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A key task in today's inorganic synthetic chemistry is to develop effective reactions, routes, and associated techniques aiming to create new functional materials with specifically desired multilevel structures and properties. Herein, we report an ultrathin two‐dimensional layered composite of graphene ribbon and silicate via a simple and scalable one‐pot reaction, which leads to the creation of a novel carbon‐metal‐silicate hybrid family: carbosilicate. The graphene ribbon is in situ formed by unzipping carbon nanotubes, while the ultrathin silicate is in situ obtained from bulk silica or commercial glass; transition metals (Fe or Ni) oxidized by water act as bridging agent, covalently bonding the two structures. The unprecedented structure combines the superior properties of the silicate and the nanocarbon, which triggers some specific novel properties. All processes during synthesis are complementary to each other. The associated synergistic chemistry could stimulate the discovery of a large class of more interesting, functionalized structures and materials. [ABSTRACT FROM AUTHOR]

Deep oxidation/dehydrogenation are longstanding problems for decades in catalytic oxidative dehydrogenation (ODH) of cyclohexane and other alkanes. Here we show a metal‐free catalyst of nanodiamonds (NDs) with unique sp3@sp2 hybrid structure that catalyzes COx‐resistant cyclohexane ODH with remarkable reactivity towards cyclohexene production. The selectivity of cyclohexene can reach as high as 67 % with significantly suppressed COx emission (<5 %), which is on top of the highest reported values among other metal(oxide)/metal‐free catalysts. Structural evolution of sp3@sp2 NDs under annealing treatments and their specific surface functional groups are systematically studied using TEM, XPS, Raman and TPD. By comparing with carbon nanotubes (CNTs), we found that the carbonyl groups stabilized on strained sp3@sp2 core‐shell NDs enhanced the cyclohexene selectivity via preferential cleavage of C−H over C−C bond. Kinetic studies further revealed the underlying reaction pathways that cyclohexane is rapidly dehydrogenated to cyclohexene which subsequently transforms into benzene (fast) and COx (slow). Deep oxidation of both cyclic hydrocarbons is largely suppressed due to the low density of electrophilic functional groups on strongly curved graphitic surface of sp3@sp2 NDs. [ABSTRACT FROM AUTHOR]

The development of environmentally benign catalysts for highly regioselective hydroxylation of phenol remains an unsolved challenge in both industry and academia because the electrophilic substitution of phenol simultaneously occurs on both ortho- and para-positions. Herein, we report a designed atomically dispersed iron-based heterogeneous catalyst, in which the iron species is coordinated by a functionalized ionic liquid monolayer on carbon nanotubes. The catalyst exhibits an unprecedented level of regioselectivity (>99%) towards the hydroxylation of phenol and displays a much better activity (TOF towards catechol productivity, 1.79 s−1) compared to the homogeneous free ion system (TOF towards catechol productivity, 0.44 s−1). Both experimental and theoretical investigations confirm that the catalytic oxidation with hydroperoxide undergoes a non-radical addition process and substitutes only the ortho-positions of phenol. This finding provides not only a quite active and selective catalyst for industrially very important reactions, but also a promising methodology of designing biomimetic iron-based heterogeneous catalysts at the atomic level. [ABSTRACT FROM AUTHOR]

Green NH3 production by direct electrocatalytic synthesis from N2 and H2O is still a challenging reaction, which requires us to better understand the nature of the active materials. We show here that iron oxide (Fe2O3) nanoparticles (supported over carbon nanotubes, CNTs) become more active than the corresponding samples after reduction to form Fe‐ or Fe2N‐supported nanoparticles, both indicated as active species in the thermal catalytic reduction of N2 to ammonia. Characterization data, however, indicate that even for these Fe‐ and Fe2N−CNT samples, obtained from Fe2O3−CNT by reduction in H2 or NH3 at 500 °C, the active species responsible for N2 reduction reaction (NRR) at low applied potential (−0.5 V vs RHE) are the same, that is, small (<1–2 nm) iron oxide nanoparticles that are not detected by XRD, but evidenced by XPS and which amount could be correlated to the rate of ammonia formation. This species is stable for at least 24 h of electrocatalytic flow tests. However, at higher applied potentials, sintering/transformation of this species occurs, with loss of the electrocatalytic activity, and Fe2N nanoparticles may also be reduced in situ, forming ammonia, but with irreversible deactivation. [ABSTRACT FROM AUTHOR]

