Formation Of RuO2 Research Articles

Titania-Supported Catalysts for Levulinic Acid Hydrogenation: Influence of Support and its Impact on γ-Valerolactone Yield.

A series of titania-supported ruthenium and platinum catalysts was investigated in the levulinic acid hydrogenation towards γ-valerolactone, a key reaction for the catalytic transformation of biomass. It was shown that various morphologies and phases of titania strongly influence the physicochemical and catalytic properties of supported Ru and Pt catalysts in different ways. In the case of the catalyst supported on mixed TiO2 phases, Ru particles are exclusively located on the minority rutile crystallites, whereas such an effect was not observed for platinum. The platinum catalyst activity could be increased when the metal was dispersed on the large surface-area anatase, which was not the case for ruthenium as a result of its agglomeration on this support. The activity of ruthenium on anatase could be increased in two ways: a) when RuO2 formation during catalyst preparation was avoided; b) when pure anatase support material was modified so that it exhibited no microporosity. The obtained results allow a better understanding of the role of the support for Ru and Pt catalysts.

Surface Chemistry on Small Ruthenium Nanoparticles: Evidence for Site Selective Reactions and Influence of Ligands

The reactivity of two classes of ruthenium nanoparticles (Ru NPs) of small size, either sterically stabilized by a polymer (polyvinylpyrrolidone, PVP) or electronically stabilized by a ligand (bisdiphenylphosphinobutane, dppb) was tested towards standard reactions, namely CO oxidation, CO2 reduction and styrene hydrogenation. The aim of the work was to identify the sites of reactivity on the nanoparticles and to study how the presence of ancillary ligands can influence the course of these catalytic reactions by using NMR and IR spectroscopies. It was found that CO oxidation proceeds at room temperature (RT) on Ru NPs but that the system deactivates rapidly in the absence of ligands because of the formation of RuO2. In the presence of ligands, the reaction involves exclusively the bridging CO groups and no bulk oxidation is observed at RT under catalytic conditions. The reverse reaction, CO2 reduction, is achieved at 120 °C in the presence of H2 and leads to CO, which coordinates exclusively in a bridging mode, hence evidencing the competition between hydrides and CO for coordination on Ru NPs. The effect of ligands localized on the surface is also evidenced in catalytic reactions. Thus, styrene is slowly hydrogenated at RT by the two systems Ru/PVP and Ru/dppb, first into ethylbenzene and then into ethylcyclohexane. Selectively poisoning the nanoparticles with bridging CO groups leads to catalysts that are only able to reduce the vinyl group of styrene whereas a full poisoning with both terminal and bridging CO groups leads to inactive catalysts. These results are interpreted in terms of location of the ligands on the particles surface, and evidence site selectivity for both CO oxidation and arene hydrogenation.

Supercapacitive performance of hydrous ruthenium oxide (RuO2 · nH2O) thin films synthesized by chemical route at low temperature

In the present investigation, we report the synthesis of ruthenium oxide (RuO2 · nH2O) thin films by simple chemical bath deposition (CBD) method at low temperature on the stainless steel substrate. The prepared thin films are characterized for their structural and morphological properties by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT–IR) and scanning electron microscopy (SEM). The structural study revealed that the ruthenium oxide thin films are amorphous. Scanning electron microscopy study shows compact morphology with small overgrown particles on the surface of the substrate. FT–IR study confirms the formation of RuO2 · nH2O material. The supercapacitor behaviour of RuO2 · nH2O thin film was studied using cyclic voltammetry (CV) technique in 0 · 5 M H2SO4electrolyte. RuO2 · nH2O film showed maximum specific capacitance of 192 F · g− 1at a scan rate of 20 mV · s− 1. The charge–discharge studies of RuO2 · nH2O carried out at 300 μA · cm− 2current density revealed the specific power of 1 · 5 kW.kg− 1and specific energy of 41 · 6 Wh.kg− 1with 95% coulombic efficiency.

Synthesis and Electrochemical Characterization of RuO<sub>2</sub>·<em>x</em>H<sub>2</sub>O/Graphite Nanosheet Composite Array Electrodes for Supercapacitors

We used electrochemical exfoliation to construct graphite nanosheet(GNS) arrays,in which the varying number of nanosheet layers were parallel to each other and perpendicular to the carbon substrate.Hydrous ruthenium oxide(RuO_2 ? xH_2O) was then loaded directly on the surface of nanosheets using cathodic reduction electrodeposition,resulting in the formation of RuO_2 ? xH_2O/GNS composite array electrodes.Electrochemical measurements showed that the composite array electrodes exhibited excellent capacitive behaviors,and achieved specific capacitance values as high as 4226 F ? m~(-2) in the potential window up to 0.9 V,with a scan rate of 5 mV ? s~(-1) in 0.5 mol ? L~(-1) H_2SO_4 solution.The RuO_2? xH_2O/GNS composite array electrodes showed good cycling abilities,and maintained 94.18%of their maximum performance after 20000 cycles.

