Enhancing the selectivity of hydrocarbon products remains a key challenge to achieving artificial energy sustainability via closing the carbon cycle. While copper-based electrodes uniquely yield hydrocarbon products, the improvement of their product selectivity through physical morphology regulation shows great potential and requires further investigation. Here, we show the distinct morphological influences of the Cu electrode on the reaction selectivity. We synthesize binder-free, vertically aligned, nanoid forest-like copper electrocatalysts for superior improved methane conversion selectivity with respect to planar Cu. These Cu nanocomposites are fabricated through the conformal coating of vertically aligned multiwalled carbon nanotube array electrodes, which have matured to a cost-effective and scalable technology over the past two decades. Simulations reveal that carbon intermediates and protons can be confined in the gaps of the nanoid copper forest, which are formed in situ and in turn cover the catalytic sites and facilitate the simultaneous transfer of coupled electrons and protons. Such forest-like antenna morphology benefits from a threefold improvement of the CO2 electroreduction performance through a decreased reaction onset potential, an increased current density, and enhanced hydrocarbon selectivity.

Further modifications to carbon nanotube (CNT) are often necessary in various application scenarios, however, polluting oxidation processes are typically difficult to be avoided. Efforts were devoted to developing green and facile methods to oxidize CNT. Herein, A hydrothermal process for efficient and eco-friendly oxidization of CNT was explored. The oxidized CNTs were carefully characterized to get clear the transformation in both chemical and physical properties. By comparing both the strength and the toughness of the composites obtained after introducing the oxidized CNTs into epoxy matrices, the oxidation effect was further verified. The strengthening and toughening mechanisms were then studied and attributed to the nicely built chemical and physical interactions. Compared with the concentrated HNO3 oxidized CNT, the hydrothermal method oxidized CNT performed much better reinforcing ability to epoxy, which suggested great potentials for the green hydrothermal method to replace the polluting concentrated HNO3 oxidation method to fabricate high-performance CNT/epoxy composites.

Carbon materials have shown outstanding and stable performance in many reactions and are considered as attractive alternatives for both traditional supports for metal-based catalysts because of their unique physical and chemical properties, especially the surface area, defects, conjugated π electron system, surface functional groups, and doped heteroatoms. The carbonaceous supports have tunable functional groups, high acid/base resistance, high hydrothermal stability, and convenient recycle of metal. Some carbon-supported metal catalysts have already been applied in industry, especially in the hydrogenation process. Basic concepts and regularities in carbon-catalyzed reactions, especially in gas-phase reactions (direct dehydrogenation or oxidative dehydrogenation), have been well established and accepted in related fields. The activity comes from the surface functionalities or defects on carbon catalysts. Surface modification or incorporation of heteroatoms into the graphene framework could effectively influence the electronic structure of the catalysts, thus improving the activity or selectivity of the catalysts.

The Cover Feature shows 2D MoS2 edge-confined single-atom catalysts with pocket-like active sites that act like enzyme catalyst. In their Full Paper, Y. Lou et al. propose a new conceptual approach of fabricating enzyme-like catalysts by anchoring single Pt atoms on the edge sites of 2D MoS2 nanosheets (Pt1/MoS2 SAC), which shows excellent catalytic activity and selectivity for the hydrogenation of α, β-unsaturated aldehydes to unsaturated alcohols. The tactics of fabricating pocket-like active sites with metal single atoms and 2D nanosheet edges in this work shed a light on developing highly selective catalysts for biomass conversion reactions. More information can be found in the Full Paper by Y. Lou et al.

