Ru Oxidation Research Articles

Hydrogenation of CO2 to formic acid over efficient heterogeneous ruthenium oxide supported on cubic phase zirconium oxide catalyst

The development of active, cost-effective heterogeneous catalysts for the hydrogenation of CO2 to chemicals is currently progressing rapidly. In this study, we have demonstrated a significantly lower weight percentage (wt.%) RuO2/ZrO2 oxide catalyst that is effective for CO2 hydrogenation to formic acid (FA) synthesis. RuO2/ZrO2 was synthesized using a co-precipitation followed by a hydrothermal method. The X-ray diffraction pattern exhibits the cubic phase of ZrO2 with an average crystal size of 80.7 nm and tetragonal Ru oxide. Scanning electron microscopy and transmission electron microscopy confirmed that RuO2 was uniformly dispersed on the ZrO2 surface, with fringes measuring 0.22 and 0.25 nm corresponding to tetragonal Ru, which were incorporated in the ZrO2 oxide. XPS analysis showed that the Ru3/4+ chemical state strongly interacts with the ZrO2 facet, as confirmed via the Ru (110) and (211) planes. The outstanding performance of the 2.7 wt% RuO2/ZrO2 catalyst for CO2 hydrogenation yielded 40 mmol of FA with 39.7 TON. Based on the above investigations, we proposed a plausible mechanistic pathway for the hydrogenation of CO2 to FA over a RuO2/ZrO2 catalyst.

Nanocomposite of nickel benzene‐1,3,5‐tricarboxylic acid metal organic framework with multiwalled carbon nanotubes: A robust and effective electrocatalyst for oxygen evolution reaction in water splitting

In the current era, the development of robust, eco‐friendly, and highly efficient electrocatalysts for generating hydrogen energy by water electrolysis has become a major challenge. This work explains the electrocatalytic performance of cost‐effective and amiable novel Ni‐BTC‐MWCNTs‐a as an active and effective electrocatalyst for OER in alkaline media. The catalytic activity of the nanocomposite is increased by heat treatment at 400°C temperature for 3 h. Systematic morphological and structural characterization studies of solvothermal synthesized materials were carried out by X‐ray powder diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy technique, scanning electron microscopy (SEM) analysis, and energy dispersive X‐ray spectroscopy (EDS) analysis techniques. Metal–organic framework (MOF)‐based composites exhibit improved catalytic performance owing to the synergistic effect of Nickel BTC MOF, MWCNTs support, and high‐temperature annealing (400°C). Among all as‐synthesized materials, the annealed Ni‐BTC‐MWCNT‐a exhibits admirable catalytic performance for oxygen evolution reaction (OER) at low value for over potential (η) 243 m V, small Tafel slope value 57 mV dec−1, smaller charge transfer resistance (0.274 Ω), and higher electrochemical active surface area (2000 cm2) with maximum durability for 23 h and utilized as auspicious alternate with excellent catalytic activity in water splitting OER process for producing hydrogen energy at large scale other than highly expensive electrocatalysts of Ir, Ru, Pd, and Pt oxides.

Atomically dispersed Ru oxide catalyst with lattice oxygen participation for efficient acidic water oxidation

Atomically dispersed Ru oxide catalyst with lattice oxygen participation for efficient acidic water oxidation

Electrooxidation of Methanol on Pt, Ru, and Metal Oxides Nanoparticles Modified with Polyaniline-Carbon Nanotube Hybrid Electrodes

Electrooxidation of Methanol on Pt, Ru, and Metal Oxides Nanoparticles Modified with Polyaniline-Carbon Nanotube Hybrid Electrodes

Ru-MnOx Interaction for Efficient Hydrodeoxygenation of Levulinic Acid and Its Derivatives.

