Sites For Dissociation Research Articles

Enhanced low-temperature methane oxidation over Pd supported Mn-doped NiO catalyst

This study introduces a novel catalyst system comprising Pd nanoparticles loaded onto Mn-doped NiO for the efficient oxidation of methane (CH4) at low temperatures. The loading of Pd nanoparticles onto the Mn-doped support has yielded a catalyst with exceptional activity and stability, as evidenced by the lowest T50 temperature of 276 °C and a CH4 conversion reaching 97% at 325 °C. The catalyst demonstrates optimized reaction kinetics with the lowest activation energy of 69.2 kJ mol–1. The catalyst's superior performance is attributed to the synergistic effects of the Pd/Mn-NiO composite, which include a higher Pd2+/Pd4+ ratio, increased adsorptive oxygen concentration (Oads/Ototal), and a reduced Ni3+/Ni2+ ratio. These characteristics collectively enhance the catalytic activity for CH4 oxidation. The Mars-van Krevelen mechanism underpins the oxidation process, with Pd2+ identified as the principal active site for CH4 adsorption and dissociation. Diffuse reflectance infrared Fourier transform spectroscopy coupled with mass spectrometry elucidates the pathway of surface reactive oxygen species in the formation of key intermediates, such as formates, and underscores the accelerated decomposition of carbonate facilitated by the Pd modification on the Mn-NiO surface. The findings signify a significant advancement in the development of catalysts for environmental and energy-related applications, particularly in the mitigation of CH4 emissions.

A Multi‐Site Synergistic Effect in High‐Entropy Alloy for Efficient Hydrogen Evolution

AbstractUnraveling the mechanism driven by electronegativity‐dominated electronic configuration is crucial for developing high‐entropy alloys as efficient catalyst for hydrogen evolution reaction (HER). In this work, different atoms with diverse electronegativities are explored to regulate the electrocatalytic activity of PtFeCoNi@HCS toward HER, resulting in PtFeCoNiCuCr@HCS with an overpotential of 29 mV at 10 mA cm−2 and enhanced durability surpassing that of commercial 20% Pt/C in KOH environment. Based on various physicochemical and electrochemical techniques as well as density functional theory calculations, a multi‐site synergistic effect within PtFeCoNiCuCr@HCS material is elucidated in terms of both structural composition and electrocatalytic process. Briefly, Pt and Cu serve as the fundamental elements to form face‐centered cubic crystal framework, Cr primarily functions as an electron donor to regulate the electronic configuration, Co serves as the main active site for water dissociation, and the produced hydrogen species prefer to transfer toward Pt, Fe, and Cu sites for hydrogen formation. This work offers an in‐depth insight on the synergistic mechanism in high entropy alloys and is helpful for designing efficient electrocatalysts.

Constructing CO-immune water dissociation sites around Pt to achieve stable operation in high CO concentration environment

The serious problem of carbon monoxide (CO) poisoning on the surface of Pt-based catalysts has long constrained the commercialization of proton exchange membrane fuel cells (PEMFCs). Regeneration of Pt sites by maintaining CO scavenging ability through precise construction of the surface and interface structure of the catalyst is the key to obtaining high-performance CO-resistant catalysts. Here, we used molybdenum carbide (MoCx) as the support for Pt and introduced Ru single atoms (SA-Ru) at the Pt-MoCx interface to jointly decrease the CO adsorption strength on Pt. More importantly, the MoCx and SA-Ru are immune to CO poisoning, which continuously assists in the oxidation of adsorbed CO by generating oxygen species from water dissociation. These two effects combine to confer this anode catalyst (SA-Ru@Pt/MoCx) remarkable CO tolerance and the ability to operate stably in fuel cell with high CO concentration (power output 85.5 mW cm−2@20,000 ppm CO + H2 – O2), making it possible to directly use the cheap reformed hydrogen as the fuel for PEMFCs.

