Rh Ions Research Articles

Theoretical Study on the Electronic Configurations and Nature of Chemical Bonds of Dirhodium Tetraacetato Complexes [Rh2(CH3COO)4(L)2] (L = H2O, Free): Broken Symmetry Approach

Abstract The electronic configurations and the nature of chemical bonds of the classical lantern-type dinuclear rhodium(II) tetraacetato complexes [Rh2(CH3COO)4(L)2] (L = H2O, free) have been carefully investigated with broken symmetry (BS) Hartree–Fock (HF), BS density functional theory (DFT), and BS hybrid DFT (HDFT) methods. Several electronic configurations have been proposed for the ground states of the [Rh2(RCOO)4(H2O)2] complexes. In this study, we concluded that those different electronic configurations originate from the position of the axial H2Os, and not along the Rh–Rh length. The BS(U)B3LYP calculation indicates that the stability of the σ and δ orbitals changed when the Rh–OH2 length was 2.35 Å. The natural orbital (NO) analyses and chemical indices clearly indicate that there is a σ-type single bond between the Rh ions, and that the axial H2Os does not affect the overlap.

Water Splitting over New Niobate Photocatalysts with Tungsten‐Bronze‐Type Structure and Effect of Transition Metal‐Doping

Photophysical properties and photocatalytic activities for water splitting over KM(2)Nb(5)O(15) (M = Sr and Ba) and K(2)LnNb(5)O(15) (Ln = La, Pr, Nd, and Sm) with tungsten bronze-type structure were investigated. Single phases of KM(2)Nb(5)O(15) and K(2)LnNb(5)O(15) were successfully prepared by solid-state reaction (SSR) method and polymerizable complex (PC) method. The band gaps of these niobates were estimated to be 3.1-3.5 eV. These metal oxides loaded with an activated NiO(x) cocatalyst showed photocatalytic activities for water splitting into H(2) and O(2) under UV irradiation. When K(2)LaNb(5)O(15) was doped by Rh ions, a new visible-light absorption band was observed around 400-500 nm in addition to the band gap absorption band of the K(2)LaNb(5)O(15) host. K(2)LaNb(5)O(15):Rh showed photocatalytic activities for H(2) or O(2) evolution from an aqueous solution containing a sacrificial reagent under visible-light irradiation.

Ionic liquid ultrasound assisted dispersive liquid–liquid microextraction method for preconcentration of trace amounts of rhodium prior to flame atomic absorption spectrometry determination

In this article, we consider ionic liquid based ultrasound-assisted dispersive liquid–liquid microextraction of trace amounts of rhodium from aqueous samples and show that this is a fast and reliable sample pre-treatment for the determination of rhodium ions by flame atomic absorption spectrometry. The Rh(III) was transferred into its complex with 2-(5-bromo-2-pyridylazo)-5-diethylamino phenol as a chelating agent, and an ultrasonic bath with the ionic liquid, 1-octyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide at room temperature was used to extract the analyte. The centrifuged rhodium complex was then enriched in the form of ionic liquid droplets and prior to its analysis by flame atomic absorption spectrometry, 300 μL ethanol was added to the ionic liquid-rich phase. Finally, the influence of various parameters on the recovery of Rh(III) was optimized. Under optimum conditions, the calibration graph was linear in the range of 4.0–500.0 ng mL −1, the detection limit was 0.37 ng mL −1 (3 S b/ m, n = 7) and the relative standard deviation was ±1.63% ( n = 7, C = 200 ng mL −1). The results show that ionic liquid based ultrasound assisted dispersive liquid–liquid microextraction, combined with flame atomic absorption spectrometry, is a rapid, simple, sensitive and efficient analytical method for the separation and determination of trace amounts of Rh(III) ions with minimum organic solvent consumption.

Investigation of the Formation Process of Photodeposited Rh Nanoparticles on TiO2 by In Situ Time-Resolved Energy-Dispersive XAFS Analysis

