Ru Particles Research Articles

Comparative evaluation of Ru-coated fecralloy and SiC monolithic catalysts in catalytic partial oxidation of natural gas for hydrogen production

The catalytic activity of structured catalysts comprising Fecralloy and SiC monoliths coated with Ru/Mg-Al oxide by deposition–precipitation was evaluated in the partial oxidation of natural gas and compared with that of a conventional pellet catalyst. The geometric surface area (GSA) of the Fecralloy and SiC monolithic catalysts were 377.0 × 10-4 and 118.5 × 10-4 m2, respectively; significantly larger than that of the 0.5% Ru/Al2O3 pellet catalyst (89.6 × 10-4 m2). Owing to the high GSA of the structured catalysts, a small amount of Ru (0.070–0.12 wt%) resulted in highly dispersed uniform loading. Thus, the structured catalysts exhibited higher performance for catalytic partial oxidation at varying C/O2 ratio, inlet temperature, and gas hourly space velocity (GHSV) than the pellet catalyst. However, in a stability test at high GHSV (50,000 h−1), the CH4 conversion of the Fecralloy monolithic catalyst decreased rapidly from 90% to less than 70% in 150 min. In addition, the Mg-Al oxide layer of the Fecralloy monolithic catalyst was damaged owing to material deterioration, resulting in a loss of Ru particles. In contrast, CH4 conversion catalyzed by the SiC monolithic catalysts remained above 85% even after 1000 min, and the material or support layer was not damaged even under severe conditions.

Modification of the Electrochemical Surface Oxide Formation and the Hydrogen Oxidation Activity of Ruthenium by Strong Metal Support Interactions

A major hurdle for the wide spread commercialization of proton exchange membrane based fuel cells (PEMFCs) and water electrolyzers are the durability and high cost of noble metal catalysts. Here, alternative support materials might offer advantages, as they can alter the properties of a catalyst by means of a strong metal support interaction (SMSI) that has been shown to prevent platinum oxidation and suppress the oxygen reduction reaction on titanium oxide supported platinum nanoparticles deposited on a carbon support (Pt/TiOx/C). Herein, we report a novel Ru/TiOx/C catalyst that according to tomographic transmission electron microscopy analysis consists of partially encapsulated Ru particles in a Ru/TiOx-composite matrix supported on a carbon support. It is shown by cyclic voltammetry and X-ray photoelectron spectroscopy that ruthenium oxidation is mitigated by an SMSI between Ru and TiOx after reductive heat-treatment (Ru/TiOx/C400°C,H2 ). As a result, the catalyst is capable of oxidizing hydrogen up to the onset of oxygen evolution reaction, in stark contrast to a Ru/C reference catalyst. PEMFC-based hydrogen pump measurements confirmed the stabilization of the hydrogen oxidation reaction (HOR) activity on Ru/TiOx/C400°C,H2 and showed a ≈3-fold higher HOR activity compared to Ru/C, albeit roughly two orders of magnitude less active than Pt/C.

New catalysts based on reduced graphene oxide for hydrogen production from ammonia decomposition

Promising and highly novel catalysts based on ruthenium (Ru) supported on reduced graphene oxide were synthesized, characterized and tested for COx-free hydrogen generation by catalytic ammonia decomposition. Metal loading and amount of a pre-reducing agent clearly affect the catalytic properties of the final catalysts. A Ru loading higher than 2.5 wt% resulted in Ru particles of size higher than 5 nm, which were agglomerated, thus decreasing the amount of the most active sites (B5 type-sites) and therefore the ammonia conversion. Additionally, a graphene oxide (GO) hydrothermal pre-reduction with 2-chloroethylamine hydrochloride, led materials with a more ordered structure which is associated with a good electronic conductivity and, higher basicity. Optimal catalytic activity is achieved using a reducing agent/GO ratio of 5/3 (wt/wt) and a Ru loading of 2.5 wt%. Thus, 2.5Ru/10C-rGO catalyst resulted in excellent hydrogen (H2) production from ammonia decomposition, with an ammonia conversion close to 96% and hydrogen production rate of 9.1 mmolH2 gcat−1 min−1 at 400 °C. Reduced graphene oxide proved to be a suitable support in the development of nanosized Ru catalysts being the optimal one highly active in COx-free hydrogen generation during more than 60 h of reaction, providing virtuous stability.

