Fullerene‐based ruthenium catalysts in cinnamaldehyde hydrogenation

Ruthenium on fullerenes and ruthenium and palladium on activated carbon were compared for their catalytic activity and selectivity in cinnamaldehyde hydrogenation. The fullerene support had a marked effect on the selectivity, even though the fullerenes themselves showed no catalytic activity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Iron versus ruthenium oxidation in 1,1′-bis(diphenylphosphino)ferrocene–ruthenium(II) complexes: EPR and spectroelectrochemical evidence

Oxidation of [Cp^*RuH(dppf)] (1), dppf=1,1′-bis(diphenylphosphino)ferrocene, and [(Cym)RuCl(dppf)](PF₆) (2), Cym=p-cymene, occurs at ruthenium for 1 but yields a ferrocenium species for compound 2.     

Thermally stable pseudo-third-generation Grubbs ruthenium catalysts with pyridine–phosphinimine ligand

The ligand precursors 2-(R₃PN)CH₂Py (R = Ph(1a), Cy(2a)) were prepared from reaction of pyridine azide with various phosphine ligands. Reaction of 1a or 2a with RuCl₂(CHPh)(Py)₂(H₂IMes) (Py = pyridine) afforded the ruthenium alkylidene complex RuCl₂(CHPh)(PyCH₂(NPR₃))(H₂IMes) (R = Ph(1), Cy(2)). Both catalysts showed good thermal stability and latent behavior toward RCM and ROMP reactions.     

Selective oxidation of cyclohexene catalyzed by polymer-bound ruthenium–2,2′-bipyridine complexes

Cyclohexene was oxidized to 2-cyclohexen-1-ol and 2-cyclohexen-1-one by atmospheric pressure of molecular oxygen in the presence of linear polystyrene-bound-2,2′-bipyridine–ruthenium complexes in the absence of solvent at 70±5°C selectively. The alcohol/ketone molar ratio of the products can be adjusted by employing different additives or by varying the reaction pH.     

A high-performance three-dimensional micro supercapacitor based on ripple-like ruthenium oxide–carbon nanotube composite films

A micro-supercapacitor with a three-dimensional configuration has been fabricated using an inductively coupled plasma etching technique. A ruthenium oxide–carbon nanotube (CNT) composite with a ripple-like morphology is successfully synthesized using a cathodic deposition technique while using silica-based three-dimensional microstructures as a template. The desired network of carbon nanotubes in the composite facilitates electrolyte penetration and proton exchange/diffusion. A single three dimensional microelectrode is studied using cyclic voltammetry, and a specific capacitance of 272 mF·cm⁻² is observed at 5 mV s⁻¹ in a neutral Na₂SO₄ solution. The accelerated cycle life is tested at 80 mV s⁻¹, and a satisfactory cyclability is observed. When placed on a chip, the symmetric cell exhibits good supercapacitor properties, the specific capacitance up to 37.23 mF cm⁻² and specific power density up to 19.04 mW cm⁻² were obtained at 50 mA cm⁻².     

Synthesis and evaluation of a ruthenium–copper oxide/silica catalyst derived from microemulsion processing

Bimetallic Ru–Cu catalysts supported on SiO₂ have been synthesized in microemulsions using sodium metasilicate (Na₂SiO₃), copper nitrate (Cu(NO₃)_2·3H₂O) and ruthenium chloride (RuCl₃) at 28 °C. The microemulsion system consists of sodium 1,4‐bis(2‐ethylhexyl) sulfosuccinate (AOT) and sodium dodecyl sulphate (SDS), cyclohexane, and an aqueous solution of sodium metasilicate or metal salts. The catalysts have been characterized by XPS, EDX/SEM with line scanning and they possess a very narrow pore size distribution (around 38 Å) and relatively high specific surface areas (around 400 m²/g). The catalytic results of the N₂O decomposition reveal that higher conversions of N₂O can be achieved by the catalysts synthesized from the microemulsion process at lower temperatures (around 400 °C).     

Catalytic oxygenation ofβ,γ-unsaturated 3-ketosteroids in the presence of ruthenium tetramesitylporphyrin complexes

Cholest-5-ene-3-one1 is oxidized by air at room temperature in the presence of trans-di-oxoruthenium(VI)tetramesitylporphyrin Ru(O)₂ (tmp) to a mixture of the 6- and 6-alcohols3 and4, and of the enedione5. Similar results are obtained in the presence of carbonylruthenium(II)tetramesitylporphyrin Ru(CO) (tmp) as catalyst. Iron(III) and manganese(III) tetramesitylporphyrins are weakly active or inactive as catalysts for the aerobic oxidation of1. Similarly, 17-acetoxy-estr-5(10)-ene-3-one2 is oxidized to 17-acetoxy-10-hydroxyestr-4-ene-3-one7 in 42% yield in a highly-stereoselective manner in the presence of Ru(O)₂ (tmp).     

