Metal Vapor Synthesis Research Articles

XPS/TEM characterisation of PtAu/C cathode electrocatalysts prepared by metal vapour synthesis

AbstractMonometallic Pt/C, Au/C and bimetallic PtAu/C nanocomposites have been prepared by metal vapour synthesis using Vulcan XC‐72R carbon support. X‐ray photoelectron spectroscopy and transmission electron microscopy were used to evaluate the structure and properties of the metallic nanoparticles. XPS data show the absence of any significant electron transfer in bimetallic PtAu/C system prepared by successive deposition of Au and Pt nanoparticles. The only evidence of PtAu interaction is the narrowing Au 4f peaks in PtAu/C catalyst in comparison with those of Au/C system. Copyright © 2010 John Wiley & Sons, Ltd.

Effect of Reaction Driving Force on Copper Nanoparticle Preparation by Aqueous Solution Reduction Method

The preparation of copper nanoparticle is currently an area of intensive scientific research, as copper nanoparticle is viewed as possible replacements for Ag and Au particles in certain potential applications such as catalyst and conductive paste. 1–3) Currently, many well-known copper nanoparticle preparation methods exist, such as radiation, microemulsion, supercritical, thermal reduction, sonochemical reduction, laser ablation, metal vapor synthesis, and chemical reduction methods, as well as vacuum vapor deposition and supercritical techniques. 4) Among these, the aqueous solution reduction method is a widely adopted approach due to its advantages such as convenient operation, high yield rate and quality, low equipment requirement and controllability. In previous research, much work has been completed to explore the optimal conditions of nanoparticle preparation. However, the reaction mechanism has been seldom reported, which can help elucidate the reduction process. Therefore, the effect of different reductants on copper nanoparticle preparation was investigated to explore the reaction mechanism. C6H8O6 ,H 3PO2 ,T i 2(SO4)3 and NaBH4 were used as the reductants. 2. Principle of Experiment The reduction of Cu 2þ to Cu atom is the result of redox reaction, in which electrons are transferred from the reductant to Cu 2þ . To discuss the reaction mechanism, reaction driving force (� E) was introduced in this paper. During the redox reaction process two half-cell reactions take place. One is the reduction of Cu 2þ to Cu atom, and the other is the oxidation of reductant. The oxidation half-cell reaction

Gold- and silver-containing fibroporous polytetrafluoroethylene obtained under laser irradiation, supercritical carbon dioxide treatment, and metal-vapor synthesis

A combined approach to the synthesis of functional nanocomposite materials based on fibroporous polytetrafluoroethylene (PTFE) prepared by the CO2 laser irradiation of the block PTFE sample (fluoroplastic-4) has been developed. Fibroporous materials (FPM) such as cotton and felt were modified by supercritical carbon dioxide treatment to create nano- and micropores in the surface layers of FPM fibers. The gold- and silver-containing fibroporous nanocomposites have been obtained by processing the nano-structured FPM with the organosols of the metal nanoparticles in isopropanol prepared by metal-vapor synthesis. The composition and structure of the metal-containing fluoropolymers have been investigated by X-ray analysis and electron microscopy.

Solvated gold atoms in the preparation of efficient supported catalysts: Correlation between morphological features and catalytic activity in the hydrosilylation of 1-hexyne

In the last 20 years, nanostructured gold species have received increasing attention due to their activity in many reactions such as selective oxidations and reductions of fine organic chemicals, both in gas phase and in liquid phase. Here, we report that gold nanoparticles prepared from Au/CH 3COCH 3 solution (obtained from gold vapours and acetone by the Metal Vapour Synthesis technique) can be directly deposited on a wide series of different supports (C, Al 2O 3, Fe 2O 3, CeO 2, TiO 2 and ZrO 2) with their small dimensions being maintained. The supported gold nanoclusters thus obtained are effective catalysts for the hydrosilylation of acetylenic compounds. The catalytic performance of Au is defined by two major factors: particle size and choice of support. For instance, the results obtained from the reaction of 1-hexyne with triethylsilane in the presence of Au/γ-Al 2O 3 (0.05 mol%) demonstrate the high selectivity and the excellent specific activities typical of these gold catalysts.

