Purified oxygenand nitrogen-modified multi-walled carbon nanotubes as metal-free catalysts for selective olefin hydrogenation

Oxygen and nitrogen-functionalized carbon nanotubes （OCNTs and NCNTs） were applied as metal-free catalysts in selective olefin hydro- genation. A series of NCNTs was synthesized by NH3 post-treatment of OCNTs. Temperature-programmed desorption, N2 physisorption, Raman spectroscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy were employed to characterize the surface properties of OCNTs and NCNTs, aiming at a detailed analysis of the type and amount of oxygen- and nitrogen-containing groups as well as surface defects. The gas-phase treatments applied for oxygen and nitrogen functionalization at elevated temperatures up to 600 ℃ led to the increase of surface defects, but did not cause structural damages in the bulk. NCNTs showed a clearly higher activity than the pristine CNTs and OCNTs in the hydrogenation of 1,5-cyclooctadiene, and also the selectivity to cyclooctene was higher. The favorable catalytic properties are ascribed to the nitrogen-containing surface functional groups as well as surface defects related to nitrogen species. In contrast, oxygen-containing surface groups and the surface defects caused by oxygen species did not show clear contribution to the hydrogenation catalysis.

Facile synthesis of molybdenum carbide nanoparticles in situ decorated on nitrogen-doped porous carbons for hydrogen evolution reaction

Molybdenum-based electrocatalysts are promising candidates of platinum (Pt)-based materials in electrocatalyzing hydrogen evolution reaction (HER), due to their cost-efficient and resembled electronic properties. Reported herein is the preparation of molybdenum carbide nanoparticles uniformly decorated on nitrogen-modified carbons (Mo2C/NC) through the carbonization of Mo-based polymers under hydrogen atmosphere by using poly(p-phenylenediamine) and ammonium heptamolybdate polymer analogue as precursors. And the molybdenum nitride nanoparticles loaded on porous N-doped carbons (Mo2N/NC) are also fabricated by calcination the polymer precursors in nitrogen gas. The Mo2C/NC shows more excellent electrocatalytic activity than Mo2N/NC in 0.5 M H2SO4, together with robust long-term durability. The well-crystalline nanoparticles and the increased electron conductivity are the main characters responded for the high catalytic efficiency of the fabricated electrocatalysts. This easily fabrication procedure may provide a facile route to prepare non-noble metal carbide/nitride catalysts featuring wellengineered structural and textural peculiarities for realistic energy conversion system.

Enhanced photocatalytic hydrogen production from Co-MOF/CN by nitrogen and sulfur co-doped coal-based carbon quantum dots

A novel composite photocatalyst for photocatalytic decomposition of water for hydrogen evolution was successfully synthesized by in-situ growth of nitrogen and sulfur co-doped coal-based carbon quantum dots(NSCQDs)nanoparticles on the surface of sheet cobalt-based metal-organic framework(Co-MOF)and graphitic carbon nitride(g-C_(3)N_(4),CN).The structure and properties of the obtained catalysts were systematically analyzed.NSCQDs effectively broaden the absorption of Co-MOF and CN in the visible region.The new composite photocatalyst has high hydrogen production activity and the hydrogen production rate reaches 6254μmol/(g·h)at pH=9.At the same time,NSCQDs synergy Co-MOF/CN composites have good stability.After four cycles of hydrogen production,the performance remains relatively stable.The tran sient photocurrent response and Nyquist plot experimental results further demonstrate the improvement of carrier separation efficiency in composite catalysts.The semiconductor type(n-type semico nductor)of the single-phase catalyst was determined by the Mott-Schottky test,and the band structure was analyzed.The conductive and valence bands of CN are-0.99 and 1.72 eV,respectively,and the conduction and valence bands of Co-MOF are-1.85 and 1.33 eV,respectively.Th e mechanism of the photocatalytic reaction can be inferred,that is,Z-type heterojunction is formed between CN an d Co-MOF,and NSCQDs was used as cocatalyst.