Metal-oxide interaction was widely observed in supported metal catalysts, playing a significant role in tuning the catalytic performance. Here, we reported that the interaction of Ru and MnOx was able to facilitate the hydrodeoxygenation of levulinic acid (LA) to 2-butanol with a high turnover frequency (1.99 × 106 h-1), turnover number (4411), and yield (98.8%). Moreover, this catalyst was capable of removing the hydroxymethyl group of lactones and diol with high yields of products. The high activity of the Ru-MnOx catalyst was due to the strong Ru-MnOx interaction, which facilitated reduction of Ru oxide to Ru0 and Mn oxide to Mn2+. The increased fractions of Ru0 and Mn2+ provided metal and Lewis acid sites, respectively, and therefore facilitated LA hydrodeoxygenation. A linear correlation between the hydrodeoxygenation activity of the Ru-MnOx catalyst and [Mn2+]ln([Ru0]) was observed.

Surface-limited deuterium uptake of Ru films under plasma exposure

Blister formation has been an emerging research topic for extreme ultraviolet (EUV) mirrors exposed to hydrogen plasmas. Similar to plasma-facing materials in nuclear fusion reactors, it has been reported that blister formation in EUV mirrors is initiated by hydrogen uptake due to hydrogen ion or atom bombardment. However, the research so far has focused on Mo/Si multilayers exposed to only hydrogen ions or atoms, while the EUV mirror typically has a Ru capping layer facing hydrogen plasmas. We present experimental work to measure plasma-induced hydrogen uptake of Ru films. We bombarded our designed Ru-capped target with a low-temperature deuterium plasma and measured the deuterium retention using elastic recoil detection. Contrary to ion-driven deuterium uptake, the deuterium uptake rate of the Ru film had no dependence on the deuterium ion flux or energy after a period of plasma exposure. A reaction–diffusion model has been built to calculate the time evolution of deuterium retention, which well fits the experimental data. Based on this model, we conclude that the surface composition of the Ru film is the limiting factor for the deuterium uptake, which is seriously weakened when the surface is covered by Ru oxide. After the Ru oxide is reduced by the plasma, the uptake rate is predominantly driven by the deuterium surface coverage on metallic Ru. Our model also indicates that at the deuterium-populated Ru surface, deuterium has a low absorption barrier to penetrate the surface, which is supported by previously reported computational work.

Study of oxidation behaviour of Ruthenium thin film after thermal annealing in oxygen environment

In the present study, 20 nm thick Ru film ion beam sputtered on Si substrate is annealed at different temperatures ranging from 100 °C to 600 °C for 2 hours in an oxygen environment. The sample was characterized by grazing incidence x-ray reflectivity and grazing incidence x-ray diffraction techniques that revealed that there is no oxidation of Ru below 400 °C in 150 standard cubic centimetre O2 flow environment. At 400 °C, the oxidation of the Ru thin film starts and at 500 °C both Ru and RuO2 phases co-exists. At higher temperature (600 °C), the Ru thin film oxidized into RuO2 phase and an intermixed layer of Ru and Si at the film substrate interface is revealed.

On the Role of Interfacial Water Dynamics for Electrochemical Stability of RuO2 and IrO2

AbstractBased on the coincident onsets of oxygen evolution reaction (OER) and metal dissolution for many metal‐oxide catalysts it was suggested that OER triggers dissolution. It is believed that both processes share common intermediates, yet exact mechanistic details remain largely unknown. For example, there is still no clear understanding as to why rutile IrO2 exhibits such an exquisite stability among water‐splitting electrocatalysts. Here, we employ density functional theory calculations to analyze interactions between water and the (110) surface of rutile RuO2 and IrO2 as a response to oxygen evolution involving lattice oxygen species. We observe that these oxides display qualitatively different interfacial behavior that should have important implications for their electrochemical stability. Specifically, it is found that IrO2(110) becomes further stabilized under OER conditions due to the tendency to form highly stable low oxidation state Ir(III) species. In contrast, Ru species at RuO2(110) are prone to facile reoxidation by solution water. This should facilitate the formation of high Ru oxidation state intermediates (>IV) accelerating surface restructuring and metal dissolution.