Atomically dispersed ruthenium in transition metal double layered hydroxide as a bifunctional catalyst for overall water splitting

Efficient and sustainable energy conversion depends on the rational design of single-atom catalysts. The control of the active sites at the atomic level is vital for electrocatalytic materials in alkaline and acidic electrolytes. Moreover, fabrication of effective catalysts with a well-defined surface structure results in an in-depth understanding of the catalytic mechanism. Herein, a single atom ruthenium dispersed in nickel-cobalt layered hydroxide (Ru-NiCo LDH) is reported. Through the precise controlling of the atomic dispersion and local coordination environment, Ru-NiCo LDH//Ru-NiCo LDH provides an ultra-low overpotential of 1.45 mV at 10 mA cm−2 for the overall water splitting, which surpasses that of the state-of-the-art Pt/C/RuO2 redox couple. Density functional theory calculations show that Ru-NiCo LDH optimizes hydrogen evolution intermediate adsorption energies and promotes O-O coupling at a Ru-O active site for oxygen evolution, while Ni serves as the water dissociation site for effective water splitting. As a potential model, Ru-NiCo LDH shows enhanced water splitting performance with potential for the development of promising water-alkaline catalysts.

Nickel oxide/nickel nanohybrids for oxygen and hydrogen evolution in alkaline media

Ni-based materials are cost-efficient electrocatalysts for the oxygen and hydrogen evolution reactions (OER and HER). Specifically, high-valence nickel oxides have been recently identified as highly active for both reactions; however, the origin of their activity during operation, particularly towards the HER, is still undefined. Herein, electrodeposition was used to produce Ni-based electrocatalysts supported on carbon fiber paper, followed by UV/O3 treatment to oxidize and modify their surface chemistry. The resulting electrodes were composed of nanoclusters formed by a metallic nickel core and ultrathin sheets of a high-valence nickel oxide whose crystalline structure was similar to NiO2, with Ni2+/Ni3+ oxidation states. Upon investigating the effect of the electrochemical conditioning of these high-valence nickel oxide/nickel electrodes, confirming the formation of surface β-Ni(OH)2. This surface layer improved the performance of the electrode by providing active sites for H2O adsorption and dissociation, as indicated by detailed density functional theory (DFT) calculations. The origin of the higher HER activity of β-Ni(OH)2 (001) surface compared to NiO2 (2D), and Ni (111) surfaces is attributed to its unique electronic structure. The high valence nickel oxide/nickel electrodes possessed robust long-term OER and HER stability over 24h Finally, the potential for modifying the structural composition of these electrodes and their use as bifunctional electrocatalysts for the water-splitting reaction was demonstrated by using the resulting electrodes in an electrolyzer coupled with/without a photovoltaic cell.

Breakthrough in CO2 Electroreduction to Multi‐Carbon Products at Ampere‐Level Enabled by Active Sites Engineering

AbstractEfficient production of value‐added chemicals with high selectivity from CO2 electroreduction at industrial‐level current density is highly demanded, yet remains a big challenge. In a recent issue of Angewandte Chemie, Han and colleagues have elegantly increased the Faradaic efficiency (FE) of multi‐carbon (C2+) products to over 70 % at amperes level (1.4 A cm−2) by engineering the active sites for the key reactions involved in the CO2 electroreduction. In this study, the highly dispersed Pd atoms have two unique functions: active sites for water dissociation and to induce the electron rearrangement of the surrounding Cu atoms to form new active sites for CO conversion, while the Cu far from Pd are the active sites for efficient CO2 conversion to CO, the synergistic functions of these three active sites result in high FE and yields of C2+ products at industrial‐level current density. This research is a remarkable step forward in the methodology for developing efficient and durable catalysts for CO2 electroreduction and beyond.

Hydrogenation of inert aromatic compounds under mild conditions catalyzed by confined trimetal sites in porous metal silicate materials

Complete hydrogenation of aromatic compounds is an important subject in various industry fields. However, due to the high stabilization energy of aromatic compounds resulting from their high aromaticity and non-polarity, the hydrogenation reaction is usually performed under harsh reaction conditions in the presence of noble metal-based catalysts. We report herein a porous metal silicate (PMS) material PMS-58, which consists of Cu, Ce and Co trimetal active sites, demonstrating high catalytic activity and selectivity in hydrogenating of a series of aromatic compounds under mild conditions (60 °C and 0.5 MPa H2). PMS-58 is superior to the previously reported non-noble metal-based catalysts and could be favorably compared to noble metal-based catalysts. The unique catalytic properties of PMS-58 are derived from the synergistic work of trimetal sites with Ce species serving as strong Lewis acid sites for dissociation of dihydrogen, Co species stabilizing Cu(I) species, and Cu(I) species playing a crucial role in activating aromatic rings. Therefore, this work provides a new approach in developing highly efficient non-noble metal catalysts for complete hydrogenation of arenes under mild conditions, which could be applied in removal of aromatic compounds in petroleum products.

