Ru-Co Catalysts Research Articles

Electronic Modulation of RuCo Catalysts on TiO2 Nanotubes Promoting Durable Acidic Overall Water Splitting

Electronic Modulation of RuCo Catalysts on TiO₂ Nanotubes Promoting Durable Acidic Overall Water Splitting

Efficient hydrodeoxygenation of lignin-derived phenolics to cyclohexanol with N-doped alumina- carbide‐based RuCo catalysts derived from MOF under mild conditions

In this work, a novel RuCo bimetallic supported on N-doped carbon support containing alumina was prepared by in-situ pyrolysis using MOF-303 as the support precursor (Ru3Co1@CN-Al2O3), and it was applied to the efficient hydrodeoxygenation (HDO) of guaiacol under mild conditions (0.01 MPa H2, 200 °C, 3h), the yield of cyclohexanol reaches an impressive 83.12 %. In the absence of external hydrogen (2 MPa N2, 220 °C, 2 h), complete conversion of guaiacol was achieved, along with a remarkable 97.81 % selectivity towards cyclohexanol. The HDO of guaiacol under different atmospheres was further studied, and the possible mechanism was proposed. Characterization results indicated that the supported metals (Ru and Co) not only interacted with the N in the MOF-303 to enhance catalyst stability but also that the synergistic effect between Ru and Co was key to promoting the high yield of cyclohexanol through catalytic transfer hydrodeoxygenation (CTHDO) in isopropanol. Additionally, Ru3Co1@CN-Al2O3 was also effective in achieving the HDO of macromolecular lignin. This study provides a feasible approach for the high value-added green transformation of lignin and its derivatives under mild conditions, highlighting the significant potential of MOFs for lignin valorization.

Correlation between existential form of ruthenium cocatalyst and photocatalytic hydrogen evolution of carbon nitride

Catalysts composed of nanocluster and single-atom (SA) were extensively used to enhance electrocatalytic water splitting performance, whereas study of their photocatalytic hydrogen (H2) evolution activity was limited. Herein, carbon nitride (CN) decorated by ruthenium (Ru) cocatalysts existed as SA + cluster, cluster + nanoparticles (NPs), and NPs were prepared by impregnation and calcination processes. The correlation between existential form, content of Ru cocatalyst and H2 evolution rate were carefully discussed. It was found that Ru NPs were favor for water molecule adsorption, whereas Ru SAs and clusters facilitated H2 desorption. Theoretical calculations revealed that Ru clusters + NPs cocatalyst were beneficial for H* intermediate formation. Water splitting tests found that 1.07 wt% Ru NPs + cluster modified CN showed the highest H2 evolution rate of 13.64 mmol h−1 g−1, which was 266.4 and 1.5 times higher than those of CN and Ru NPs (2.33 wt%) decorated CN, respectively. This work deeply reveals the influences of existential form of Ru cocatalysts on photocatalytic water splitting of CN, and provides thought in designing new cocatalysts to largely enhance H2 evolution.

Fischer–Tropsch synthesis over RuCo catalysts: An effect of ligands on the active phase properties and catalytic activity

High quality synthetic fuels could be obtained using the Fischer–Tropsch process. Development of new catalysts for this process is very important for the selective formation of fuel fractions. RuCo catalysts prepared bymodifyingthe support with ethylenediaminetetraacetic acid, urea, acetone azine,or citric acidwasinvestigated for the first timein orderto see theeffect oftheligand on the catalytic properties ofthebimetallic system. The catalysts were characterized by TEM, STEM, XRF, H2-TPR, NH3-TPD, and XPS. It was assumed that total acidity, reducibility, dispersion and atomic surface composition of the catalysts are dependent on the ligands used. The catalyst obtained after modification of Al2O3 with citric acid was characterized by low activity and the predominant formation of solid paraffins. The use of EDTA resulted in a highly active catalyst with highest selectivity to gasoline. Catalyst modified with acetone azine showed a high α (0.898) as well as a selectivity to the diesel fraction of 64.1 %, but average CO conversion of 23.3 %. The optimalcatalytic systemamongthosestudied was Ru/Co/Al2O3-urea.This system hada high conversionrateof 37.3 %anda selectivitytowardsC5+ hydrocarbons of 79.4 %.Thediesel fractionwas also produced in high yield.