SrZrO3 Cube-Decorated PbS Nanoflowers as Robust Electrocatalysts for the Oxygen Evolution Reaction

Shrinkage of reservoirs of fossil fuels has already created an alarming situation in the energy sector, and the side products produced during their burning affect the environment adversely. Therefore, it is a need of time to replace fossil fuels with any other source with huge reservoirs. Herein, we fabricated a PbS/SrZrO3 nanocomposite, exhibiting promising oxygen evolution reaction activity. The synthesized samples were characterized by various techniques to confirm the material phase, morphology, surface area, composition, and oxidation states. As a result, it displays a very promising overpotential of 228 mV at a current density of 10 mA/cm2, a lower Tafel slope of 64 mV/dec, a higher turnover frequency of 1.45 s–1, an electrochemically active surface area of 280 cm2/g, and high stability up to 24 h, in contrast to the most advanced noble metal electrocatalysts Pt, oxides of Ir and Ru, and their constituents. High activity and low cost make this material one of the best to endeavor in the field of water splitting.

Unveiling the role of Ni in Ru-Ni oxide for oxygen evolution: Lattice oxygen participation enhanced by structural distortion

Introducing Ni in Ru oxide is a promising approach to enhance the catalytic activity for the oxygen evolution reaction (OER). However, the role of Ni (which has a poor intrinsic activity) is not fully understood. Here, a RuNiOx electrode fabricated via a modified dip coating method exhibited excellent OER performance in acidic media, and neutral media for CO2 reduction reaction. We combined in-situ/operando X-ray absorption near-edge structure and on-line inductively coupled plasma mass spectrometry studies to unveil the role of the Ni introduced in the Ru oxide. We propose that the Ni not only transforms the electronic structure of the Ru oxide, but also produces a large number of oxygen vacancies by distorting the oxygen lattice structure at low overpotentials, increasing the participation of lattice oxygen for OER. This work demonstrates the real behavior of bimetallic oxide materials under applied potentials and provides new insights into the development of efficient electrocatalysts.

Origin of Podiform Chromitites in the Sebuku Island Ophiolite (South Kalimantan, Indonesia): Constraints from Chromite Composition and PGE Mineralogy

The presence of PGM associated with the podiform chromitites in the Jurassic–Cretaceous ophiolite of Sebuku Island (South Kalimantan, Indonesia) is reported for the first time. Two types of chromitite have been recognized; one with high-Cr composition (Cr/(Cr + Al) > 0.7) occurs in the deep mantle, the other, high-Al (Cr/(Cr + Al) < 0.6), is located close to the Moho transition zone. The TiO2-Al2O3 relations indicate affinity to IAT and MORB, for the high-Cr and high-Al chromitites, respectively. However, both are believed to have formed by mantle/melt reaction and differentiation of a magma characterized by an initial IAT composition related to an SSZ. Primary magmatic inclusions (<10 μm) of laurite characterized by Ru/Os chondritic ratio are the only PGM found in the high-Cr chromitites, indicating crystallization from undifferentiated magma, at low fS2 in the mantle. In contrast, the high-Al to chondrite, suggesting the increase of fS2 in the evolved melt. Besides laurite, the high-Al chromitite contains a complex assemblage of secondary PGM (Pt-Fe, garutiite, iridium, ruthenium–magnetite aggregates, zaccariniite and unnamed Ru and Mn oxides). These secondary PGM have an irregular shape and occur exclusively in the chlorite matrix sometimes associated with Mn-Ni-Fe-Cr hydroxides. They are interpreted to have formed by desulfuration of primary interstitial PGM sulfides or to have precipitated from secondary fluids during low T alteration. The relative abundance of PPGE in the high-Al chromitite is interpreted as a result of PGE fractionation during differentiation of the parent melt of the chromitites.

Surface facet dependence of Ru and Ru-based alloy oxidation resistance using ab initio thermodynamics calculation

Recent studies exemplify the high activity of Ru for electrochemical catalytic reactions. However, among these reactions, Ru catalysts are known to easily oxidize with accompanying metal dissolution in the aqueous solution. Therefore, materials design for Ru-based materials should take into consideration its high oxidative property. In this study, we take into consideration the effective facet energy to describe surface energy and evaluate facet dependence of oxidation resistance. The effective facet energy is expressed as an energy correction to the bulk cohesive energy that minimizes layer dependence of surface energy calculation. We used this surface corrected energy to simulate the Pourbaix diagram of the first oxidation of Ru to Ru2O3 as a function of surface facets using Ab Initio thermodynamics calculations. Results show that there is a relatively higher potential for oxidation on the Ru (0001) facet as compared with the Ru (101¯0) facet, predicting that the former facet shows higher oxidation resistance. We further extend our analysis on the oxidation of RuIr alloy and found that the oxidation potential is increased through alloying. Similarly, a relatively higher oxidation resistance on the RuIr (0001) are observed as compared with the RuIr (101¯0). These results are important for materials design that considers control of the surface termination.

