RuPd Alloy Nanoparticles Supported on N-Doped Carbon as an Efficient and Stable Catalyst for Benzoic Acid Hydrogenation

RhRu Bimetallic Oxide Cluster Catalysts for Cross-Dehydrogenative Coupling of Arenes and Carboxylic Acids

Noble-metal-based bimetallic oxide clusters are promising novel catalysts. In this study, we developed carbon-supported RhRu bimetallic oxide clusters (RhRuOx/C) with a mean diameter of 1.2 nm, which showed remarkable catalytic activity for the cross-dehydrogenative coupling (CDC) of arenes and carboxylic acids with O2 as the sole oxidant. RhRu bimetallic oxide cluster formation was confirmed by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy and synchrotron X-ray absorption spectroscopy. Kinetic isotope and substituent effects indicated that arene C-H bond cleavage was the rate-determining step and proceeded via electrophilic concerted metalation-deprotonation mechanism, with a carboxylate as an internal base. Density functional theory calculations supported the proposed mechanism and indicated that the active center for C-H bond activation was Rh(V) rather than Rh(III), while Ru enhanced the electrophilicity of the Rh(V) site by decreasing the negative charge of the surrounding oxygen atoms. Electron-rich arenes showed relatively high reactivity for the RhRuOx/C-catalyzed CDC reaction, and both aliphatic and aromatic carboxylic acids were applicable to the reaction. The RhRuOx/C catalyst is promising for the CDC reaction of arenes and carboxylic acids to produce aryl esters. This work promotes the development of noble-metal-based bimetallic oxide clusters for C-H bond activation reactions.

First synthesis of RuSn solid-solution alloy nanoparticles and their enhanced hydrogen evolution reaction activity

Solid-solution alloys based on platinum group metals and p-block metals have attracted much attention due to their promising potential as materials with a continuously fine-tunable electronic structure. Here, we report on the first synthesis of novel solid-solution RuSn alloy nanoparticles (NPs) by electrochemical cyclic voltammetry sweeping of RuSn@SnOx NPs. High-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy maps confirmed the random and homogeneous distribution of Ru and Sn elements in the alloy NPs. Compared with monometallic Ru NPs, the RuSn alloy NPs showed improved hydrogen evolution reaction (HER) performance. The overpotentials of Ru0.94Sn0.06 NPs/C and Ru0.87Sn0.13 NPs/C to achieve a current density of 10 mA cm-2 were 43.41 and 33.19 mV, respectively, which are lower than those of monometallic Ru NPs/C (53.53 mV) and commercial Pt NPs/C (55.77 mV). The valence-band structures of the NPs investigated by hard X-ray photoelectron spectroscopy demonstrated that the d-band centre of RuSn NPs shifted downward compared with that of Ru NPs. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure analyses indicated that in the RuSn alloy NPs, charge transfer occurs from Sn to Ru, which was considered to result in a downward shift of the d-band centre in RuSn NPs and to regulate the adsorption energy of intermediate Hads effectively, and thus enable the RuSn solid-solution alloy NPs to exhibit excellent HER catalytic properties.

Ultrasonic in-situ reduction preparation of SBA-15 loaded ultrafine RuCo alloy catalysts for efficient hydrogen storage of various LOHCs