The partial gas‐phase hydrogenation of benzene to cyclohexene on supported and coated ruthenium catalysts

The conversion of benzene to useful products such as cyclohexene is of industrial interest because of the expected surplus of benzene due to its substitution in gasoline by other nonpolluting components in the next years. Therefore, the partial gasphase hydrogenation of benzene to cyclohexene at atmospheric pressure was performed in order to develop catalysts as an alternative to those used in liquidphase hydrogenation. Two types of rutheniumcontaining catalysts were investigated, viz. supported catalysts with different support materials and coated catalysts with electrolytically formed alumina as support. In order to yield the desired cyclohexene the presence of methanol as a reaction modifier was necessary in the gas phase during the reaction. The hydrogenation on supported Ru catalysts gave selectivities of about 35%, while on coated Ru catalysts selectivities up to 45% were obtained at conversion degrees of 5%. Improved catalyst performance, especially higher selectivity and yield, was obtained at increased partial pressure of methanol and hydrogen and by addition of copper as second metal in the oxide layer of the coated catalysts.     

Fischer–Tropsch synthesis. Effect of CO pretreatment on a ruthenium promoted Co/TiO2

The effect of pretreatment, using hydrogen or carbon monoxide, on the activity and selectivity of a ruthenium promoted cobalt catalyst (Ru(0.20 wt%)/Co(10 wt%)/TiO₂) during Fischer–Tropsch (FT) synthesis was studied in a continuous-stirred tank reactor (CSTR). The hydrogen reduced catalyst exhibited a high initial synthesis gas conversion (72.5%) and reached steady state after 40 h on stream, after which the catalyst deactivated slightly with time on stream. The carbon monoxide reduced catalyst reached steady state quickly and showed a lower activity and a good stability. Methane selectivity on the carbon monoxide reduced catalyst was 15–20% (carbon base), much higher than that on the hydrogen reduced catalyst (5–10%). Carbon monoxide regeneration increased the activity on the hydrogen reduced catalyst; however, it did not have significant effect on the carbon monoxide reduced catalyst.     

The formation of σ-phenylethynyl and σ-diphenylbutenynyl complexes in the reaction of σ-alkenyl ruthenium(II) complexes with phenylacetylene. The X-ray structure of a ruthenium(II) complex containing a σ-phenylethynyl ligand

Ruthenium(II) complexes containing both σ-alkenyl and η²-carboxylate ligands Ru(O₂CR²)(CHCHR¹)(CO)(PPh₃)₂ (R¹^tBu, Ph; R²=CHCHCHCHCH₃) react with phenylacetylene in two stages. Their reaction with an equivalent amount of the alkyne led to the formation of a σ-alkynyl-containing ruthenium(II) complex Ru(O₂CR²)(CCPh)(CO)(PPh₃)₂ (R²=CHCHCHCHCH₃), the molecular structure of which was established by X-ray diffraction. This σ-alkynyl complex then reacts with phenylacetylene to form a σ-butenynyl-containing compound Ru(O₂CR²)(C(CCPh)CPhH)(CO)(PPh₃)₂ (R²=CHCHCHCHCH₃). Both reactions support the key role of alkynyl ligands in the dimerization of alkynes.     

A study of sodium promotion in Fischer–Tropsch synthesis: electrochemical control of a ruthenium model catalyst

Sodium supplied to the surface of a ruthenium thin film catalyst by electro‐pumping from a solid electrolyte (Na–β″‐alumina) strongly alters the activity and selectivity of the latter in Fischer–Tropsch synthesis. Thus the range of utility of electrochemical promotion has been broadened, this being the first application to a C–C bond forming reaction. The methanation rate is strongly suppressed resulting in a marked increase in selectivity towards C₂–C₄ hydrocarbons, accompanied by an increase in the alkene : alkane ratio. The results obtained with this model system, including the “C₂ anomaly”, are in close agreement with those found for classically promoted conventional dispersed catalysts. Alkali substantially increases the probability of chain growth and CO dissociation is not rate controlling; mechanistic implications are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrogenation of succinic acid to γ-butyrolactone (GBL) over ruthenium catalyst supported on surfactant-templated mesoporous carbon

