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Low temperature dry reforming of methane using Ru-Ni-Mg/ceria-zirconia catalysts: Effect of Ru loading and reduction temperature
Dry reforming catalysts, especially those with activity at moderate temperatures, have been intensely investigated to enhance the conversion of biogas. Here, Ru is evaluated as a promoter for Ni-Mg based catalysts. Catalysts based on 1.4 wt%Ni-1.0 wt%Mg-Ce 0.6 Zr 0.4 O 2 with Ru (0.02–0.32 wt%) were prepared using incipient wetness. The reducibility of the catalysts and conversions increased with increasing Ru content. Increases in conversions with increasing Ru loading was attributed to the additional active sites and synergistic effect between Ru and Ni, which weakened Ni-Mg interactions. Samples showed dry reforming activity at low temperatures (450–510 °C). Reaction rates and activation energies of higher loading Ru samples (1.4 wt%Ni-1.0 wt%Mg/Ce 0.6 Zr 0.4 O 2 with 0.16 and 0.32 wt%Ru) decreased when the reduction temperature was raised from 300 to 400 °C. A 20 h TOS study showed stable catalytic activity with minimal coke deposition. Furthermore, the results suggest that Ru is an alternative to Pt in promoting low temperature dry reforming of methane.
Access to Ru(IV)–Ru(V) and Ru(V)–Ru(VI) Redox in Layered Li 7 RuO 6 via Intercalation Reactions
The push to increase the capacity of oxides to store charge as Li-ion battery cathodes has challenged our knowledge of the boundaries of redox chemistry and its relationship to the atomic structure. Layered phases with Ru are now classical models in the quest for refined theories. Current understanding dictates that the highest formal state that can be reached in them is Ru(V), after which activity centered at the oxide anions is triggered. Yet, this picture is challenged by this investigation of the intercalation chemistry of Li 7 RuO 6 . Coupling structural and spectroscopic analysis with computational simulations, we show that Li 7 RuO 6 is capable of highly reversible lithiation to Li 8 RuO 6 through the Ru(V)/Ru(IV) redox couple. Further, Li 7 RuO 6 can also undergo anodic Li deintercalation, showing clear evidence of the reversible formation of Ru(VI) with octahedral coordination, an unusual state that is not accessible in other layered oxides. The results highlight the versatility of the Ru-O bond to undergo distinct redox transitions depending on the specific layered arrangements. They enrich our understanding of redox chemistry in solids while underscoring the need for descriptions of charge compensation that reflect the nuance of covalent interactions.
A new synthetic method of [Ru(2,2′:6′,2″-terpyridine)(2,2′-bipyridine)Cl] + complexes using cis -[Ru(2,2′:6′,2″-terpyridine)(NCCH 3 ) 2 Cl] + as an intermediate and comparison to a method using [Ru(benzene)(2,2′-bipyridine)Cl] + intermediates
A new method of synthesizing [Ru(terpy)(bpy)Cl] + (terpy = 2,2′:6′,2″-terpyridine, bpy = 2,2′-bipyridine) complexes using the starting material cis-[Ru(terpy)(NCCH 3 ) 2 Cl](PF 6 ) is reported. The yields of four derivatives ([Ru(terpy)(NN)Cl](PF 6 ): NN = bpy, 1; 4,4′-(MeO) 2 bpy, 2; 4,4′-(CF 3 ) 2 bpy, 3; 2,2′-biquinoline, 4) with this method range from 58 to 94 % and are similar to or greater than a known reaction in which the starting material is [Ru(benzene)(NN)Cl](PF 6 ). However, the use of cis-[Ru(terpy)(NCCH 3 ) 2 Cl](PF 6 ) results in lower levels of homoleptic Ru byproducts in the synthesis of 1 as compared to the use of [Ru(benzene)(bpy)Cl](PF 6 ) as determined by 1 H NMR spectroscopy. In addition, a high-purity and gram-scale synthesis of cis-[Ru(terpy)(NCCH 3 ) 2 Cl](PF 6 ) that does not use column chromatography is reported, in contrast to the original synthesis disclosed in the literature.