SBA-15-loaded RuCo alloy nanoparticle catalysts (RuxCoy/S15-SU) for the efficient catalysis of hydrogen storage by various liquid organic hydrogen carriers (LOHCs) were prepared via strong electrostatic adsorption (SEA)-ultrasonic in-situ reduction (UR) technology. The above prepared catalysts were subjected to a series of characterization, such as XPS, H2-TPD/TPR, N2 adsorption-desorption, ICP, CO-chemisorption, FT-IR, XRD and TEM. Ru3+ and Co2+ were evenly anchored on the surface of SBA-15 by SEA, and ultrafine RuCo alloy nanoparticles were formed by UR without any chemical reducing or stabilizing agents. The addition of Co enhanced the dispersion and antioxidant capacity of the RuCo alloy NPs with an average particle size of 2.07 nm and increased the number of catalytically active sites. The synergistic effect of ultrafine particle size and electron transfer between Co and Ru improved the catalytic performance of monobenzyltoluene (MBT) for hydrogen storage. SEA-UR technology strengthened the coordination effect between RuCo alloy NPs and Si-OH, which enhanced the catalytic stability. H2-TPD and H2-TPR indicated that the addition of Co led to more activated H2 to produce hydrogen overflow. For the hydrogenation of MBT, the produced Ru2Co1/S15-SU showed excellent catalytic performance. The hydrogen storage efficiency of MBT was 99.98 % under 110 °C and 6 MPa H2 for 26 min, and the TOF was 145 min-1, which is significantly superior to that of Ru/S15-SU catalyst and that reported in the literature. The hydrogen storage efficiency was still as high as 99.7 % after ten cycles, which was much better than that of Ru/S15-SU and commercial 5 wt% Ru/Al2O3. Ru2Co1/S15-SU is also suitable for efficiently catalyzing hydrogen storage of N-ethylcarbazole, dibenzyltoluene and acenaphthene.

Optimizing the synergy between alloy and alloy-oxide interface for CO oxidation in bimetallic catalysts

Creating synergetic metal-oxide interfaces is a promising strategy to promote the catalytic performance of heterogeneous catalysts. However, this strategy has been mainly applied to monometallic catalysts, while scarcely applied to alloy catalysts. In this work, we present a comprehensive study on the synergetic alloy-oxide interfaces in the bimetallic Pt-Co/Al₂O₃ catalysts for CO oxidation. A series of Pt₁Co_x/Al₂O₃ catalysts with various Co/Pt molar ratios with x ranging from 0.5 to 3.8 was synthesized via a facile wet-chemistry strategy. Among them, the Pt₁Co_0.5/Al₂O₃ catalyst exhibits the best catalytic performance for CO oxidation, with the lowest CO complete conversion temperature of -10 °C and the highest mass specific rate of 2.61 (mol CO) h^-1 (g Pt)^-1. From in situ X-ray absorption fine structure and diffuse reflectance infrared Fourier-transform spectroscopy studies, the superior catalytic performance of Pt₁Co_0.5/Al₂O₃ originates from the optimal length of the three-dimensional alloy-oxide perimeter sites. We further extended this strategy to other bimetallic systems of Pt-Fe and Pt-Ni, which also show similar structural properties and remarkable promotional effects on the catalytic activity.

MOF-derived Ru@ZIF-8 catalyst with the extremely low metal Ru loading for selective hydrogenolysis of C–O bonds in lignin model compounds under mild conditions

A MOF-derived Ru@ZIF-8 catalyst with extremely low Ru loading effectively cleaved the C–O bonds of lignin model compounds under mild conditions.

N-doped graphitized carbon supported Co@Ru core–shell bimetallic catalyst for hydrogen storage of N-ethylcarbazole

We investigate the hydrogenation of one promising liquid organic hydrogen carrier N-ethylcarbazole on the N-doped graphitized carbon (NGC) supported Co@Ru core–shell bimetallic catalyst.

Nitrogen-Doped Reduced Graphene Oxide Supported Pd4.7Ru Nanoparticles Electrocatalyst for Oxygen Reduction Reaction