Architectural design of core-shell nanotube systems based on aluminosilicate clay.

A nanoarchitectural approach to the design of functional nanomaterials based on natural aluminosilicate nanotubes and their catalysis, and practical applications are described in this paper. We focused on the buildup of hybrid core–shell systems with metallic or organic molecules encased in aluminosilicate walls, and nanotube templates for structured silica and zeolite preparation. The basis for such an architectural design is a unique Al2O3/SiO2 dual chemistry of 50 nm diameter halloysite tubes. Their structure and site dependent properties are well combined with biocompatibility, environmental safety, and abundant availability, which makes the described functional systems scalable for industrial applications. In these organic/ceramic hetero systems, we outline drug, dye and chemical inhibitor loading inside the clay nanotubes, accomplished with their silane or amphiphile molecule surface modifications. For metal–ceramic tubule composites, we detailed the encapsulation of 2–5 nm Au, Ru, Pt, and Ag particles, Ni and Co oxides, NiMo, and quantum dots of CdZn sulfides into the lumens or their attachment at the outside surface. These metal–clay core–shell nanosystems show high catalytic efficiency with increased mechanical and temperature stabilities. The combination of halloysite nanotubes with mesoporous MCM-41 silica allowed for a synergetic enhancement of catalysis properties. Finally, we outlined the clay nanotubes’ self-assembly into organized arrays with orientation and ordering similar to nematic liquid crystals, and these systems are applicable for life-related applications, such as petroleum spill bioremediation, antimicrobial protection, wound healing, and human hair coloring.

Size effect of Ru particles on the self-reforming-driven hydrogenolysis of a lignin model compound

The size effect of Ru/NiAl2O4 catalysts on the self-reforming-driven hydrogenolysis of a lignin model compound is investigated.

Highly selective synthesis of primary amines from amide over Ru-Nb2 O5 catalysts.

Amines are an important class of compounds in natural products and medicines. The universal availability of amides provides a potential way for the synthesis of amines. Herein, Ru/Nb2 O5 catalyst is demonstrated to be highly efficient and stable for the selective hydrogenation of propionamide to propylamine (as a model reaction), with up to 91.4% yield of propylamine under relatively mild conditions. Results from XPS analyses, CO chemisorption, TEM images and DRIFTS spectra revealed that the unique properties of Nb2 O5 can effectively activate the C=O group of amides, and the smaller Ru particles on Nb2 O5 could further promote the activation, leading to superior catalytic performance of Ru/Nb2 O5 for amide hydrogenation. Meanwhile, reducing the surface acidity of Nb2 O5 can greatly inhibit the side reactions to by-products, and further enhance the selectivity to amine. Moreover, this catalytic system is also applicable for the hydrogenation of a variety of amides and provides high potential for the industrial production of primary amines from amides.

Adsorption States of N2/H2 Activated on Ru Nanoparticles Uncovered by Modulation-Excitation Infrared Spectroscopy and Density Functional Theory Calculations.

The adsorption states of N2 and H2 on MgO-supported Ru nanoparticles under conditions close to those of ammonia synthesis (AS; 1 atm, 250 °C) were uncovered by modulation-excitation infrared spectroscopy and density functional theory calculations using a nanoscale Ru particle model. The two most intense N2 adsorption peaks corresponded to the vertical chemisorption of N2 on the nanoparticle's top and bridge sites, while the remaining peaks were assigned to horizontally adsorbed N2 in view of the site heterogeneity of Ru nanoparticles. Long-term observations showed that vertically adsorbed N2 molecules gradually migrated from the top sites to the bridge sites. Compared to those adsorbed vertically, N2 molecules adsorbed horizontally exhibited a lower dipole moment, an increased N─N bond distance, and a decreased N─N bond order (i.e., were activated), which was ascribed to enhanced Ru-to-N charge transfer. H2 molecules were preferentially adsorbed horizontally on top sites and then rapidly dissociated to afford strongly surface-bound H atoms and thus block the active sites of Ru nanoparticles. Our results clarify the controversial adsorption/desorption behavior of N2 and H2 on AS catalysts and facilitate their further development.

