Ru Catalysts Research Articles

Crystal facet-controlled brookite TiO2 nanostructures coupled with Ru nanoparticles for enhancing selective hydrogenation of benzene to cyclohexene

Coupling active metal nanoparticles (NPs) with oxide nanocrystals enclosed by specific facets is a promising strategy to enhance their catalytic performances. Here, brookite TiO2 nanoplates exposed with {11 1¯} facets, nanorods enclosed by {121} facets, and nanosheets exposed with {211} facets were synthesized and coupled with Ru NPs, aiming at improving their catalytic efficiency in selective hydrogenation of benzene to cyclohexene (SHBC) and discriminating the critical roles of brookite facets. The comprehensive characterizations recognized that the successive exposure of brookite TiO2 {11 1¯}, {121}, and {211} facets resulted in a more suitable adsorption strength of C6H6 and an increment of chemisorption capacity of C6H6 on medium-strength acid sites, contributing to a promotion of the turnover frequency (TOF) of C6H6. The kinetics investigations, density functional theory (DFT) simulations, and Mulliken population analysis unveiled that the increased Ti3+ species as a result of the successive exposure of brookite TiO2 {11 1¯}, {121}, and {211} facets brought in an increment of the net production rate of C6H10 in SHBC, and the electronic interaction between C6H10 and these facets is gradually weakened, which contributed to an improvement of C6H10 selectivity. As a consequence, an initial C6H10 selectivity (S0) of 91 % and a C6H10 yield of 47 % achieved on the brookite TiO2-supported Ru catalyst enclosed by TiO2 {211} facets.

Homogeneous Catalytic Process of a Heterogeneous Ru Catalyst in Li-O2 via X-ray Nanodiffraction Observation.

In recent years, lithium oxygen batteries (Li-O2) have received considerable research attention due to their extremely high energy density. However, the poor conductivity and ion conductivity of the discharge product lithium peroxide (Li2O2) result in a high charging overpotential, poor cycling stability, and low charging rate. Therefore, studying and improving catalysts is a top priority. This study focuses on the commonly used heterogeneous catalyst ruthenium (Ru). The local distribution of this catalyst is controlled by using sputtering technology. Moreover, X-ray nanodiffraction is applied to observe the relationship between the decomposition of Li2O2 and the local distribution of Ru. Results show that Li2O2 decomposes homogeneously in liquid systems and heterogeneously in solid-state systems. This study finds that the catalytic effect of Ru is related to electrolyte decomposition and that its soluble byproducts act as electron acceptors or redox mediators, effectively reducing charging overpotential but also shortening the cycle life.

Pore surface engineering of Al2O3-supported Ru catalysts with TiO2 for enhanced selective CO methanation

Hydrogen-rich gas derived from hydrocarbons contains large amounts of CO2 and CO, with the latter being poisonous for low-temperature polymer exchange membrane fuel cell anodes. Therefore, the efficient removal of CO from reformate gases is crucial while minimizing the methanation of CO2 to reduce unnecessary hydrogen consumption. In this study, Ru-based catalysts, which are ready to be employed in a chemical reactor, are developed to selectively convert CO into CH4 with minimal CO2 methanation using a simulated gas mixture composed of 75 % H2, 24 % CO2, and 1 % CO. The CO adsorption capability of Ru catalysts was enhanced by controlling the surface pores with a TiO2 coating layer. In this process, egg-shell type TiO2/Al2O3 supports were synthesized by wet impregnation method, and then Ru was impregnated on the supports. This modification enabled the Ru/TiO2/Al2O3 to preferentially adsorb CO over CO2. Furthermore, by systematically varying the TiO2 loading, the electronic structure of Ru is modified to induce CO adsorption, resulting in a catalyst with maximum activity for selective CO methanation. The catalyst demonstrates a turnover frequency value of 8.6 × 10−3 s−1 at 190°C, surpassing the performance of previously reported catalysts.