Reactivity and Mechanisms of Photoactivated Heterometallic [Ru II Ni II ] and [Ru II Ni II Ru II ] Catalysts for Dihydrogen Generation from Water
Abstract Two heterometallic photocatalysts were designed and probed for water reduction. Both [(bpy) 2 Ru II Ni II (L 1 )](ClO 4 ) 2 ( 1 ) and [(bpy) 2 Ru II Ni II (L 2 ) 2 Ru II (bpy) 2 ](ClO 4 ) 2 ( 2 ) can generate the low‐valent precursor involved in hydride formation prior to dihydrogen generation. However, while the bimetallic [Ru II Ni II ] ( 1 ) requires the presence of an external photosensitizer to trigger catalytic activity, the trimetallic [Ru II Ni II Ru II ] ( 2 ) displays significant coupling between the catalytic and light‐harvesting units to promote intramolecular multielectron transfer and perform photocatalysis at the Ni center. A concerted experimental and theoretical effort proposes mechanisms to explain why 1 is unable to achieve self‐supported catalysis, while 2 is fully photocatalytic.
Sacrificial Synthesis of Supported Ru Single Atoms and Clusters on N-doped Carbon Derived from Covalent Triazine Frameworks: A Charge Modulation Approach
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Stacking Faults and Short-Range Magnetic Correlations in Single Crystal Y 5 Ru 2 O 12 : A Structure with Ru +4.5 One-Dimensional Chains
In this paper, the synthesis, structure, and physical properties of Y 5 Ru 2 O 12 , a new member of the Ln 5 B 2 O 12 class (Ln = lanthanide, B = Ru, Re, Mo) are reported. Single crystals of Y 5 Ru 2 O 12 are synthesized using a high-temperature, high-pressure (700 °C, 200 MPa) hydrothermal method. The structure features edge-sharing Ru—O—Ru 1D chains of distorted RuO6 octahedra. The YO n (n = 6 and 7) polyhedral groups bridge Ru—O—Ru chains across the unit cell by forming a complex 3D structure. The Ru—O—Ru chains contain alternating shorter and longer Ru—Ru distances along the chain. Single crystal neutron diffraction shows streak-like diffuse scattering along the H-direction, due to stacking faults. Temperature-dependent anisotropic magnetic measurements reveal a broad feature over a wide temperature range, with a maximum at ≈70 K indicating potential short-range ordering, with canted antiferromagnetic behavior below 30 K. The dominant magnetic interactions are antiferromagnetic with a large negative Weiss temperature θ ≈ –200 K. The compound has an effective magnetic moment that is anomalously large for this class of compounds (≈4 μ B Ru –1 ), and a phenomenological spin Hamiltonian describing the unusual anisotropic magnetization of Y 5 Ru 2 O 12 is proposed.
Ring-opening and hydrodenitrogenation of indole under hydrothermal conditions over Ni, Pt, Ru, and Ni-Ru bimetallic catalysts
Here, the activity and selectivity of activated-carbon-supported Ni, Pt, Ru, and Ni-Ru bimetallic catalysts was examined for hydrothermal denitrogenation of indole. The molar yield of pyrrole ring-opening compounds, without an added hydrogen source, are in the order: Ni < Pt < Ni 90 Ru 10 < Ni 75 Ru 25 < Ni 50 Ru 50 ~ Ni 25 Ru 75 ~ Ru. Ru-containing catalysts facilitated production of hydrocarbons (hydrodenitrogenation (HDN) products) when used with added formic acid (hydrogen source). We elucidated catalytic hydrothermal HDN pathways for indole based on the product distributions and the variation of their yields with time. Hydrogenation of indole to indoline is the primary pathway and ring-opening of indoline to form alkyl anilines is faster than forming HDN products (alkyl benzenes). DFT calculations confirmed experimental activity trends, showing Ru is more active than Ni for indole ring opening and for o-toluidine deamination. If no hydrogen source is present, directly breaking the N-C bond in the pyrrole ring is more favorable than breaking the C-N bond with an aromatic carbon. If a H source is provided, the pyrrole ring hydrogenates first, forming indoline, followed by cleavage of the C-N bond.