The Relation between Nature and Stability of H2‐Dissociating Sites and Propene Selectivity in Silica‐Supported (Ga,Al)2O3 Mixed Oxide Propane Dehydrogenation Catalysts

AbstractColloidal solutions of gallia‐alumina (Ga,Al)2O3(x:y) solid‐solution nanoparticles with nominal atomic Ga : Al (x:y) ratios of 1 : 6, 1 : 3, 3 : 1, and 1:0 were used to prepare silica‐supported catalysts for propane dehydrogenation (PDH). A comparison of the unsupported and silica‐supported catalysts reveals that the dispersion on silica increases the Ga‐normalized PDH rates for all catalysts, albeit with a notably lower propene selectivity for (Ga,Al)2O3(1:6)/SiO2. Fourier transform infrared (FTIR) spectroscopy allows contrasting the H2 dissociation sites in the calcined and H2‐treated (Ga,Al)2O3(x:y)/SiO2, indicating a transformation of Ga3+ surface sites with Al (mainly) and Ga atoms in the second coordination sphere (Ga(Al/Ga) sites) in the calcined (Ga,Al)2O3(1:6)/SiO2 to predominantly Ga(Ga/Si) surface sites in the H2‐treated material. The resulting sites are similarly unselective as in amorphous gallia on silica. H2 produced during the PDH reaction can cause a similar transformation as H2 pretreatment in (Ga,Al)2O3(1:6)/SiO2, rapidly resulting in a notably lowered selectivity. The stable and selective Ga(Al/Ga) surface sites in (Ga,Al)2O3(1:3)/SiO2 yield a Ga−H band at ca. 1990 cm−1 under H2 dissociation conditions while the less selective surface sites, observed for the other Ga : Al ratios, give Ga−H bands at ca. 2040 and 2060 cm−1.

Manipulation of Oxidation States on Phase Boundary via Surface Layer Modification for Enhanced Alkaline Hydrogen Electrocatalysis.

In alkaline water electrolysis and anion exchange membrane water electrolysis technologies, the hydrogen evolution reaction (HER) at the cathode is significantly constrained by a high energy barrier during the water dissociation step. This study employs a phase engineering strategy to construct heterostructures composed of crystalline Ni4W and amorphous WOx aiming to enhance catalytic performance in the HER under alkaline conditions. This work systematically modulates the oxidation states of W within the amorphous WOx of the heterostructure to adjust the electronic states of the phase boundary, the energy barriers associated with the water dissociation step, and the adsorption/desorption properties of intermediates during the alkaline HER process. The optimized catalyst, Ni4W/WOx-2, with a quasi-metallic state of W coordinated by a low oxygen content in amorphous WOx, demonstrates exceptional catalytic performance (22 mV@10mA cm-2), outperforming commercial Pt/C (30 mV@10mA cm-2). Furthermore, the operando X-ray absorption spectroscopy analysis and theoretical calculations reveal that the optimized W atoms in amorphous WOx serve as active sites for water dissociation and the nearby Ni atoms in crystalline Ni4W facilitated the release of H2. These findings provide valuable insights into designing efficient heterostructured materials for energy conversion.

Dynamic restructuring of nickel sulfides for electrocatalytic hydrogen evolution reaction

Transition metal chalcogenides have been identified as low-cost and efficient electrocatalysts to promote the hydrogen evolution reaction in alkaline media. However, the identification of active sites and the underlying catalytic mechanism remain elusive. In this work, we employ operando X-ray absorption spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy to elucidate that NiS undergoes an in-situ phase transition to an intimately mixed phase of Ni3S2 and NiO, generating highly active synergistic dual sites at the Ni3S2/NiO interface. The interfacial Ni is the active site for water dissociation and OH* adsorption while the interfacial S acts as the active site for H* adsorption and H2 evolution. Accordingly, the in-situ formation of Ni3S2/NiO interfaces enables NiS electrocatalysts to achieve an overpotential of only 95 ± 8 mV at a current density of 10 mA cm−2. Our work highlighted that the chemistry of transition metal chalcogenides is highly dynamic, and a careful control of the working conditions may lead to the in-situ formation of catalytic species that boost their catalytic performance.