Effects of preparation conditions on catalytic activity of Ru/AC catalyst to reduce bromate ion in water

The effects of Ru precursor, Ru loading and calcination conditions on the properties and catalytic activities of ruthenium catalysts supported on activated carbon (Ru/AC) to remove bromate ion in water were investigated. A series of Ru/AC catalysts were prepared by the impregnation method and were characterized. From the examination of X-ray photoelectron spectra, RuO2 was deemed as the major active component on the Ru/AC catalysts to reduce bromate ion. The Ru precursors have significant effect on the activities of Ru/AC catalysts, due mainly to that (NH4)2RuCl6 was prone to generate metallic Ru, while RuCl3·3H2O could form RuO2. It was also found that calcination of Ru/AC in pure nitrogen gas favored the RuO2 formation compared with those calcined in vacuum and 1.5 vol.% H2/N2. The maximum bromate reduction efficiency around 95 % can be successfully achieved by Ru/AC prepared when the Ru loading, calcination temperature and time were 0.1 wt.%, 900 °C, and 3 h, in order, in a pure N2 atmosphere. From the characterization of catalysts, it was found that the excellent performance of Ru/AC would benefit from two aspects: one is that the structure and texture of the support carbon was strengthened during the calcination process, and the other is that an even distribution of RuO2 particles was obtained.

Promotion of Pt–Ru/C catalysts driven by heat treated induced surface segregation for methanol oxidation reaction

Carbon supported Pt–Ru/C (1:1) alloy catalysts supplied by E-TEK are widely used for fuel cell research. Heat treatments in various atmospheres are conducted for the promotion of the methanol oxidation reaction (MOR) and the investigation of the structure–activity relationship (SAR) of the catalysts. The alloy structures, surface compositions, surface species, and electro-catalytic activities of the alloy catalysts are characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV), respectively. The as-received Pt–Ru/C catalysts have a Ru rich in the inner core and Pt rich on the outer shell structure. Thermal treatments on the catalysts induce Ru surface segregation in different extents and thereby lead to their alteration of the alloying degrees. O 2 treatment results in obvious Ru segregation and formation of RuO 2. Catalysts treated in H 2 have the highest I f/ I b value in the CV scans among all samples, indicating the catalysts have the excellent CO de-poisoning ability as evidenced by anodic CO stripping experiments. N 2 treatment may serve as an adjustment process for the surface composition and structure of the catalysts, which can suppress the surface Pt depletion (∼60% Pt on the surface), make the components stable and hence promote the MOR significantly.

ChemInform Abstract: Decomposition of Ruthenium Oxides in Lead Borosilicate Glass.

Behaviors of apparent phase changes of Ru-containing oxides in lead borosilicate glass at high temperature have been investigated using X-ray diffraction and transmission electron microscopy in application to thick-film resistors. During firing of thick films containing Ru oxide powder and lead borosilicate glass frits, apparent phase changes of Ru oxides have been found to occur both ways between ruthenium dioxide and lead ruthenate pyrochlore via decomposition of one phase in glass and subsequent formation of the other. The formation of pyrochlore occurs in a lead-rich form, Pb 2 (Ru 2-x Pb x )O 6.5 , whereas the formation of RuO 2 is characterized by a platelike morphology instead of initial globular morphology. A general tendency is observed that RuO 2 is stable in low-PbO glass compositions and at high temperatures, while Pb 2 (Ru 2-x Pb x )O 6.5 is stable in high-PbO glass compositions and at low temperatures, with the implication that the stability of these phases is dictated by the chemical activity of PbO in the glass melt.

Morphology of RuO2(110) oxide films on Ru(0001) studied by scanning tunneling microscopy

Using scanning tunneling microscopy we have investigated the morphology of RuO2(110) films grown on Ru(0001). The films were prepared by dosing 2 x 10(5) to 1 x 10(6) L of O2 at temperatures between 650 and 850 K. It was found that the films are between 2 and 5 RuO2(110) layers thick, largely independent of the growth conditions. Within the temperature range investigated the perfectness of the films varied significantly. The morphology can be understood according to the habit of RuO2 single crystals, namely, the formation of extended (110), (100), and (101) surfaces. Upon annealing the films decompose by the formation of holes that go down to the metal substrate rather than in a layer-by-layer fashion. The Ru atoms released during decomposition form terraces with shapes similar to the terraces obtained by homoepitaxial metal-on-metal growth. Under the oxidation conditions used, we have not observed suboxides RuOx or the O-Ru-O trilayer that had been postulated to play a role for the RuO2 formation. The partially covered surfaces exclusively showed RuO2 and the known phases of adsorbed O atoms on the metallic Ru.