Boosting Fischer–Tropsch Synthesis via Tuning of N Dopants in TiO2@CN-Supported Ru Catalysts

Nitrogen (N)-doped carbon materials as metal catalyst supports have attracted significant attention, but the effect of N dopants on catalytic performance remains unclear, especially for complex reaction processes such as Fischer–Tropsch synthesis (FTS). Herein, we engineered ruthenium (Ru) FTS catalysts supported on N-doped carbon overlayers on TiO2 nanoparticles. By regulating the carbonization temperatures, we successfully controlled the types and contents of N dopants to identify their impacts on metal–support interactions (MSI). Our findings revealed that N dopants establish a favorable surface environment for electron transfer from the support to the Ru species. Moreover, pyridinic N demonstrates the highest electron-donating ability, followed by pyrrolic N and graphitic N. In addition to realizing excellent catalytic stability, strengthening the interaction between Ru sites and N dopants increases the Ru0/Ruδ+ ratios to enlarge the active site numbers and surface electron density of Ru species to enhance the strength of adsorbed CO. Consequently, it improves the catalyst’s overall performance, encompassing intrinsic and apparent activities, as well as its ability for carbon chain growth. Accordingly, the as-synthesized Ru/TiO2@CN-700 catalyst with abundant pyridine N dopants exhibits a superhigh C5+ time yield of 219.4 molCO/(molRu·h) and C5+ selectivity of 85.5%.

Alleviating anode flooding by mesoporous carbon supports for alkaline polymer electrolyte fuel cells

Water management is one of the critical issues affecting the performance and stability of alkaline polymer electrolyte fuel cells (APEFCs). This study focuses on the effect of carbon supports on the water management of APEFCs. A series of carbon-supported Ru catalysts (Ru/MCP-x) were prepared using mesoporous carbon powder (MCP-x) with three-dimensional through-nanopore structures as supports and compared with Ru/XC72. The results show that although the catalysts’ hydrogen oxidation reaction (HOR) catalytic activities are similar in KOH solutions, the APEFCs performance can be severely different. APEFCs assembled with Ru/MCP-x and Ru/XC72 (noted as Ru/MCP-x cell and Ru/XC72 cell) have little performance difference at high inlet H2 flow (1000 mL/min), but have a noticeable difference at low inlet H2 flow (200 mL/min). By combining the electrochemical AC impedance and distribution of relaxation time (DRT) method, we quantitatively identify that severe gas transfer resistance occurred in the anode catalyst layer of the Ru/XC72 cell under low inlet H2 flow, which is more in line with the actual APEFCs operating conditions, led to considerable degradation of the Ru/XC72 cell performance. The high gas transfer resistance is later ascribed to the anode flooding by combining the voltammetry curves and DRT plots. In contrast, for Ru/MCP-x cells, increasing the carbon supports’ mesopore diameter dramatically reduced the gas transfer resistance and mitigated the anode flooding. This study shows a quantitative comparison of the impacts of different carbon supports on APEFCs performance and gas transfer resistance, indicating that mesoporous carbon materials have the potential to be supports for APEFCs anode catalysts to alleviate the anode flooding.

Effects of the chemical states of N sites and mesoporosity of N-doped carbon supports on single-atom Ru catalysts during CO2-to-formate conversion

This study explores the fabrication and characterization of mesoporous nitrogen-doped carbon replicas (MNCs) as Ru catalyst supports for CO2 hydrogenation to formate. MNC supports with a cubic Ia3d-like structure were successfully synthesized from a KIT-6 template. The mesoporosity, N content, and N states in the MNCs differed according to the precursor type, which substantially influenced the stability of single-atom Ru catalysts during CO2 conversion. In hydrogenation tests, the Ru/MNC prepared using acrylonitrile precursor (Ru/MNC-A) demonstrated the best stability, whereas the Ru/MNCs prepared using pyrrole and melamine exhibited low activity owing to Ru agglomeration and limited reactant diffusion, respectively. The excellent stability of Ru/MNC-A resulted from Ru migration and rearrangement, as evidenced by near edge X-ray absorption fine structure analyses. Ru/MNC-A and Ru/MNC-A-400 achieved an outstanding turnover number of 69,000 in CO2 hydrogenation over 72 h. Remarkably, the Ru/MNC-A catalyst demonstrated exceptional stability, attaining a TON of 315,840 over 360 h.