The photodeposition process of Rh metal nanoparticles on a TiO(2) photocatalyst from RhCl(3) aqueous solution in the presence of methanol as a sacrificial oxidant, which consists of the direct reduction of Rh(3+) ions to Rh metal and the formation of Rh nanoparticles, was uncovered by in situ time-resolved energy-dispersive X-ray absorption fine structure (DXAFS) analysis in a liquid-solid suspension state. The fractions of Rh metal particles and Rh(3+) precursor were estimated by the least-squares fitting of each X-ray absorption near-edge structure (XANES) spectrum by a linear combination of authentic spectra corresponding to Rh(0) and Rh(3+). The fraction of Rh metal linearly increased with photoirradiation time and saturated after 90 min of photoirradiation. The coordination number (Rh-Rh pair) was evaluated by the curve fitting of the Rh-Rh scattering at 2.45 A in the Fourier transforms (FT) of extended XAFS (EXAFS) spectra. The coordination number linearly increased with photoirradiation time and attained a constant value of 10 after 90 min of photoirradiation. This value is lower than that for the Rh foil (12). These suggest the formation of fine Rh metal nanoparticles on TiO(2). In addition, the diminution rate of Rh(3+) as determined by ICP analysis was in good agreement with the increased rates for the fraction of Rh metal particles estimated by XANES spectra and the coordination number (Rh-Rh pair) evaluated by FT-EXAFS spectra. This result strongly supports the fact that electrons generated by charge separation reduce the Rh(3+) precursor to an Rh metal particle at a moment in time and at a constant rate. The Rh particles do not grow in incremental steps, but Rh particles with a uniform size appear one after another on the surface.

Application of organo-nanoclay as a solid sorbent for rhodium complex separation and preconcentration

An organo-nanoclay is used as a new, easily accessible, and stable solid sorbent for the preconcentration of trace amounts of rhodium ions from aqueous solution, this followed by its determination by flame atomic absorption spectrometry (FAAS). Rh(III) ion was first complexed with 2,3,5,6-tetra(2-pyridyl) pyrazine (TPPZ) at pH values between 3.0 and 4.7, and then the complex was then adsorbed onto the nanoclay. The rhodium ions were eluted from the sorbent with HCl. The rhodium in the effluent was determined by FAAS. The linear analytical range is between 0.14 ng mL−1 and 20.0 μg mL−1 in the initial solution, the relative standard deviation at 2.0 μg mL−1 of rhodium is 2.6% (n = 8), the detection limit is 0.03 ng mL−1, and the preconcentration factor is 140. Experimental parameters including the pH, eluent type, interference by other ions and breakthrough volume were optimized. The method was applied to the determination of rhodium in water, road dust and synthetic samples.

Transition metal complexes of 2-formylpyridinethiosemicarbazone (HFpyTSC) and X-ray crystal structures of [Pd(FpyTSC)(PPh 3)]PF 6 and [Pd(FpyTSC)(SCN)

The syntheses of five new complexes of the 2-formylpyridinethiosemicarbazone ligand (HFpyTSC) with Pd(II) and Rh(III) ions are described, viz., [Pd(FpyTSC)(PPh 3)]PF 6, [Pd(FpyTSC)(SCN)], [Pd(FpyTSC)Br], [Pd(HFpyTSC) 2]Br 2 and [Rh(FpyTSC)(PPh 3) 2Cl]ClO 4. The formulation of the complexes is discussed in terms of their elemental analyses and IR, Raman, NMR ( 1H, 13C and 31P), mass and electronic spectra. The X-ray crystal structures of [Pd(FpyTSC)(PPh 3)]PF 6 and [Pd(FpyTSC)(SCN)] show that the HFpyTSC ligand coordinates to the central Pd(II) ion in a planar conformation through the pyridyl nitrogen, the azomethine nitrogen and the deprotonated thiol sulphur atom. Thus, HFpyTSC is a versatile ligand that usually acts as a mononegative tridentate ligand bonding through N py, N C N and C–S − while, in the case of [Pd(HFpyTSC) 2]Br 2, it behaves as a neutral bidentate ligand via N C N and C S.

Adsorption of Rh(III) complexes from chloride solutions obtained by leaching chlorinated spent automotive catalysts on ion-exchange resin Diaion WA21J

It was found that Rh, Pd and Pt contained in the spent ceramic automotive catalysts could be effectively extracted by dry chlorination with chlorine. In order to concentrate Rh(III) ions contained in the chloride solutions obtained, thermodynamic and kinetics studies for adsorption of Rh(III) complexes from the chloride solutions on an anionic exchange resin Diaion WA21J were carried out. Rh, Pd, Pt, Al, Fe, Si, Zn and Pb from the chloride solution could be adsorbed on the resin. The distribution coefficients ( K d) of Rh(III) decreased with the increase in initial Rh(III) concentration or in adsorption temperature. The isothermal adsorption of Rh(III) was found to fit Langmuir, Freundlich and Dubinin–Kaganer–Radushkevich models under the adsorption conditions. The maximum monolayer adsorption capacities Q max based on Langmuir adsorption isotherms were 6.39, 6.61 and 5.81 mg/g for temperatures 18, 28 and 40 °C, respectively. The apparent adsorption energy of Rh was about −7.6 kJ/mol and thus Rh(III) adsorption was a physical type. The experimental data obtained could be better simulated by pseudo-first-order kinetic model and the activation energy obtained was 6.54 J/mol. The adsorption rate of Rh(III) was controlled by intraparticle diffusion in most of time of adsorption process.