Mesoporous carbon support (denoted as STC) was prepared by a surfactant-templating method for use as a support for ruthenium catalyst. For comparison, porous carbon (denoted as TC), spherical carbon (denoted as SC), and microporous carbon (denoted as DC) supports were also prepared by a templating method, hydrothermal method, and direct carbonization method, respectively. Ruthenium catalysts supported on carbon supports (Ru/C) were then prepared by an incipient wetness impregnation method. The Ru/C (Ru/DC, Ru/SC, Ru/TC, and Ru/STC) catalysts were characterized by FE-SEM, N₂ adsorption–desorption isotherm, BET, XRD, and HR-TEM analyses. Liquid-phase hydrogenation of succinic acid to γ-butyrolactone (GBL) was carried out over Ru/C catalysts in a batch reactor. In the hydrogenation of succinic acid, Ru/STC catalyst showed the highest conversion of succinic acid and the highest yield for GBL. The superior catalytic performance of Ru/STC catalyst compared to the other catalysts (Ru/TC, Ru/SC, and Ru/DC) was due to fine dispersion of ruthenium (ruthenium surface area). Thus, ruthenium surface area played a key role in determining the catalytic performance in the liquid-phase hydrogenation of succinic acid to GBL over Ru/C catalysts.     

Carbonyl and chloro complexes of ruthenium(II) containing 3,3′-diester-2,2′-bipyridyl ligands

A series of 3,3′-dialkoxycarbonyl-2,2′-bipyridines (alkyl=Me, Et, i-Pr, i-Bu) has been prepared in good yield from 1,10-phenanthroline. The synthesis and characterization of the corresponding trans-(Cl)-Ru(L)(CO)₂Cl₂ and cis-Ru(L)₂Cl₂ complexes are described.     

Temperature dependence of dual emission in ruthenium(II) complexes containing 3,3′-bi-1,2,4-triazine derivatives

Three new ruthenium(II) polypyridyl complexes with highly π-deficient ligands, [Ru(bpy)₂(btm)]²⁺ (1), [Ru(bpy)₂(btb)]²⁺ (2) and [Ru(bpy)₂(btp)]²⁺ (3) (bpy = 2,2′-bipyridine, btm = 3,3′-bis(5,6-dimethyl-1,2,4-triazine, btb = 3,3′-bis(5,6-diphenyl-1,2,4-triazine, btp = 3,3′-bis(phenanthro[9,10-e][1,2,4]triazine) were synthesized and characterized. Electrochemical data together with molecular calculations show that the first redox process in these complexes is not bpy based. Complexes 1, 2 and 3 display luminescence in ethanol/methanol (4/1, V/V) at 80 K, and all three complexes exhibit a temperature switch from single (150 K) to dual (80 K) emission behavior.     

Electrochemical behaviour of olefins: oxidation at ruthenium–titanium dioxide and iridium–titanium dioxide coated electrodes

The electrocatalytic behaviour of a series of olefins was studied on thermally prepared Ti/MO₂ and Ti/M_0.3Ti_0.7O₂ electrodes (M = Ru, Ir) in 1.0 M HClO₄ in mixed solvent (AN/H₂O, 40/60v/v). The voltammetric investigation was limited to the potential region preceding the OER on these electrodes materials (E < 1.2 V vs SSCE). Aliphatic olefins (isophorone and cyclohexene) are inactive while the aromatic olefins show a single (safrole) or two (isosafrole) oxidation peaks. The overall catalytic activity of these electrode materials is about the same for both substrates. However, when morphological effects (differences in electrode surface area) are taken into account, normalizing the geometric current density (or faradaic charge) per surface site activity, a slightly better efficiency of the active surface sites is observed for Ru-based electrodes when compared to the equivalent Ir-based materials. Partial substitution of the noble metal catalysts by TiO₂ results in a synergetic effect depressing the efficiency of the active surface sites of the TiO₂-stabilized electrocatalysts. The decrease with potential cycling of the substrate oxidation current is attributed to dimeric/polymeric film formation blocking the electrode surface. Reflectance and FTIR spectroscopy as well as ohmic resistance data support film formation.     

Optical and photoelectrochemical properties of a TiO2 thin film doped with a ruthenium–tungsten bimetallic complex

Optical and photoelectrochemical (PEC) properties of a TiO₂ thin film electrode doped with a new variation of ruthenium–(4,4′dimethyl-2,2′-bipyridine)–isothiocyanato–tungsten[bis-(phenyl-1,2-ethilenodithiolenic)] bimetallic complex (BM) were investigated. Physical adsorption process was used to immobilise the BM on the TiO₂ thin film. Crystalline structure and surface morphology of the thin films were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) techniques. N3 commercial dye was also used as a dopant to the TiO₂ films for comparison. Light absorption spectra and bandgap energy of the thin films were determined using UV–vis spectroscopy. Light absorption of the TiO₂ thin film doped with BM was better than the TiO₂ doped with the N3 commercial dye. Band edges of the TiO₂ thin film and the BM were determined via cyclic voltammetry (CV) measurements. Top-edge of the BM valence band (VB) was more positive than the bottom edge of the conduction band (CB) of the TiO₂ film (vs. NHE). PEC analysis indicated that photocurrent of TiO₂ doped with the BM electrode was higher than TiO₂ doped with the N3 in the beginning of illumination process, but the performance was defeated after a while. Based on the optical properties and the PEC analyses, BM has potential to be used as dye sensitisers for a PEC cell.     