Ligand Modifications on a Cp(quinolate)Ru Catalyst to Improve Its Stability in a Bio-orthogonal Deprotection Reaction

Ligand Modifications on a Cp(quinolate)Ru Catalyst to Improve Its Stability in a Bio-orthogonal Deprotection Reaction

Ru(II) Catalyzed Oxidative Dehydrogenative Annulation and Spirocyclization of Isoquinolones with N‐Substituted Maleimides

AbstractA Ruthenium(II) catalyzed additive‐free oxidative, dehydrogenative annulation of different malemides on 3,4‐disubstituted isoquinolone to afford fused and spiro‐cyclized isoquinolo‐isoquinolone and isoindolo‐isoquinolone derivatives is reported here. By simply changing solvent and oxidizing agents, under two different conditions, this methodology produced two different poly‐N‐heterocyclized products. Isoquinolone‐NH was strategically used as the internal directing group in the ortho C−H activation using Ru(II) catalyst. Mechanistically dehydrogenative, oxidative C−C followed by C−N cross‐coupling and aza‐michael reaction pathway led to the corresponding fused and spiro‐products respectively. A diversified library of eighty‐one (81) such two products were synthesized by employing this methodology. The fused and the spirocyclized polyheterocyclic compounds absorbed at λmax 240–270 nm range, however only spiro‐compounds produced blue fluorescence at λem 391–450 nm range.

Copper/Ruthenium Relay Catalysis for Stereodivergent Access to δ-Hydroxy α-Amino Acids and Small Peptides.

An atom- and step-economical and redox-neutral cascade reaction enabled by asymmetric bimetallic relay catalysis by merging a ruthenium-catalyzed asymmetric borrowing-hydrogen reaction with copper-catalyzed asymmetric Michael addition has been realized. A variety of highly functionalized 2-amino-5-hydroxyvaleric acid esters or peptides bearing 1,4-non-adjacent stereogenic centers have been prepared in high yields with excellent enantio- and diastereoselectivity. Judicious selection and rational modification of the Ru catalysts with careful tuning of the reaction conditions played a pivotal role in stereoselectivity control as well as attenuating undesired α-epimerization, thus enabling a full complement of all four stereoisomers that were otherwise inaccessible in previous work. Concise asymmetric stereodivergent synthesis of the key intermediates for biologically important chiral molecules further showcases the synthetic utility of this methodology.

Copper/Ruthenium Relay Catalysis for Stereodivergent Access to δ‐Hydroxy α‐Amino Acids and Small Peptides

AbstractAn atom‐ and step‐economical and redox‐neutral cascade reaction enabled by asymmetric bimetallic relay catalysis by merging a ruthenium‐catalyzed asymmetric borrowing‐hydrogen reaction with copper‐catalyzed asymmetric Michael addition has been realized. A variety of highly functionalized 2‐amino‐5‐hydroxyvaleric acid esters or peptides bearing 1,4‐non‐adjacent stereogenic centers have been prepared in high yields with excellent enantio‐ and diastereoselectivity. Judicious selection and rational modification of the Ru catalysts with careful tuning of the reaction conditions played a pivotal role in stereoselectivity control as well as attenuating undesired α‐epimerization, thus enabling a full complement of all four stereoisomers that were otherwise inaccessible in previous work. Concise asymmetric stereodivergent synthesis of the key intermediates for biologically important chiral molecules further showcases the synthetic utility of this methodology.

Supported Ruthenium catalysts with electronic effect and acidity-basicity for efficient reductive amination of biomass-based carbonyl compounds

The efficiently reductive amination of carbonyl compounds to the corresponding primary amines under mild condition with NH3 and H2 as nitrogen and hydrogen sources is a challenging task in the chemistry community. Therefore, supported Ru catalysts with excellent catalytic activity for reductive amination of carbonyl compounds were synthesized in this work using a simple impregnation method. Among them, Ru/SBA-15 showed excellent catalytic performance for reductive amination of carbonyl compounds, and the yields were more than 91%. The Ru nanoparticles (Ru NPs) were uniformly dispersed on the support, and the structure of the support was not destroyed. The acidity-basicity and the appropriate electron density are the reasons for the high activity and selectivity of supported Ru catalysts. The catalyst design concept with both electronic effect and acidity-basicity combination provides a new strategy for the conversion of biomass-based carbonyl compounds.