Palladium nanoparticles supported on polyvinylpyridine: Catalytic activity in Heck-type reactions and XPS structural studies

Palladium nanoparticles, obtained by metal vapour synthesis (MVS), were deposited on cross-linked polyvinylpyridine. The Pd/PVPy system showed high catalytic activity in the Heck C C coupling reaction of iodo- and bromo-arenes (iodobenzene, bromobenzene, p-nitrobromobenzene, p-bromoacetophenone, p-(methoxy)bromobenzene) with alkyl acrylates (methyl acrylate, n-butyl acrylate, ethylhexyl trans-3-(4-methoxyphenyl)acrylate) at 100 °C–175 °C working under nitrogen atmosphere as well as in air. The catalyst is stable and the leaching of metal in solution is very low. When reused, the recovered Pd/PVPy maintains the catalytic activity of the pristine material. XPS structural studies performed on the starting catalyst as well as on the recovered one indicate the presence of a interaction between the basic nitrogen of the pyridine present in the polymer and the metal.

The control of the growth of Pt clusters in solution: A way to prepare Pt particles of tailored size

Abstract The growth of Pt particles in mesitylene-solvated metal atoms, obtained by metal vapour synthesis (MVS), has been followed at two temperatures (−40 and 25 °C) by NMR DOSY technique. The addition of 1,3-divinyltetramethyldisiloxane (DVS) at different time allows to quench the growth process and to make the resulting thermally stable solutions suitable for the evaluation of the Pt particles size at that moment. These solutions can be conveniently used to prepare supported Pt systems containing Pt particles of tailored size.

Supported rhodium nanoparticles obtained by Metal Vapour Synthesis as catalysts in the preparation of valuable organic compounds

Abstract Rhodium nanoparticles, derived from mesitylene-solvated rhodium atoms, deposited on γ-Al 2 O 3 , are excellent catalysts for the selective hydrogenation of the double bond in α,β-unsaturated carbonyl compounds. The low metal loading Rh on γ-Al 2 O 3 catalyst, containing trioctylamine, TOA, as stabilizing agent of the metal nanoparticles, Rh(TOA)/γ-Al 2 O 3 , 0.1 wt.% Rh, showed the highest catalytic activity. Using this catalyst 4-(6,-methoxy-2,-naphthyl)-3-buten-2-one was reduced to the anti-inflammatory drug 4-(6,-methoxy-2,-naphthyl)-butan-2-one, Nabumetone™, with complete selectivity and under mild reaction conditions (room temperature, atmospheric pressure of hydrogen). Similarly, 2-acetyl-5,8-dimethoxy-3,4-dihydronaphthalene was hydrogenated with high selectivity (85%) to 2-acetyl-5,8-dimethoxy-1,2,3,4-tetrahydronaphthalene, precursor of antitumor anthracyclinic compounds, which was obtained chemically pure by crystallization. No leaching of rhodium was observed. The catalyst was completely recovered and, if reused, it works without loss of activity. 1 H NMR DOSY analysis of the Rh(TOA)/mesitylene solution evidenced the presence of nanoparticles with a diameter of about 1.1 nm.

An XPS study of the synergetic effect of gold and nickel supported on SiO 2 in the catalytic isomerization of allylbenzene

A synergetic effect and catalytic activity in allylbenzene isomerization have been found for the Au–Ni/SiO2 system prepared by metal-vapour synthesis.