Unraveling the size-dependent effect of Ru-based catalysts on Ammonia synthesis at mild conditions

Identifying optimal Ru size in NH3 synthesis can improve reaction activity and maximize the utilization of Ru to reduce catalyst cost. However, previous researches are focused on large Ru particle size (≥2 nm) while that below 2 nm in NH3 synthesis is unclear. Here we synthesized a series of Rux/BaCeO3 with different Ru sizes (x = 1.1–3.0 nm) through size-controlled Ru colloid. With the decrease of Ru size, NH3 synthesis rate over Ru1.1/BaCeO3 increases to 19.4 mmol gcat−1h−1 at 400 °C and 1 MPa, which is 5.7 times that of Ru3.0/BaCeO3 and superior to most of Ru-based catalysts previously reported. It reveals that the reduction of Ru size enhances the generation of Ce3+ and oxygen vacancies in BaCeO3, which can donate electron to Ru centers and promote N2 dissociation. Moreover, the small Ru size enhances hydrogen spillover from Ru to BaCeO3 to alleviate hydrogen poisoning, resulting in efficient NH3 synthesis.

Surface tailored Ru catalyst on magadiite for efficient hydrogen generation

In the present study, a uniformly dispersed, highly durable and efficient ruthenium (Ru) catalyst for hydrogen production was successfully prepared by a facile template method induced by surface-tailored magadiite. The catalyst was systematically characterized and the results revealed that the uniformly dispersed Ru particles with showing an average size of 1.2 nm preferred to anchor on the surface of magadiite, rather than intercalated into the support. Catalytic activity and reutilization of the catalysts were evaluated by evaluating the H2 generation rate (HGR) from an alkaline NaBH4 solution. The maximum HGR at 25 °C reached 59276 ± 500 mL·min−1·g−1 (Ru) with the presence of 3 wt% NaOH and 1 wt% NaBH4. More importantly, the catalytic activity of the reused catalyst still remained 95.7% of the initial HGR after 20 runs. Thus, the catalyst shows high durability and excellent reutilization towards the hydrolysis of alkaline NaBH4 solution. The uniform decoration of Ru particles on magaditte surface is responsible for the high efficiency of the catalyst. This work has revealed that tailoring the distribution of Ru particles on magadiite surface via a simple template method is a promising route for fabricating high-performance hydrogen production catalysts.

Ammonia decomposition Ru catalysts supported on alumina nanofibers for hydrogen generation

The study of ruthenium catalysts for ammonia decomposition on carbonized and noncarbonized Al2O3 nanofibers (ANF) showed that activity of the catalysts with carbonized supports (ANFC) was twofold higher as compared to noncarbonized ones. Thus, on Ru/ANFC and Ru-Cs/ANFC the release of hydrogen reached 8.7 and 18.3 mmol H2/(min·gcat), respectively, whereas on Ru/ANF and Ru-Cs/ANF, only 4.4 and 9.6 mmol H2/(min·gcat), respectively. According to TEM, Ru particles on ANFC have a greater size than on ANF but are distributed more uniformly. As shown by TEM, XRD and XPS data, ANFC and ANF fibers are strongly different.

Transformations of citral over bifunctional Ru-H-Y-80 extrudates in a continuous reactor