Ammonia synthesis over cesium-promoted mesoporous-carbon-supported ruthenium catalysts: Impact of graphitization degree of the carbon support

Carbon-supported ruthenium catalysts facilitate electrically-assisted Haber–Bosch ammonia synthesis. However, the relationship between carbon supports and catalytic performance remains ambiguous. We developed ordered mesoporous carbon plates (MCPs) with varying graphitization degrees as Cs-promoted Ru catalyst supports, examining correlations between ammonia synthesis rate and key structural parameters, included graphitization degree, Ru nanoparticle size, and Cs/Ru ratio. High-graphitization-degree carbon supports resisted methanation and facilitated formation of reductive activation enabled dynamic Cs0 species as electronic promotor, induced by spillover hydrogen from the Ru surface to CsOH. Density functional theory calculations further revealed that CsOH alleviated hydrogen poisoning. Notably, the catalyst supported on MCP-1100—which exhibited the highest graphitization degree among the supports and superior stability—with 10 wt% 2.3-nm-sized Ru nanoparticles and Cs/Ru = 2.5 achieved high ambient-pressure ammonia synthesis rates (7.9–43 mmolNH3·g−1·h−1) below 410 °C. Furthermore, it functioned under intermittent operating conditions, potentially integrating renewable-electricity-based electrolytic hydrogen production.

Effects of low crystallinity cerium oxide on ammonia synthesis activity for cerium oxide supported ruthenium catalyst

AbstractRuthenium (Ru) catalysts supported on cerium oxide (CeO2), which was composed of high crystallinity (HC) CeO2 covered by low crystallinity (LC) CeO2 were investigated. The ammonia synthesis activities of a series of Ru/CeO2(LC)/CeO2(HC), having different LC/HC ratios were evaluated, and various characterizations, such as N2 adsorption, X‐ray diffraction, hydrogen temperature‐programmed reduction (H2‐TPR), and hydrogen temperature‐programmed desorption (H2‐TPD), were performed. Ru/CeO2(LC)/CeO2(HC) (0.1) demonstrated higher activity. H2‐TPR revealed that H2 consumption increased as the LC/HC ratio increased. This indicates that the larger the amount of low crystallinity CeO2, the higher the reducibility. However, the results of H2‐TPD imply that the larger the amount of low crystallinity CeO2, the higher the interaction between adsorbed H2 and the catalyst surface. These results indicate that the balance of reducibility and hydrogen adsorption strength plays an important role in increasing the ammonia synthesis activity.

Support Effect of Boron Nitride on the First N-H Bond Activation of NH3 on Ru Clusters.

Support effect is an important issue in heterogeneous catalysis, while the explicit role of a catalytic support is often unclear for catalytic reactions. A systematic density functional theory computational study is reported in this paper to elucidate the effect of a model boron nitride (BN) support on the first N-H bond activation step of NH3 on Run (n = 1, 2, 3) metal clusters. Geometry optimizations and energy calculations were carried out using density functional theory (DFT) calculation for intermediates and transition states from the starting materials undergoing the N-H activation process. The primary findings are summarized as follows. The involvement of the model BN support does not significantly alter the equilibrium structure of intermediates and transition states in the most favorable pathway (MFP). Moreover, the involvement of BN support decreases the free energy of activation, ΔG≠, thus improving the reaction rate constant. This improvement is more obvious at high temperatures like 673 K than low temperatures like 298 K. The BN support effect leading to the ΔG≠ decrease is most significant for the single Ru atom case among all three cases studied. Finally, the involvement of the model BN may change the spin transition behavior of the reaction system during the N-H bond activation process. All these findings provide a deeper insight into the support effect on the N-H bond activation of NH3 for the supported Ru catalyst in particular and for supported transition metal catalysts in general.

Hydrogenation of CO2 to formate catalyzed by a Ru catalyst supported on a copolymerized porous organic polymer.