Complex magnetic structure in Ba 5 Ru 3 O 12 with isolated Ru 3 O 12 trimer
We report detailed magnetic, transport, heat-capacity, and neutron diffraction measurements of Ba 5 Ru 3 O 12 , a compound consisting of isolated Ru 3 O 12 trimers. We show that this system develops long-range antiferromagnetic ordering at T N ~ 60 K without structural distortion or metal-insulator-type transition, which is in sharp contrast to other Barium Ruthenate trimer systems such as 9R-BaRuO 3 and Ba 4 Ru 3 O 10 . A complex magnetic structure is revealed which is attributable to the magnetic frustration due to competing exchange interactions between Ru ions on different crystallographic sites within the Ru 3 O 12 trimer and different degree of orbital hybridization on different Ru-sites. In conclusion, we have also investigated the magnetic structure of Ba 4 Ru 3 O 10 for comparisons.
Redistribution of Ru in Fe 2 O 3 –Ru Nanocatalysts through an Oxidative Pretreatment Improves Reverse Water–Gas Shift Activity
We have synthesized Fe–Ru nanoparticles via a solvothermal method to create catalysts for the reverse water–gas shift reaction and demonstrated the impact of reductive and oxidative pretreatments on both catalytic performance and structure. Catalytic testing showed improved activity after exposure to O 2 at 600 °C. In contrast, the activity became lower if then exposed to H 2 at 600 °C. Environmental scanning transmission electron microscopy and scanning electron microscopy showed that exposure to O 2 at 600 °C changes the morphology and completely oxidizes Fe into Fe 2 O 3 . Exposure to H 2 at elevated temperature caused Ru coalescence at the surface of the nanoparticle, forming clusters which decreased the optimization of Ru. Reoxidation of the particles exposed to H 2 , however, caused a redistribution of Ru that appears beneficial in maximizing Ru exposure and synergy with Fe oxide, with no major changes in the morphology and oxide structure. Furthermore, our diagnostics demonstrate the complex and reversible rearrangements possible in these multicomponent particles and the benefits of oxidative pretreatment to enhance or regenerate Fe–Ru catalysts in other important catalytic reactions such as Fischer–Tropsch synthesis.
New precious metal containing normal spinels: LiRhRu 1-x Ir x O 4 , LiFeIr 1-x Ru x O 4 , and LiCoIr 1-x Ru x O 4
Large spin-orbit-coupled cations in geometrically frustrated crystal structures have the most suitable setting for exploring novel exotic states of matter. Spinel oxides (AM 2 O 4 ) are well-known examples of geometrically frustrated systems. In this study, we report for the first time the synthesis of compositions LiRhRu 1-x Ir x O 4 (x = 0–0.5), LiFeIr 1-x Ru x O 4 (x = 0–0.5), and LiCoIr 1-x Ru x O 4 (x = 0–0.3) containing precious metal cations on edge-sharing octahedral M-sites, and systematically investigate their magnetic and electrical properties. 57 Fe Mössbauer spectroscopy revealed that iron is trivalent in all LiFeIr 1-x Ru x O 4 solid solutions. Magnetic measurements indicate deviations from theoretical spin-only magnetic moment values, indicating the influence of spin-orbit coupling owing to the presence of 4d and 5d block elements. The LiFeIr 1-x Ru x O 4 series shows spin-glass-like freezing behavior with T g ≈ 20 K, and a small frustration index (f ≈ 1-2), indicating that the frustration originates from site disorder. LiRhRu 1-x Ir x O 4 and LiCoIr 1-x Ru x O 4 exhibit strongly geometrically frustrated magnetism. Electrical resistivity measurements as a function of temperature indicate that all phases are semiconducting. Seebeck coefficient measurements show that LiRhRu 1-x Ir x O 4 and LiFeIr 1-x Ru x O 4 are p-type semiconductors with holes as the major charge carriers. A sign reversal of the Seebeck coefficient indicates both holes and electrons as carriers for LiCoIr 1-x RuxO 4 (x = 0–0.2), but only holes as major carriers for x = 0.3. Here, the Seebeck coefficient and power factor increase drastically in the LiRhRu 1-x Ir x O 4 solid solution with Ir substitution, reaching a maximum of ≈ +125 μV/K and ≈2.3×10 -6 W/mK 2 at ∼650 K for x = 0.5.