One-pot transformations of citral were investigated over Ru-catalysts in a batch and a continuous mode over a powder catalyst and extrudates, respectively. Ru/H-Y-80 catalysts were prepared by different impregnation methods to obtain different particle sizes of Ru.The highest yield of isopulegols was 15% and yield of menthols was 3% with stereoselectivity to the desired (±)-menthol isomer of 42% after 5 h over the Ru/H-Y-80 powder catalyst with the smallest metal particles prepared by the incipient wetness impregnation method with six impregnation steps using Ru(NO)(NO3)3 as a precursor. This catalyst was synthesized with the Bindzil binder and shaped by extrusion.For comparison, also a catalyst with Ru deposited on the binder was prepared. Addition of 30 wt% Bindzil binder to Ru/H-Y-80 catalyst caused significant catalyst deactivation. Z/E-citral ratio decreased with increasing Ru particle size. Citral conversion and the yield of acyclic hydrogenation products were higher over the powder catalysts containing a mixture of zeolite and binder with a larger distance between the metal and the acid sites, i.e. with Ru deposited on the Bindzil binder. Long-term experiments in the continuous mode revealed comparable catalytic behaviour of both Ru-extrudates with the controlled metal location due to the presence of diffusion regime. The maximum yield of menthols, 6%, with stereoselectivity to the desired (±)-menthol of 73% was obtained during the transient state, below 2 h of time-on-stream. The reuse of Ru/H-Y-80 extrudates was successfully demonstrated.

An Active K‐OMS‐2 Supported Catalyst for Hydrogenolysis of Glycerol

AbstractPropanediols are very important chemical intermediates, which need to be prepared through commercially viable routes. Cryptomelane type octahedral molecular sieve‐2 (K‐OMS‐2), a cheap and environmentally benign microporous oxide was employed to support Ru and used as a catalyst to get 1,2‐propanediol (1,2‐PDO) selectively through hydrogenolysis of glycerol. Three catalysts with different Ru content were prepared and evaluated for glycerol hydrogenolysis. Among these, 1 wt.% Ru‐K‐OMS‐2 showed reasonably good activity towards 1,2‐PDO formation under moderate reaction conditions even at lower Ru loading (0.9 wt.%). When other metals such as Cu and Ni were supported on K‐OMS‐2, their performance was inferior compared to Ru‐supported catalysts. All the catalysts were characterized using various physicochemical techniques like XRD, N2‐sorption, TPD, H2‐TPR, TGA, ICP‐OES, FE‐SEM and TEM. The enhanced catalytic activity with the 1 wt.%Ru‐K‐OMS‐2 catalyst was attributed to the better Ru metal dispersion, higher active metal surface area, basic strength, and porosity of the support. The catalyst was found to be recyclable. Analysis of spent catalyst by TEM showed disintegration of Ru nanoparticles to smaller ones, under high H2 pressure at the reaction temperature. Smaller Ru particles are expected to promote C−C bond cleavage thus suppressing 1,2‐PDO formation. Furthermore, a relationship between the TOF value, Ru nanoparticles size, and the basic strength of the catalysts was established, which provides dipper insight into the different catalytic behavior of the catalysts.

Activated Carbon-Supported Ruthenium as a Catalyst for the Solvent- and Initiator-Free Aerobic Epoxidation of Limonene

The activity and selectivity of ruthenium catalysts supported on various activated carbons have been investigated in the epoxidation of limonene using molecular oxygen, the greenest oxidizing agent, under solvent/reductant- and initiator-free reaction conditions. The catalysts were prepared via different methods including impregnation, sol immobilization, and cation exchange. Supported Ru catalysts with a metal particle size ranging from 1.8 to 21 nm were obtained. The catalyst prepared by cation exchange using Darco G60, with the highest mesopore surface area and pore volume and the lowest Ru particle size (1.8 nm), was found to give the best combination of limonene conversion of 35% and higher selectivity for epoxidation products (Sepox) of 57% at 80 °C and 3 bar oxygen pressure, compared to the total selectivity of 25.5% for allylic oxidation products (Sallyl). Other activated carbon supports, e.g., Darco MRX, Norit RB4C, and Norit RX3, were found to yield less effective catalysts. In addition, the sol immobilization method led to the highest conversion of limonene (40.4%) but with a lower total selectivity toward epoxidation products (Sepox) of 36.8% and that toward allylic oxidation products (Sallyl) of 33.6%. The textural parameters of carbon-supported Ru catalysts were determined by BET, TEM, SEM, TPR, and CO chemisorption. Highly dispersed Ru particles were found to promote the formation of limonene epoxides via the reaction of limonene hydroperoxide with limonene instead of hydroperoxide decomposition to allylic radicals. Finally, the appropriate reaction conditions to maximize the selectivity of the epoxides and the reusability of the catalyst were established.