Free radical reactions at the Ru(0 0 0 1) surface: Atomic oxygen and dissociated NH 3

X-ray photoelectron spectroscopy was used to study the effect of atomic oxygen on Ru(0 0 0 1), and the effect of dissociated ammonia on RuO 2/Ru(0 0 0 1), in UHV conditions at ambient temperature. The Ru(0 0 0 1) surface was exposed, at ambient temperature, to a mixed flux of atomic and molecular oxygen generated by dissociation of O 2 in a thermal catalytic cracker, with ∼45% dissociation efficiency. The detailed study of the XPS spectra shows the formation of a disordered multilayer oxide (RuO 2). No formation of higher oxides of Ru was observed. The formation of RuO 2 proceeded without saturation for total oxygen exposures of up to 10 5 Langmuir, at which point an average oxide thickness of 68 Å was observed. RuO 2 formed by the reaction with atomic oxygen was exposed to a flux of NH x ( x = 1, 2) + H generated by the cracker. The reduction of RuO 2 to Ru metal was observed by XPS. An exposure of 3.6 × 10 2 L of NH x + H, resulted in the observation of adsorbed H 2O and OH, but no evidence of lattice oxide. The chemisorbed species were removed by additional NH x + H exposure. No nitrogen adsorption was observed.

Compatibility of RuO2 electrodes with PZT ceramics

Because of its high electrical conductivity and good diffusion barrier properties ruthenium dioxide (RuO2) is a good electrode material for use with ferroelectric lead zirconate-titanate (PZT) solid solutions. Under certain conditions, RuO2 can react with PZT to form lead ruthenate (Pb2Ru2O6·5) during processing at elevated temperatures resulting in lead depletion from PZT. The standard Gibbs energies of formation of RuO2 and Pb2Ru2O6·5 and activities of components of the PZT solid solution have been determined recently. Using this data along with older thermodynamic information on PbZrO3 and PbTiO3, the stability domain of Pb2Ru2O6·5 is computed as a function of PZT composition, temperature and oxygen partial pressure in the gas phase. The results show PbZrO3-rich compositions are more prone to react with RuO2 at all temperatures. Increasing temperature and decreasing oxygen partial pressure suppress the reaction. Graphically displayed are the reaction zones as a function of oxygen partial pressure and PZT composition at temperatures 973,1173 and 1373 K.

Kinetic studies for the non-isothermal decomposition of un-irradiated and γ-irradiated ruthenium(III) acetylacetonate

Kinetic studies for the non-isothermal decomposition of un-irradiated and γ-irradiated ruthenium(III) acetylacetonate in air were carried out. The results show that the decomposition proceeds in one major step in the temperature range of 150–250 °C with the formation of RuO2 as a final solid residue for un-irradiated Ru(acac)3. For γ -irradiated Ru(acac)3 with 102 KGy total γ-ray dose, the decomposition goes eventually to completion with almost 100% decomposition and proceeds in one major step, which contains four overlapping decomposition stages in the temperature range of 200–320 °C. The kinetics is shown to be non-isothermal, using both model-fitting and model-free approaches. Infrared (IR) spectroscopy and X-ray powder diffraction techniques were employed to follow the chemical composition of the solid residue obtained at different temperatures.

Synthesis and utilization of RuO2·xH2O nanodots well dispersed on poly(sodium 4-styrene sulfonate) functionalized multi-walled carbon nanotubes for supercapacitors

RuO2·xH2O nanodots highly dispersed onto the surfaces of poly(sodium 4-styrene sulfonate) (PSS) functionalized multi-walled carbon nanotubes (FMWCNTs) were successfully synthesized via a polymer-assisted technique under mild hydrothermal conditions. Here, PSS served as a bifunctional molecule both for solubilizing and dispersing MWCNTs into aqueous solution and for tethering Ru3+ to facilitate the subsequent uniform formation of RuO2·xH2O nanodots on their surfaces. The dependence of electrochemical utilization of RuO2·xH2O nanodots on their dispersity was evidenced by cyclic voltammetry results. The maximum specific capacitance of 1474 F g−1 and electrochemical utilization of 71% for the Ru species were obtained from RuO2·xH2O/FMWCNTs nanocomposite with 10 wt% RuO2·xH2O. And even for the 45 wt% RuO2·xH2O loading, the utilization of 34% still could be delivered, much higher than that of just 23% for the bare RuO2·xH2O nanodots. Such good supercapacitive performance of the nanocomposites should result from the high dispersity of the electroactive RuO2·xH2O nanodots on the FMWCNTs, resulting in the abundant electroactive surface atoms contacted by the H+ ions through the three-dimensional mesoporous conducting matrix easily even in the case of the high loadings of ruthenium oxide.