Abstract: Transition‐metal oxide/nanocarbon hybrids are known to deliver a cooperative oxygen reduction reaction (ORR) with a synergistic effect of the hybrid interface. This work assesses a series of first‐row transition‐metal oxides in the form of surface‐confined clusters on carbon nanotubes, as a mimic of fully exposed hybrid interfaces, providing an activity benchmark for hybrid catalysts. Among the selected metal oxides, MnOx and CoOx are found to be the most active first‐row transition‐metal oxide clusters for the ORR, given their excellent peroxide‐reducing capability at low overpotential. FeOx and CuOx are also active for the same role, except their peroxide‐reducing activity is only activated with substantial overpotential. Other metal oxides (NiOx and ZnOx) do not appear to show any activity toward the ORR, even with an integrated interface as a source for the possible synergistic effect. [ABSTRACT FROM AUTHOR]

Surface functionalized and defect enriched carbon nanotubes (oCNTs) by green ozone/H2O treatment can efficiently anchor gold nanoparticles. This Au/oCNT could be stabilized and well dispersed after thermal treatment and showed robust catalytic activity (20.6 mmol gcat−1 h−1) for the oxidative self-coupling of benzylamine to imine in solvent free conditions. [ABSTRACT FROM AUTHOR]

The selective oxidation of hydrocarbons to the corresponding ketones with solvent-free and molecular oxygen as an oxidant is of great importance in academic and industrial fields in view of economy and environment. In this respect, we present the facile synthesis and characterization of excellent catalysts comprising cobalt nanoparticles encapsulated into graphitic nitrogen-doped carbon nanotubes (Co@GCNs) via one-pot pyrolysis of a chelate compound containing citric acid, melamine, and CoCl2·6H2O. The selective oxidation of ethylbenzene under molecular oxygen and solvent-free conditions is employed as a probe reaction to investigate the catalytic performance; the optimized catalyst shows the best conversion (68%) and selectivity for acetophenone (93%). Combination of the catalytic results of the control group and the different characterization methods demonstrates that high catalytic activity is due to the synergistic effect between metallic cobalt and nitrogen-doped carbon nanotubes. Moreover, the catalyst has high catalytic activity for the aerobic and solvent-free oxidation of other arylalkane substrates. The proposed mechanistic study illustrates that the reaction is a free radical reaction progressing through superoxide radical anions (ṖO2−). [ABSTRACT FROM AUTHOR]