Cobalt nanoparticles encapsulated in nitrogen-doped carbon for room-temperature selective hydrogenation of nitroarenes

Here,we report cobalt nanoparticles encapsulated in nitrogen‐doped carbon(Co@NC)that exhibit excellent catalytic activity and chemoselectivity for room‐temperature hydrogenation of nitroarenes.Co@NC was synthesized by pyrolyzing a mixture of a cobalt salt,an inexpensive organic molecule,and carbon nitride.Using the Co@NC catalyst,a turnover frequency of^12.3 h?1 and selectivity for 4‐aminophenol of>99.9%were achieved for hydrogenation of 4‐nitrophenol at room temperature and 10 bar H2 pressure.The excellent catalytic performance can be attributed to the cooperative effect of hydrogen activation by electron‐deficient Co nanoparticles and energetically preferred adsorption of the nitro group of nitroarenes to electron‐rich N‐doped carbon.In addition,there is electron transfer from the Co nanoparticles to N‐doped carbon,which further enhances the functionality of the metal center and carbon support.The catalyst also exhibits stable recycling performance and high activity for nitroaromatics with various substituents.

Facile Fabrication of Platinum Nanoparticles Supported on Nitrogen-doped Carbon Nanotubes and Their Catalytic Activity

A facile impregnation method under mild condition is designed for synthesis of highly dispersed Pt nanoparticles with a narrow size of 4-7 nm on nitrogen-doped carbon nanotubes （CNx）. CNx do not need any pre-surface modification due to the inherent chemical activity. The structure and nature of Pt/CNx were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy spectrum. All the experimental results revealed that the large amount of doped nitrogen atoms in CNx was virtually effective for capturing the Pt（IV） ions. The improved surface nitrogen functionalities and hydrophilicity contributed to the good dispersion and immobi- lization of Pt nanoparticles on the CNx surface. The Pt/CNx served as active and reusable catalysts in the hydrogenation of allyl alcohol. This could be attributed to high dispersion of Pt nanoparticles and stronger interaction between Pt and the supports, which prevented the Pt nanoparticles from aggregating into less active Pt black and from leaching as well.

A host-guest approach to fabricate metallic cobalt nanoparticles embedded in silk-derived N-doped carbon fibers for efficient hydrogen evolution

Hydrogen evolution reaction(HER) plays a key role in generating clean and renewable energy. As the most effective HER electrocatalysts, Pt group catalysts suffer from severe problems such as high price and scarcity. It is highly desirable to design and synthesize sustainable HER electrocatalysts to replace the Pt group catalysts. Due to their low cost, high abundance and high activities, cobalt-incorporated N-doped nanocarbon hybrids are promising candidate electrocatalysts for HER. In this report, we demonstrated a robust and eco-friendly host-guest approach to fabricate metallic cobalt nanoparticles embedded in N-doped carbon fibers derived from natural silk fibers. Benefiting from the onedimensional nanostructure, the well-dispersed metallic cobalt nanoparticles and the N-doped thin graphitized carbon layer coating, the best Cobased electrocatalyst manifests low overpotential(61 mV@10 mA/cm^2) HER activity that is comparable with commercial 20% Pt/C, and good stability in acid. Our findings provide a novel and unique route to explore high-performance noble-metal-free HER electrocatalysts.

Electrocatalytic water splitting at nitrogen-doped carbon layers-encapsulated nickel cobalt selenide

Generally,the catalytic overpotentials of hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)are unavoidable because of the low charge transfer.In this work,two strategies of alloying of Co with Ni and enclosing of electrocatalysts with carbonaceous materials were both used to accelerate the catalytic efficiency of cobalt selenide for water splitting.The nitrogen-doped carbon(NC)layer improves the reaction kinetics by efficient charge transfer.The alloying of metal into composited electrocatalysts can modify the electronic properties of host materials,thereby tuning the adsorption behavior of intermediate and improving the electrocatalytic activity.As expected,Nyquist plots reveal that the charge-transfer resistance(Rct)of nickel cobalt selenide encapsulated into nitrogen-doped carbon layer(CoNiSe/NC-3,Co:Ni=1:1)are just 5 and 9 for HER and OER,respectively,which are much lower than those of CoSe/NC-1(Co:Ni=1:0)(81 and 138)and CoNiSe/NC-3 without NC(CoNiSe-3)(54 and 25).With the high charge transfer and porous structure,CoNiSe/NC-3 shows good performance for both HER and OER.When current density reaches 10 m A cm-2,only 100 and 270 mV overpotentials are required for HER and OER,respectively.With the potential of 1.65 V,full water splitting also can be catalyzed by Co Ni Se/NC-3 with current density of 20 m A cm-2,suggesting that CoNiSe/NC-3 could be used as replacement for noble metal electrocatalysts.

