Ru Crystals Research Articles

Tuning the morphology and crystal phase of Ru nanocatalysts for efficient hydrogen evolution

Regulation of crystal phase of Ru nanocatalysts has been identified as an effective approach in regulating the bonding strength of reaction intermediates to Ru and improving the intrinsic activity of Ru-based catalysts during electrocatalytic hydrogen evolution reaction (HER). Here, we reported that the morphology and crystal phase of Ru nanocatalysts could be facilely regulated by halide anions in hydrothermal synthesis. Structural characterization revealed that halogen anions directed the anisotropic growth of hcp Ru, stabilized Ru crystals from aggregation, and increased the abundance of grain boundaries. As a result, The Ru polycrystalline networks exhibited excellent HER activity and durability with a smaller Tafel slope of 21 mV dec−1 and overpotential (η50) of 18 mV. This work sheds light on the shape and phase control of nanocrystals and future design of high-efficient non-Pt electrocatalysts with enhanced HER performance.

Activation of two highly stable molecules – nitrogen and methane to co-produce ammonia and ethylene

Two highly stable molecules, CH4 and N2 were simultaneously activated in a single-stage microwave-heated catalytic reactor to form ammonia, ethane, ethylene, and acetylene at atmospheric pressure. Density functional calculations and micro-kinetics modelling were used to predict the reaction behavior at temperatures ranging from 573 K to 973 K and validated with experimental analysis. The influences of terrace (111) and step (211) sites on K promoted Ru crystals were established in product formation and catalyst coking. NH3 formation occurs predominantly on the step (211) sites while C2 product formation can occur on both the sites. It was found that the elementary reaction steps leading to NH3 synthesis occurs due to the non-thermal effects of microwave irradiation while C2 products formed simultaneously are due to the thermal effects only. A reaction mechanism is postulated on the catalyst coking and validated experimentally by in-situ regeneration using H2 and O2.

Investigation on the holographic storage properties varied with ZrO2 co-doping in Ru:Fe:LiNbO3 crystals

Zr, Ru and Fe co-doped LiNbO3 crystals with various level of Zr4+ doping were grown in air by the conventional Czochralski method via the optimum growth condition. The defect structure of Zr:Ru:Fe:LiNbO3 crystals was analyzed by UV-visible absorption spectra. The holographic storage properties of Zr:Ru:Fe:LiNbO3 crystals were investigated by two-wave coupling experiment. The results showed that holographic storage performance improved with increase of Zr4+ doping concentration and the Zr (5 mol%):Ru:Fe:LiNbO3 crystal is promising candidate for holographic storage.

Electron transfer in the structure of a photorefractive doped Bi12TiO20: Ru crystal

The ac conductivity of Bi12TiO20: Ru crystals has been studied in the frequency range 102–106 Hz and at temperatures 293–773 K. The experimental data have been analyzed in the framework of the model of correlated barrier hops. In this material, the potential barriers are due to the existence of a block structure, crystal lattice defects, and also the presence of a ruthenium impurity. The microparameters characterizing the charge transfer in doped bismuth titanate single crystals have been determined.

Flexible thin metal crystals as focusing mirrors for neutral atomic beams

The development of novel reflective optical elements is essential to improve the focusing of neutral atomic beams. The recent availability of commercial thin crystals led to a renewed interest in curved mirrors as reflective elements for He microscopy. We have investigated the reflectivity to incoming He atoms of Cu(111), Ni(111), and Ru(0001) crystals of thickness between 50 and 150 $\ensuremath{\mu}\mathrm{m}$. The results have been compared with the ones obtained from bulk crystal surfaces. Our study reveals that a 100 $\ensuremath{\mu}\mathrm{m}$ thick Cu(111) crystal is the best candidate to be employed as a curved mirror, with an absolute reflectivity of 20% and a long-range crystalline order larger than 200 nm. In contrast, much lower reflectivities (3%--14%) have been measured for thin Ni(111) and Ru(0001) crystals. Finally, we show that a thin (100 $\ensuremath{\mu}\mathrm{m})$ Cu(111) crystal can be bent by an electrostatic field to focus an incoming He beam to a spot of 350 $\ensuremath{\mu}\mathrm{m}$. Due to the focusing properties of the mirror, a direct beam with less collimation can be used, leading to a larger reflected intensity. The absolute focused intensity is two orders of magnitude larger than previously reported. This represents a big step forward towards achieving the goal of building a high-resolution scanning helium atom microscope.