We report herein a green and economical strategy for oxidative modification of carbon nanotubes (CNT) by a facile ozone treatment in the presence of solvent vapor (H2O, 30% H2O2 solution and ethanol). This procedure is able to introduce a considerable level of oxygen groups with a dominant population of carboxyl groups at near ambient temperature. The optimization study of the process provides the reaction temperature and time, as well as the source and partial pressure of the vapor, key parameters determining the oxidation efficiency. The process efficiency and sustainability are assessed to compare with conventional oxidative treatment (e.g., nitric acid oxidation). Ozone treatment assisted by water or H2O2/H2O vapor can introduce abundant oxygenated groups on the sidewalls of CNT, and the process with H2O2/H2O vapor can deliver a much higher selectivity towards carboxyl species on the sidewalls of CNT. With the appropriate functionalization temperature (40 °C) and incremental partial pressure of vapor, the surface defect and oxygen content on the CNT could be dramatically increased. The ozone treated CNT can be used for diverse applications such as metal-free catalyst and support; the modified CNT display higher activity for the ring-opening reaction of styrene oxide than HNO3 treated CNT and develop strong interaction for anchoring iron oxide nanoparticles even up to 350 °C. This ozone treatment in the presence of vapor could also be accomplished by using compressed air as the carrier gas, which can be considered an efficient and eco-friendly functionalization process. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) are functionalized with nitrogen atoms for reduction of carbon dioxide (CO2). The investigation explores the origin of the catalyst′s activity and the role of nitrogen chemical states therein. The catalysts show excellent performances, with about 90 % current efficiency for CO formation and stability over 60 hours. The Tafel analyses and density functional theory calculations suggest that the reduction of CO2 proceeds through an initial rate-determining transfer of one electron to CO2, which leads to the formation of carbon dioxide radical anion (CO2.−). The initial reduction barrier is too high on pristine CNTs, resulting in a very high overpotentials at which the hydrogen evolution reaction dominates over CO2 reduction. The doped nitrogen atoms stabilize the radical anion, thereby lowering the initial reduction barrier and improving the intrinsic activity. The most efficient nitrogen chemical state for this reaction is quaternary nitrogen, followed by pyridinic and pyrrolic nitrogen. [ABSTRACT FROM AUTHOR]

The lithium-oxygen (Li-O2) battery is a very appealing candidate for advanced high energy applications owing to its exceptionally high specific energy. However, its poor energy efficiency, rate capability, and cyclability remain key barriers to its practical application. In this work, using a rationally designed cathode based on a bimodal mesoporous nitrogen-doped graphene/carbon nanotube (NGC) composite, we have developed a Li-O2 battery demonstrating enhanced round-trip efficiency (ca. 85 %) and excellent cyclability over 400 cycles under a high current rate of 500 mA g−1. The excellent cyclability and rate capability are attributed to improved stability of the aggressive LiO2 intermediate on the nitrogen-doped carbon surface in addition to the favorable hierarchical architecture of NGC. These results demonstrate a valuable research direction to achieve highly stable and reversible Li-O2 batteries through tuning the surface chemistry of the cathode in addition to finding a stable electrolyte solvent. [ABSTRACT FROM AUTHOR]

Exploring the potential catalytic applications of boron-doped carbon materials is a fascinating challenge. Here we describe that boron-doped onion-like carbon and carbon nanotubes as metal-free catalysts exhibit excellent catalytic activity and stability in nitroarene reduction under a stoichiometric amount of reductant. [ABSTRACT FROM AUTHOR]

A new concept of ionic liquid (IL) mono-dispersing catalyst on nanocarbon surface is presented. The liquid mixture of IL and model catalyst (1-octyl-3-methyl imidazolium phosphotungstate, OPW) on carbon nanotube is in a solid state which can be easily characterized and give a fundamental understanding of the interaction between the catalyst and the IL. The condensed IL is found to weaken the W=O bond of a catalyst that favours its interaction with an oxidizing agent that exhibited a reaction rate of 176 times to the performance of a single OPW during the oxidation of dibenzothiophene. Due to the heterogenization of this system, the catalyst can be easily recycled by a simple gravity separation. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a decisive role for the efficiency of fuel cells and metal-air batteries. The nitrogen doped carbon materials with low cost and long durability are potential catalysts to replace precious metal catalyst for oxygen electrochemistry; however, the unexposed active sites induced by the bulk dopant atoms are hardly accessible and consequently scarcely contribute to the catalytic property. In this study, carbon nanotubes (CNTs) are selected as the platform to demonstrate the potential of full exposure of 'active sites' at the surface. Novel N-doped carbon coaxial nanocables with the pristine CNTs as the core and the N-doped carbon layers as the shell are proposed. The accessible and efficient utilization of the integrated nitrogen atoms enriched on the surface, together with the undestroyed intact inner walls, render the electrocatalyst much enhanced electrocatalytic activity and high electrical conductivity of 3.3 S cm−1, therefore, N-doped nanocables afford higher oxygen reduction current, ∼51 mV positively shift onset potential, low peroxide generation, as well as lower overpotential and higher current for oxygen evoluation reaction. [ABSTRACT FROM AUTHOR]