Elucidation of Metal‐Ion Accumulation Induced by Hydrogen Bonds on Protein Surfaces by Using Porous Lysozyme Crystals Containing RhIIIIons as the Model Surfaces

Metal-ion accumulation on protein surfaces is a crucial step in the initiation of small-metal clusters and the formation of inorganic materials in nature. This event is expected to control the nucleation, growth, and position of the materials. There remain many unknowns, as to how proteins affect the initial process at the atomic level, although multistep assembly processes of the materials formation by both native and model systems have been clarified at the macroscopic level. Herein the cooperative effects of amino acids and hydrogen bonds promoting metal accumulation reactions are clarified by using porous hen egg white lysozyme (HEWL) crystals containing Rh(III) ions, as model protein surfaces for the reactions. The experimental results reveal noteworthy implications for initiation of metal accumulation, which involve highly cooperative dynamics of amino acids and hydrogen bonds: i) Disruption of hydrogen bonds can induce conformational changes of amino-acid residues to capture Rh(III) ions. ii) Water molecules pre-organized by hydrogen bonds can stabilize Rh(III) coordination as aqua ligands. iii) Water molecules participating in hydrogen bonds with amino-acid residues can be replaced by Rh(III) ions to form polynuclear structures with the residues. iv) Rh(III) aqua complexes are retained on amino-acid residues through stabilizing hydrogen bonds even at low pH (approximately 2). These metal-protein interactions including hydrogen bonds may promote native metal accumulation reactions and also may be useful in the preparation of new inorganic materials that incorporate proteins.

Noble Metal Ionic Catalysts

Because of growing environmental concerns and increasingly stringent regulations governing auto emissions, new more efficient exhaust catalysts are needed to reduce the amount of pollutants released from internal combustion engines. To accomplish this goal, the major pollutants in exhaust-CO, NO(x), and unburned hydrocarbons-need to be fully converted to CO(2), N(2), and H(2)O. Most exhaust catalysts contain nanocrystalline noble metals (Pt, Pd, Rh) dispersed on oxide supports such as Al(2)O(3) or SiO(2) promoted by CeO(2). However, in conventional catalysts, only the surface atoms of the noble metal particles serve as adsorption sites, and even in 4-6 nm metal particles, only 1/4 to 1/5 of the total noble metal atoms are utilized for catalytic conversion. The complete dispersion of noble metals can be achieved only as ions within an oxide support. In this Account, we describe a novel solution to this dispersion problem: a new solution combustion method for synthesizing dispersed noble metal ionic catalysts. We have synthesized nanocrystalline, single-phase Ce(1-x)M(x)O(2-delta) and Ce(1-x-y)Ti(y)M(x)O(2-delta) (M = Pt, Pd, Rh; x = 0.01-0.02, delta approximately x, y = 0.15-0.25) oxides in fluorite structure. In these oxide catalysts, Pt(2+), Pd(2+), or Rh(3+) ions are substituted only to the extent of 1-2% of Ce(4+) ion. Lower-valent noble metal ion substitution in CeO(2) creates oxygen vacancies. Reducing molecules (CO, H(2), NH(3)) are adsorbed onto electron-deficient noble metal ions, while oxidizing (O(2), NO) molecules are absorbed onto electron-rich oxide ion vacancy sites. The rates of CO and hydrocarbon oxidation and NO(x) reduction (with >80% N(2) selectivity) are 15-30 times higher in the presence of these ionic catalysts than when the same amount of noble metal loaded on an oxide support is used. Catalysts with palladium ion dispersed in CeO(2) or Ce(1-x)Ti(x)O(2) were far superior to Pt or Rh ionic catalysts. Therefore, we have demonstrated that the more expensive Pt and Rh metals are not necessary in exhaust catalysts. We have also grown these nanocrystalline ionic catalysts on ceramic cordierite and have reproduced the results we observed in powder material on the honeycomb catalytic converter. Oxygen in a CeO(2) lattice is activated by the substitution of Ti ion, as well as noble metal ions. Because this substitution creates longer Ti-O and M-O bonds relative to the average Ce-O bond within the lattice, the materials facilitate high oxygen storage and release. The interaction among M(0)/M(n+), Ce(4+)/Ce(3+), and Ti(4+)/Ti(3+) redox couples leads to the promoting action of CeO(2), activation of lattice oxygen and high oxygen storage capacity, metal support interaction, and high rates of catalytic activity in exhaust catalysis.