Kinetic-oriented design of pyrrolic-N induced Ni and C dual sites for exceptional H2O dissociation and alkaline HER

Due to the sluggish water dissociation in the alkaline hydrogen evolution reaction (HER), the developed electrocatalysts are crucial for enhanced water electrolysis. Herein, we present the nickel metal confined in pyrrolic-N-rich carbon nanoplates (Ni@NCP) for efficient alkaline HER. Benefiting from the polydopamine-derived pyrrolic-N-rich carbon, the uniformly distributed nickel nanoparticles maximize the electrocatalytic sites and are stable without severe corrosion under alkaline media. The in-situ and ex-situ analyses and density functional theory demonstrate that the pyrrolic-N modulates the Ni and C as dual active sites to facilitate the cleavage of the HO-H bond and the proton spillover, resulting in an acceleration of water dissociation and HER kinetics. As a result, Ni@NCP exhibits a low overpotential of 42 mV at 10 mA/cm2 current density and a Tafel slope of 94.9 mV/dec. This study not only provides insights into the structure-properties relationships, also emphasizes the importance of kinetically designing for various electrocatalytic applications.

Pinning-effect single-atom NiCo alloy embedded graphene-aerogel in electro-fenton process for rapid degradation of emerging contaminants

Inspired by the growing development of dual single-atom catalysts (SACs), a bimetallic single-atom alloy (SAA) based macro-assembled graphene aerogel (MAGA) was synthesized in this study. The single-atom NiCo alloy-based graphene aerogel (i.e., NiCo/GO aerogel) with pinning effect was used as a sustainable cathode material in an in-situ H2O2 generation system (i.e., electro-Fenton (EF) process). The atomic structure of NiCo/GO aerogel was identified by the combined microscopic and spectroscopic techniques. The SAA cathode exhibited a remarkable catalytic activity towards the two-electron-dominated oxygen reduction reaction (ORR) with the EF process for wastewater treatment. The energy consumption was calculated to be around 0.660 kW·h/t for treatment of water containing 2 mg L−1 ibuprofen (IBU). Density functional theory (DFT) analysis revealed the specific roles of the dual-functional NiCo SAA in the GO aerogel cathode, i.e., the Co sites more preferentially adsorb O2 molecules for H2O2 generation while the Ni sites function as the active sites for H2O2 dissociation and activation. The research findings shed light on the controlled synthesis of SAAs for advanced catalysis and its potential application in the treatment of emerging organic contaminants for water safety and pollution control.

Unlocking the electrochemical signature of Naringenin: Implications for screening in pharmaceutical formulations

Naringenin (NAR) is a versatile herbal flavonoid known for its broad pharmacological benefits, including antioxidant, anti-inflammatory, and anticancer properties. These properties underscore its potential and necessity for industrial applications within the pharmaceutical sector, making its detection and quantification crucial for ensuring the quality and efficacy of pharmaceutical products. Addressing the imperative for a sensitive and sustainable screening approach, this research leverages electrochemical analysis techniques including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). Complementary to experimental investigations, the electronic structure of NAR was probed using B3LYP/Def2-TZVPPD calculations alongside Fukui and dual descriptor analyses. Our findings delineate the dissociation kinetics of the hydroxyl groups within NAR, with particular emphasis on the phenolic group’s proton as the primary dissociation site, elucidating pivotal insights into the oxidation mechanism of NAR. Noteworthy is the irreversibility of the electrochemical oxidation process observed on both non-modified glassy carbon electrode (GCE) and gold electrode (GE), indicating a one-electron-one-proton mechanism. Utilizing the external calibration method and GCE, a linear range from 1.36 to 19.1 mg L-1 in Britton-Robinson (BR) supporting electrolyte was established, exhibiting a limit of detection (LOD) of 0.11 mg L-1 (R2 = 0.9945). For GE, the standard addition calibration approach revealed one linear range, from 0.27 to 0.48 mg L-1 (LOD of 0.04 mg L-1, R2 = 0.9960). Importantly, the proposed methodologies demonstrate satisfactory selectivity against potential interferences, with intra- and inter-day precision exhibiting low relative standard deviation (RSD) values. This study introduces a simple, sensitive, stable, selective, and sustainable electroanalytical method for the detection of NAR in pharmaceutical formulations, harnessing the advantages of unmodified electrodes and rigorous experimental validation.