It is crucial to accurately describe the interaction between the surface functionality and the supported metal catalyst because it directly determines the activity and selectivity of a catalytic reaction. It is, however, challenging with a metal-carbon catalytic system owing to the ultrafine feature, instability, and subtle response of the components upon application of an external field. Herein, we use in situ TEM, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy techniques to record the interaction in palladium on carbon nanotubes (CNTs) from room temperature to 600?°C. We focus on probing the effects of oxygen and nitrogen-containing functional groups on supported palladium nanoparticles (NPs) in the model catalytic system. The stability of palladium NPs supported on CNTs depends strongly on the surface properties of CNTs. Moreover, the oxygen-containing functional groups on the CNT surfaces, such as carboxylic acids and anhydrides, have an even stronger interaction with palladium NPs than the nitrogen-containing counterparts. Our work contributes to elucidation of the complex metal-carbon interaction and unlocks potential in activity and selectivity control of these catalytic systems. [ABSTRACT FROM AUTHOR]

A prototype supported solid-acid catalyst composed of a heteropoly acid (HPA) and nitrogen-functionalized carbon nanotubes (NCNT) has been developed. The chemical structure and acid strength of the HPA/NCNT hybrid have been characterized thoroughly by IR spectroscopy, X-ray photoelectron spectroscopy, TEM, and titration measurements. NCNT supports provide the HPA with an ideal hydrophobic environment, which could prevent the deactivation of the acid sites effectively in aqueous media. HPA/NCNT hybrid catalysts tend to adsorb and enrich hydrophobic substrates (ester) and release the product with high polarity (ethanol) in the aqueous phase, and this synergistic effect facilitates the catalytic process and enhances the activity of HPAs for ester hydrolysis reactions. The HPA and NCNT combine through electrostatic interactions, which ensures the relatively high stability and easy regeneration of the HPA/NCNT hybrid catalysts. The present approach provides a promising and universal strategy for the construction of hybrid catalysts based on HPA and nanocarbon with unique acidic or redox properties. [ABSTRACT FROM AUTHOR]

Different sp2@sp3 core-shell structures are obtained on nanodiamond by using annealing treatment at increasingly higher temperatures. The resulting nanocarbons can serve as model catalysts to investigate the structural effect on the evolution and chemical nature of oxygen functional groups for oxidative dehydrogenation reactions. We studied in situ reactions and characterization data and found that the initial existence of oxygen-containing groups on a catalyst surface had a low contribution to the catalytic performance. The active oxygen species can be generated promptly in situ by the chemisorption of O2 under the reaction conditions and involved in catalytic dehydrogenation process following a redox mechanism. For different hybridized nanostructures, the same types of generated active oxygen groups show different catalytic capabilities, which can be regulated by the sp2-hybridized carbon fraction of nanodiamond. The ketonic carbonyl groups formed on graphitic onion-like carbon surface are more active and can improve the selectivity to alkenes significantly compared with the initial nanodiamond and traditional carbon nanotubes. [ABSTRACT FROM AUTHOR]

Ketonic carbonyl groups are catalytic active sites for oxidative dehydrogenation (ODH) reactions on carbon nanotubes. The quantity of these groups could be calculated from chemical titration with hydrazine compounds. ODH catalytic activity of nanocarbon is directly correlated with surface concentration of ketonic carbonyl groups, and the turnover frequency normalized by the number of active sites reflects the intrinsic activity of nanocarbon catalysts. [ABSTRACT FROM AUTHOR]

What not to wear: This work illustrates the clothing of 1 D carbon nanotubes at desired locations with nanoengineered metal nanostructures in a ring pattern for nanodevice applications, such as catalysis. [ABSTRACT FROM AUTHOR]

