Clean Ru Research Articles

Potential–dependent Ru (0 0 0 1) surface oxidative corrosion and OER performance by grand canonical method

Applied external potential and the exposed solvent condition have significant impact on the surface state of electrodes in electrochemical reactions. In this work, the grand canonical density functional theory (DFT) calculations were performed to systematically investigate the surface state and oxygen evolution reaction (OER) performances of the Ru (0001) surface. Equilibrium Pourbaix diagrams demonstrated the oxidation state of either O* or OH*. Even in the negative polarized potential of USHE < 0.0 V, the Ru (0001) surface exhibited the surface state of 1/9 ML O* preoccupying instead of the clean surface. Mechanistic studies of OER on the clean Ru (0001) surface and Ru (0001)O* (1/9 ML) surface revealed that in acidic OER process on clean Ru (0001) surface, the oxygen coupling mechanism is more favorable than the nucleophilic attack mechanism involving OOH* intermediate formation.

Ru‐Catalyzed Hydrogenolysis of Methanol: A Computational and Kinetics Study

AbstractIn spite of numerous kinetic studies, the mechanism of the polyol hydrogenolysis on a Ru catalyst surface is still not fully understood. Here, the decomposition of the C1 alcohol methanol can serve as an entry to the clarification of the mechanism. Therefore, kinetic experiments using a Ru/C catalyst and periodic DFT calculations on a Ru(0001) model surface were performed. A modeling of the Ru surface revealed that the surface is most likely covered with hydrogen adsorbates under experimental conditions. On a clean Ru model surface, the overall activation barrier is lower if less dehydrogenation steps occur on the substrate methanol before the C−O bond cleavage. Transferring the results from the clean to the hydrogen‐saturated Ru surface, the pathway via CH2O O−H formation and subsequent C−O cleavage is found to be the most favorable. This study shows that the surface coverage has a significant influence on the activation barrier.

Instant micro-arc oxidation constructing the ultrafine nanoparticles as high-performance catalyst and mechanism study

The instant synthesis of ultrafine, clean surface Ru nanoparticle (NP) catalysts embedded on a porous MgO support was achieved by instant micro-arc oxidation (IMAO). The high temperature from the micro-arc discharge facilitates the rapid decomposition of the catalyst precursor RuCl3 into homogeneous nanoparticles, while the fast quenching process ensures instantaneous encapsulation of the formed NPs by the MgO support. The obtained Ru/MgO catalyst exhibited attractive catalytic behaviour for sodium borohydride and ammonia borane hydrolysis, with activities of 100,917 mL min−1·g−1 and 2336 mol min−1·mol−1, respectively. Moreover, this catalyst exhibited an excellent sintering resistance in high-temperature environment that was well retained after 40 cycles, indicating superior recyclability. This work provides a novel pathway for the direct and rapid synthesis of high-quality nanocatalyst and can be generalized to prepare other supported metal nanocatalyst (e.g. Pd/MgO).

STM Visualization of N2 Dissociative Chemisorption on Ru(0001) at High Impinging Kinetic Energies.

This paper examines the reactive surface dynamics of energy- and angle-selected N2 dissociation on a clean Ru(0001) surface. Presented herein are the first STM images of highly energetic N2 dissociation on terrace sites utilizing a novel UHV instrument that combines a supersonic molecular beam with an in situ STM that is in-line with the molecular beam. Atomically resolved visualization of individual N2 dissociation events elucidates the fundamental reactive dynamics of the N2/Ru(0001) system by providing a detailed understanding of the on-surface dissociation dynamics: the distance and angle between nitrogen atoms from the same dissociated N2 molecule, site specificity and coordination of binding on terrace sites, and the local evolution of surrounding nanoscopic areas. These properties are precisely measured over a range of impinging N2 kinetic energies and angles, revealing previously unattainable information about the energy dissipation channels that govern the reactivity of the system. The experimental results presented in this paper provide insight into the fundamental N2 dissociation mechanism that, in conjunction with ongoing theoretical modeling, will help determine the role of dynamical processes such as energy transfer to surface phonons and nonadiabatic excitation of electron-hole pairs (ehps). These results will not only help uncover the underlying chemistry and physics that give rise to the unique behavior of this activated dissociative chemisorption system but also represent an exciting approach to studying reaction dynamics by pairing the angstrom-level spatiotemporal resolution of an in situ STM with nonequilibrium fluxes of reactive gases generated in a supersonic molecular beam to access highly activated chemical dynamics and observe the results of individual reaction events.