Borocarbonitrides (BCNs) have emerged as highly selective catalysts for the oxidative dehydrogenation (ODH) reaction. However, there is a lack of in-depth understanding of the catalytic mechanism over BCN catalysts due to the complexity of the surface oxygen functional groups. Here, BCN nanotubes with multiple active sites are synthesized for oxygen-assisted methanol conversion reaction. The catalyst shows a notable activity improvement for methanol conversion (29%) with excellent selectivity to formaldehyde (54%). Kinetic measurements indicate that carboxylic acid groups on BCN are responsible for the formation of dimethyl ether, while the redox catalysis to formaldehyde occurs on both ketonic carbonyl and boron hydroxyl (B─OH) sites. The ODH reaction pathway on the B─OH site is further revealed by in situ infrared, x-ray absorption spectra, and density functional theory. The present work provides physical-chemical insights into the functional mechanism of BCN catalysts, paving the way for further development of the underexplored nonmetallic catalytic systems.

Epoxy-based composites are one of the most promising lightweight materials, while the obtention of fire safety usually accompanies with the sacrifice of mechanical properties. Herein, efforts were paid to coordinate the mechanical performance and the fire safety of the epoxy-based composite. Nanodiamond (ND) was modified with P species, Cu species, and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) step by step, to strengthen the mechanical performance and further optimize the fire safety of the ammonium polyphosphate (APP)/epoxy composite simultaneously. The developed composite successfully improved the APP/epoxy composite on tensile properties, glass transition temperature (Tg) and heat release performance in the fire, meanwhile, kept the advantages on storage modulus and other fire safety performances (vertical burning test, limited oxygen index (LOI) and cone calorimeter). After studying the changes to ND and the composite performances that brought about by the every-step modification to ND, the nice improvement on heat release performance was supposed to be mainly contributed to the improved charring effect and the free radical scavenging effect of TND, and the improved tensile properties were due to the formed CuN bond in the curing process that connected Cu species, ND and epoxy matrix together. Model experiments were designed to further verify the reinforcing mechanism.

In situ modulation of surface reaction is a powerful approach to drive high-yield H2O2 electrosynthesis on metal-free carbon. Here, we discover that cationic surfactants can work efficiently as an in situ kinetic promoter for the oxygen-to-peroxide reaction on a car bon black electrode, achieving a peroxide yield above 90% (up to 95.2%) across a >0.8 V window in alkaline media, the best among reported H2O2 electrocatalysts. Our characterizations and kinetic model analysis show that the high peroxide selectivity is attributable to surface carboxylates (-COO-) with weak peroxide binding under a Coulombic pull imposed by an adsorbed cationic layer. Although surface carbonyls (-C=O) also participate in the peroxide synthesis, they exhibit strong binding to peroxide and promote on-site reduction at moderate-to-high overpotential. At only a minute amount of cationic surfactant, a chronoamperometry experiment with a carbonyl-free system can deliver a peroxide production at a sustainably high selectivity (similar to 96%) over 10h.

Pristine carbon nanotubes (CNTs) were treated to make them rich in carbon-centered free radicals. CNTs with various contents of carbon-centered free radicals were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electron paramagnetic resonance (EPR). The CNTs were used to reinforce epoxy resins, and the fire safety (limited oxygen index (LOI), vertical burning test (UL-94), and cone calorimeter test) and mechanical performances (tensile properties, impact strength, and dynamic mechanical analysis (DMA)) of the obtained composites were tested. It was found that the carbon-centered free radical-rich CNTs increased the LOI value of the epoxy matrix dramatically and exhibited obvious advantages over the other CNTs. In addition, the carbon-centered free radical-rich CNTs also had the best reinforcing effect on the mechanical properties. Based on comparison experiments and attempts at correlating the fire performance of the composite with the free radical content and edge content of the CNTs, the improved fire safety was attributed to the free radical scavenging effect of the numerous dangling bonds on the carbon-centered free radical-rich CNTs. In situ EPR experiments revealed the evolution of the free radical scavenging effect during the thermal decomposition of the composite. Carbon-centered free radical-rich CNTs were found to retard the development of fire in the initial period.

•Green chemical synthesis of ethyl pyruvate.•Nanocarbon materials catalyze oxidative dehydrogenation of ethyl lactate.•Active site identification via chemical titration method.•Structural evolution of carbon catalysts during oxidative dehydrogenation reactions.•Reaction mechanism for carbon catalyzed liquid-phase reactions revealed via multiple in situ characterization methods.