Insights into the Performance of Bimetallic Ru-Co/TiO2 Catalysts Carrying out a Low Temperature C3H8 Oxidation Reaction

The performance of a set of bimetallic Ru-Co catalysts dispersed on the TiO2 anatase phase, synthesized by the co-deposition–precipitation with urea method, was tested in the CO2 production by the entire oxidation of C3H8. The presence of properly dispersed ruthenium nanoparticles on a Co/TiO2-anatase support was notably favorable for enhancing the C3H8 activity/selectivity. Likewise, an increase in the combined acidity (Brönsted and Lewis) was also observed, and the interaction between Ru0-CoOx species stabilized on TiO2 prompted the C3H8 oxidation at low temperature. The performance of bimetallic Ru-Co/TiO2 catalysts was enhanced by increasing Ru0 species and loading, showing more efficient C3H8 oxidation by the combination of Ru0-CoOx, as revealed by DRIFTS, XPS, H2-TPR, and HAADF-STEM characterization outcomes. The higher acidity of the catalysts containing Ru (1.5 wt%) and Co (3 wt%) as well as the reducibility enhancement of the Ru and Co species led to the best capacity of these catalysts for C3H8 oxidation to CO2 under the experimental conditions employed in this study.Graphical

Aqueous phase selective C[dbnd]O hydrogenation of cinnamaldehyde over bimetallic RuCo catalysts with electronic and geometric modification

Aqueous phase selective hydrogenation of cinnamaldehyde (CALD), as a representative α,β-unsaturated aldehyde, into cinnamyl alcohol (CALA) has been investigated over monometallic Ru and bimetallic RuCo catalysts on pristine h-BN support. Using water as the solvent, the optimal 0.5%Ru-1.1%Co/h-BN catalyst exhibits 510 h−1 specific reaction rate and 78.9 % CALA selectivity as well as good recycling stability at 100 °C. Based on the structure characterizations of catalysts, metal nanoparticles consisting of metallic Ru0 and partially oxidized Ruδ+ sites are uniformly dispersed on h-BN thin sheets. In comparison to monometallic catalysts, additive Co metals in bimetallic RuCo/h-BN catalysts play significant geometric and electronic modification roles on Ru active sites depending on the Ru/Co ratio, and therefore remarkably enhances the preferential activation of CALD CO bond and selectivity of CALA product as well as accelerates the catalytic reaction. Furthermore, the hydrogen dissociative activation ability of various Ru and RuCo catalysts was evaluated, while the superior catalytic performance in water than other commonly used solvents was also clarified and discussed.

Highly efficient CO2 photoreduction by ultralow-Ru-Loading ZIF-67

Developing highly efficient and low-cost photocatalysts for CO2 reduction is of critical importance for the conversion of CO2 to value-added chemicals. Here we report a Co-based zeolitic imidazole framework (ZIF-67) based photocatalyst with exceptional photocatalytic activity and durability for CO2 reduction. ZIF-67 is doped with dicyandiamide (DCD), the intermediate link with the trace Ru cocatalyst (0.0127 wt. %). The underlying reduction mechanism was unraveled by the joint experiment-theory study. The strong orbital coupling of ZIF-67-DCD-Ru series structure leads to strong CO2 adsorption, electron enrichment on cocatalyst, and minimum Gibbs free energy barrier of CO generation. The synthesized ZIF-67/DCD/Ru sample exhibits excellent CO2 photoreduction performance with a CO generation rate of 1495 mmol gRu−1 h−1 and achieves a record turnover frequency (TOF) of 151 h−1, representing top-level photocatalytic activity among all reported ZIFs-based photocatalysts. For the first time, our work points out a novel way to achieve high activity of ultralow noble metal loading photocatalyst and provides an in-depth understanding of the advances of the series structure.

Defective ZrO2−x supported Ru nanoparticles as a Mott–Schottky photocatalyst for efficient ammonia synthesis under ambient conditions

The supported Ru co-catalyst induces upward band bending in the defective ZrO2−x, forming an interfacial Schottky barrier that facilitates the separation of photogenerated charge carriers and provides energetic electrons for nitrogen activation.