Dielectric response of doped Bi12TiO20: Ru crystals in an alternating electric field

The results of examination of AC dependences of capacitance and dielectric loss tangent of sillenite Bi12TiO20 crystals doped with ruthenium on frequency are presented. Non-Debye dispersion of dielectric coefficients is found in the frequency interval of 5 × 102–105 Hz, and a resonance phenomenon is observed. Polarization processes in the studied samples are attributed to relaxators associated with metal–oxygen vacancies and structural elements incorporating 6s 2 lone-pair electrons.

OH− absorption and one-color holographic recording in Ru:Fe:LiNbO3 crystals varied co-doped with HfO2

A series of Ru:Fe:LiNbO3 crystals with various doping concentrations of HfO2 were grown by the Czochralski technique. Their defect structures were analyzed by the infrared absorption spectra and the Lorentzian fitting. The one-color holographic storage characteristics of these crystals were investigated by means of two-wavelength technology. The experimental results showed that fast response time of 12.7s and high one-color holographic recording sensitivity of 0.53cm/J were obtained in Hf(5mol%):Ru:Fe:LiNbO3 crystal, meanwhile the fixed diffraction efficiency was as high as 44.3%. These results indicated Hf, Ru and Fe co-doped LiNbO3 crystals were outstanding media for holographic storage applications.

Composition and evolution of PGE mineralization in chromite ores from the Il’chir ophiolite complex (Ospa–Kitoi and Khara-Nur areas, East Sayan)

Data are presented on chromitites from the northern and southern sheets of the Il’chir ophiolite complex (Ospa–Kitoi and Khara-Nur (Kharanur) massifs). The new and published data are used to consider similarities and differences between ore chrome-spinel from the chromitites of the northern and southern ophiolite sheets as well as the species diversity of PGE minerals and the evolution of PGE mineralization. Previously unknown PGE minerals have been found in the studied chromitites.Ore chrome-spinel in the chromitites from the northern sheet occurs in medium- and low-alumina forms, whereas the chromitites from the southern sheet contain only medium-alumina chrome-spinel. The PGE minerals in the chromitites from the southern sheet are Os–Ir–Ru solid solutions as well as sulfides and sulfoarsenides of these metals. The chromitites from the northern sheet contain the same PGE minerals and diverse Rh–Pt–Pd mineralization: Pt–Ir–Ru–Os and isoferroplatinum with Ir and Os–Ir–Ru lamellae. Areas of altered chromitites contain a wide variety of low-temperature secondary PGE minerals: Pt–Cu, Pt–Pd–Cu, PdHg, Rh2SnCu, RhNiAs, PtAs2, and PtSb2. The speciation of the PGE minerals is described along with multiphase intergrowths. The relations of Os–Ir–Ru solid solutions with laurite and irarsite are considered along with the microstructure of irarsite–osarsite–ruarsite solid solutions. Zoned Os–Ir–Ru crystals have been found. Zone Os82–99 in these crystals contains Ni3S2 inclusions, which mark off crystal growth zones. Different sources of PGE mineralization are presumed for the chromitites from the northern and southern sheets.The stages of PGE mineralization have been defined for the chromitites from the Il’chir ophiolite belt. The Pt–Ir–Ru–Os and (Os, Ru)S2 inclusions in Os–Ir–Ru solid solutions might be relics of primitive-mantle PGE minerals. During the partial melting of the upper mantle, Os–Ir–Ru and Pt–Fe solid solutions formed syngenetically with the chromitites. During the late-magmatic stage, Os–Ir–Ru solid solutions were replaced by sulfides and sulfarsenides of these metals. Mantle metasomatism under the effect of reduced mantle fluids was accompanied by PGE remobilization and redeposition with the formation of the following assemblage: garutiite (Ni,Fe,Ir), zaccariniite (RhNiAs), (Ir,Ni,Cu)S3, Pt–Cu, Pt–Cu–Fe–Ni, Cu–Pt–Pd, and Rh–Cu–Sn–Sb. The zoned Os–Ir–Ru crystals in the chromitites from the northern sheet suggest dissolution and redeposition of Os–Ir–Ru primary-mantle solid solutions by bisulfide complexes. Most likely, the PGE remobilization took place during early serpentinization at 450–600 ºC and 13–16 kbar.During the crustal metamorphic stage, tectonic movements (obduction) and a change from reducing to oxidizing conditions were accompanied by the successive transformation of chrome-spinel into ferrichromite–chrome-magnetite with the active participation of a metamorphic fluid enriched in crustal components. The orcelite–maucherite–ferrichromite–sperrylite assemblage formed in epidote-amphibolitic facies settings during this stage.The PGE mineral assemblage reflects different stages in the formation of the chromitites and dunite-harzburgite host rocks and their transformation from primitive mantle to crustal metamorphic processes.