High CO-Tolerant Ru-Based Catalysts by Constructing an Oxide Blocking Layer.

CO poisoning of Pt-group metal catalysts is a long-standing problem, particularly for hydrogen oxidation reaction in proton exchange membrane fuel cells. Here, we report a catalyst of Ru oxide-coated Ru supported on TiO2 (Ru@RuO2/TiO2), which can tolerate 1-3% CO, enhanced by about 2 orders of magnitude over the classic PtRu/C catalyst, for hydrogen electrooxidation in a rotating disk electrode test. This catalyst can work stably in 1% CO/H2 for 50 h. About 20% of active sites can survive even in a pure CO environment. The high CO tolerance is not via a traditional bifunctional mechanism, i.e., oxide promoting CO oxidation, but rather via hydrous metal oxide shell blocking CO adsorption. An ab initio molecular dynamics (AIMD) simulation indicates that water confined in grain boundaries of the Ru oxide layer and Ru surface can suppress the diffusion and adsorption of CO. This oxide blocking layer approach opens a promising avenue for the design of high CO-tolerant electrocatalysts for fuel cells.

(Electro)chemical and antimicrobial characterization of novel Ru(II) bipyridine complexes with acetylpyridine analogs

Three ruthenium-bipyridine complexes (1–3) carrying acetylpyridine ligand unit were synthesized in methanol via the reaction of [RuCl2(bpy)2] with corresponding acetylpyridine (2-, 3-, and 4-acpy). Obtained complexes were characterized by (1H and 13C) NMR and IR spectroscopy, MS spectrometry, UV‒vis spectrophotometry, and cyclic voltammetry. Their structural characterization revealed bidentate coordination mode for 2-acpy while 3- and 4-acpy acted as monodentate ligands. The electrochemical profile of newly synthesized compounds was investigated by cyclic voltammetry which confirmed their electrochemical activity. Voltammetric responses within the −1.20 < Ep < 1.50 V range of potentials were summarized in two major events: Ru(II)→Ru(III) oxidation spotted at app. ΔEp = 0.65 V and successive reductions of bpy units located from ‒0.79 V to 0.47 V (vs. Ag/AgCl (3 M) electrode). The DNA-binding activity of the complexes was evaluated by both UV‒vis spectrophotometry and cyclic voltammetry indicating DNA-intercalation with a slight contribution of electrostatic interactions. Furthermore, antimicrobial activity was tested against bacterial and fungal strains, for which moderate activity was observed. Assessment of in vitro toxicity against freshly hatched nauplii of Artemia salina as well as radical scavenging capacity was evaluated. The test compounds showed neither toxicity nor antioxidant activity.

A trace of Pt can significantly boost RuO2 for acidic water splitting

The development of highly potential electrocatalysts for acidic water electrolysis is particularly desirable for many energy-related processes. Herein, we demonstrated a versatile strategy to activate and stabilize RuO2-based electrocatalyst for acidic water splitting by a trace of Pt, where Pt plays an essential role in promoting oxygen evolution reaction (OER), and can simultaneously act as the active site for hydrogen evolution reaction (HER). Compared with pure Ru oxide nanosheet assemblies (Ru ONAs), the “5%Pt-containing” Ru ONAs (5%Pt-Ru ONAs) achieve much enhanced OER activity in 0.5 and 0.05 mol/L H2SO4, with much lower overpotentials of 227 and 234 mV at 10 mA cm−2, respectively. Experimental and theoretical analyses reveal that the atomically dispersed Pt incorporating into RuO2 lattice is conducive to increasing the concentration of O vacancies, which effectively enhances the interaction with reaction intermediate and thus lowers the energy barrier for the formation of OOH*. Moreover, benefited from the presence of Pt, the formation of RuO2 is more achievable when proper annealing is applied. In addition to OER, due to the presence of active Pt, the HER performance of 5%Pt-Ru ONAs can also be ensured, thereby realizing efficient acidic overall water splitting. Finally, the excellent activity can also be achieved without sacrificing stability. This work highlights an attractive strategy for designing active and stable RuO2-based electrocatalysts for acidic overall water splitting.