Crystal phase engineering of Ru for simultaneous selective photocatalytic oxidations and H2 production.

Noble metal nanoparticles are often used as cocatalysts to enhance the photocatalytic efficiency. While the effect of cocatalyst nanoparticle size and shape has widely been explored, the effect of the crystal phase is largely overlooked. In this work, we investigate the effect of Ru nanoparticle crystal phase, specifically regular hexagonal close-packed (hcp) and allotropic face-centered cubic (fcc) crystal phases, as cocatalyst decorated onto the surface of TiO2 photocatalysts. As reference photocatalytic reaction the simultaneous photocatalytic production of benzaldehyde (BAD) and H2 from benzyl alcohol was chosen. Both the fcc Ru/TiO2 and hcp Ru/TiO2 composites exhibit enhanced BAD and H2 production rates compared to pristine TiO2 due to the formation of a Schottky barrier promoting the photogenerated charge separation. Moreover, a 1.9-fold photoactivity enhancement of the fcc Ru/TiO2 composite is achieved as compared to the hcp Ru/TiO2 composite, which is attributed to the fact that the fcc Ru NPs are more efficient in facilitating the charge transfer as compared to hcp Ru NPs, thus inhibiting the recombination of electron-hole pairs and enhancing the overall photoactivity.

Li-intercalated CeO2 as an ideal substrate for boosting ammonia synthesis.

We present a Li-intercalated-CeO2 catalyst that exhibits outstanding activity for ammonia synthesis. The incorporation of Li significantly reduces the activation energy and suppresses hydrogen poisoning of the Ru co-catalysts. As a result, the lithium intercalation enables the catalyst to achieve ammonia production from N2 and H2 at substantially lower operating temperatures.

The role and effects of Ru1−xTixO2 solid solution transition layer in Ru/TiO2 composite photocatalyst by DFT calculations

In order to more clearly analyze the effects of Ru cocatalyst on TiO2 photocatalyst, two typical Ru1−xTixO2 solid solutions were selected as the transition layer of Ru/TiO2 hetero-structure for further in-depth analysis and discussion in this work, based on our previous works. The interface mismatch and interface formation energy between Ru1−xTixO2 solid solution transition layer and TiO2 layer or RuO2 layer are lower. Therefore, the introduction and existence of Ru1−xTixO2 solid solution transition layer can reduce the interface stress and imbalance of abrupt-type RuO2/TiO2 hetero-structure and make it more stable. By bridging oxygen atoms on the interface, electron transfer occurs between Ru1−xTixO2 solid solution transition layer and TiO2 layer or RuO2 layer, so as to form a smoother electrostatic potential distribution between them. More importantly, the pseudo-bandgap value of the selected Ru1−xTixO2 solid solution transition layer is between the bandgap values of TiO2 or RuO2, which can form a transition band offset between them. This effect reduces the unfavorable large band offset of abrupt-type RuO2/TiO2 hetero-structure. The above effects illustrate that the introduction of Ru1−xTixO2 solid solution transition layer can ensure the effective synergy of Ru cocatalyst, so as to significantly improve the quantum conversion efficiency of Ru/TiO2 composite photocatalyst.

CO2 Reduction Using Water as an Electron Donor over Heterogeneous Photocatalysts Aiming at Artificial Photosynthesis.