Dissociative adsorption of H2O and CO2 on the clean and O-pre-covered high index Ru surfaces: Corrugated Ru(11−21) and stepped Ru(20−21) surfaces

Periodic density functional theory (RPBE) computation has been used to assess dissociative adsorption of H2O and CO2 on the clean and O-pre-covered Ru(11−21) and Ru(20−21) surfaces. It is found that surface H2O prefers desorption on the clean Ru(11−21) and Ru(20−21) surfaces, while dissociative adsorption on O-pre-covered Ru(11−21) and Ru(20−21) surfaces, in contrary to that on O-pre-covered Ru(0001) surface. The H2O dissociation capability on these clean and O pre-covered Ru surfaces follows a sequence of Ru(11−21) > (20−21) > (0001). In addition, CO2 desorption energy is comparable with the barrier of CO2 dissociation on Ru(11−21) and Ru(20−21) (0.81 vs. 0.77 eV, 0.14 vs. 0.20 eV, respectively), indicating that CO2 would not desorb in quantity before it occurs dissociation, which is contrary to the case on Ru(0001) (-0.32 vs. 0.23 eV). For surface O removed via H2O or CO2 formation, H2O formation has lower effective barrier than CO2 formation on these three Ru surfaces, in line with the experiments, and the effective barrier of H2O and CO2 formation follows the increasing order of Ru(11−21) < (20−21) < (0001).

Determining the structure of a layer under 2D-cover: the case of Pb underneath epitaxial graphene on Ru(0001)

Intercalation of solid and molecular species underneath 2D materials is one of the hottest topics in physics and chemistry nowadays – being important from the point of view of well-defined 2D materials-metals contacts formation, as well as performing catalytic reactions under cover. The confined space available for the intercalated layer’s formation often favours unique structural arrangements which are, however, difficult to study directly using conventional surface science techniques. We used directional elastic peak electron spectroscopy (DEPES) in combination with low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) to determine the structure of a Pb layer underneath epitaxial graphene (Gr) on Ru(0001). The results reveal that Pb forms a (√7×√7)R19.1° structure underneath Gr, which is similar to that formed by Pb on clean Ru(0001). As DEPES measurements utilize conventional LEED/AES optics commonly available in surface science laboratories, our approach can be adapted by other groups for the determination of the structure of various layers under 2D-covers.

The orientation of CO intercalated between graphene and Ru(0001)

13CO molecules are intercalated under a single layer graphene film on Ru(0001) and interrogated with helium low energy ion scattering. Single scattering is used to determine the mass distribution of atomic species visible to the ion beam and detector, and the scattering angle is varied to distinguish adsorbed from intercalated molecules. At room temperature, CO intercalates as molecules that sit upright with the O end on top, as on clean Ru. When the temperature is raised, the intercalated CO tilts more than it does on clean Ru. This is presumably due to increased vibrational amplitudes combined with the confining effect of the graphene film.

Collision Induced Desorption of Large Molecules From Surfaces: Trimethylamine Removal from Ru(0001)

The effect of incident kinetic energy of colliding molecules or atoms on the outcome of activated reactions on metallic surfaces is of general interest in model heterogeneous catalysis. Previous studies have focused on small molecules involved in both direct molecule-surface collisions and collision induced processes. This work presents a study of the interaction of incoming energetic colliders, Ar and Kr, with the large molecule trimethylamine (TMA). In these experiments, the TMA is adsorbed on either a clean Ru(0001) surface or an oxygen covered Ru(0001). The results show that at an incident collider energy of 1.0–2.8 eV, collision induced desorption (CIDE) is the dominant reactivity pathway over collision induced dissociation (CIDI). These observations suggest that energy redistribution within the adsorbed molecule following collision is fast and prevents channeling of the collision energy to internal bond scission.

Neon diffraction from graphene on Ru(0001)

The structure of graphene on Ru(0001) has been studied with neon atom scattering. Angular distributions of Ne scattered in the quantum regime have been recorded for a variety of incident conditions. For both in-plane and out-of-plane spectra, the intensity of the measured diffraction beams is comparable to that of the specular peak. This is in contrast with He diffraction results reported previously for the same system, where diffraction peaks are one order of magnitude less intense than the specular peak. The Ne diffraction data are consistent with a large corrugation amplitude ( ∼ 1 Å), in agreement with values reported with different techniques for this system. Our data provide strong evidence for the absence of anticorrugating effects in the case of Ne diffraction from both clean Ru(0001) and Gr/Ru(0001), and suggests that such effects might be present for He scattering. Our study proves that Ne diffraction gives a more accurate picture of the surface structure than the one deduced from He diffraction.