Synergistic effect of Ru single atom and nanoparticle on photothermal methane dry reforming reaction

Dry reforming of methane is indeed an attractive pathway for converting greenhouse gases into syngas. However, owing to the strong-endothermic nature of this reaction, high reaction temperature is commonly involved which causes high energy consumption, catalytic deactivation by sintering of active species, and/or coke formation. Herein, a RuSA+NP/TiO2 composite catalyst consisting of uniformly dispersed Ru nanoparticles (RuNP) and Ru single atoms (RuSA) on TiO2 sheet is fabricated. This catalyst demonstrates remarkable syngas generation rates of 1380 mmol g-1h−1 for CO and 933 mmol g-1h−1 for H2 at 500 °C under light irradiation. It is concluded that the presence of Ru single atoms modulates the electronic structure of catalyst, reducing energy barrier in the DRM process. Additionally, the electron-deficient Ru nanoparticles provide effective sites for CH4 dissociation. Light irradiation is found to reduce the apparent activation energy (Ea) of DRM and enhance durability of catalyst by retarding coking process.

Promoting CO Electroreduction to C2+ Oxygenates by Distribution of Water Dissociation Sites.

The electrocatalytic CO2 or CO reduction reaction is a complex proton-coupled electron transfer reaction, in which protons in the electrolyte have a critical effect on the surface adsorbed *H species and the multi-carbon oxygenate products such as ethanol. However, the coupling of *H and carbon-containing intermediates into C2+ oxygenates can be severely hampered by the inappropriate distributions of those species in the catalytic interfaces. In this work, the controlled distribution of highly dispersed CeOx nanoclusters is demonstrated on Cu nanosheets as an efficient CO electroreduction catalyst, with Faradaic efficiencies of ethanol and total oxygenates of 35% and 58%, respectively. The CeOx nanoclusters (2-5 nm) enabled efficient water dissociation and appropriate distribution of adsorbed *H species on the Cu surface with carbon-containing species, thus facilitating the generation of C2+ oxygenate products. In contrast, pristine Cu without CeOx tended to form ethylene, while the aggregated CeOx nanoparticles promoted the surface density of *H and subsequent H2 evolution.

Oxophilic vanadium and deprotonated ruthenium atoms on tungsten carbide with accelerated intermediate migration for high-performance seawater hydrogen evolution

Compared with traditional freshwater electrolysis, the seawater electrolysis process is confronted with low activity and poor stability problems due to the deposition of insoluble hydroxides and corrosion of chloride species; thus, engineering efficient catalysts for seawater electrolysis are extremely desirable but remain challenging. Herein, we have developed an efficient and robust electrocatalyst by engineering oxophilic vanadium and deprotonated ruthenium atoms on tungsten carbide (WC-RuV) as a highly active and anti-poisoning cathode material for superior seawater electrolysis. Benefiting from the high oxophilicity and electron transfer ability of V, the interaction between the OH* generated via water dissociation and Ru sites is weakened, which facilitates the OH* transfer process and consequently attenuates the formation of insoluble hydroxides. Notably, when working in simulated seawater electrolytes, the WC-RuV requires an ultralow overpotential, and the WC-RuV@carbon cloth can maintain high activity and stability even at 200 mA cm−2. The assembled WC-RuV||RuO2 anion exchange membrane (AEM) electrolyzer realizes long-term stability at the current of 100 mA cm−2 and achieves continuous operation powered by commercially available solar panels. This work provides an efficient strategy for modulating the water dissociation process and offers a new perspective for designing high-performance catalysts for the forthcoming application of seawater electrolysis.

Breakthrough in CO2 Electroreduction to Multi-Carbon Products at Ampere-Level Enabled by Active Sites Engineering.