ConspectusPhotocatalytic and photoelectrochemical CO2 reduction of artificial photosynthesis is a promising chemical process to solve resource, energy, and environmental problems. An advantage of artificial photosynthesis is that solar energy is converted to chemical products using abundant water as electron and proton sources. It can be operated under ambient temperature and pressure. Especially, photocatalytic CO2 reduction employing a powdered material would be a low-cost and scalable system for practical use because of simplicity of the total system and simple mass-production of a photocatalyst material.In this Account, single particulate photocatalysts, Z-scheme photocatalysts, and photoelectrodes are introduced for artificial photosynthetic CO2 reduction. It is indispensable to use water as an electron donor (i.e., reasonable O2 evolution) but not to use a sacrificial reagent of a strong electron donor, for achievement of the artificial photosynthetic CO2 reduction accompanied by ΔG > 0. Confirmations of O2 evolution, a ratio of reacted e– to h+ estimated from obtained products, a turnover number, and a carbon source of a CO2 reduction product are discussed as the key points for evaluation of photocatalytic and photoelectrochemical CO2 reduction.Various metal oxide photocatalysts with wide band gaps have been developed for water splitting under UV light irradiation. However, these bare metal oxide photocatalysts without a cocatalyst do not show high photocatalytic CO2 reduction activity in an aqueous solution. The issue comes from lack of a reaction site for CO2 reduction and competitive reaction between water and CO2 reduction. This raises a key issue to find a cocatalyst and optimize reaction conditions defining this research field. Loading a Ag cocatalyst as a CO2 reduction site and NaHCO3 addition for a smooth supply of hydrated CO2 molecules as reactant are beneficial for efficient photocatalytic CO2 reduction. Ag/BaLa4Ti4O15 and Ag/NaTaO3:Ba reduce CO2 to CO as a main reduction reaction using water as an electron donor even in just water and an aqueous NaHCO3 solution. A Rh–Ru cocatalyst on NaTaO3:Sr gives CH4 with 10% selectivity (Faradaic efficiency) based on the number of reacted electrons in the photocatalytic CO2 reduction accompanied by O2 evolution by water oxidation.Visible-light-responsive photocatalyst systems are indispensable for efficient sunlight utilization. Z-scheme systems using CuGaS2, (CuGa)1–xZn2xS2, CuGa1–xInxS2, and SrTiO3:Rh as CO2-reducing photocatalyst, BiVO4 as O2-evolving photocatalyst, and reduced graphene oxide (RGO) and Co-complex as electron mediator or without an electron mediator are active for CO2 reduction using water as an electron donor under visible light irradiation. These metal sulfide photocatalysts have the potential to take part in Z-scheme systems for artificial photosynthetic CO2 reduction, even though their ability to extract electrons from water is insufficient.A photoelectrochemical system using a photocathode is also attractive for CO2 reduction under visible light irradiation. For example, p-type CuGaS2, (CuGa)1–xZn2xS2, Cu1–xAgxGaS2, and SrTiO3:Rh function as photocathodes for CO2 reduction under visible light irradiation. Moreover, introducing a conducting polymer as a hole transporter and surface modification with Ag and ZnS improve photoelectrochemical performance.

Restructured Co‐Ru alloys via electrodeposition for efficient hydrogen production in proton exchange membrane water electrolyzers

The design of robust and high-performance hydrogen evolution reaction (HER) catalysts is crucial for the scalable production of hydrogen by electrochemical water splitting. In this work, we fabricated hierarchically porous Co-Ru catalysts with excellent catalytic activity and durability in acidic media. The morphology of the Co-Ru catalysts was successfully controlled through an optimized electrochemical process. Among all Co-Ru samples prepared in this study, the Co72Ru28 catalyst exhibited the largest catalytic surface area, as well as excellent HER activity (overpotential of 26.4 mV at −10 mA cm−2) and durability. X-ray photoelectron spectroscopy measurements revealed the electron transfer between Co and Ru, indicating that the formation of the Co-Ru alloy improved the activity and durability of the catalyst. Furthermore, a proton exchange membrane water electrolyzer (PEMWE) prepared with the Co72Ru28 sample showed excellent performances (3.4 A cm−2 at 2.0 Vcell), illustrating the promising potential of the present Co-Ru catalysts as cathode materials for PEMWE systems.

Natural aluminosilicate nanotubes loaded with RuCo as nanoreactors for Fischer-Tropsch synthesis

ABSTRACT Following nanoarchitectural approach, mesoporous halloysite nanotubes with internal surface composed of alumina were loaded with 5–6 nm RuCo nanoparticles by sequential loading/reduction procedure. Ruthenium nanoclusters were loaded inside clay tube by microwave-assisted method followed by cobalt ions electrostatic attraction to ruthenium during wetness impregnation step. Developed nanoreactors with bimetallic RuCo nanoparticles were investigated as catalysts for the Fischer-Tropsch process. The catalyst with 14.3 wt.% of Co and 0.15 wt.% of Ru showed high activity (СO conversion reached 24.6%), low selectivity to methane (11.9%), CO2 (0.3%), selectivity to C5+ hydrocarbons of 79.1% and chain growth index (α) = 0.853. Proposed nanoreactors showed better selectivity to target products combined with high activity in comparison to the similar bimetallic systems supported on synthetic porous materials. It was shown that reducing agent (NaBH4 or H2) used to obtain Ru nanoclusters at first synthesis step played a very important role in the reducibility and selectivity of resulting RuCo catalysts.