MVS-derived palladium nanoparticles deposited on polydimethylphosphazene as recyclable catalysts for Heck-type reactions: Preparation, structural study, and catalytic activity

Palladium nanoparticles, obtained by the metal vapor synthesis (MVS) technique, were deposited on polydimethylphosphazene (PDMP). The Pd/PDMP system showed high catalytic activity in the Heck C C coupling of iodobenzene and methyl acrylate, with greater activity than commercially available catalysts such as Pd(OAc) 2 and Pd on carbon. The Pd/PDMP is soluble in the reaction solvent, 1-methyl-2-pyrrolidinone, and can be quantitatively recovered at the end of the reaction by precipitation without loss of metal. When reused, the recovered Pd/PDMP retains its catalytic activity. A multinuclear ( 31P, 13C, 15N) solid-state NMR study identified and characterized the strong structural and dynamic modifications induced by Pd nanoparticles on PDMP. Moreover, solid-state NMR studies and HRTEM analyses, performed on the pristine catalyst and on the catalyst recovered after the reaction, highlighted the almost complete structural invariability of the Pd/PDMP, pointing out the high stability toward agglomeration of the palladium nanoparticles in such a system. Pd/PDMP in the presence of triphenylphosphine was also active in the alkylative cyclization of 7-octen-1-ynes, an important C C coupling reaction to obtain substituted 1,2-bis(alkylidene)cyclohexanes, which are valuable building blocks in fine chemistry.

Nanostructured gold/conjugated polymer hybrids: Preparation, chemical structure and morphology

Conjugated micro and nanostructured Pd containing polymers, derived from a monosubstituted acetylene, namely 3-dimethylamino-1-propyne (DMPA), has been synthesized and used as matrix for the preparation of hybrid systems containing Au(0) nanoparticles, obtained by means of Metal Vapor Synthesis (MVS) technique. By this way the formation of a new heterobimetallic Au/Pd polymeric material was achieved. The novel hybrid was characterized by means of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and high resolution transmission microscopy (HRTEM) showing the Au/polymer interaction and the particle dispersion in the nanostructured polymer matrix. The morphology of the pristine polymer shows dendritic structures or compact enamels and upon formation of the hybrid a high surface extension was observed. HRTEM measurements showed in the Au/Pd–PDMPA hybrid system an almost homogeneously distributed population of gold particles with a main size value of 3.4±1.4 nm.

MOCVD of iron with [(arene)(diene)Fe(0)] precursors in a fluidized bed reactor

Abstract MOCVD of thin iron films at moderate temperature ( T 1 ) and [(1,3-cyclohexadiene)(toluene)Fe(0)] ( 2 ) were synthesized by metal vapor synthesis. They were characterized by their vapor pressure at different temperatures and their decomposition behavior. 1 and 2 were used to coat alumina powder with iron through MOCVD in a fluidized bed reactor (FB-MOCVD) to prepare potential supported iron metal catalysts. The new materials were compared to an iron coated sample, which was prepared by conventional wet impregnation technique. Both were characterized by different methods like ICP OES, SEM/EDX, particle size analysis, H 2 /TPR and CO adsorption. The iron layer of the FB-MOCVD samples forms nanocrystals, which are homogeneously distributed over the surface. They are much smaller in size and show a higher dispersion with respect to the conventionally prepared iron catalysts. As a consequence, the nanocrystals are significantly more reactive with respect to redox processes and adsorb about 40% more carbon monoxide, than the conventionally prepared material, thus indicating a higher catalytic activity.

Adsorption and catalytic conversion of hydrocarbons on nanosized gold particles immobilized on alumina

Gold and nickel particles immobilized on alumina were prepared by the metal vapor synthesis and anionic adsorption methods. The dispersion of metals was determined by X-ray diffraction and transmission electron microscopy. The activity of nanoparticles, tested in model catalytic reactions of CCl4 addition to multiple bonds and allyl isomerization of allylbenzene, changes in a wide range (from 1 to 3000 (mole of product) (mole of Au)−1 h−1) and is parallel to the chromatographically measured heats of adsorption of the corresponding unsaturated substrates. The heat of adsorption of unsaturated hydrocarbons can serve as a criterion for the efficiency of the gold-containing catalyst in olefin conversion.