Steering the selectivity in CO2 reduction on highly active Ru/TiO2 catalysts: Support particle size effects

Aiming at a better understanding of the functioning of oxide-supported Ru catalysts in the reduction of CO2, a highly attractive reaction from ecologic reasons, we systematically investigated the influence of the support particle size on the performance of highly active Ru/TiO2 catalysts. Employing mixed rutile-anatase supported catalysts with different TiO2 particle size, but similar Ru particle size and loading, we found that after a reductive high-temperature (HT) treatment their selectivity can be controlled by the TiO2 particle size, from 100% methanation to 100% CO formation. Comprehensive characterization of the catalysts shows that the changes in reaction behavior are paralleled by significant modifications of their structural, chemical and electronic properties. We propose that the change in reaction characteristics is due to a HT-induced increase in O-vacancies and charge transfer to Ru interface atoms, which is more pronounced for high-surface-area catalysts. We see this approach as interesting strategy for tailoring catalyst properties.

Ru surface density effect on ammonia synthesis activity and hydrogen poisoning of ceria-supported Ru catalysts

Evaluating the effect of metal surface density on catalytic performance is critical for designing high-activity metal-based catalysts. In this study, a series of ceria (CeO2)-supported Ru catalysts (Ru/CeO2) were prepared to analyze the effect of Ru surface density on the catalytic performance of Ru/CeO2 for ammonia synthesis. For the Ru/CeO2 catalysts with Ru surface densities lower than 0.68 Ru nm−2, the Ru layers were in close contact with CeO2, and electrons were transferred directly from the CeO2 defect sites to the Ru species. In such cases, the adsorption of hydrogen species on the Ru sites in the vicinity of O atoms was high, leading to a high ammonia synthesis activity and strong hydrogen poisoning. In contrast, the preferential aggregation of Ru species into large particles on top of the Ru overlayer resulted in the coexistence of Ru clusters and particles, for catalysts with a Ru surface density higher than 1.4 Ru nm−2, for which Ru particles were isolated from the direct electronic influence of CeO2. Consequently, the Ru−CeO2 interactions were weak, and hydrogen poisoning can be significantly alleviated. Overall, electron transfer and hydrogen adsorption synergistically affected the synthesis of ammonia over Ru/CeO2 catalysts, and catalyst samples with a Ru surface density lower than 0.31 Ru nm−2 or exactly 2.1 Ru nm−2 exhibited high catalytic activity for ammonia synthesis.

Chimerism of Carbon by Ruthenium Induces Gradient Catalysis

AbstractImproving the round‐trip efficiency and cycle life of lithium‐oxygen batteries (LOBs) through the cathode design is essential for their employment in electric vehicles. Here, a neoteric chimeric air‐cathode is proposed, in which ultra‐dispersed ruthenium (Ru) nanoparticles are partially confined by microtube walls of free‐standing carbon textiles, but petty parts of Ru with catalytic surfaces are exposed. The special chimeric structure benefits not only for preventing nanocatalysts agglomeration but also tailoring the formation/decomposition mechanisms of lithium peroxide (Li2O2) during oxygen reduction/evolution reactions. Critically, theoretical simulations disclose that the enlarged chimeric catalyst‐support interphase between the Ru and carbon matrix enhances the electron density of Ru particles and then induces a gradient Gibbs free energy of LiO2 adsorption energy at active sites, and thus fundamentally modulates the morphology evolution mechanism of finial Li2O2. In the LOBs, the chimeric electrode affords a remarkably high energy efficiency of 84.1% and long‐term cyclability (260 cycles at 300 mA g−1).