Characterization of Rh/Al2O3 catalysts after calcination at high temperatures under oxidizing conditions by luminescence spectroscopy and catalytic hydrogenolysis

Rhodium/alumina catalysts with Rh loadings of 0.01–0.5wt.% with substantially different thermal stability of supports with respect to phase transformation to corundum were studied. It was shown that the stability of alumina support with respect to its transformations to corundum is one of the important factors accounting for irreversible deactivation of Rh/Al2O3 catalysts. We used laser-induced luminescence (LIL) of Cr3+ impurity and Rh3+ in α-Al2O3 and XRD for studying catalysts with different calcination temperatures. Catalytic ethane hydrogenolysis was used as a test for Rh loading on the catalyst surface. This method reliably detects Rh ions on the surface starting from concentrations as low as 0.01%. The results of LIL spectroscopy indicated that in all cases Rh3+ ions were incorporated in the bulk of the newly formed α-Al2O3 phase, and quite possible can initiates the formation of the corundum phase in catalysts with high-thermal stability.

Complexes of hydrophilic triphenylphosphines modified with gem-bis(phosphonate) moiety. An unusual simultaneous cis and trans arrangements in the Pt(ii) dinuclear complex

New triphenylphosphines substituted with the gem-bis(phosphonate) moiety in the form of ethyl esters, tetraethyl [4-(diphenylphosphanyl)benzyl]methylene-bis(phosphonate) (2a) and octaethyl bis[4-(diphenylphosphanyl)benzyl]methylene-bis(phosphonate) (2b), and the corresponding free acids 3a and 3b were prepared by a multi-step synthesis and characterized by multinuclear NMR spectroscopy and mass spectrometry. The ester ligands 2a and 2b were conveniently purified through their borane adducts. The X-ray structure of 2b x 2BH3 x H2O was determined. Coordination properties of new ligands towards Rh(I), Pd(II) and Pt(II) ions were studied. 1H, 31P and 195Pt NMR spectroscopy showed that ligands 2a and 3a form the expected [RhCl(eta2:eta2-cod)(L)] (cod = cycloocta-1,5-diene) and [MCl2(L)2] (M = Pd, Pt) complexes. The compounds 2b and 3b behave as bridging bidentate ligands forming dinuclear complexes of the {[RhCl(eta2:eta2-cod)]2(mu-L-kappa2P,P')} and [M2Cl4(mu-L-kappa2P,P')2] (M = Pd, Pt) type. These findings are consistent with mass spectrometry and far-IR and Raman spectroscopy results. X-Ray structures of trans-[PdCl2(2a-kappaP)2] and cis,trans-[Pt2Cl4(mu-2b-kappa2P,P)2] were determined; the dinuclear complex exhibits a different arrangement on the Pt(II) centres which was observed for the first time in the solid state. Salts of complexes of the free acid 3a are highly soluble in water.

Photocatalytic H2 evolution by layered perovskite Ca3Ti2O7 codoped with Rh and Ln (Ln = La, Pr, Nd, Eu, Gd, Yb, and Y) under visible light irradiation

Layered perovskite Ca3Ti2O7 codoped with Rh and Ln (Ca3-xLnxTi1.9Rh0.1O7; Ln = La, Pr, Nd, Eu, Gd, Yb, and Y; 0 ≤ x ≤ 0.15) was synthesized by a conventional solid-state reaction to investigate the effects of Rh and Ln codoping on the photocatalytic activity. Rh and Ln-codoped Ca3Ti2O7 exhibited a higher photocatalytic activity than Rh-doped Ca3Ti2O7 for H2 production from an aqueous methanol solution under visible light irradiation (λ > 420 nm). In addition, the induction period for H2 production was shortened by codoping with Rh and Ln. The codoped elements helped control the oxidation state of Rh ions and suppressed the formation of oxygen defects, improving the activity of the Rh-doped Ca3Ti2O7 photocatalyst.