Modification of Surface Reactivity by CO: Effects on Decomposition and Polymerization of Acetaldehyde on Ru(0001)

The adsorption and reaction of acetaldehyde on the clean and CO pre-covered Ru(0001) surfaces have been investigated using temperature programmed desorption method. On the clean Ru(0001) surface, the decomposition of acetaldehyde is the main reaction channel, with little polymerization occurring. However, on the CO pre-covered Ru(0001) surface, the decomposition of acetaldehyde is inhibited considerably with increasing CO coverage. Whereas, the polymerization occurs efficiently, especially at high CO coverage (θCO&amp;gt;0.5 ML), which is strongly CO coverage dependent. Combined with previous studies, the well-ordered hexagonal structure of CO layer formed on the Ru(0001) surface at high CO coverage that matches the configuration of paraldehyde is likely to be the origin of this remarkable phenomenon.

Quantum Decoherence Behavior in Neon Scattering from Ru(0001) and Graphene/Ru(0001) Surfaces: Experiment and Comparison with Calculations

We report Ne atom scattering from clean Ru(0001) and from Ru(0001) covered with a single layer of graphene. For both systems, the quantum and classical regimes are observed and analyzed. The quantum to classical boundary is explored by varying both the surface temperature and the incident Ne kinetic energy. The classical smooth surface model is used to perform theoretical simulations in order to reproduce the angular distributions in the classical regime and determine the effective surface mass and hence allow determination of the Debye temperature. The theoretical calculations, in agreement with experiments, predict angular distributions that are subspecular at low energies and shift to supraspecular with increasing incident energy. The energy-resolved spectra in the classical regime exhibit only a single and somewhat broad multiphonon peak, but this peak persists into the regime where quantum features are also observed; thus care must be taken to avoid misinterpretation of the multiphonon background pea...

Selective Hydrogenation of Acrolein to Propanal on a Pseudomorphic Pt/Ru(001) Bimetallic Surface

The selective hydrogenation of acrolein has been studied on different pseudomorphic Pt/Ru(001) bimetallic surfaces with platinum coverages of 0.28, 1.1, and 3.7 ML, using temperature-programmed reaction spectroscopy (TPRS), reflection absorption infrared spectroscopy (RAIRS), and Auger electron spectroscopy (AES). The submonolayer (0.28 ML) Pt/Ru(001) surface was found to be inactive towards acrolein hydrogenation and behaves mostly like a clean Ru(001) surface with the platinum layers enhancing the decarbonylation and decomposition pathways. The multilayer (3.7 ML) Pt/Ru(001) surface behaved like a Pt(111) surface with the acrolein mostly decomposing to CO and surface carbon with no observable hydrogenation activity. However, the 1 ML Pt/Ru(001) pseudomorphic surface was found to display properties different from those of Ru(001) and Pt(111) surfaces with the desorption of propanal, the only hydrogenation product, around 330 K, and propylene around 370 K. A submonolayer (0.67 ML) PtRu/Ru(001) alloy system prepared to study the effect of surface mixing (with small amounts of subsurface platinum) gave results similar to those of surface platinum at submonolayer coverages. This suggests that, at submonolayer coverages, there is little difference in the properties of these surfaces with respect to the location of the platinum atoms in the Pt/Ru(001) system.

Reactivity of O2 on Pd/Ru(0001) and PdRu/Ru(0001) surface alloys.

