Search

Two-dimensional (2D) transition metal carbides/nitrides (MXenes) materials exhibit potential as catalysts for the hydrogen evolution reaction (HER) due to their large surface area, excellent conductivity, and notable electrical properties. Despite these advantages, pristine MXenes often display insufficient catalytic activity compared to noble metal electrocatalysts. Enhancing the HER performance of MXenes by introducing nonmetal atoms on the surface has proven effective. However, understanding the precise regulation of the HER performance by nonmetal atoms remains challenging. In this study, we utilized density functional theory calculations to explore how the introduction of fourteen distinct nonmetal atoms into Mo 2 CO 2 catalysts (NM-Mo 2 CO 2) influences the catalytic behavior in HER. The results indicated that nonmetal atom doping significantly activates oxygen atoms, substantially enhancing catalytic activity. Notably, the addition of nonmetal atoms like chlorine (Cl), bromine (Br), and iodine (I) onto the Mo 2 CO 2 surface effectively improved HER activity, showcasing their potential as HER catalysts. Our study proved that nonmetal atom doping not only causes localized structural distortions but also charge redistribution, influencing the HER performance of NM-Mo 2 CO 2. Furthermore, we developed two descriptors to quantify the regulation mechanism of nonmetal atoms, successfully predicting the HER activity of NM-Mo 2 CO 2 and extending these insights to NM-Cr 2 CO 2 and NM-V 2 CO 2. These findings offer a comprehensive understanding of how nonmetal atom doping enhances HER activity, providing valuable insights for innovative catalyst design. [Display omitted] • NM doping activates oxygen atoms, boosting catalytic activity in Mo 2 CO 2 for HER. • Chlorine, bromine, and iodine enhance Mo 2 CO 2 , showcasing potential as HER catalysts. • Study unveils localized structural distortions and charge redistribution in NM-Mo 2 CO 2. • Two descriptors predict and extend insights to NM-Cr 2 CO 2 and NM-V 2 CO 2. [ABSTRACT FROM AUTHOR]

• Mo, Re, Ni and Ru carbides supported over activated carbon were able to be obtained. • CO formation during TPR experiment could be taken as a proof of carbide formation. • Guaiacol conversion over carbide give mainly phenol as products. In the present work, the preparation and use of new supported transition metal carbides as catalyst for the conversion of guaiacol was investigated. Several metals (Mo, Re, Ru, Ni, Fe, and Cu) were impregnated over activated carbon and carburized under a mixture of H 2 /C 2 H 4 at 700 °C. Catalysts were characterized by XRD, N 2 physisorption, XPS, CO chemisorption, and TPR-MS. Evidence for carbide formation was obtained in the case of Mo, Re, Ni and Ru, based primarily on CO formation during the TPR-MS analysis. It was found that carbides were mainly active for primary guaiacol conversion to phenol and catechol through demethoxylation and demethylation. Completely deoxygenated products such as benzene and cyclohexane were also formed. The highest selectivity in benzene was obtained for the Re-TPR catalyst while Ni-TPR was the most hydrogenative one. [ABSTRACT FROM AUTHOR]

Electrocatalytic Ammonia Synthesis Process on the Mo 2 TiC 2 MXene. • Nineteen different possible pathways (five association pathway and fourteen dissociation pathway) analyzed by DFT calculation and Gibbs free energy calculation. • Valid N 2 -philicity, N≡N triple bond of the N 2 molecule (the optimal distance) is sufficiently activated, from 1.11 Å to 1.268Å • Mo 2 TiC 2 MXene can reduce the overpotential by changing the reaction pathway. • Mo 2 TiC 2 as an ordered, double transition metals carbides is an eligible electrocatalyst for the NRR Electrocatalytic ammonia synthesis provides an energy-efficient alternative to the Haber−Bosch process. The aim is to find promising electrocatalysts which are able to change the reaction pathway and reduce the overpotential. Here, based on density functional theory, a comprehensive mechanism study of the N 2 activation and NH 3 synthesis on the Mo 2 TiC 2 MXenes is presented. For catalytic reaction mechanism, nineteen different possible pathways are screened for the lowest overpotential, where the corresponding potential-determining step are compared by Gibbs free energy calculation. The result reveals Mo 2 TiC 2 MXenes exhibit both valid N 2 -philicity and high catalytic activity for electrocatalytic ammonia synthesis through a dissociation mechanism with a low overpotential of 0.26 V. Further, the competing reaction of H 2 evolution is simultaneously suppressed which shows a relatively high potentials of 0.74 V. This study shows a brand new material for catalyzing NH 3 synthesis under ambient conditions and provides the theory background to reduce the overpotential by changing the reaction pathway. [ABSTRACT FROM AUTHOR]

Transition metal carbide (TMC) catalysts, due to their noble metal like characteristics,have emerged as potential candidates for the hydrodeoxygenation (HDO) of biomass derived species, including the pyrolysis product bio-oil. However, the selectivity for deoxygenation, excessive hydrogenation and stability under operating conditions,remain as key challenges. Hence, this paper presents a comprehensive review of the state of the art with regard to (i) the preparation and structure of TMCs, (ii) characterization of active sites on TMCs and (iii) fundamental knowledge of the reaction mechanisms/pathways and associated energetics of HDO of model compounds which are present in biomass derived bio-oil. We believe that this fundamental knowledge will greatly assist researchers to systematically modify the composition and structure of TMCs to optimize their HDO performance. [Display omitted] • Catalytic Hydrotreatment of pyrolysis bio-oil as a sustainable pathway to produce fuels and chemicals. • Transition metal carbides and their noble metal like properties. • Recent advances in the synthesis of transition metal carbides. • Overview of selective oxygen removal ability of transition metal carbides from bio-oil derivatives. • Need to develop novel bimetallic carbides to avoid excessive hydrogen consumption. [ABSTRACT FROM AUTHOR]