Effects of support and promoter on Ru catalyst activity in microwave-assisted ammonia synthesis

Microwave-assisted ammonia synthesis is a promising alternative to the energy-intensive Haber-Bosch process, specially at small- and medium-scale with renewable H2 as resource. Here, we report that Cs promoted Ru/CeO2 catalyst exhibits considerable activity at 533 K and ambient pressure. In this work, the combined theoretical and experimental approaches are adopted to optimize the electronic and geometric structures of Ru on the catalysts. Both DFT modeling work and structural characterization show that the strong interaction between Ru and CeO2 results in the formation of highly dispersed Ru particles favoring ammonia synthesis. The higher electron donating ability of CeO2 and lower electronegativity of Cs promoter result in higher electron density on Ru reducing the N≡N dissociation barrier. The work demonstrates the potential of microwave-assisted catalytic process in activating stable molecules for ammonia synthesis.

The effect of Sibunit graphitization on the stability of Ru/(Pt, Pd)/Sibunit catalysts in an oxidizing atmosphere at elevated temperatures

The effect of high-temperature treatment on the thermal stability of a graphitic carbon material Sibunit in an oxidizing medium was studied in dependence on the presence of active component – Pt, Pd or Ru. According to thermal analysis data, a high-temperature pretreatment of Sibunit increases the onset temperature of carbon oxidation. It was found that holding of the Ru/Sibunit samples for 4 h in a nitrogen: air (1 : 1) mixture at a temperature of 400 °С resulted in a partial destruction of the pyrocarbon matrix of Sibunit and increased the mean size of Ru particles. It was demonstrated that ruthenium catalysts can efficiently oxidize CO at a temperature not higher than 200 °С and withstand overheats up to 400 °С without a significant loss in activity.

Ru-M (M = Fe or Co) Catalysts with high Ru surface concentration for Fischer-Tropsch synthesis

Ru-Co/Al2O3 and Ru-Fe/Al2O3 have been prepared by the reduction-deposition method. This approach favours the interaction between Ru and Fe or Co in the final catalysts, while increasing surface enrichment of Ru. Their performance for the Fischer-Tropsch Synthesis (FTS) has been evaluated in a fixed bed reactor. Ru-Co/Al2O3 displays the highest activity in the series, doubling the steady-state CO conversion rate of a Ru/Al2O3 catalyst with 3 times higher Ru loading. Ru-Fe/Al2O3 displays higher initial CO conversion and -CH2- productivity than Ru/Al2O3, but its activity declines during operation reaching lower conversion rates than Ru/Al2O3. In addition to CO2, Ru-Fe/Al2O3 produces oxygenated products, mainly alcohols. To a lesser extent, the formation of oxygenates over Ru-Co/Al2O3 and Ru/Al2O3 is also observed, and ascribed to the small crystallite size of the Ru particles. The evolution of CO2 during time on stream indicates that Fe is segregated to the surface of this catalyst during the FTS.

Hydrodeoxygenation of guiacol over ion-exchanged ruthenium ZSM-5 and BEA zeolites

Ion exchanged Ru/ZSM-5 and Ru/BEA catalysts, prepared by replacing the extra framework NH4+ cations in zeolites with Ru3+ ions, are employed for the hydrodeoxygenation of guaiacol. The performance results indicate ion-exchanged Ru zeolites, with extremely low Ru contents (~0.2 wt%), possess a high intrinsic HDO activity compared to the catalysts prepared by the incipient wetness impregnation method. On the basis of TEM, FTIR, XPS and TPD analysis, the NH4+ ions in zeolite were substituted by Ru species, with metal particles entered the zeolite cages and finely dispersed on the support. These ion-exchanged Ru particles exhibit a strong electronic interaction with oxygen atoms of zeolite framework with a mixed Ru(0)-Ru(III) species observed in the reduced samples. In contrast, only Ru0 was detected in the reduced impregnated Ru/ZSM-5. The partial-reduced Ru species over the ion-exchanged Ru/ZSM-5 catalyst shows a high H2 adsorption activity facilitating the hydrogenation of guaiacol to the saturated products (such as 2-methoxycyclohexanol). In addition, ion-exchanged Ru-ZSM-5 and Ru-BEA catalysts present a similar normalized cyclohexane formation rate (based on the concentration of acid sites), suggesting the acid sites play a pivotal role in the deoxygenation of 2-methoxycyclohexanol to cyclohexane.