The reactivity of a Pd monolayer epitaxially grown on Ru(0001) toward O2 has been investigated by molecular beam techniques. O2 initial sticking coefficients were determined using the King and Wells method in the incident energy range of 40-450 meV and for sample temperatures of 100 K and 300 K, and compared to the corresponding values measured on the clean Ru(0001) and Pd(111) surfaces. In contrast to the high reactivity shown by Ru(0001) at 100 K, the Pd/Ru(0001) system exhibits a monotonic decrease in the sticking probability of O2 as a function of normal incident energy. At room temperature, the system was found to be inert. Thermal desorption measurements show that O2 is adsorbed molecularly at 100 K. A completely different behaviour has been measured for the Pd0.95Ru0.05/Ru(0001) surface alloy. On this surface, the O2 sticking probability increases with incident energy and resembles the one observed on the clean Ru(0001) surface, even at 300 K. Thermal desorption measurements point to dissociative adsorption of O2 in this system. Both the charge transfer from the Pd to the Ru substrate and the compressive strain on the Pd monolayer contribute to decrease in the reactivity of the Pd/Ru(0001) system well below those of both Ru(0001) and Pd(111).

Adsorption and dissociation of H2O and CO2 on the clean and O-pre-covered Ru(0001) surface

Periodic density functional theory (revised PBE; RPBE) and ab initio atomistic thermodynamics were used to assess the dissociative adsorption of H2O and CO2 on a (5×5) Ru(0001) surface model. For H2O dissociation on clean Ru(0001) [H2O→OH+H→O+2H], the first step has lower barrier than the second step (0.75 vs. 0.80eV). On O pre-covered Ru(0001), H2O dissociation [H2O+O→2OH] has lower barrier (0.62eV) and is more exothermic (−0.29 vs. −0.15eV). CO2 dissociation on clean Ru(0001) [CO2→CO+O] needs low barrier (0.23eV) and is highly exothermic by 1.47eV. In turn, CO2 formation from surface O removal by CO has barrier of 1.70eV, in agreement with the experimentally detected 1.80±0.15eV. That the computed CO desorption energy (1.55eV) is smaller than CO oxidation barrier is in agreement with the experimental finding. The computed desorption temperatures of H2O, CO and CO2 under ultrahigh vacuum conditions agree perfectly with the experiments. In addition, high oxygen and OH pre-coverage do not significantly affect the energetics of the dissociation of H2O and CO2. The excellent agreement between theory and experiment confirms the applied models and methods, and in turn, gives the reliability and confidence about the further predicted results.

Coexistence of ice clusters and liquid-like water clusters on the Ru(0001) surface.

The RAIRS spectra of water adsorbed on Ru(0001) at 85 K are recorded from 600 cm-1 to 4000 cm-1. Measured at water coverages from 0.13 ML to 2.0 ML, the RAIRS spectra suggest that chemisorption of water on Ru(0001) depends on coverage. Water adsorbs on a clean Ru surface as chemisorbed ice-like clusters (likely through an O-Ru bond) up to 0.33 ML. Above this coverage, the chemisorbed layer saturates. Upon more exposure, water adsorbs as a liquid-like H-bonded layer without bonding to the Ru substrate. The chemisorbed water absorbs 7 times less IR per molecule than the liquid-like structure, which indicates that the orientation of the chemisorbed water is more parallel to the surface. Additionally, the influence of water-Ru bonding on H-bonding is reflected in the OH symmetric stretching mode. Under perturbation from water-Ru bonding, a large red shift (40 cm-1) in the free OH stretching frequency is observed in the chemisorbed clusters. By deconvoluting the main H-bonded OH stretching peak into five Gaussian sub-bands at 2945 ± 5 cm-1, 3210 ± 5 cm-1, 3300 ± 15 cm-1, 3430 ± 5 cm-1 and 3570 ± 10 cm-1, changes in the H-bonding network are rationalized in terms of H-bonding motifs. The donor-acceptor-acceptor motif is significant only in the chemisorbed clusters. On the other hand, the donor-acceptor motif dominates in the liquid-like structure, which increases the disorder present in the adlayer. Although chemisorption is suppressed above 0.33 ML, no structural changes in the ice-like clusters are observed up to multilayer coverage. Therefore, ice-like and liquid-like water coexist in a meta-stable state at 85 K.

Low-energy excitations of graphene on Ru(0 0 0 1)

The structure and the acoustic phonon branches of graphene on Ru(0001) have been experimentally investigated with helium atom scattering (HAS) and analyzed by means of density functional theory (DFT) including Grimme dispersion forces. In-plane interactions are unaffected by the interaction with the substrate. The energy of 16meV for the vertical rigid vibration of graphene against the Ru(0001) surface layer indicates an interlayer effective force constant about five times larger than in graphite. The Rayleigh mode observed for graphene/Ru(0001) is almost identical to the one measured on clean Ru(0001). This is accounted for by the strong bonding to the substrate, which also explains the previously reported high reflectivity to He atoms of this system. Finally, we report the observation of an additional acoustic branch, closely corresponding to the one already observed by HAS in graphite, which cannot be ascribed to any phonon mode and suggests a possible plasmonic origin.