Foam party: A new method is reported for the immobilization of carbon nanotubes (CNTs) onto silicon carbide foam to afford a CNT/SiC monolith catalyst for sustainable chemistry applications. The as‐synthesized monolith displayed good stability and high catalytic performance in the oxidative dehydrogenation (ODH) of 1‐butene into butadiene. [ABSTRACT FROM AUTHOR]

More than scratching the surface: The mechanism by which supported Pd nanoparticles (PdNPs) catalyze cross‐coupling reactions is the subject of debate. The changes in supported PdNPs during coupling reactions are studied by exploiting modified carbon nanotubes (CNTs) as support materials. After catalysis, CNTs with scratched walls and PdNPs with surface crystalline distortions were discovered, offering insights into the catalytic mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Uniformly dispersed ruthenium nanoparticles supported on non-functional carbon nanotubes (CNT) have been successfully synthesized by using a facile and solvent-free microwave-assisted thermolytic method with dodecacarbonyltriruthenium as the precursor. The results show that 2–4nm sized spheres of Ru nanoparticles were uniformly dispersed and supported on non-functional CNT by several minutes'' exposure to microwave irradiation without solvent. The Ru/CNT catalysts show the desired conversion of about 80% and selectivity to hydrocinnamaldehyde of about 72% in the selective hydrogenation of cinnamaldehyde, where the catalytic performance has been found to depend on both the Ru loading and the surface properties of CNT. [Copyright &y& Elsevier]

• Optimized Pt x Co y -oCNTs were synthesized by a modified oleyamine reduction method. • With the decrease of Pt/Co ratio, the selectivity of C = O bonds increased obviously. • The structural evolution of catalyst was studied by identical location TEM method. The selective hydrogenation of cinnamaldehyde (CAL) is an extremely important transformation. Herein, oxygen functionalized carbon nanotubes (oCNTs) supported a series of Pt x Co y bimetallic nanoparticles (NPs) with varied Pt to Co ratios were synthesized. The introduction of Co significantly affects the electronic structure of Pt NPs, which clearly promotes the selectivity to cinnamyl alcohol (COL). Among all Pt x Co y -oCNTs catalysts, PtCo 3 -oCNTs exhibited the best catalytic performance and a selectivity of over 76% towards COL at a CAL conversion of 99% was obtained. Further characterization of the fresh, used and cycled catalysts revealed that the NP structures were stable and did no change. The structural evolutions during the catalytic reaction were also investigated by identical location transmission electron microscopy (IL-TEM) method in detail, which found that the deactivation of PtCo 3 -oCNTs catalyst during the cycle experiment results from the agglomeration and detachment of PtCo 3 NPs. [ABSTRACT FROM AUTHOR]

[Display omitted] • N -doped carbon nanotubes (NCNTs) facilitated the uniform distribution of Pd NPs. • The surface N groups of NCNTs are beneficial to the formation of metallic Pd. • Pd/NCNTs catalyst shows a higher mass activity than of commercial Pd/C for EOR. • The degradation mechanism of Pd/NCNTs is investigated by IL-TEM and XPS in depth. Herein, we report a facile method to prepare palladium nanoparticles (Pd NPs) anchored on nitrogen-doped carbon nanotubes (Pd/NCNTs) with particle size distribution uniformed. The Pd/NCNTs exhibits excellent ethanol oxidation reaction (EOR) mass activity of 2,489 A g−1, which is 5.1 times higher than commercial Pd/C. However, the anodic reaction of EOR suffers from poor efficiency and low durability. In order to solve the problem of low durability and have better understanding of the degradation mechanism of anodic catalysts, identical-location transmission electron microscopy (IL-TEM), X-ray photoelectron spectroscopy (XPS), and electrochemical measurements were carried out. These were applied to Pd/NCNTs catalyst under EOR in alkaline media. The results showed that the leaching of Pd NPs and the reduction of surface metallic Pd0 were the main reasons for the decreased EOR activity. These findings provide practical guidance for the development of catalysts with higher activity and stability for energy conversion. [ABSTRACT FROM AUTHOR]