Epitaxial Core-Shell Oxide Nanoparticles: First-Principles Evidence for Increased Activity and Stability of Rutile Catalysts for Acidic Oxygen Evolution.

Due to their high activity and favorable stability in acidic electrolytes, Ir and Ru oxides are primary catalysts for the oxygen evolution reaction (OER) in proton‐exchange membrane (PEM) electrolyzers. For a future large‐scale application, core‐shell nanoparticles are an appealing route to minimize the demand for these precious oxides. Here, we employ first‐principles density‐functional theory (DFT) and ab initio thermodynamics to assess the feasibility of encapsulating a cheap rutile‐structured TiO2 core with coherent, monolayer‐thin IrO2 or RuO2 films. Resulting from a strong directional dependence of adhesion and strain, a wetting tendency is only obtained for some low‐index facets under typical gas‐phase synthesis conditions. Thermodynamic stability in particular of lattice‐matched RuO2 films is instead indicated for more oxidizing conditions. Intriguingly, the calculations also predict an enhanced activity and stability of such epitaxial RuO2/TiO2 core‐shell particles under OER operation.

Highly sensitive determination of capsaicin with tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence

A highly sensitive tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)32+] electrogenerated chemiluminescence (ECL) detection method for the determination of capsaicin has been developed. In this study, capsaicin was worked as a coreactant in the oxidative-reduction pathway of the Ru(bpy)32+ ECL. The oxidation of Ru(bpy)32+ together with coreactant capsaicin on a bare glassy carbon electrode at an applied potential of + 1.10 V vs. Ag/AgCl (3 M NaCl) led to a strong ECL emission. The Ru(bpy)32+ ECL emission of capsaicin was strongly dependent upon the buffer solution pH, in which a strong ECL was obtained in alkaline buffer solution. Under the optimized conditions, the present Ru(bpy)32+ ECL detection method showed a linear response to capsaicin in the linear range from 1.0 × 10-7 M to 1.0 × 10-4 M with a limit of detection of 9.4 × 10-8 M (S/N = 3). In addition, the present method can detect dihydrocapsaicin and nordihydrocapsaicin with a detection limit of 1.9 × 10-7 M and 2.2 × 10-7 M, respectively. The present ECL method shows good analytical performance for capsaicinoids in terms of linear dynamic range and detection limit compared to those obtained at other electrochemical methods even without the employment of additional modification of electrode surfaces to enhance the detection responses. In addition, no analyte preconcentration was required. The recovery tests performed for spiked capsaicin in real pepper samples were satisfactory with the recovery from 95% to 103%. To the best of our knowledge, this is the first report on the application of ECL for the quantitative determination of capsaicinoids. Since the present method is very simple, fast and sensitive, it could be applied for the determination of capsaicin in food and pharmaceuticals.

Crystal structure and electronic property modification of Ca2RuO4 thin films via fluorine doping