It is imperative to design an inexpensive, active, and durable electrocatalyst in oxygen reduction reaction (ORR) to replace carbon black supported Pt (Pt/CB). In this work, we synthesized Pd_4.7Ru nanoparticles on nitrogen-doped reduced graphene oxide (Pd_4.7Ru NPs/NrGO) by a facile microwave-assisted method. Nitrogen atoms were introduced into the graphene by thermal reduction with NH₃ gas and several nitrogen atoms, such as pyrrolic, graphitic, and pyridinic N, found by X-ray photoelectron spectroscopy. Pyridinic nitrogen atoms acted as efficient particle anchoring sites, making strong bonding with Pd_4.7Ru NPs. Additionally, carbon atoms bonding with pyridinic N facilitated the adsorption of O₂ as Lewis bases. The uniformly distributed ~2.4 nm of Pd_4.7Ru NPs on the NrGO was confirmed by transmission electron microscopy. The optimal composition between Pd and Ru is 4.7:1, reaching −6.33 mA/cm² at 0.3 V_RHE for the best ORR activity among all measured catalysts. Furthermore, accelerated degradation test by electrochemical measurements proved its high durability, maintaining its initial current density up to 98.3% at 0.3 V_RHE and 93.7% at 0.75 V_RHE, whereas other catalysts remained below 90% at all potentials. These outcomes are considered that the doped nitrogen atoms bond with the NPs stably, and their electron-rich states facilitate the interaction with the reactants on the surface. In conclusion, the catalyst can be applied to the fuel cell system, overcoming the high cost, activity, and durability issues.

Electrocatalytic hydrogenation of benzoic acids in a proton-exchange membrane reactor

The highly efficient chemoselective electrocatalytic hydrogenation of benzoic acids (BAs) to cyclohexanecarboxylic acids (CCAs) was carried out in a proton-exchange membrane reactor under mild conditions without hydrogenation of the carboxyl group. Among the investigated catalysts, the PtRu alloy catalyst was found to be the most suitable for achieving high current efficiencies for production of CCAs. An electrochemical spillover mechanism on the PtRu alloy catalyst was also proposed.

Hydrogenation of benzoic acid derivatives over Pt/TiO2 under mild conditions

Hydrogenation of benzoic acid (BA) to cyclohexanecarboxylic acid (CCA) has important industrial and academic significance, however, the electron deficient aromatic ring and catalyst poisoning by carboxyl groups make BA hydrogenation a challenging transformation. Herein, we report that Pt/TiO₂ is very effective for BA hydrogenation with, to our knowledge, a record TOF of 4490 h^-1 at 80 °C and 50 bar H₂, one order higher than previously reported results. Pt/TiO₂ catalysts with electron-deficient and electron-enriched Pt sites are obtained by modifying the electron transfer direction between Pt and TiO₂. Electron-deficient Pt sites interact with BA more strongly than electron-rich Pt sites, helping the dissociated H of the carboxyl group to participate in BA hydrogenation, thus enhancing its activity. The wide substrate scope, including bi- and tri-benzoic acids, further demonstrates the high efficiency of Pt/TiO₂ for hydrogenation of BA derivatives.

Effects of Surface Oxygen-Containing Groups of the Flowerlike Carbon Nanosheets on Palladium Dispersion, Catalytic Activity and Stability in Hydrogenolytic Debenzylation of Tetraacetyldibenzylhexaazaisowurtzitane

The influence of the surface chemical properties of the carbon support on the Pd dispersion, activity and stability of Pd(OH)2/C catalyst for the hydrogenolytic debenzylation of tetraacetyldibenzylhexaazaisowurtzitane (TADB) was studied in detail. The flowerlike nanosheet carbon material (NSC) was chosen as the pristine support, meanwhile chemical oxidation with nitric acid and physical calcination at 600 °C treatments were used to modify its surface properties, which were denoted as NSCox-2 (treated with 20 wt% HNO3) and NSC-600, respectively. The three carbon supports and the corresponding catalysts of Pd/NSC, Pd/NSC-600, and Pd/NSCox-2 were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), nitrogen sorption isotherm measurement (BET), powder X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectra (XPS), temperature-programmed desorption (TPD), temperature-programmed reduction (H2-TPR), thermogravimetric analysis (TG), and element analysis. The debenzylation activities of Pd/NSC, Pd/NSC-600, and Pd/NSCox-2, as well as the three catalysts after pre-reduction treatment were also evaluated. It was found that the activity and stability of the Pd(OH)2/C catalysts in the debenzylation reaction highly depended on the content of surface oxygen-containing groups of the carbon support.