Preparation of nanostructured organometallic polymer/palladium hybrids by metal vapoursynthesis: structure and morphology

Pd(0) nanoclusters were dispersed by using the metal vapour synthesis technique inorganometallic polymers of chemical structure (M = Pd,Pt), namely Pd-DEBP and Pt-DEBP. The hybrids were characterized by means of solid state13C and 31P nuclear magnetic resonance, which highlighted the chain organization and theplasticizing effect of the nanoparticles on the polymers. Scanning electron microscopyimages of the pristine organometallic polymers, and of their hybrids containingPd(0), exhibited a growth of nanosized fibrils on glass substrates. High resolutiontransmission electron microscopy measurements showed a narrow distribution ofPd(0) nanoparticles which have dimensions in the range 1.0–5.0 nm in the caseof Pd/Pd-DEBP hybrids and 0.5–2.0 nm in the case of Pd/Pt-DEBP hybrids.

Functional resins in palladium catalysis: promising materials for Heck reaction in aprotic polar solvents

The performances of palladium metal catalysts supported by organic resins containing tertiary amino, cyano, carboxyl, and pyridyl groups have been investigated in standard Heck reactions. The catalysts were prepared by either immobilization in the resins of palladium(II) precursors and chemical reduction thereof or by deposition of solvated metal atoms obtained by means of metal vapor synthesis (MVS). Particular attention was paid to the nature of catalysis in the presence of these materials. As the observed catalytic activity turned out to be generally associated with metal leaching, the reaction was most likely catalyzed in solution by soluble, active palladium species. However, a MVS 1% (w/w) catalyst supported by a commercial polyvinylpyridine resin cross-linked with divinylbenzene exhibited an appreciable catalytic activity with a possible partial contribution from supported active palladium species.

Substituent effects in bis(arene)chromium compounds containing a CN group in the aromatic ring

The crystal structures of Cr(PhCN)(2) (2), (PhCN)Cr(PhCH(3)) (3) and (PhCN)Cr(PhCF(3)) (4) prepared by means of the Metal Vapor Synthesis (MVS) technique have been determined. Compounds (2), (3) and (4) crystallize as discrete sandwich complexes having intrinsic C(2v)(mm2), C(s)(m) and C(1)(1) symmetries, respectively. The X-ray diffraction study has revealed a synperiplanar conformation for (2) and (3), and a synclinal conformation for (4) with a torsion angle (C(ipso)1-Centroid1-Centroid2-C(ipso)2) of phi = 63.5 degrees . The angles between the ligand planes are 2.2, 3.9 and 1.8 degrees , respectively. The Cr atom is slightly (by 0.04-0.06 A) displaced towards the substituents from the line connecting the centers of the opposite aromatic rings. The Cr-C(ipso) distances are 2.115 (2)-2.137 (2), 2.112 (2) and 2.185 (3) A for CN, CF(3) and CH(3) groups, respectively. The CN groups as well as the H atoms lie out of the C(6) ring planes and are bent towards the Cr atom, but the C atom of the CH(3) group also lying out of the C(6) ring plane is bent away from the Cr atom. The C atom of the CF(3) group is essentially coplanar to the C(6) ring plane. There are no unusual intermolecular contacts in the structures of (2)-(4).

Novel Pt 0 catalysts supported on functional resins for the chemoselective hydrogenation of citral to the [formula omitted]-unsaturated alcohols geraniol and nerol

Nanoclustered Pt 0 catalysts based on cross-linked macromolecular matrices are evaluated in the hydrogenation of an α , β -unsaturated aldehyde (citral). Matrices and catalysts are characterized by inverse steric exclusion chromatography, scanning electron microscopy, X-ray microprobe analysis, and transmission electron microscopy. The monometallic catalysts exhibit remarkable selectivity for geraniol/nerol when 2–3-nm, regularly shaped, spherical metal nanoclusters are deposited on the supports from solutions of solvated platinum atoms prepared by metal vapor synthesis (MVS). The immobilization in the polymer framework of ions of a second metal such as Fe(II), Co(II), or Zn(II) enhances the selectivity of the Pt catalysts by up to more than 90%.