Separation and Optical Resolution of a Pair of atrop Diastereomers of the Octahedral Rhodium(III) Complex with a Nine-Membered S,S-Chelate Ring

Treatment of fac-[Rh(aet) 3] (aet = 2-aminoethanethiolate) with 2,2'-bis(bromomethyl)-1,1'-biphenyl gave a mononuclear rhodium(III) complex with a nine-membered S, S-chelate ring, fac-[Rh(aet)(L)] (2+) ([ 1] (2+), L = 2,2'-bis(2-aminoethylthiomethyl)-1,1'-biphenyl). Complex [ 1] (2+) afforded a pair of atrop diastereomers, Delta SS( S ax)/Lambda RR( R ax)-[ 1] (2+) ([ 1a] (2+)) and Delta SS( R ax)/Lambda RR( S ax)-[ 1] (2+) ([ 1b] (2+)), which involves the axial chirality ( R ax/ S ax) about a biphenyl moiety of L, besides the central chirality (Delta/Lambda) about a Rh (III) ion bound by two asymmetric ( R/ S) thioether donors. The atrop diastereomers ([ 1a] (2+) and [ 1b] (2+)) were successfully separated, isolated, and optically resolved, and the circular dichroism (CD) contribution from the axial chirality was evaluated by CD spectral analyses.

Probing the Photoexcited States of Rhodium Corroles by Time-Resolved Q-Band EPR. Observation of Strong Spin−Orbit Coupling Effects

The photoexcited states of two 5,10,15-tris(pentafluorophenyl)corroles (tpfc), hosting Rh(III) in their core, namely Rh(pyr)(PPh 3)(tpfc) and Rh(PPh 3)(tpfc), have been studied by time-resolved electron paramagnetic resonance (TREPR) combined with pulsed laser excitation. Using the transient nutation technique, the spin polarized spectra are assigned to photoexcited triplet states. The spectral widths observed for the two Rh(III) corroles crucially depend on the axial ligands at the Rh(III) metal ion. In case of Rh(PPh 3)(tpfc), the TREPR spectra are found to extend over 200 mT, which exceeds the spectral width of non-transition-metal corroles by more than a factor of 3. Moreover, the EPR lines of the Rh(III) corroles are less symmetric than those of the non-transition-metal corrroles. The peculiarities in the TREPR spectra of the Rh(III) corroles can be rationalized in terms of strong spin-orbit coupling (SOC) associated with the transition-metal character of the Rh(III) ion. It is assumed that SOC in the photoexcited Rh(III) corroles effectively admixes metal centered (3)dd-states to the corrole centered (3)pipi*-states detected in the TREPR experiments. This admixture leads to an increased zero-field splitting and a large g-tensor anisotropy as manifested by the excited Rh(III) corroles.

Synergistic effect of binary component ligands in chiral catalyst library engineering for enantioselective reactions

This article highlights our recent efforts in the development of highly efficient and cost-effective chiral catalysts for asymmetric reactions through a combinatorial approach by assembling the component ligands (at least one of which is in non-racemic form, while the other might be optically pure, racemic or achiral) with metal ions to generate modular chiral catalyst libraries. The synergistic effect of the binary ligands in terms of both enantioselectivity and activity of the catalysis has been observed in a variety of catalyst systems, including catalysts containing Ti(IV), Zn(II), Rh(I) or Ru(II) ions, for asymmetric hetero-Diels-Alder, carbonyl-ene, alkylation, and hydrogenation reactions, respectively.

Pd ion substituted CeO2: A superior de-NO catalyst to Pt or Rh metal ion doped ceria

Abstract Pd, Pt and Rh ion doped CeO2, Ce1−xMxO2−δ (M = Pd2+, Pt2+, Rh3+) were synthesized by solution combustion synthesis method and the deNOx activity was investigated by NO + CO reaction. Ionically dispersed Pd in CeO2 was found to have better catalytic activity than ionically dispersed Pt or Rh in CeO2. High rates of NO conversion and high selectivity of N2 is observed over Ce0.98Pd0.02O2−δ. A bi-functional reaction mechanism is proposed, which fits very well with the experimental results. The oxide ion vacancy present in the CeO2 matrix seems to play an important role for product selectivity and high rate of reaction.