Evidence of Quadrupole and Octupole Deformations in Zr 96 + Zr 96 and Ru 96 + Ru 96 Collisions at Ultrarelativistic Energies
In the hydrodynamic model description of heavy-ion collisions, the elliptic flow v 2 and triangular flow v 3 are sensitive to the quadrupole deformation β 2 and octupole deformation β 3 of the colliding nuclei. The relations between v n and β n have recently been clarified and were found to follow a simple parametric form. The STAR Collaboration has just published precision v n data from isobaric Ru 96 + Ru 96 and Zr 96 + Zr 96 collisions, where they observe large differences in central collisions v 2 , Ru > v 2 , Zr and v 3 , Ru < v 3 , Zr . Using a transport model simulation, we show that these orderings are a natural consequence of $\beta_{2,Ru} \gg \beta_{2,Zr}$ and $\beta_{3,Ru} \ll \beta_{3,Zr}$ We reproduce the centrality dependence of the v 2 ratio qualitatively and v 3 ratio quantitatively and extract values of β 2 and β 3 that are consistent with those measured at low-energy nuclear structure experiments. STAR data provide the first direct evidence of strong octupole correlations in the ground state of Zr 96 in heavy-ion collisions. Our analysis demonstrates that flow measurements in high-energy, heavy-ion collisions, especially using isobaric systems, are a new precision tool to study nuclear structure physics.
The Importance of Decarbonylation Mechanisms in the Atomic Layer Deposition of High-Quality Ru Films by Zero-Oxidation State Ru(DMBD)(CO) 3
Achieving facile nucleation of noble metal films through atomic layer deposition (ALD) is extremely challenging. To this end, η 4 -2,3-dimethylbutadiene ruthenium tricarbonyl (Ru(DMBD)(CO) 3 ), a zero-valent complex, has recently been reported to achieve good nucleation by ALD at relatively low temperatures and mild reaction conditions. Here, we study the growth mechanism of this precursor by in situ quartz-crystal microbalance and quadrupole mass spectrometry during Ru ALD, complemented by ex situ film characterization and kinetic modeling. These studies reveal that Ru(DMBD)(CO) 3 produces high-quality Ru films with excellent nucleation properties. This results in smooth, coalesced films even at low film thicknesses, all important traits for device applications. However, Ru deposition follows a kinetically limited decarbonylation reaction scheme, akin to typical CVD processes, with a strong dependence on both temperature and reaction timescale. The non-self-limiting nature of the kinetically driven mechanism presents both challenges for ALD implementation and opportunities for process tuning. By surveying reports of similar precursors, we suggest that the findings can be generalized to the broader class of zero-oxidation state carbonyl-based precursors used in thermal ALD, with insight into the design of effective saturation studies.
A single-Pt-atom-on-Ru-nanoparticle electrocatalyst for CO-resilient methanol oxidation
Single Pt atom catalysts are key targets because a high exposure of Pt substantially enhances electrocatalytic activity. In addition, PtRu alloy nanoparticles are the most active catalysts for the methanol oxidation reaction. To combine the exceptional activity of single Pt atom catalysts with an active Ru support we must overcome the synthetic challenge of forming single Pt atoms on noble metal nanoparticles. In this report we demonstrate a process that grows and spreads Pt islands on Ru branched nanoparticles to create single-Pt-atom-on-Ru catalysts. By following the spreading process by in situ TEM, we found that the formation of a stable single atom structure is thermodynamically driven by the formation of strong Pt–Ru bonds and the lowering of the surface energy of the Pt islands. The stability of the single-Pt-atom-on-Ru structure and its resilience to CO poisoning result in a high current density and mass activity for the methanol oxidation reaction over time.