Chemical and catalytic activity of copper nanoparticles prepared via metal vapor synthesis

Nanocrystalline particles of copper have been prepared using the solvated metal atom dispersion (SMAD) technique. Their chemical and catalytic reactivity have been tested in the Ullman reaction (aryl homocoupling) and the hydrogenation of CO2 to form CH3OH. The powders obtained from different solvents have surface areas of 24–30 m2/g, particle sizes of 20–45 nm, and crystallite sizes of 8–12 nm. The order of activity found toward the aryl homocoupling reaction is Cu*/toluene > Cu*/THF > Cu*/pentane > Cu*/diglyme, with a maximum biphenyl yield of 90% at 150 °C after 6 h for the Cu*/toluene sample. For the CO2 to CH3OH reaction, a maximum conversion of 80% was obtained for the Cu*/pentane/NC-ZnO sample. In general, the Cu*/nanocrystalline (NC)-ZnO samples show a larger conversion of CO2 to methanol at 450 °C compared with NC-ZnO and NC-ZnO/CuO.

Synthesis and characterization of samarium, europium and ytterbium aryloxidesCrystal structure of [Yb6(OH)4(OC6H4OMe)14]a4THF

Abstract The reactions of samarium, europium and ytterbium metals with the potential bidentate ligand 2-methoxyphenol were investigated. The europium and ytterbium aryloxides were synthesized by dissolution of the metals in liquid ammonia, whereas the samarium aryloxide was synthesized by metal vapour synthesis (MVS). The compounds obtained were formulated as Ln(OC 6 H 4 OMe) 3 , Ln=Sm, Yb and Eu(OC 6 H 4 OMe) 2 . Recrystallization of Yb(OC 6 H 4 OMe) 3 in the presence of THF/pentane resulted in the crystallographically characterized complex [Yb 6 (μ 3 -OH) 4 (μ-OC 6 H 4 -η-OMe) 10 (OC 6 H 4 -η-OMe) 2 (OC 6 H 4 OMe) 2 ]·4THF.

Synthesis and characterization of samarium, europium and ytterbium aryloxides: Crystal structure of [Yb 6(OH) 4(OC 6H 4OMe) 14]·4THF

The reactions of samarium, europium and ytterbium metals with the potential bidentate ligand 2-methoxyphenol were investigated. The europium and ytterbium aryloxides were synthesized by dissolution of the metals in liquid ammonia, whereas the samarium aryloxide was synthesized by metal vapour synthesis (MVS). The compounds obtained were formulated as Ln(OC 6H 4OMe) 3, Ln=Sm, Yb and Eu(OC 6H 4OMe) 2. Recrystallization of Yb(OC 6H 4OMe) 3 in the presence of THF/pentane resulted in the crystallographically characterized complex [Yb 6(μ 3-OH) 4(μ-OC 6H 4-η-OMe) 10(OC 6H 4-η-OMe) 2(OC 6H 4OMe) 2]·4THF.

The catalytic hydrogenation of adiponitrile to hexamethylenediamine over a rhodium/alumina catalyst in a three phase slurry reactor

Abstract Adiponitrile was hydrogenated to hexamethylenediamine in a three phase stirred slurry reactor at 353 K and 3 MPa using rhodium on γ-alumina powder as a catalyst. Rhodium, with a very high metal dispersion, was deposited on the alumina support using the metal vapour synthesis technique. The performances of this supported catalyst were compared to those of one currently used in industrial processes (Raney Ni). The Rh/Al 2 O 3 catalyst showed interesting hexamethylenediamine selectivity and adiponitrile conversion. Both the temperature and pressure positively influenced conversion and selectivity, and under a certain pressure threshold the formation of hexamethylenediamine was negligible.