over the γ-Al₂O₃/cordierite support. The monoliths were characterised by atomic absorption, electron probe microscopy and transmission electron microscopy. Axially non-uniform catalyst distributions were obtained. The palladium profile was affected by the sublimation temperature of Pd(acac)₂, deposition temperature of the monolith, carrier gas flowrate and deposition time. Palladium particles obtained were small enough to warrant their use in catalytic applications.     

Catalytic wet air oxidation of carboxylic acids at atmospheric pressure

Catalytic wet air oxidation of carboxylic acids (maleic acid, oxalic acid and formic acid) was carried out in a batch reactor operated at 160 psi or atmospheric pressure. Pt/Al₂O₃ and the sulfonated poly(styrene-co-divinylbenzene) resin were used as catalysts. Maleic acid was proved to be a refractory substance which could not be oxidized on the Pt/Al₂O₃ catalyst at all atmoshperic pressure, and needed high pressure and high temperature operation for its oxidation. On the contrary, oxalic acid and formic acid were readily oxidized into carbon dioxide and water at 353 K and atmospheric pressure. The pathways of maleic acid oxidation were proposed, and the conversion of maleic acid into oxalic acid was the rate-determining step. When the sulfonated resin catalyst was present together with the Pt/Al₂O₃ catalyst, maleic acid could be oxidized at 353 K and atmospheric pressure. The sulfonated resin catalyst was suggested to hydrolyze maleic acid into readily oxidizable compounds.     

The Adhesion of Evaporated Copper to Dow Cyclotene 3022®, Determined by Microscratch Testing

The mechanical integrity, stability, and strong interfacial adhesion between Cu, a high conductivity metal, and Dow Cyclotene 3022^®, a low permittivity polymer, are important for their application in future high-speed microelectronic devices. In the present study, Cu was deposited by both evaporation and sputtering, and various Cyclotene surface modifications were carried out. These modifications included low pressure N₂ plasma and Ar⁺ treatments and the use of a Ti interlayer. The adhesion was evaluated by use of the microscratch test, and complemented by an adhesive tape peel test and XPS. The N₂ plasma treatment was found to lead to a dramatic increase in adhesion, which was influenced to a minor extent by the adhesion promoter that was used at the Cyclotene/Si substrate interface. This significant Cu/Cyclotene adhesion enhancement is interpreted in terms of the chemical groups present at the Cyclotene surface and the bonds formed on Cu deposition.     

Hydrodesulfurization of thiophene, dibenzothiophene and gas oil on various Co---Mo/TiO2-Al2O3 catalysts

Evaluation of Co---Mo catalysts prepared on various TiO₂-Al₂O₃ supports has been made for thiophene under atmospheric pressure, dibenzothiophene under high pressure and gasoil in a classical pilot plant. Comparison of activities indicates DBT as more representative of a real feedstock and the Co---Mo/TiO₂ (50%)-Al₂O₃ (50%) catalyst appears more active than the Co---Mo/Al₂O₃ sample toward HDS, HDN and hydrodearomatization.     

过氧化氢蒽醌加氢流化床Pd/Al_2O_3催化剂载体性质与催化性能的关系

以氯化钯为前驱体,活性氧化铝为载体,采用等体积浸渍法制备蒽醌加氢流化床Pd/Al_2O_3催化剂。考察载体比表面积、孔容、孔径、粒度分布及表面形貌与催化剂催化性能的关系,结果表明,载体比表面积较高,小孔径且孔径分布不均匀,粒度较大且粒度分布均匀,载体表面光滑且成球性好的载体对应的催化剂性能较好。采用优化后活性氧化铝载体制备的Pd/Al_2O_3催化剂的氢化效率和选择性分别为9.98 g·L-1和80.3%。     

Catalytic hydrodechlorination of 1-chlorooctadecane, 9,10-dichlorostearic acid, and 12,14-dichlorodehydroabietic acid in supercritical carbon dioxide

Kinetic and thermodynamic analyses of catalytic hydrodechlorinations in supercritical carbon dioxide (SC-CO₂) were performed using 5% Pd supported on γ-Al₂O₃. The selected standard compounds used for the study represented chlorinated wood resins commonly found in pitch deposits; 1-chlorooctadecane (C₁₈-Cl), 9,10-dichlorostearic acid (Stearic-Cl₂), and 12,14-dichlorodehydroabietic acid (DHA-Cl₂). The reaction utilized isopropanol as a hydrogen donor. Pressure, temperature, and the concentrations of isopropanol and palladium were varied to study the effect of each parameter and to optimize the dechlorination yield. The reaction in SC-CO₂ was compared to the one in liquid solvents at atmospheric pressure. By applying a Langmuir–Hinshelwood kinetic model, the rate-determining step of the reaction was deduced to be adsorption of the chlorinated molecules on the palladium surface. The apparent activation energies of the reactions for C₁₈-Cl, Stearic-Cl₂, DHA-Cl₂ were 43±5, 40±7, and 135±7 kJ mol⁻¹, respectively, in SC-CO₂. The relatively high activation energy for DHA-Cl₂ was apparently due to structural differences from the other two compounds. The apparent activation energy of dechlorination of C₁₈-Cl in liquid isopropanol at atmospheric pressure was determined to be 35±3 kJ mol⁻¹, leading to the conclusion that the rate-determining step is the same for this compound in both fluid systems. The enthalpies of desorption of stearic acid and dehydroabietic acid were determined to be 18±2 and 12±2 kJ mol⁻¹, respectively. These values being less than half of the apparent activation energies of dechlorination of their corresponding chlorinated compounds indicates that desorption of the dechlorinated products is not the rate-determining step of the reaction. This was consistent with the conclusion that the rate-determining step is adsorption, on the understanding that the reaction mechanism is same in both fluid systems.     