The catalytic hydrogenation of carbon dioxide to formate is of great interest due to its significant role in CO2 utilization. In this study, a novel heterogeneous Ru(III) catalyst was prepared by immobilizing RuCl3 on a porous organic polymer (POP) obtained from 1,4-phthalaldehyde (PTA) and 4,4'-biphenyldicarboxaldehyde (BPDA) with melamine. A copolymerization strategy utilizing monomers of varying lengths was employed to prepare the POP-supported Ru catalyst with adjustable porosity. The optimization of the framework porosity resulted in enhanced CO2 affinity, accelerated mass transfer, and a remarkable enhancement in catalytic activity. A high turnover number (TON) of 2458 was achieved for the CO2 hydrogenation to formate in 2 h with catalyst Cat-3 under 3 MPa (CO2/H2 = 1 : 1) at 120 °C in 1 M Et3N aqueous solution. Moreover, the Cat-3 demonstrated good recyclability and was able to be reused for five consecutive runs, resulting in a high total TON of 9971.

Influence of Ru-substitution on the performance of pyrochlore catalysts in oxidative steam reforming of ethanol

This study reveals that La2Zr2−xRuxO7−δ optimizes hydrogen production and ethanol conversion, particularly at a 2.66% Ru concentration, outperforming traditional 5 wt% Ru catalysts through superior long-term stability and efficiency.

Ru incorporated into Se vacancy-containing CoSe2 as an efficient electrocatalyst for alkaline hydrogen evolution.

In alkaline media, slow water dissociation leads to poor overall hydrogen evolution performance. However, Ru catalysts have a certain water dissociation performance, thus regulating the Ru-H bond through vacancy engineering and accelerating water dissociation. Herein, an excellent Ru-based electrocatalyst for the alkaline HER has been developed by incorporating Ru into Se vacancy-containing CoSe2 (Ru-VSe-CoSe2). The results from X-ray photoelectron spectroscopy, kinetic isotope effect, and cyanide poisoning experiments for four catalysts (namely Ru-VSe-CoSe2, Ru-CoSe2, VSe-CoSe2, and CoSe2) reveal that Ru is the main active site in Ru-VSe-CoSe2 and the presence of Se vacancies greatly facilitates electron transfer from Co to Ru via a bridging Se atom. Thus, electron-rich Ru is formed to optimize the adsorption strength between the active site and H*, and ultimately facilitates the whole alkaline HER process. Consequently, Ru-VSe-CoSe2 exhibits an excellent HER activity with an ultrahigh mass activity of 44.2 A mgRu-1 (20% PtC exhibits only 3 A mgRu-1) and a much lower overpotential (29 mV at 10 mA cm-2) compared to Ru-CoSe2 (75 mV), VSe-CoSe2 (167 mV), CoSe2 (190 mV), and commercial Pt/C (41 mV). In addition, the practical application of Ru-VSe-CoSe2 is illustrated by designing a Zn-H2O alkaline battery with Ru-VSe-CoSe2 as the cathode catalyst, and this battery shows its potential application with a maximum power density of 4.9 mW cm-2 and can work continuously for over 10 h at 10 mA cm-2 without an obvious decay in voltage.

Valorization of polycaprolactone for the production of nylon-6 monomers

A one-pot approach is presented to upgrade PCL into nylon-6 monomers (EACA and CPL) over Ru catalysts, affording products in a total yield of EACA and CPL up to 90.2%.

Rationally constructing hollow N-doped carbon supported Ru catalysts for enhanced hydrogenation catalysis

The Ru catalyst with an interior cavity exhibits good performance due to its unique structure, promoting the mass transport and enrichment of reactants.

Electrochemical-catalytic NH3 synthesis from H2O and N2 using an electrochemical cell with a Ru catalyst, Pd–Ag membrane cathode, and NaOH–KOH molten salt electrolyte at 250 °C

At 250 °C, using an electrochemical setup with a Ru catalyst, Pd alloy H2-permeable membrane cathode, NaOH–KOH molten salt electrolyte, and Ni anode, NH3 was synthesized from H2O and N2 with 30 mA cm−2 current density of and 25% current efficiency.