Ru Nanocrystals with Shape-Dependent Surface-Enhanced Raman Spectra and Catalytic Properties: Controlled Synthesis and DFT Calculations

Despite its multidisciplinary interests and technological importance, the shape control of Ru nanocrystals still remains a great challenge. In this article, we demonstrated a facile hydrothermal approach toward the controlled synthesis of Ru nanocrystals with the assistance of first-principles calculations. For the first time, Ru triangular and irregular nanoplates as well as capped columns with tunable sizes were prepared with high shape selectivity. In consistency with the experimental observations and density functional theory (DFT) calculations confirmed that both the intrinsic characteristics of Ru crystals and the adsorption of certain reaction species were responsible for the shape control of Ru nanocrystals. Ultrathin Ru nanoplates exposed a large portion of (0001) facets due to the lower surface energy of Ru(0001). The selective adsorption of oxalate species on Ru(10-10) would retard the growth of the side planes of the Ru nanocrystals, while the gradual thermolysis of the oxalate species would eliminate their adsorption effects, leading to the shape evolution of Ru nanocrystals from prisms to capped columns. The surface-enhanced Raman spectra (SERS) signals of these Ru nanocrystals with 4-mercaptopyridine as molecular probes showed an enhancement sequence of capped columns > triangle nanoplates > nanospheres, probably due to the sharp corners and edges in the capped columns and nanoplates as well as the shrunk interparticle distance in their assemblies. CO-selective methanation tests on these Ru nanocrystals indicated that the nanoplates and nanospheres had comparable activities, but the former has much better CO selectivity than the latter.

Enhanced nonvolatile holographic properties in Zn, Ru and Fe co-doped LiNbO3 crystals

A series of LiNbO3 crystals doped with various concentrations of ZnO and fixed concentrations of RuO2 and Fe2O3 have been grown by the Czochralski method from the congruent melts. The type of charge carriers was determined by Kr+ laser (476nm) and He–Ne laser (633nm). The results revealed that the holes were the dominant charge carriers at blue light irradiation. Dual-wavelength and two-color techniques were employed to investigate the nonvolatile holographic storage properties of Ru:Fe:LiNbO3 and Zn doped Ru:Fe:LiNbO3 crystals. The essential parameters of blue nonvolatile holographic storage in Zn:Ru:Fe:LiNbO3 crystals were enhanced greatly with the increase of Zn concentration. This indicates that the damage resistant dopants Zn2+ ions enhance the photorefractive properties at 476nm wavelength instead of suppressing the photorefraction. The different mechanisms of blue photorefractive and nonvolatile holographic storage properties by dual wavelength recording in Zn:Ru:Fe:LiNbO3 crystals were discussed.

Carbon Nanofiber-Supported Ru Catalysts for Hydrogen Evolution by Ammonia Decomposition

Carbon nanofibers (CNFs) with fish-bone graphene alignment and carbon nanotubes (CNTs) were used to support ruthenium for ammonia decomposition. The Ru nanoparticles on the CNF supports are more active than those on CNT supports. The Ru particle size was adjusted by changing the Ru loading or by introducing oxygen containing groups onto the CNF surface. The site activity increases when the Ru crystal size increases. The oxygen groups on the CNFs have a remarkable effect on ammonia decomposition over the Ru nanoparticles. On identically sized Ru crystals, oxygen on the CNFs clearly enhances ammonia decomposition over the Ru/CNFs.