Reply to comment on “CO oxidation on ruthenium: The nature of the active catalytic surface” by H. Over, M. Muhler, A.P. Seitsonen

We first state that the premise of our Letter [1] was to state emphatically that the early studies of Peden and Goodman (PG) [2] can be entirely explained by and are only consistent with the active surface being a monolayer oxygen-covered Ru(0001) surface. Contrary to the authors’ contention in their Comment, the reaction conditions addressed in the experiments of PG [2] spanned the temperature range 375 to 600 K, a pressure range of O2 and CO pressures from 0.5 to 500 Torr, and CO/O2 ratios from 60 to .03. The authors state in their introduction that “the oxidation of Ru metal takes place to RuO2 only for temperatures higher than 500 K. Here we do not wish to address the oxidation of Ru in all morphologies, but rather the specific reaction conditions required for RuO2 to form on Ru(0001), the catalyst used in the experiments of PG and the subject of our previous Letter [1]. Indeed, as pointed out in our Letter [1], Over and coworkers in a very definitive piece of work [3] showed that the critical conditions required for the formation of RuO2 on Ru(0001) were far outside those used in the experiments of PG with respect tomore » temperature and oxygen chemical potential. Based on our earlier studies [2] and the work of Over and coworkers [3] we concluded in our Letter that RuO2 could not have formed to any appreciable extent in the PG experiments.« less

CO oxidation on ruthenium: The nature of the active catalytic surface

CO oxidation over ruthenium has been extensively studied over the last several decades from ultrahigh (UHV) vacuum to ambient pressures. While Ru is an inferior catalyst for this reaction compared to Pt, Rh, and Pd under ultrahigh vacuum conditions, it is comparable to these metals at or near atmospheric reaction conditions. Recent studies have suggested that the transformation from an inactive to an active catalyst can be attributed to a structural transformation of Ru to RuO2 and that an epitaxial film of RuO2(110) on Ru(0001) is the active catalytic surface under stoichiometric CO/O2 reaction condition at or approaching one atmosphere. Furthermore recent experimental and theoretical studies have suggested that under such elevated reactant pressures, a strongly bound CO (120 kJ/mol) on RuO2 reacts with O atoms from the oxide surface to form the CO2 product. However, that the active surface on Ru(0001) is a multilayer RuO2(110) oxide and that the CO reactant is strongly bound is inconsistent with early elevated pressure studies of CO oxidation on Ru showing: (i) the formation of a single surface oxide layer under elevated pressure reactant conditions; (ii) a weakly bound CO (<40 kJ/mol) is the reactant under elevated pressure reactant conditions; and (iii) themore » formation of RuO2 deactivates Ru as a catalyst. This article reviews CO oxidation over Ru for the last several decades emphasizing those aspects that rationalize the connection between the vacuum and high pressure results.« less

Kinetic Analysis of Thermal Decomposition of Unirradiated and γ-Irradiated Tris(ACEtylacetonato)-Ruthenium(III) [Ru(acac)3

The thermal decompositions of unirradiated and γ-irradiated Ru(acac)3 were studied in air. The results show that decomposition proceeds in one major step in the temperature range of 150-250°C with the formation of RuO2 as a final solid residue for unirradiated Ru(acac)3. For γ-irradiated Ru(acac)3, with a total γ-ray dose of 102kGy, the decomposition goes eventually to completion with almost 100% decomposition and proceeds in one major step which contains four overlapping decomposition stages in the temperature range of 200 −320°C. The kinetics were followed isothermally and non-isothermally using both model-fitting and model-free approaches. IR spectroscopy and X-ray powder diffraction techniques were employed to follow the chemical composition of the solid residues obtained at different temperatures. In a model-fitting approach, the kinetic triplet, i.e. the apparent activation energy Ea, the pre-exponential factor, ln A, and the reaction model f (α), were analyzed and calculated using straight line plots, and reduced time plots by isothermal measurements. For non-isothermal measurements we have applied the Coats and Redfern, and Kennedy and Clark methods. In the model-free approach, the non-thermal data for both unirradiated and γ-irradiated Ru(acac)3 samples were analyzed using the Flynn-Wall-Ozawa (FWO), Tang (T), and Vyazovkin (Vyz) isoconversional methods. The results of application of model-free and model-fitting approaches to the thermal decompositions of both unirradiated and γ-irradiated Ru(acac)3 were compared and evaluated to deduce the most probable kinetic triplet that describes correctly the thermal behavior of Ru(acac)3. Discussion of the results is preceded by a short review of the models relevant to this study.