Cobalt and nitrogen codoped porous carbon as superior bifunctional electrocatalyst for oxygen reduction and hydrogen evolution reaction in alkaline medium

Cobalt and nitrogen codoped carbon materials(Co-N-C) were fabricated by pyrolysis of the mixture of poly(4-vinylpyridine) and cobalt chloride using SiO_2 nanoparticles as hard template, which were the first transition metal/nitrogen-codoped carbon bifunctional electrocatalyst derived from noncarbonizable polymer for ORR and HER. The as-made Co-N-C possessed hierarchical pore structure and high specific surface area, achieving excellent electrocatalytic performances for ORR and HER. Its ORR catalytic performances were comparable to those of Pt/C catalyst and its HER catalytic performances were superior to those of most doped carbon catalysts in KOH electrolyte. Moreover, its bifunctional electrocatalytic performances for ORR and HER were better than those of most bifunctional doped carbon catalysts in alkaline electrolyte.

Doped graphene/carbon black hybrid catalyst giving enhanced oxygen reduction reaction activity with high resistance to corrosion in proton exchange membrane fuel cells

Nitrogen doping of the carbon is an important method to improve the performance and durability of catalysts for proton exchange membrane fuel cells by platinum–nitrogen and carbon–nitrogen bonds. This study shows that p-phenyl groups and graphitic N acting bridges linking platinum and the graphene/carbon black(the ratio graphene/carbon black = 2/3) hybrid support materials achieved the average size of platinum nanoparticles with(4.88 ± 1.79) nm. It improved the performance of the lower-temperature hydrogen fuel cell up to 0.934 W cm^(-2) at 0.60 V, which is 1.55 times greater than that of commercial Pt/C. Doping also enhanced the interaction between Pt and the support materials, and the resistance to corrosion, thus improving the durability of the low-temperature hydrogen fuel cell with a much lower decay of 10 mV at 0.80 A cm^(-2) after 30 k cycles of an in-situ accelerated stress test of catalyst degradation than that of 92 mV in Pt/C, which achieves the target of Department of Energy(<30 mV). Meanwhile,Pt/Nr EGO_(2)-CB_(3) remains 78% of initial power density at 1.5 A cm^(-2) after 5 k cycles of in-situ accelerated stress test of carbon corrosion, which is more stable than the power density of commercial Pt/C, keeping only 54% after accelerated stress test.

Charge Engineering of Mo2C@Defect-Rich N-Doped Carbon Nanosheets for Efficient Electrocatalytic H2 Evolution

Charge engineering of carbon materials with many defects shows great potential in electrocatalysis,and molybdenum carbide(Mo2C)is one of the noble-metal-free electrocatalysts with the most potential.Herein,we study the Mo2C on pyridinic nitrogen-doped defective carbon sheets(MoNCs)as catalysts for the hydrogen evolution reaction.Theoretical calculations imply that the introduction of Mo2C produces a graphene wave structure,which in some senses behaves like N doping to form localized charges.Being an active electrocatalyst,MoNCs demonstrate a Tafel slope as low as 60.6 mV dec-1 and high durability of up to 10 h in acidic media.Besides charge engineering,plentiful defects and hierarchical morphology also contribute to good performance.This work underlines the importance of charge engineering to boost catalytic performance.

Ultrafine molybdenum carbide nanoparticles supported on nitrogen doped carbon nanosheets for hydrogen evolution reaction

Molybdenum carbides(Mo_xC)/nitrogen doped carbon nanosheets(NCS) composites are synthesized via simple mixing melamine and ammonia molybdate, followed by a high-temperature treatment. Metal carbide nanoparticles with ultra-small size(13nm) are uniformly supported on nitrogen doped carbon nanosheets. The hydrogen evolution reaction(HER) is investigated in both 0.5 mol/L H_2SO_4 and 1 mol/L KOH media. Mo_2C/NCS-10(melamine/ammonia molybdate weight ratio of 10:1) exhibits excellent performance with a low overpotential of 130 mV in 0.5 mol/L H_2SO_4 solution and 108 mVin 1mol/L KOH solution at the current density of 10 mA/cm^2. The better electrocatalytic activity could be ascribed to Ndoped carbon nanosheets, small particle size, mesoporous structure, and large specific surface area,which could provide the large electrochemical active surface area and facilitate mass transport.