Insights into the Interfacial Effects in Heterogeneous Metal Nanocatalysts toward Selective Hydrogenation

Heterogeneous metal catalysts are distinguished by their structure inhomogeneity and complexity. The chameleonic nature of heterogeneous metal catalysts have prevented us from deeply understanding their catalytic mechanisms at the molecular level and thus developing industrial catalysts with perfect catalytic selectivity toward desired products. This Perspective aims to summarize recent research advances in deciphering complicated interfacial effects in heterogeneous hydrogenation metal nanocatalysts toward the design of practical heterogeneous catalysts with clear catalytic mechanism and thus nearly perfect selectivity. The molecular insights on how the three key components (i.e., catalytic metal, support, and ligand modifier) of a heterogeneous metal nanocatalyst induce effective interfaces determining the hydrogenation activity and selectivity are provided. The interfaces influence not only the H₂ activation pathway but also the interaction of substrates to be hydrogenated with catalytic metal surface and thus the hydrogen transfer process. As for alloy nanocatalysts, together with the electronic and geometric ensemble effects, spillover hydrogenation occurring on catalytically "inert" metal by utilizing hydrogen atom spillover from active metal is highlighted. The metal-support interface effects are then discussed with emphasis on the molecular involvement of ligands located at the metal-support interface as well as cationic species from the support in hydrogenation. The mechanisms of how organic modifiers, with the ability to induce both 3D steric and electronic effects, on metal nanocatalysts manipulate the hydrogenation pathways are demonstrated. A brief summary is finally provided together with a perspective on the development of enzyme-like heterogeneous hydrogenation metal catalysts.

Ru x Pd y Alloy Nanoparticles Uniformly Anchored on Reduced Graphene Oxide Nanosheets (Ru x Pd y @rGO): A Recyclable Catalyst

In this work, Ru _x Pd _y alloy nanoparticles were uniformly decorated on a two-dimensional reduced graphene oxide (rGO) sheet by an in situ chemical co-reduction process. The resulting products were characterized by various physiochemical techniques such as X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma atomic absorption spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. Further, the synthesized Ru _x Pd _y @rGO nanocomposites have been employed as a heterogeneous catalyst for three different catalytic reactions: (1) dehydrogenation of aqueous ammonia borane (AB); (2) hydrogenation of aromatic nitro compounds using ammonia borane as the hydrogen source, and (3) for the synthesis of aromatic azo derivatives. The present work illustrates the sustainable anchoring of metal nanoparticles over the surface of rGO nanosheets, which could be used for multifarious catalytic reactions.

Ruthenium nanodendrites on reduced graphene oxide: an efficient water and 4-nitrophenol reduction catalyst

A green and efficient protocol is reported for the elegant design of reduced graphene oxide (rGO)-supported Ru nanodendrites for promotion of electrochemical water reduction in a wide pH range as well as for environmental remediation.

Microcalorimetric adsorption and infrared spectroscopic studies of supported Pd, Ru and Pd–Ru catalysts for the hydrogenation of aromatic rings with carboxyl groups

Pd–Ru/SiO₂ showed special surface chemical properties that were totally different from those of Pd/SiO₂ and Ru/SiO₂ and exhibited high activity and selectivity for the hydrogenation of benzoic acid to cyclohexanecarboxylic acid.

Chemoselective hydrogenation of heteroarenes and arenes by Pd-Ru-PVP under mild conditions

Monometallic (Pd, Ru or Rh) and bimetallic (Pd_0.5–Ru_0.5) alloy NPs catalysts were examined for the hydrogenation of quinoline. Pd–Ru alloy catalyst showed superior catalytic activity to the traditional Rh catalyst. The characterization of Pd_0.5–Ru_0.5 catalysts, HAADF-EDX mapping and XPS analysis suggested that the alloy state of PdRu catalysts remained unchanged in the recovered catalyst. Furthermore, the catalyst was highly selective for the hydrogenation of different arenes.