Effect of the anchorage of Rh(III) ions by imidazoline type ligands on the location of Rh 0 particles within the calcined form of the SBA-15 support

Two series of mesoporous SBA-15 silica materials with N-propyl-4,5-dihydroimidazole groups have been prepared. It is shown that up to 15% of the silicon atoms can be provided by the organosilane precursor, N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole (Si-Imi), either by one-pot (SBA-OP x%) or post-synthesis (SBA-GR x%) procedures. The hybrid solids were characterised by elemental analysis, XRD, TEM, nitrogen sorption isotherms, 29Si or 13C NMR, FTIR and UV–Vis spectroscopy. Higher apparent yields of Si-Imi incorporation were obtained in the grafting mode. However, a large number of ethoxysilane groups remain unaltered in comparison to those of SBA-OP x% solids. Furthermore, post-synthesis conditions favour the deposition of large fractions of the organic function on the external surface. Well structured SBA-15 type solids with a large proportion of imidazoline groups inside the pores were obtained by the co-condensation method provided that TEOS was pre-hydrolysed. Complexes of rhodium(III) with imidazoline ligands supported by SBA-GR or OP 5% were successfully tested as precursors of small rhodium(0) nanoparticles. Their location in the two solids (Rh 0-SBA-Gr 5% and Rh 0-SBA-OP 5%), obtained by a two-step calcination/reduction process, appears to reflect that of the ligands. Particles generated in the reference solids prepared by the impregnation of SBA-15 with rhodium(III) in the presence of NH 3 are not included in the pores. The different materials were tested in the room-temperature hydrogenation of styrene and anisole in 1 atm H 2. Their catalytic activities vary in the following order: Rh 0-SBA-NH 3 ≪ Rh 0-SBA-GR 5% < Rh 0-SBA-OP 5%.

Catalysis by Ir(III), Rh(III) and Pd(II) metal ions in the oxidation of organic compounds with H2O2

AbstractCatalytic activities of three transition metals, as iridium (III) chloride, rhodium (III) chloride and palladium (II) chloride, were compared in the oxidation of six aromatic aldehydes (benzaldehyde, p‐chloro benzaldehyde, p‐nitro benzaldehyde, m‐nitro benzaldehyde, p‐methoxy benzaldehyde and cinnamaldehyde), two hydrocarbons (viz. (anthracene and phenanthrene)) and one aromatic and one cyclic alcohol (cyclohexanol and benzyl alcohol) by 50% H2O2. The presence of traces (substrate: catalyst ratio equal to 1:62500 to 1:1961) of the chlorides of iridium(III), rhodium(III) and palladium(II) catalyze these oxidations, resulting in good to excellent yields. It was observed that in most of the cases palladium(II) chloride is the most efficient catalyst. Conditions for the highest and most economical yields were obtained. Deviation from the optimum conditions decreases the yields. Oxidation in aromatic aldehydes is selective at the aldehydeic group only and other groups remain unaffected. This new, simple and economical method, which is environmentally safe, also requires less time. Reactive species of catalysts, existing in the reaction mixture are also discussed. Copyright © 2007 John Wiley &amp; Sons, Ltd.

CO2 reforming of methane over argon plasma reduced Rh/Al2O3 catalyst: a case study of alternative catalyst reduction via non-hydrogen plasmas

An argon glow discharge plasma was used to reduce RhCl3 impregnated Al2O3 powder at room temperature. The obtained sample was characterized by chemisorption, X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) equipped with an energy dispersion X-ray spectrometer (EDX). XRD and EDX analyses confirmed that Rh ions were reduced into metallic Rh during the plasma reduction. TEM analysis revealed that the argon plasma reduction induces a high dispersion of Rh nano-particles. The average particle size of Rh is 1.2 nm, estimated by chemisorption. For the CO2 reforming of methane, the plasma reduced Rh/Al2O3 shows comparable activity to a conventional hydrogen reduced catalyst. The value of the standard electrode potential can be employed for the assessment of reducibility of metal ions. The catalyst reduction using argon glow discharge plasma at room temperature will provide a promising alternative to hydrogen reduction for catalyst preparation.

Rhodium deposition onto a 4-mercaptopyridine SAM on Au(1 1 1)

The application of a recently developed method for the deposition of Pd and Pt on top of a SAM, has been successfully extended to Rh, thus proving the versatility of the new concept. Experimental evidence from cyclic voltammetry, in situ STM and ex situ X-ray photoemission spectroscopy is presented for the deposition of monoatomic high rhodium islands onto a 4-mercaptopyridine self-assembled monolayer on a Au(1 1 1) electrode. By repetitive complexation of the Rh ions to the ring-nitrogen and reduction in a Rh-ion free solution, an almost completely covered SAM is obtained. The consequences of making contacts for molecular electronics are briefly discussed.