Sol–Gel Processing and Characterization of Pure and Metal-Doped SnO2 Thin Films

A chloride-based inorganic sol–gel route was used for preparing pure and metal (osmium, nickel, palladium, platinum)-doped SnO₂ sol. SnCl₄ was first reacted with propanol, then the resulting compound was hydrolyzed and subsequently mixed with solutions of the metal dopants. The obtained sols were used for depositing thin films by spin coating or for preparing powders by solvent evaporation at 110°C. FTIR spectroscopy and thermal analysis of the powders revealed that chlorine still bound to tin stabilized the sol against gelation by hindering the condensation reactions. Film characterizations showed that platinum and palladium, unlike nickel and osmium, were likely to form nanoparticles in the SnO₂ lattice. This result was discussed with regard to the different ways that platinum and palladium, on one hand, and nickel and osmium, on the other, modified the growth of SnO₂ grains and the film roughness and morphology. Dopants that formed nanoparticles (platinum, palladium) resulted in the roughest film, while dopants that did not form particles (nickel, osmium) resulted in SnO₂ grain size very close to that of pure SnO₂.     

Selective oxidation with air on metal catalysts

Oxidation of organic molecules with air on metal catalysts has been known for a long time but there has been a renewed interest in recent years because these catalytic reactions are environmentally safe and could replace stoichiometric oxidations. This paper describes several oxidation reactions conducted either at high temperatures in the gas phase or at moderate temperatures in the liquid phase; in both cases they proceed via a mechanism of oxidative dehydrogenation on the metal surface. Ethylene glycol was converted to glyoxal at 550°C on Ag/SiC catalyst with a 70% yield provided promoters were added to the reaction feed (diethylphosphite or iodine) or deposited on the catalyst (LiPO₄ or H₃PO₄). The promoters improve the conversion and selectivity by modifying the structure and the oxygen concentration on the surface of silver. Oxidation of glyoxal to glyoxylic acid, glucose to gluconic acid and glycerol to various oxygenated derivatives were conducted in water at 60°C in the presence of carbon-supported palladium or platinum catalysts. Bismuth promoter, deposited on the platinum metals by redox reaction, improves the catalyst activity by preventing over-oxidation of the metal surface and favors the oxidation of secondary alcohol functions into keto-derivatives. At higher reaction temperatures, platinum catalysts produce C-C bond rupture with the formation of carboxylic acids with smaller chains. Thus, cyclohexanol was converted into C₆, C₅, and C₄ diacids with a 45% selectivity to adipic acid on Pt/C catalysts at 150°C.     

High-Temperature Oxidation of Molybdenum Disilicide

The oxidation of MoSi₂ in air at atmospheric pressure was studied by electron diffraction, X-ray diffraction, and thermogravimetric analyses. The oxidation process occurs in two parts: (1) formation of MoO₃ and SiO₂ at temperatures below the boiling point of MoO₃, and (2) formation of Mo₅Si₃ and SiO₂ at higher temperatures. Evidence is presented which indicates that oxygen permeation through a silica layer, which may be of a mixed crystalline-glassy nature, controls reaction rate at high temperatures and that Mo₅Si₃ is present directly beneath the protective oxide. The activation energy for oxidation of MoSi₂ above 1200°C was calculated as 81.3 kcal mole⁻¹.     

Thermal Stability of Gallium Orthoferrite in the System Fe2O3-FeO-Ga2O3

Gallium orthoferrite (Ga_{2- x} Fe _x O₃) has a maximum thermal stability which coincides roughly with liquidus temperatures at oxygen pressures near atmospheric. As a result, changes in ambient oxygen pressure between 0.2 and 10 atm have a pronounced effect on equilibria. The compound exhibits a wide range in Ga:Fe ratio on both sides of the stoichiometric GaFeO₃ but is essentially invariant in oxygen content to 1500°C in air. The orthoferrite bears many similarities to the corresponding aluminum compound Al₂- _x Fe _x O₃.