Microscopic Topography of Heterocrystal Interfaces

Real-time in situ atomic force microscopy (AFM) of the (010) and (001) planes of isomorphous [1,4-bis(amidinium)benzene]2M(CN)6·8H2O (M = Fe, Ru) crystals, known to exhibit growth of one of the metalate compounds on the other to produce “core−shroud” heterocrystals, reveals high-fidelity epitaxial growth during heterocrystal formation or roughened surfaces, depending on the crystal face and crystallization conditions. The roughened crystal surfaces that define the interface between heteroepitaxial layers under typical growth conditions are consistent with the interface structure observed by electron dispersive spectrometry, which indicated intermixing of the two materials throughout a 0.7 μm thick interfacial region, but could not distinguish between various possible mechanisms for the intermixing. The crystal topography and roughness under various conditions reveal that the intermixing zone observed during heterocrystal formation may be a consequence of a rough growth surface on the inner “core” crystal upon evaporation of solvent prior to immersion in the growth medium used for epitaxial crystallization of the second compound. These observations suggest that the roughness of the growth interface can be regulated using specific growth protocols that minimize the intermixing of the two compounds.

Ruthenium Barrier/Seed Layer for Cu/Low- κ Metallization: Crystallographic Texture, Roughness, Diffusion, and Adhesion

Ru is examined as a barrier/seed layer in different layer stacks, with and without Ta, for a Cu/low-κ system. Ru was found to promote a more pronounced Cu(111) texture than Ta, and the texturing appears to increase with the increase of the Ru-layer thickness. Physical-vapor-deposited Cu films on both Ru and layers are adequately smooth with root–mean–square roughness of . Ru crystals on a low-κ layer have a columnar microstructure. Cu and Ru diffusion into the low-κ occurred after thermal annealing at for . A four-point bend adhesion study demonstrates a sufficiently high Ru/low-κ adhesion strength in comparison to Ta/low-κ .

Electron-beam tip/sample heating device for a scanning tunneling microscopy

We present an electron-beam heating device for a scanning tunneling microscopy (STM) that can be used for heating both the STM tip and the sample to 2200K. Mounted on a linear bellows with electrical feedthroughs, the device can be readily installed into the transfer path of a vacuum load lock. We demonstrate the heating capability of the device by flash cleaning Ru(0001) and Fe(001) crystals, and W tips. The flash-cleaned W tips are coated with Fe and further used for spin-polarized imaging of the Mn∕Fe(001) system.

Graphitic Nanofilaments as Novel Support of Ru–Ba Catalysts for Ammonia Synthesis

A novel graphitic-nanofilament- (GNF-) supported Ru–Ba catalyst is prepared and used in ammonia synthesis reaction. The Ru–Ba/GNFs catalyst shows remarkably high activity and stability for ammonia synthesis, which can be attributed to high purity and graphitization of GNFs with unique structure. TEM micrographs of the Ru–Ba/GNFs catalysts show that Ru metal particles uniformly disperse on the outer wall of GNFs, and the particles become bigger than that before ammonia synthesis reaction after 50 h of operation at 500°C and 7.0 MPa, probably due to the Ru crystals covered by promoter and support materials and/or sintering of Ru crystals.