Bottom electrodes dependence of microstructures and dielectric properties of compositionally graded (Ba 1− xSr x)TiO 3 thin films

Compositionally graded (Ba 1− x Sr x )TiO 3 (BST) thin films, with x decreasing from 0.3 to 0, were deposited on Pt/Ti/SiO 2/Si and Ru/SiO 2/Si substrates by radio frequency magnetron sputtering technology. The microstructure and dielectric properties of the graded BST thin films were investigated. It was found that the films on Ru electrode have better crystallization, and that RuO 2 is present between the Ru bottom electrode and the graded BST thin films by X-ray diffraction and SEM analysis. Dielectric measurement reveals that the graded BST thin films deposited on Ru bottom electrode have higher dielectric constant and tunability. The enhanced dielectric behavior is attributed to better crystallization as well as smaller space charge capacitance width and the formation of RuO 2 that is more compatible with the BST films. The graded BST films on Ru electrode show higher leakage current due to lower barrier height and rougher surface of bottom electrode.

Improved Performance of Direct Methanol Fuel Cells by Anodic Treatment

Anodic treatment of direct methanol fuel cell single cells was carried out at anode potentials of 0.1, 0.4, 0.7, and 1.0 V. An increase in maximum power density by 48% was achieved after anodic treatment at 0.7 V. Electrochemical impedance spectroscopy showed that the methanol electro-oxidation activity of the PtRu catalyst was promoted by the anodic treatment. Oxidation states of Ru changed from Ru metal (43%) and RuO 2 (57%) to RuO 2 (33%) and RuO x H y (67%), which were studied by X-ray photoelectron spectroscopy. The results showed that the formation of RuO x H y occurred at a potential range of 0.4-0.7 V.

Coalescence inhibition of hydrous RuO2 crystallites prepared by a hydrothermal method

Coalescence of particulates accompanied with crystal growth upon annealing at/above 200°C, found for hydrous RuO2 (RuO2∙nH2O) prepared by a sol-gel process, is effectively inhibited by the formation of RuO2∙nH2O nanocrystallites in a hydrothermal process. This thermal stability, attributable to the barrier originated from the lattice energy of crystallites, maintains high water content, nanocrystalline structure, and porous nature of RuO2∙nH2O annealed at elevated temperatures from 200to400°C. A hydrothermal derived RuO2-based supercapacitor with high specific capacitance (ca. 200Fg−1 measured at 100mAcm−2) and a cycle lifetime longer than 40000cycles, resulting from thermal stability, is demonstrated.

Oxidation and Morphology Change of Ru Films Caused by Sputter Deposition of Ta2O5 Films

Ta2O5 films were sputter deposited on Ru films and Ta2O5/Ru double layers were prepared as a model capacitor. The effects of Ta2O5 deposition temperature on oxidation of the Ru films and surface morphology of the double layers were examined. The surface roughness of the double layers increased with increasing deposition temperature of the Ta2O5 films. 1) Crystallization of Ta2O5 films, 2) crystal grain growth of Ru films, and 3) formation of RuO2 due to the oxidation of Ru were found to be the reasons for surface roughening.

Effect of the Mg/Al ratio of the hydrotalcite-type precursor on the dispersion and activity of Rh and Ru catalysts for the partial oxidation of methane

Active and stable catalysts for the partial oxidation of methane based on Rh and Ru nanoparticles strongly interacting with a MgO or spinel matrix have been prepared by calcination and reduction of hydrotalcite-type precursors. A Rh catalyst containing an high metal loading was used to calculate, by Rietveld analysis, the distribution of the Rh in the MgO-type and spinel-type phases obtained after calcination. The Rh particle size distribution analysed after reduction by HRTEM, has evidenced that the size of Rh particles supported on MgO is smaller than that of Rh particles supported on spinel matrix. The differences in the catalytic activity of the two type of matrix have been studied changing the Mg/Al ratio of the precursor. High Mg/Al ratio depressed the formation of the spinel and led to a narrow distribution of the particle size. The sample with the highest percentage of the MgO phase showed the highest activity. Similar tests have been carried out with Ru containing samples and in this case the increase of the MgO phase decreases the formation of RuO2.