Efficient production of value-added chemicals with high selectivity from CO2 electroreduction at industrial-level current density is highly demanded, yet remains a big challenge. In a recent issue of Angewandte Chemie, Han and colleagues have elegantly increased the Faradaic efficiency (FE) of multi-carbon (C2+) products to over 70 % at amperes level (1.4 A cm-2) by engineering the active sites for the key reactions involved in the CO2 electroreduction. In this study, the highly dispersed Pd atoms have two unique functions: active sites for water dissociation and to induce the electron rearrangement of the surrounding Cu atoms to form new active sites for CO conversion, while the Cu far from Pd are the active sites for efficient CO2 conversion to CO, the synergistic functions of these three active sites result in high FE and yields of C2+ products at industrial-level current density. This research is a remarkable step forward in the methodology for developing efficient and durable catalysts for CO2 electroreduction and beyond.

Catalytic hydrogenation of CO2 to DME on surface Cu via highly efficient electron redistribution at the Cu0/Cu+ interface

The activity of copper-based bifunctional catalysts for CO2 hydrogenation to dimethyl ether (DME) is generally constrained by the loss of Cu0 sites during the reaction. Previous studies have focused on introducing additional elements to improve the stability of active sites. In this study, an electron redistribution of the Cu/Cu2O interface was constructed. Surface Cu0 provides active sites for H2 adsorption and dissociation, and the Cu0/Cu+ interface sites are more beneficial for the activation and hydrogenation of CO2. The Ointer–H moieties that form at interface sites reduce the reaction energy barrier of CH3OH synthesis, and the decomposition of H2COOH* to CH2O* species is the rate-limiting step. In addition, the Cu0/Cu+ interface restricts the migration of copper species and protects the weak acid sites of HZSM-5 during the reaction. The present work provides an atomic-level description of H2 dissociation and CO2 activation by Cu0/Cu+ surface and interface sites.

Electron transfer from yttrium hydride to Mo-carbonitride boosts low-temperature ammonia synthesis

Ammonia is pivotal to various chemical industries, which is produced using the Haber-Bosch process. This process requires harsh conditions (e.g., 20.0 MPa and (500–600)°C) to generate ammonia and thus, is an energy intensive process. The growing consensus is to mild the conditions for ammonia generation. Herein, we demonstrate the use of hydride to increase the activity of molybdenum carbonitride (MCN). YH@MCN (95:5, w/w) generates ammonia at a rate of 448μmolg−1h−1 at 255 °C and 0.1 MPa. To address the stability issue of hydride, we incorporate iron. The experiment demonstrates two-fold rates for such catalyst, comparing MCN alone. The activation energy (19.73kJmol-1) for YFeH@MCN is considerably low, owing to the electron transfer from YH to MCN that facilitates nitrogen dissociation. Hence, the use of distinct sites for easy dissociation of nitrogen molecules, and the synergy between them, results in an activity that exceeds of conventional molybdenum and iron-based catalysts, and is comparable to ruthenium-based catalysts. Our results illustrate the potential of using synergistic multiple active sites in catalysts, and introduce a design concept for ammonia synthesis catalysts, using readily available elements.

Mitigating the Poisoning Effect of Formate during CO2 Hydrogenation to Methanol over Co-Containing Dual-Atom Oxide Catalysts.

During the hydrogenation of CO2 to methanol over mixed-oxide catalysts, the strong adsorption of CO2 and formate poses a barrier for H2 dissociation, limiting methanol selectivity and productivity. Here we show that by using Co-containing dual-atom oxide catalysts, the poisoning effect can be countered by separating the site for H2 dissociation and the adsorption of intermediates. We synthesized a Co- and In-doped ZrO2 catalyst (Co-In-ZrO2) containing atomically dispersed Co and In species. Catalyst characterization showed that Co and In atoms were atomically dispersed and were in proximity to each other owing to a random distribution. During the CO2 hydrogenation reaction, the Co atom was responsible for the adsorption of CO2 and formate species, while the nearby In atoms promoted the hydrogenation of adsorbed intermediates. The cooperative effect increased the methanol selectivity to 86% over the dual-atom catalyst, and methanol productivity increased 2-fold in comparison to single-atom catalysts. This cooperative effect was extended to Co-Zn and Co-Ga doped ZrO2 catalysts. This work presents a different approach to designing mixed-oxide catalysts for CO2 hydrogenation based on the preferential adsorption of substrates and intermediates instead of promoting H2 dissociation to mitigate the poisonous effects of substrates and intermediates.