TiO2 photocatalyst with single and dual noble metal co-catalysts for efficient water splitting and organic compound removal

Photocatalysts can be used both for air cleaning and solar energy harvesting through water splitting. However, pure TiO2 photocatalysts are often inefficient and therefore co-catalysts are needed to improve the yield. To achieve this goal, we prepared TiO2 and deposited Pt, Ir and Ru co-catalysts on its surface. Two base TiO2 nanoparticles were used: P25 and rutile TiO2 synthesized via hydrothermal method. Co-catalysts were deposited by wet impregnation technique using single element and a combination of two elements (Pt and Ir or Pt and Ru), followed by annealing in either air or H2/Ar. Annealing in reducing atmosphere increased the photocatalytic activity of oxidation of isopropanol compared to annealing in air. We demonstrated a clear influence of the co-catalysts on the photocatalytic degradation of isopropanol and on electrochemical water-splitting reaction. The platinum-containing samples showed the best HER activity.

Structure-tunable pompon-like RuCo catalysts: Insight into the roles of atomically dispersed Ru-Co sites and crystallographic structures for guaiacol hydrodeoxygenation

Currently, the highly efficient conversion of biomass resources into highly valuable chemicals and biofuels is one of the most prospective approaches to reduce greenhouse gases emission and environmental pollution caused by excess consumption of fossil fuels. Herein, three-dimensional pompon-like well-defined RuCo particles with tunable crystallographic structures and surface atomically dispersed Ru atoms were constructed and intensively investigated as support-free metal catalysts in the hydrodeoxygenation (HDO) of lignin-derived guaiacol. It was demonstrated that the 300 °C-reduced RuCo sample possessed the hexagonal close-packed (hcp) crystallographic structure with surface abundant atomically dispersed Ru atoms, whereas 600 °C-reduced RuCo sample presented the face-centered cubic phase with lower surface Ru concentration. The as-fabricated RuCo-300 sample showed excellent catalytic HDO activity with a high cyclohexane yield of 85.3%. Comprehensive structural characterizations unveiled that the introduction of atomically dispersed Ru atoms into the RuCo-300 favored the formation of abundant surface Ru-Co sites, as well as electron-rich Ru0, and such-constructed Ru-Co sites were highly beneficial to the hydrogen dissociation on single Ru0 atoms and the further hydrogen spillover to adjacent Co0 atoms to promote the HDO process. Moreover, density functional theory (DFT) calculations revealed that the hcp structure of RuCo catalysts benefited the adsorption of guaiacol. The unique pompon-like microstructure of RuCo catalysts was conducive to the exposure of active sites and provided more open channels for the easy diffusion of reactants and products. Over the RuCo-300 catalyst, the guaiacol HDO could proceed rapidly via an initial demethoxylation reaction. The present Ru-Co synergetic catalysis in the structure of RuCo catalysts would provide a new strategy for constructing robust heterogeneous bimetal catalysts applied in practical HDO processes of a variety of lignin-derived phenolic compounds.

Effect of Ba on the catalytic performance of Co-Ru/Al2O3 catalyst for Fischer-Tropsch synthesis

Alkali earth metals and Ru are famous selectivity promoters in cobalt-based Fischer-Tropsch synthesis. Ba has displayed as an effective selectivity promoter, however, the presence of Ba leads to a dropped CO conversion yield. To combine the advantages of Ba and Ru in promoting selectivity, Ba-modified alumina was fabricated and used as the supports for Co and Co-Ru catalysts. Promotion of Co/Al2O3 by a combination of Ru and Ba achieved an increase of CO conversion and a low CH4 selectivity due to the enhanced CO dissociation than unmodified anda single additive modified catalyst. The influences of other alkali earth metal additives were also investigated, which had a similar impact that of Ba on the Co-Ru catalysts for promoting FTS reaction.