Effect of nitrogen pressure on optical properties and microstructure of diamond-like carbon films grown by pulsed laser deposition

The effect of nitrogen pressure on optical properties of hydrogen-free diamond-like carbon (DLC) films deposited by pulsed laser ablation graphite in different background pressures of nitrogen is reported. By varying nitrogen pressures from 0.05 to 15.00 Pa, the photoluminescence is gradually increased and optical transmittance is gradually decreased. Atomic force microscopy (AFM) is used to observe the surface morphology of the DLC films. The results indicate that the surface becomes unsmoothed and there a...

Regulating nitrogen vacancies within graphitic carbon nitride to boost photocatalytic hydrogen peroxide production

Introducing nitrogen vacancies is an effective method to improve the catalytic performance of g-C_(3)N_(4)-based photocatalysts,whereas understanding how nitrogen vacancies types affect the catalytic performance remains unclear.Herein,two different types of nitrogen vacancies were successfully introduced into g-C_(3)N_(4)by pyrolysis of melamine under argon and ammonia atmosphere with subsequent HNO3 oxidation.The pyrolysis atmosphere is found to have a significant influence on the introduced nitrogen vacancies type,where tertiary nitrogen groups(N_(3)C)and sp2-hybridized nitrogen atoms(N_(2)C)were the preferred sites for the formation of nitrogen vacancies under ammonia and argon pyrolysis,respectively.Moreover,nitrogen vacancies from N3C are experimentally and theoretically demonstrated to facilitate the narrowed band gap and the improved oxygen absorption capability.As expected,the optimal catalyst exhibits high H_(2)O_(2)yield of 451.8µM,which is 3.8 times higher than the pristine g-C_(3)N_(4)(119.0µM)after 4 h and good stability after10 photocatalytic runs.

Nitrogen-doped flower-like porous carbon materials directed by in situ hydrolysed MgO： Promising support for Ru nanoparticles in catalytic hydrogenations

The development of novel simple, and convenient techniques for the fabrication of porous carbon materials with desirable properties, such as tunable pore structures and the presence of nitrogen functionalities, from renewable and abundant biomasses is required. We herein describe an in situ directing method for the preparation of a nitrogen-doped flower-like porous carbon （NFPC） employing arbitrarily shaped MgO from bio-derived glucosamine chloride （GAH）. Experimental evidence demonstrated that the structure directing effect of the Mg（OH）2 nanosheets formed in situ from MgO hydrolysis was key to this process, with the original MgO morphology being irrelevant. Furthermore, this method was applicable for a wide variety of biomass-derived carbon precursors. The resulting NFPC exhibited a high nitrogen content of 〈9 wt.%, and was employed as a support to anchor small Ru nanoparticles （average size = 2.7 nm）. The resulting Ru/NFPC was highly active in heterogeneous hydrogenations of toluene and benzoic acid, which demonstrated the advantages of nitrogen doping in terms of boosting catalytic performance.

Carbon nitride with encapsulated nickel for semi-hydrogenation of acetylene: pyridinic nitrogen is responsible for hydrogen dissociative adsorption

A new mechanism of catalyst has been demonstrated in this article. With the interaction between carbon nitride(CN) and encapsulated nickel, the CN in the catalyst has been endowed with new active sites for the adsorption and activation of hydrogen while nickel itself is physically isolated from the contact with reactive molecules. For the selective hydrogenation of acetylene in large amount of ethylene, the catalyst shows excellent ethylene selectivity than the nickel catalyst itself, which is almost totally unselective. Meanwhile, the CN itself is inactive for the reaction. The results of characterization demonstrate that pyridinic nitrogen doped in the carbon matrix should be the active sites for hydrogen dissociative adsorption. The theoretical calculations further confirm the results and provide with the detail in the electron transfer between nickel and CN in the catalyst. The current results supply a new concept for design of high performance catalyst.