Graphical abstract The nature of synergistic interface between TaC and g-C emerges as an important parameter controlling the catalytic activity. This synergistic interface ensures that not only does the presence of g-C results in higher SSA but also, higher electron mobility by efficient charge transfer. TaC and g-C powders as stable catalyst for both HER (1000 cycles) and degradation of MB dye (4 cycles). Highlights • Photocatalytic and electrocatalytic properties of TaC powders are contrasted. • TaC and g-C powders as stable catalyst for both HER (1000 cycles) and degradation of MB dye (4 cycles). • The nature of synergistic interface between TaC and g-C emerges as an important parameter controlling the catalytic activity. • Phase purity and size of TaC powders are important parameters for electocatalytic and photodegradation reactions. • TaC properties modify and control the adsorption properties of the powder for HER as well as dye degradation reactions. Abstract Nano transition metal carbides (TMCs) have emerged as materials of great interest for different catalytic applications in fuel cells and also as catalysts for photo-treatment of organic effluents in industrial waste water. For both the catalytic phenomenon, the charge transfer pathways between the TMC and the surrounding carbon are of significant importance. In present work, well characterized nano powders of Tantalum Carbide (TaC) have been used as a model system to understand the effect and relative importance of powder parameters such as phase purity, particle size and amount of graphitic carbon (g-C) present (in the powder sample) in determining the performance for Hydrogen Evolution Reaction (HER) and photodegradation of Methylene Blue (MB) dye. For both the applications, TaC particle size and specific surface area (SSA) of the powder emerged as a key parameter. Larger SSA results in better performance even for powder with incomplete TaC phase formation. For same sized TaC, single phase powders give better performance. The SSA of the powders depends on the size of the carbide particles and the g-C present in the powders. The nature of synergistic interface between TaC and g-C emerges as an important parameter controlling the catalytic activity. This synergistic interface ensures that not only does the presence of g-C results in higher SSA but also, higher electron mobility by efficient charge transfer. The study of TaC powders with variable g-C content brought to fore the difference in the reaction pathways of the two catalytic systems in spite of the common requirement of charge transfer from TaC to g-C. As a consequence of the synergistic interface, dye adsorption properties of the g-C are modified by the presence of TaC and can be tailored. XPS, PL and UV data has been used to propose a possible degradation mechanism for the photo-oxidation of MB dye under visible irradiation. [ABSTRACT FROM AUTHOR]

Low temperature fuel cells technologies are currently shifting very fast from fundamental research to real growth. The development of electrocatalysts plays a vital role in the electrocatalytic reactions involved in these devices, because the catalyst determines the overall reaction efficiency, durability and cost. This article review progress in the research and development of electrocatalysts for low temperature fuel cells technologies, with especial attention in the contribution of our research teams over the last 15 years or so. The intensive research efforts in reducing or replacing Pt-based electrodes in fuel cells have been focus in the use of carbon nanomaterials as electrocatalytic supports, including carbon nanostructures tailored by surface modification or building in particular dopants/defects. Recent research effort has also led to the use of electronic conductivity noncarbon support materials. In addition, carbon-composite materials are proving to be a robust, inexpensive and active electrocatalysts, where the synergetic effect between the carbon nanomaterials and the ceramic or polymer nanostructures can lead to a superior electrocatalytic performance and durability for low temperature fuel cells. Perspectives on these catalysts and possible pathways to address current remaining challenges are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Co0.2W0.8C x and supported Co0.2W0.8C x catalysts are shown to be active for the partial oxidation of methane to synthesis gas. The catalyst stability is improved by operating at elevated pressure, or in the presence of excess methane. At atmospheric pressure the Co0.2W0.8C x catalysts deactivate by oxidation, as seen by X-ray diffraction. Manganese substituted hexaaluminate catalysts with different Mn contents have been tested as catalysts for the total combustion of methane. In particular BaMn2Al10O19 is active and stable for the combustion reaction. The temperature rise observed in the reactor was up to 300K, depending on the reaction conditions, and complete conversion of oxygen in the feed was achieved. A process for stabilising the carbide catalysts is demonstrated, combining the manganese substituted hexaaluminate total oxidation catalyst, in series before the carbide reforming catalyst: this process leads to stable operation, with no carbon formation in the reactor and no carbide catalyst oxidation observed. [Copyright &y& Elsevier]

Abstract: Mixed alcohol synthesis is an important process for the production of oxygenates fuels, fuel additives and other intermediates for chemical feedstocks via CO hydrogenation. The process is a highly exothermal reaction, which essentially needs the combination of carbon-chain growth and CO insertion functions over the catalysts. The key to the development of mixed alcohol synthesis is the selective control of alcohols and efficient removal of reaction heat via both catalyst and reactor innovation. ICC-CAS (Institute of Coal Chemistry, Chinese Academy of Sciences) has been worked on mixed alcohol synthesis over heterogeneous catalysts and gained some interesting results in the catalyst preparation and process engineering. This paper thus briefly introduced the recent research progresses at ICC-CAS. [Copyright &y& Elsevier]