Fischer–Tropsch synthesis: effect of small amounts of boron,ruthenium and rhenium on Co/TiO2 catalysts

The effect of the addition of small amounts of boron, ruthenium and rhenium on the Fischer–Tropsch (F–T) catalyst activity and selectivity of a 10 wt.% Co/TiO₂ catalyst has been investigated in a continuously stirred tank reactor (CSTR). A wide range of synthesis gas conversions has been obtained by varying space velocities over the catalysts. The addition of a small amount of boron (0.05 wt.%) onto Co/TiO₂ does not change the activity of the catalyst at lower space times and slightly increases synthesis gas conversion at higher space times. The product selectivity is not significantly influenced by boron addition for all space velocities investigated. Ruthenium addition (0.20 wt.%) onto Co/TiO₂ and CoB/TiO₂ catalysts improves the catalyst activity and selectivity. At a space time of 0.5 h-g cat./NL, synthesis gas conversion increases from 50–54 to 68–71% range and methane selectivity decreases from 9.5 to 5.5% (molar carbon basis) for the promoted catalyst. Among the five promoted and non-promoted catalysts, the rhenium promoted Co/TiO₂ catalyst (0.34 wt.% Re) exhibited the highest synthesis gas conversion, and at a space time of 0.5 h-g cat./NL, synthesis gas conversion was 73.4%. In comparison with the results obtained in a fixed bed reactor, the catalysts displayed a higher F–T catalytic activity in the CSTR.     

Influence of Mg and Ce addition to ruthenium based catalysts used in the selective hydrogenation of α,β-unsaturated aldehydes

Ce and Mg were used as promoters in two series of Ru based catalysts supported on alumina (Al₂O₃) and activated carbon (AC). The catalysts were characterized by H₂ chemisorption and temperature-programmed reduction (TPR), and studied in the crotonaldehyde (gas phase) and the citral (liquid phase) hydrogenations. Addition of MgO and CeO₂ decreased the catalytic activity in crotonaldehyde and citral hydrogenations. With regard to the selectivity towards unsaturated alcohols, similar trends were observed for the two reactions. MgO did not influence the selectivity, but CeO₂ increased the selectivity to unsaturated alcohols, especially on carbon supported catalyst. Bulk CeO₂ and Ce/AC catalyst showed low activity but very high selectivity (93 and 100%, respectively) to the unsaturated alcohols. Based on these results and the calorimetric experiments of CO adsorption it was suggested that defect sites on the surface of the promoter are the active and highly selective sites for unsaturated aldehydes due to their influence on the CO bond activation.     

Methanation of carbon dioxide over mesoporous Ni–Fe–Ru–Al2O3 xerogel catalysts: Effect of ruthenium content

Mesoporous nickel (35 wt%)–iron (5 wt%)–ruthenium (x wt%)–alumina xerogel (denoted as 35Ni5FexRuAX) catalysts with different ruthenium contents (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) were prepared by a single-step sol–gel method for use in the methane production from CO₂ and H₂. Conversion of CO₂, yield for CH₄, metal surface area, and the amount of desorbed carbon dioxide of the catalysts showed volcano-shaped trends with respect to ruthenium content. Experimental results revealed that metal surface area and the amount of desorbed carbon dioxide of 35Ni5FexRu catalysts were well correlated with conversion of CO₂ and yield for CH₄.     

Ion exchange and charge transport properties of polymeric tris(4-vinyl-4′-methyl-2,2′-bipyridine) ruthenium(II) films

Multiply charged electroactive anions [IrCl ₆ ^2? , Fe(CN) ₆ ^3? , and W(CN) ₈ ^4? ] are electrostatically incorporated in polymeric films of tris(4-vinyl-4′-methyl-2,2′-bipyridine) ruthenium(II) [poly-Ru(vbpy) ₃ ²⁺ ] from aqueous trifluoroacetate solution. Values of apparent diffusion coefficients (D _ct) and heterogenous electron transfer rates (k _et) are measured for these anions as a function of their relative concentration (Γ _M/Γ _Ru) in the film.D _ct andk _et decrease systematically asΓ _M/Γ _Ru increases in a manner that is independent of charge and chemical identity of the ion. This result suggests that a nonchemical process, presumably electrostatic cross-linking, limits diffusional motion and is responsible for the decrease inD _ct andk _et with increasing anion content. Protonated polyvinyl-pyridine films exhibit similar ranges and variations inD _ct andk _et, which suggest similar structures and mechanisms of charge transport for these films and poly-Ru(vbpy) ₃ ²⁺ .