Recyclable Pd_0.5Ru_0.5–PVP catalyst showed higher activity than monometallic Pd or Ru catalyst for the hydrogenation of quinoline. Furthermore, Pd_0.5Ru_0.5–PVP was able to hydrogenate different arenes.

Boosting Catalysis of Pd Nanoparticles in MOFs by Pore Wall Engineering: The Roles of Electron Transfer and Adsorption Energy

The chemical environment of metal nanoparticles (NPs) possesses significant influence on their catalytic performance yet is far from being well understood. Herein, tiny Pd NPs are encapsulated into the pore space of metal-organic frameworks (MOFs), UiO-66-X (X = H, OMe, NH₂ , 2OH, 2OH(Hf)), affording Pd@UiO-66-X composites. The surface microenvironment of the Pd NPs is readily modulated by pore wall engineering, via the functional group and metal substitution in the MOFs. Consequently, the catalytic activity of Pd@UiO-66-X follows the order of Pd@UiO-66-OH > Pd@UiO-66-2OH(Hf) > Pd@UiO-66-NH₂ > Pd@UiO-66-OMe > Pd@UiO-66-H toward the hydrogenation of benzoic acid. It is found that the activity difference is not only ascribed to the distinct charge transfer between Pd and the MOF, but is also explained by the discriminated substrate adsorption energy of Pd@UiO-66-X (-OH < -2OH(Hf) < -NH₂ < -OMe < -H), based on CO-diffuse reflectance infrared Fourier transform spectra and density-functional theory (DFT) calculations. The Pd@UiO-66-OH, featuring a high Pd electronic state and moderate adsorption energy, displays the highest activity. This work highlights the influence of the surface microenvironment of guest metal NPs, the catalytic activity of which is dominated by electron transfer and the adsorption energy, via the systematic substitution of metal and functional groups in host MOFs.

Heterogeneous Catalytic Hydrogenation of Levulinic Acid to γ-Valerolactone with Formic Acid as Internal Hydrogen Source

As one of the most promising biomass-based platform molecules, γ-valerolactone (GVL) can be synthesized from a variety of lignocellulosic feedstocks through different hydrogen supply pathways. Among these transformation routes, the hydrogenation of levulinic acid (LA) to GVL by using formic acid (FA) as the internal hydrogen source is regarded as a critical path for the sustainable development of renewable energy systems. Although a large number of studies on the synthesis of GVL have been reported, the FA/LA catalytic system has not been interpreted as thoroughly as it should be. In this Minireview, core concerns are focused on key issues and their effects in this FA/LA catalytic system. The catalytic mechanism, together with competitive adsorption behavior between FA and LA on heterogeneous catalysts, is presented. The effects of active metal species and catalyst supports on the overall catalytic performance are summarized, and the influences of key condition parameters, including the time, temperature, FA/LA molar ratios, and aqueous solvent, are discussed. In particular, impacts and improvements of coke deposition and metal leaching, which could greatly affect the catalyst stability, are analyzed in detail. Additionally, several feasible suggestions for the enhancement of the catalytic efficiency and stability are also proposed.

Rational Design of Ruthenium and Cobalt-Based Composites with Rich Metal-Insulator Interfaces for Efficient and Stable Overall Water Splitting in Acidic Electrolyte