Engineering Ru atomic structures toward enhanced kinetics of hydrogen generation

Herein, we demonstrate a strategy of engineering Ru atomic structures by fine-tuning Cl and Co coordination to synergize the quantity and quality of Ru active sites for boosting hydrogen generation from ammonia borane hydrolysis, via engineering the Cl-free/Cl-containing monometallic Ru catalysts and Co-leaching/Co-containing bimetallic Ru-Co catalysts. Under similar Ru particle sizes, the correlation between Ru binding energy and hydrogen generation activity affords a quantitative discrimination of Ru electronic and geometric contributions, where the site blockage and steric hindrance of Ru by Cl are more detrimental to hydrogen generation compared with the electronic modification by charge donation from Co to Ru. Reversely, the acid-leaching of Co from bimetallic catalysts creates abundant edge-like Ru active sites with much lower H2O activation barrier, as indicated by the kinetics switch from a Cl coverage-limited regime to a reactant activation regime, thus yielding a significant 4.1-fold increase in hydrogen generation activity.

Highly efficient ammonia synthesis at low temperature over a Ru-Co catalyst with dual atomically dispersed active centers.

The desire for a carbon-free society and the continuously increasing demand for clean energy make it valuable to exploit green ammonia (NH3) synthesis that proceeds via the electrolysis driven Haber–Bosch (eHB) process. The key for successful operation is to develop advanced catalysts that can operate under mild conditions with efficacy. The main bottleneck of NH3 synthesis under mild conditions is the known scaling relation in which the feasibility of N2 dissociative adsorption of a catalyst is inversely related to that of the desorption of surface N-containing intermediate species, which leads to the dilemma that NH3 synthesis could not be catalyzed effectively under mild conditions. The present work offers a new strategy via introducing atomically dispersed Ru onto a single Co atom coordinated with pyrrolic N, which forms RuCo dual single-atom active sites. In this system the d-band centers of Ru and Co were both regulated to decouple the scaling relation. Detailed experimental and theoretical investigations demonstrate that the d-bands of Ru and Co both become narrow, and there is a significant overlapping of t2g and eg orbitals as well as the formation of a nearly uniform Co 3d ligand field, making the electronic structure of the Co atom resemble that of a “free-atom”. The “free-Co-atom” acts as a bridge to facilitate electron transfer from pyrrolic N to surface Ru single atoms, which enables the Ru atom to donate electrons to the antibonding π* orbitals of N2, thus resulting in promoted N2 adsorption and activation. Meanwhile, H2 adsorbs dissociatively on the Co center to form a hydride, which can transfer to the Ru site to cause the hydrogenation of the activated N2 to generate N2Hx (x = 1–4) intermediates. The narrow d-band centers of this RuCo catalyst facilitate desorption of surface *NH3 intermediates even at 50 °C. The cooperativity of the RuCo system decouples the sites for the activation of N2 from those for the desorption of *NH3 and *N2Hx intermediates, giving rise to a favorable pathway for efficient NH3 synthesis under mild conditions.

Efficient hydrogen production from ammonia borane hydrolysis catalyzed by TiO2-supported RuCo catalysts

Hydrolysis of ammonia borane provides a reliable pathway for hydrogen production, while suitable catalysts are indispensable to make the hydrolysis reaction reach a considerable rate. In the present work, a series of TiO2-supported RuCo catalysts have been fabricated by coprecipitation and subsequent reduction of Ru3+ and Co2+ on the surface of TiO2 nanoparticles. Transmission electron microscopy and elemental mapping have verified the good distribution of metal species in the catalysts. The fabricated catalysts have shown excellent performance for catalyzing ammonia borane hydrolysis, especially in alkaline solutions with 0.5 M NaOH. For Ru1Co9/TiO2 in which Ru/Co molar ratio is 1:9, the active energy of catalyzed ammonia borane hydrolysis is 33.25 kJ/mol, and a turnover frequency based on Ru as high as 1408 molH2/(molRu·min) is obtained at 25 °C. Moreover, when different types of TiO2 substrates are used, anatase TiO2-supported catalysts show better catalytic activity than their counterparts with rutile TiO2 as substrate or mixture of anatase and rutile TiO2 as substrate.