Hydrogenation and C-S bond activation pathways in thiophene and tetrahydrothiophene reactions on sulfur-passivated surfaces of Ru, Pt, and Re nanoparticles
Thiophene-H2 reactions proceed via sulfur removal and hydrogenation routes on dispersed metal nanoparticles that become decorated by refractory S-adlayers during catalysis. The identity and kinetic relevance of the required elementary steps are described here based on rates measured at S-chemical potentials set by H2S/H2 ratios similar to those prevalent during practical catalysis on Re, ReSx, Ru, and Pt catalysts. Free energies for S adatom formation (from H2S decomposition and H2 evolution) are strongly exothermic (< -50 kJ mol-1 on Pt(111) and < -150 kJ mol-1 on Re and Ru(0001)), but strong repulsions between S adatoms cause adsorption free energies to increase significantly with coverage on all three surfaces, preventing complete monolayer formation. These adlayers, composed of unreactive S-atoms (S') that cover 1/3–2/3 ML leave residual interstitial spaces (*) that bind S-atoms (S*), intermediates, and transition states reversibly, as required for catalytic turnovers. The number and binding properties of these interstices depend on the identity and chemical state of the nanoparticle bulk phase, which influences S'-binding and coverages and cause large differences in direct desulfurization and hydrogenation turnover rates (per exposed metal atom) on dispersed Re, ReSx, Ru, and Pt. The identity and kinetic relevance of elementary steps for desulfurization (to C4¬ hydrocarbons) and hydrogenation (to tetrahydrothiophene; THT) are similar among these catalysts; they involve the kinetically-relevant formation of a thiophene-derived intermediate (monohydrothiophene on Re and ReSx; dihydrothiophene on Ru and Pt) that either cleaves its C-S bond or “over-hydrogenates” to THT in one surface sojourn. THT then undergoes C-S bond cleavage in secondary reactions that correct such over-hydrogenation to form the more unsaturated species that cleave C-S bonds. THT/C4 product ratios are insensitive to H2S/H2 ratios and thiophene pressure, even though active interstitial spaces are covered by kinetically-detectable coverages of S* and thiophene; therefore, primary and secondary reactions must involve the same active surfaces. The observed increase in THT/C4 ratios with H2 pressure shows that THT formation transition states involve a larger number of H-atoms than for C-S cleavage. The requirement for bound species with intermediate unsaturation (between THT and thiophene) for C-S bond cleavage is reminiscent of the H-shuttling required in C-C and C-O hydrogenolysis, reactions that involve the partial dehydrogenation of alkanes and alkanols, respectively, to weaken such bonds and to increase the formation entropy of the relevant transition states via the evolution of H2(g). These mechanistic details challenge prevalent paradigms about different site requirements for hydrogenation and desulfurization pathways and about how metal-sulfur bond energies act as descriptors of reactivity; in fact, such binding energies merely act to define the refractory S-adlayers that enable the formation of weakly-binding interstices that reversibly bind intermediates and transition states, thus allowing catalytic turnovers.
Disordered, Sub-Nanometer Ru Structures on CeO 2 are Highly Efficient and Selective Catalysts in Polymer Upcycling by Hydrogenolysis
We report non-degradable polyolefin plastics pose severe environmental threats, and thus demand efficient upcycling technologies. In this work, we discovered that low-loading (= 0.25 wt%) Ru/CeO 2 exhibits remarkable catalytic performance in the hydrogenolysis of polypropylene (PP), polyethylene (PE), and n-C 16 H 34 that is superior to high-loading (= 0.5 wt%) Ru/CeO 2 . They possess high PP conversion efficiency (7-fold increase over current literature reports), low selectivity towards undesired CH 4 , and good isomerization ability. In the low-loading range, the intrinsic activity of Ru in PP hydrogenolysis increases as the particle size decreases, opposite of the trend in the high-loading range. Detailed characterization revealed that the abrupt changes in catalytic behaviors coincide with Ru species transitioning from well-defined to highly disordered structures in the low-loading domain. The disordered Ru species were shown to be sub-nanometer in size and cationic. Mechanistically, the regioselectivity and the rate dependence on hydrogen pressure of C-C bond cleavage are different on low- and high-loading Ru/CeO 2 , both explained by the higher coverage of adsorbed hydrogen (*H) on low-loading Ru/CeO 2 . This work uncovers the remarkable catalytic performance of highly disordered, sub-nanometer, cationic Ru species in polyolefin hydrogenolysis, opening immense opportunities to develop effective, selective, and versatile catalysts for plastic upcycling.
Positive Ru-98 and Ru-99 Anomalies in Iron Meteorites
Small positive anomalies in Ru-98 and Ru-99 in IIAB iron meteorites relative to a terrestrial standard may reflect Tc-Ru fractionation in the precursor metal of the asteroidal core.
Ultrafast Charge Transfer and Electron Delocalization in a Cyanide-Bridged Ru-Ru Dimer Investigated with Femtosecond Transient X-Ray and IR Spectroscopies
Transient IR and X-Ray spectroscopies were used to investigate excited state delocalization of a mixed valence Ru based donor-bridge-acceptor complex on a femtosecond timescale revealing the role of the electron density on the Ru-CN-Ru fragment