Nitrogen Doped Graphene as Potential Material for Hydrogen Storage

The nitrogen doped graphene was synthesized by hydrothermal route utilizing 2-Chloroethylamine hydrochloride as nitrogen precursor in the presence of graphene oxide (GO). Nitrogen-doped graphene material is developed for its application in hydrogen storage at room temperature. Nitrogen doped graphene layered material shows ~1.5 wt% hydrogen storage capacity achieved at room temperature and 90 bar pressure.

Advanced In Situ Characterization Techniques for Direct Observation of Gas-Involved Electrochemical Reactions

Gas-involved electrochemical reactions provide feasible solutions to the worldwide energy crisis and environmental pollution.It has been recognized that various elements of the reaction system,including catalysts,intermediates,and products,will undergo real-time variations during the reaction process,which are of significant meaning to the in-depth understanding of reaction mechanisms,material structure,and active sites.As judicious tools for real-time monitoring of the changes in these complex elements,in situ techniques have been exposed to the spotlight in recent years.This review aims to highlight significant progress of various advanced in situ characterization techniques,such as in situ X-ray based technologies,in situ spectrum technologies,and in situ scanning probe technologies,that enhance our understanding of heterogeneous electrocatalytic carbon dioxide reduction reaction,nitrogen reduction reaction,and hydrogen evolution reaction.We provide a summary of recent advances in the development and applications of these in situ characterization techniques,from the working principle and detection modes to detailed applications in different reactions,along with key questions that need to be addressed.Finally,in view of the unique application and limitation of different in situ characterization techniques,we conclude by putting forward some insights and perspectives on the development direction and emerging combinations in the future.

双碳目标下的氨燃料航空动力研究进展及展望

为了获得氨燃料航空动力应用潜力评价,本文综述了氨燃料的绿色制取方法、氨燃料燃烧特性的研究成果以及氨航空发动机设计过程中可能存在的技术问题和相应的解决方案。综合已有研究成果,本文认为氨燃料航空发动机具有非常广阔的应用前景,采用氨氢混合燃烧在未来有望成为氨燃料航空动力系统的优选方案。

Plasma-assisted ammonia synthesis under mild conditions for hydrogen and electricity storage:Mechanisms,pathways,and application prospects

Ammonia,with its high hydrogen storage density of 17.7 wt.%(mass fraction),cleanliness,efficiency,and renewability,presents itself as a promising zero-carbon fuel.However,the traditional Haber−Bosch(H−B)process for ammonia synthesis necessitates high temperature and pressure,resulting in over 420 million tons of carbon dioxide emissions annually,and relies on fossil fuel consumption.In contrast,dielectric barrier discharge(DBD)plasma-assisted ammonia synthesis operates at low temperatures and atmospheric pressures,utilizing nitrogen and hydrogen radicals excited by energetic electrons,offering a potential alternative to the H−B process.This method can be effectively coupled with renewable energy sources(such as solar and wind)for environmentally friendly,distributed,and efficient ammonia production.This review delves into a comprehensive analysis of the low-temperature DBD plasma-assisted ammonia synthesis technology at atmospheric pressure,covering the reaction pathway,mechanism,and catalyst system involved in plasma nitrogen fixation.Drawing from current research,it evaluates the economic feasibility of the DBD plasmaassisted ammonia synthesis technology,analyzes existing dilemmas and challenges,and provides insights and recommendations for the future of nonthermal plasma ammonia processes.

Ni_(0.6)Cu_(0.4)O/NC催化剂的制备及其催化氨硼烷水解制氢性能研究

本研究在氮气气氛下高温碳化Ni/Cu-ZIF前驱体制备了一种含氮炭材料(Ni_(0.6)Cu_(0.4)O/NC)催化剂,并采用多种表征方法对所制备催化剂的微观结构以及组成成分进行了研究。此外,通过控制变量法探究了催化剂的催化性能以及变化规律。研究结果表明,Ni_(0.6)Cu_(0.4)O/NC催化AB水解制氢的活化能(Ea)为56.8 kJ/mol,TOF值高达1572.2 h^(−1)。该催化剂催化AB水解制氢速率对于AB自身浓度可近似看作零级反应,而相对于催化剂的用量可近似看作一级反应。催化剂经过10次循环后仍然保持良好的催化活性,表明其具有良好的稳定性。