Structure sensitivity of supported ruthenium catalysts for ammonia synthesis

The catalytic ammonia synthesis activities of four supported ruthenium catalysts are reported. It is seen that Ru/MgAl 2O 4 is more active than two similar Ru/C catalysts, which are significantly more active than Ru/Si 3N 4. The activity differences cannot be satisfactorily explained solely by the differences in dispersion. Recent results from single crystal studies and DFT calculations have shown that ammonia synthesis over ruthenium catalysts is a very structure sensitive reaction, more so than on iron catalysts. It is suggested that special B 5-type sites are primarily responsible for the catalytic activity of the present supported Ru catalysts. It is shown how the number of such B 5-type sites depends on the Ru crystal size for a given crystal morphology. We have found that the activity of the Ru/MgAl 2O 4 catalyst increases significantly during the initial part of a test run. This activity increase is paralleled by the disappearance of crystals smaller than ca. 1.0 nm due to sintering and a resulting formation of larger crystals. We conclude that there exists a lower limit to the desired crystal size of Ru in supported ammonia synthesis catalysts. This is in agreement with a low number of B 5-type sites expected for such crystal sizes. Furthermore, we suggest that the support plays a decisive role in controlling the morphology of the Ru crystals and the resulting change in abundance of B 5-type sites is the main cause for the significant activity variations observed for Ru catalysts with different supports. Finally, the support may also influence the electronic and catalytic properties of neighboring B 5-type sites.

Electrodeposition of Ir—Ru alloys from chloride melts: Steady-state potentials and cathodic processes

Steady-state potentials of Ir, Ru, and glassy carbon are measured at 500–700°C in eutectic NaCl-KCl-CsCl melts containing a mixture of Ir and Ru chlorides. The Ir and Ru steady-state potentials are more positive than their equilibrium values, due to the alloying in the metal surface layer. In the cathodic deposition of alloys, depolarization is observed. Before the limiting diffusion current, Ir-Ru alloys (solid solutions) are plated as compact layers; at higher current densities, the deposit is a powdered dendritic mixture of individual Ir and Ru crystals, rather than the alloy

Photostimulated processes in the Jahn-Teller system LiH(D):Ru

The optical absorption, luminescence and EPR methods have been used to study LiH(D) single crystals doped with Ru2+. The formation of new absorption bands and EPR signal was observed after the illumination of crystals with light at T=77 K. The possible model of photostimulated processes in LiH(D):Ru crystals is presented.

Effect of oxidation–reduction treatments on the infrared spectra of carbon monoxide chemisorbed on a Ru/TiO2catalyst

The measurement of IR spectra of CO adsorbed on H2-reduced Ru/TiO2(1% Ru, Degussa P-25 TiO2) is made difficult by the very low transparency, caused by partial reduction of the support; reduction at 758 K leads to complete opacity, but spectra can be obtained by multiple scanning on a slightly oxidised sample (transparency 0.07%). Reduction at either 433 or 623 K, however, gives products with which spectra are readily observed. On samples well reduced at 623 K the adsorption of CO gives as prevailing species Ru0—CO with ν(CO) at 2045 cm–1 at full coverage, shifting to lower frequency up to 1990 cm–1 as the coverage is decreased. At high pressures at room temperature, and especially on samples not well reduced and containing Cl–, bands are observed at 2151–2132 and 2090–2072 cm–1 which are attributed to Ru3+(CO)2 or Ru2+(CO)3 species. These species are removed by evacuation at 473 K, whereas Ru2+(CO)2 species (bands at 2101–2080 and 2038–2023 cm–1) are stable up to 573 K. At 473 K CO is an effective reductant for incompletely reduced samples. The Ru2+(CO)2 species are intermediates in the reduction by CO of the Ru/TiO2 system: at 573–623 K all the oxidised Ru species are reduced to Ru0. Spectra obtained by CO adsorption on samples reduced at 433 K are similar, save for a shoulder on the low-frequency side of the 2045 cm–1 linear Ru0—CO band. The presence of a low-frequency component at 1990 cm–1 is the fingerprint of isolated Ru0—CO species formed on very small and less perfect Ru crystals. This suggests that Ru is well dispersed. Evacuation at 758 K of unreduced RuCl3/TiO2 also results in the formation of some Ru0.

The real-time growth of atom planes on Ru, Rh and Sn microcrystals observed at atomic resolution

The growth of small Ru, Rh and Sn crystals, atomic column by atomic column, has been recorded in real time using a 400 kV high-resolution electron microscope, operated in the surface profile imaging mode. A common observation preceding the addition of a new atomic plane on the surface of the small (2–4 nm) metal crystal was the occurence of a diffuse “cloud”. Moreover, the sequential growth of an atomic plane was often preceded by the presence of such a cloud at the growth front (especially for Ru and Rh). Real-time video sequences showed that the addition of a new atomic layer typically took about 1 min.