The great promise of hydrogen energy and hydrogen production from water through proton exchange membrane (PEM) or membrane-free electrolysis drives the pursuit of highly active and acid-stable electrocatalysts with dual functionality and reduced cost for overall water splitting in acidic media. Here, we report a new Ru-modified cobalt-based electrocatalyst embedded in a nitrogen-doped carbon (NC) matrix with rationally designed Mott-Schottky heterostructure to realize high activity and stability toward overall water splitting in a strongly acidic environment. Such a composite was facilely prepared by carbonization of cobalt-based MOF, followed by galvanic exchange between cobalt and Ru, and then controlled partial oxidation. The partial oxidation of RuCo implanted inside the NC matrix led to the formation of a class of RuO₂/Co₃O₄-RuCo@NC composites with rich metal-semiconductor interfaces to facilitate the charge-transfer process. As a result, the composite displayed remarkable electrocatalytic activity toward both oxygen/hydrogen evolutions in acidic media. Significantly, they also afforded low overpotentials of 247 and 141 mV for OER and HER, respectively, and a cell voltage of 1.66 V for overall water splitting at 10 mA cm^-2. In addition, excellent operation stability in 0.5 M H₂SO₄ solutions, comparable to those of them working in alkaline conditions, is demonstrated due to the protection of a coated carbon thin film. The presented work opens a new opportunity toward designing bifunctional electrocatalysts for acidic water electrolysis.

Pd-coated Ru nanocrystals supported on N-doped graphene as HER and ORR electrocatalysts

Here, Pd-coated Ru nanocrystals supported on N-doped graphene (Pd-Ru@NG) are obtained via electroless deposition of Pd on Ru nanocrystals. We have demonstrated that Pd boosts the electrocatalytic performance of Pd-Ru@NG towards the hydrogen evolution reaction (HER) and alcohol tolerant oxygen reduction reaction (ORR) as compared to Pt/C.

Catalytic Activity of Bimetallic (Ruthenium/Palladium) Nano-alloy Decorated Porous Carbons Toward Reduction of Toxic Compounds

Chicken feather-derived high-surface-area porous activated carbon (CFAC) material was prepared using chemical activation. A new composite composed of Ru-Pd nanoparticles supported on CFAC (Ru-Pd@CFAC) has been prepared by microwave-thermal reduction in the presence of the support. Characterization by XRD, Raman, BET, FE-SEM/TEM, FT-IR, TGA, XPS, HAADF-STEM-EDS, H₂ -chemisorption, H₂ -TPR, and ICP-AES was used to analyze the catalyst. This catalyst is found to be efficient for the reduction of hexavalent chromium (Cr^VI ), potassium ferricyanide (K₃ [Fe(CN)₆ ]), 4-nitrophenol (4-NP), and pendimethalin (PDM), at room temperature, and remains stable, even after several repeated runs. Moreover, it showed excellent catalytic activity compared with the monometallic counterparts.

Self-recoverable Pd-Ru/TiO2 nanocatalysts with ultrastability towards ethanol electrooxidation

Self-recoverable Pd-Ru/TiO2 nanocatalysts have been prepared by electrochemical stripping of Pd-Ru/TiO2 precursors. For the ethanol oxidation reaction (EOR), these Pd-Ru/TiO2 nanocatalysts are used as an anode catalyst. The characterization of catalysts via chronoamperometry has been repeated 15 times. After 15 stability tests, the Pd1Ru0.69/TiO2 nanocatalysts still achieve a factor of 9.4 enhancement at the residual current density (309.42 mA mgPd-1) for the EOR over commercial Pd/C catalysts (33.01 mA mgPd-1). From the 5th to 15th test, when each 10 000 s stability test is performed in a fresh ethanol electrolyte, the initial and residual current density of the catalysts could recover to the original or even better value in a few hours before performing another 10 000 s stability test. Herein, these Pd-Ru/TiO2 nanocatalysts with ultrastability towards ethanol electrooxidation are self-recoverable. Density functional theory calculations reveal that the introduction of oxophilic metal Ru and a TiO2 support into Pd-based catalysts and the synergistic effects between Ru and TiO2 have led to the ultrastability towards the EOR. The introduction of oxophilic metal Ru and a TiO2 support into catalysts can reduce the adsorption energy of OHads on the Pd-Ru/TiO2 nanocatalysts, and it will inhibit the COads produced and adsorbed on the Pd surface.