Layered ruthenium oxyfluorides have various crystal structures and Ru oxidation states and exhibit unique physical properties. While various layered ruthenates have reportedly been topochemically fluorinated with Sr as $A$ sites, investigation of the fluorination of layered ruthenates containing smaller Ca ions is lacking. In this paper, we fabricated phase-pure and single-crystalline thin films of ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{2.5}{\mathrm{F}}_{2}$ on ${\mathrm{LaSrAlO}}_{4}$ (001) substrates via topochemical fluorination of the ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ precursor using polyvinylidene fluoride. The obtained fluorinated thin films had a chemical composition of ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{2.5}{\mathrm{F}}_{2}$ with the ${\mathrm{Ru}}^{3+}$ state, as determined by energy-dispersive x-ray spectroscopy and x-ray photoemission spectroscopy, whereas the film prepared via ${\mathrm{Sr}}_{2}{\mathrm{Ru}}^{4+}{\mathrm{O}}_{4}$ fluorination had a composition of ${\mathrm{Sr}}_{2}{\mathrm{Ru}}^{4+}{\mathrm{O}}_{3}{\mathrm{F}}_{2}$. Scanning transmission electron microscopy revealed that ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{2.5}{\mathrm{F}}_{2}$ has only 1 ${\mathrm{F}}^{\ensuremath{-}}$ site in CaO rock-salt blocks, whereas ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{3}{\mathrm{F}}_{2}$ has two inequivalent ${\mathrm{F}}^{\ensuremath{-}}$ sites in the SrO layers. The ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{2.5}{\mathrm{F}}_{2}$ film was insulating, with a resistivity (\ensuremath{\rho}) of $8.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\mathrm{cm}$ at 300 K. Moreover, the temperature behavior of \ensuremath{\rho} was well described by the two-dimensional variable range hopping model. These results demonstrate that local distortion is an important factor that governs the topochemical fluorination of ruthenates and affects the crystal and electronic structures of the reactants.

Atomically Precise Single Metal Oxide Cluster Catalyst with Oxygen‐Controlled Activity

AbstractSingle cluster catalysts (SCCs) consisting of atomically precise metal nanoclusters dispersed on supports represent a new frontier of heterogeneous catalysis. However, the ability to synthesize SCCs with high loading and to precisely introduce non‐metal atoms to further tune their catalytic activity and reaction scope of SCCs have been longstanding challenges. Here, a new interface confinement strategy is developed for the synthesis of a high density of atomically precise Ru oxide nanoclusters (Ru3O2) on reduced graphene oxide (rGO), attributed to the suppression of diffusion‐induced metal cluster aggregation. Ru3O2/rGO exhibits a significantly enhanced activity for oxidative dehydrogenation of 1,2,3,4‐tetrahydroquinoline (THQ) to quinoline with a high yield (≈86%) and selectivity (≈99%), superior to Ru and RuO2 nanoparticles, and homogeneous single/multiple‐site Ru catalysts. In addition, Ru3O2/rGO is also capable of efficiently catalyzing more complex oxidative reactions involving three reactants. The theoretical calculations reveal that the presence of two oxygen atoms in the Ru3O2 motif not only leads to a weak hydrogen bonding interaction between the THQ reactant and the active site, but also dramatically depletes the density of states near the Fermi level, which is attributed to the increased positive valence state of Ru and the enhanced oxidative activity of the Ru3O2 cluster for hydrogen abstraction.

TiO2 nanorod supported multi-metallic heterogeneous catalyst for conversion of CO2 to methanol under moderate operating conditions

Atmospheric carbon dioxide is still a concern though few technologies have demonstrated capturing and utilization. CO2 utilization with H2 seems to be promising, but the necessity for new technology to enhance the economical sourcing of H2 is critical. In this regard, an attempt is made to realize H+ and OH− in-situ on the catalyst surface for the reaction with activated CO2 molecule using thermal methods. A multi-metallic catalyst has been studied to verify the feasibility of such a reaction path. The metal oxides such as Ni, Mn, Mo, Ru, etc., are known for disassociating vapor phase H2O molecule to H+ and OH−. It is also known for CO2 to form an activated metal complex with Ni, Ti, Co, etc. In this context, a combination of selected metal oxides could result in activated CO2 reacting with H+ or OH− to form hydrocarbons. The hydrothermal synthesis method was employed for the catalyst synthesis, consisting of Ru, Ni, and Mn oxides with TiO2 nanorod as substrate material. The catalyst analysis was done using characterization techniques like XRD, FESEM, EDAX, XPS, PSA, TGA, and FTIR. The influence of the heterogeneous metal-oxides catalyst on the reduction of carbon dioxide with steam is studied to determine the effective temperature of the reaction and products. It is observed that the conversion is effective for temperatures above 400 °C. It is found that the production rate of methanol is approximately 2 mmol/gcat /hr at 425 °C, indicating the feasibility of such reaction pathway by sourcing Hydrogen on the catalyst site.