Reactivity of Pyrimidine on Clean Ru(0001): Experimental and Calculated Infrared Spectra

The chemical behavior of pyrimidine on the (0001) close-packed surface of a Ru single crystal was studied by reflection–absorption infrared spectroscopy (RAIRS) and by Hartree–Fock ab initio calculations. At 95 K, the spectra and theoretical simulations indicate molecular docking at fcc hollow sites, as a π-complex almost parallel to the surface. With increasing coverage, some η4 on-top docked species appear, and for a highly packed monolayer physically adsorbed pyrimidine, with some preferential orientation induced by the chemically bonded species, is also present. Subsequent physisorbed layers, randomly oriented, form as exposure increases. The behavior of adsorbed species with thermal activation is not coverage dependent: annealing a low temperature packed monolayer induces rearrangements toward a denser π-complex layer, at the expense of the other surface species, up to 130 K. At this temperature, a tilted intermediate and 2-pyrimidyl bonded to the surface by dehydrogenated C2 and one N, with loss of resonance, and oriented with the C–N bond tilted toward the surface are also proposed. 2-Pyrimidyl is stable between 130 and 180 K and starts desorbing or decomposing above this temperature. A multilayer formed at low temperature is stable up to 110 K and desorbs by annealing to 120 K. For higher temperatures, the composition of the surface layers is similar to that obtained from thermal activation of a dense monolayer. At 150 K, the surface adlayer has the same composition whether it results from an annealed low-temperature monolayer, an annealed multilayer, or a layer built above the stability limit of the multilayer. The relevance of the results obtained is based on the eventual extrapolation to the interactions of pyrimidinic ring molecules with ruthenium.

Investigation of surface termination by directional elastic peak electron spectroscopy: Experiment and theory

Experimental and theoretical details concerning the directional elastic peak electron spectroscopy are presented. The application of this experimental method to the identification of a crystalline structure of surface layers is shown for Cu(111) and Ru(0001), which enables the analysis of different surface terminations associated with different sequences of atoms along the surface normal. Theoretical data are obtained by applying the multiple scattering theory and different sources of phase shifts. The quantitative analysis performed by an R-factor reveals almost the same populations of A and B terminated (0001) terraces and proves explicitly the presence of steps of atomic height on the clean Ru(0001) surface. This is not the case for the Cu(111) surface, where the terrace termination does not affect the distribution of atomic directions within the first few atomic layers. The averaging of theoretical data versus scattering volume defined by the sphere radius Rmax around the emitter site is discussed in view of the computation time optimization.

Carbon-induced Ru nanorod formation

Using DFT calculations we study morphology of C-covered Ru nanostructures. We find that the equilibrium shape of clean Ru nanoparticles is a polyhedron consisting mainly of {0001}, {100}, and {101} faces. At low and intermediate coverages of C the shape does not deviate much from that of clean nanoparticles. However, at higher coverages the particle's morphology transforms from the polyhedron to a rod-like shape, which mainly consists of {100} faces. The formation of nanorods is due to a high stability of Ru(100), which is induced by the formation of chains of C atoms on this surface. We find that under conditions of Fischer–Tropsch synthesis, in which C forms from the hydrogenation of CO, the rod-like Ru nanoparticle is the most favorable shape.

Effect of van der Waals interactions on H2 dissociation on clean and defected Ru(0001) surface

Ab initio computational methods are used to study the relevance of van der Waals interactions in the case of a hydrogen molecule adsorption on the Ru(0001) surface. In addition to the clean surface, the effects of ruthenium adatom and vacancy on the process are studied. The adsorption characteristics are analyzed in terms of two dimensional cuts of the potential energy surface (PES). Based on the earlier studies for such systems, we mostly concentrate on the trajectories where the hydrogen molecule approaches the surface in parallel orientation. The results indicate that for a clean Ru(0001) the calculations applying the non-local van der Waals potentials yield higher barriers for the dissociation of the H2 molecule. Of the high symmetry sites on Ru(0001), the top site is found to be the most reactive one. The vacancy and ruthenium adatom sites exhibit high dissociation barriers compared with the clean surface.