Facile green oxidation methods are always desired to functionalize carbon nanotubes (CNTs) in the production of advanced CNT/epoxy composites. In the present work, an optimized H2O2/H2O/O3 oxidation method was developed, and performances of the H2O2/H2O/O3 oxidized CNT in epoxy matrix were tested and compared with that of the H2O/O3 oxidized CNT and the most commonly used concentrated HNO3 oxidized CNT. The physical and chemical characteristics of the obtained oxidized CNTs were systematically characterized via transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman. Mechanical performances of the obtained composites were explored by tensile tests, impact tests, dynamic mechanical analysis (DMA) and fracture toughness tests. It was found that the H2O2/H2O/O3 oxidized CNT exhibited all-around overwhelming advantages over the concentrated HNO3 oxidized CNT on reinforcing the epoxy matrix, while the H2O/O3 oxidized CNT only improved the material strength. Reinforcing mechanisms for the different methods oxidized CNTs were studied and compared. The optimized H2O2/H2O/O3 oxidation method makes scaled production possible, avoids environment pollutions, and holds great potentials to replace the most commonly used concentrated HNO3 oxidation method to oxidize CNT during the preparation of the advanced CNT/epoxy composite.

Controllable synthesis of well-defined supported intermetallic catalysts is desirable because of their unique properties in physical chemistry. To accurately pinpoint the evolution of such materials at an atomic-scale, especially clarification of the initial state under a particular chemical environment, will facilitate rational design and optimal synthesis of such catalysts. The dynamic formation of a ZnO-supported PdZn catalyst is presented, whereby detailed analyses of in situ transmission electron microscopy, electron energy-loss spectroscopy, and in situ X-ray diffraction are combined to form a nanoscale understanding of PdZn phase transitions under realistic catalytic conditions. Remarkably, introduction of atoms (H and Zn in sequence) into the Pd matrix was initially observed. The resultant PdHx is an intermediate phase in the intermetallic formation process. The evolution of PdHx in the PdZn catalyst initializes at the PdHx /ZnO interfaces, and proceeds along the PdHx ⟨111⟩ direction.

A carbon supported carbon nitride is reported here as a catalyst for the direct conversion of acetylene and 1,2-dichloroethane (EDC) to vinyl chloride monomer (VCM). We demonstrate that increasing the synthesis temperature of the carbon nitride material leads to a catalyst with higher catalytic activity toward VCM production. The catalysts were characterized by acetylene temperature-programmed desorption, X-ray photoelectron spectroscopy, high-resolution TEM, electron energy loss spectroscopy, and computational methods, showing that the improved activity for the catalysts can be ascribed to both the higher proportion of pyridinic N and the more positive lowest unoccupied molecular orbital of the catalyst, resulting from the increased degree of polymerization of carbon nitride. These findings highlight the role of polymerization conditions in increasing the catalytic activity of carbon nitride catalysts and provide a strategy for the selective synthesis of highly active carbon nitride catalysts for the one-step synthesis of VCM from acetylene and EDC.

Kinetic analysis is a powerful and effective strategy to reveal the physical-chemical nature of the promotion effect of heteroatoms to nanocarbon catalysts. The present work reported the mechanistic and kinetic analysis of ethylbenzene oxidative dehydrogenation (ODH) reactions on heteroatom (N or B) doped and undoped carbon nanotube (CNT) catalysts via active site titration, kinetic isotope effect and single reactant surface reaction experiments etc. The physical-chemical meanings behind the elementary step rate and equilibrium constants were revealed and applied for interpretations of the promotion effect of heteroatoms at molecular level. Nitrogen doped CNT exhibited both higher rate and equilibrium constants for C-H bond dissociation and O-2 adsorption than undoped one via facilitating the electron transfer process. The evolution of the active sites could be quantitatively described with rate equation via the theory of most abundant surface intermediates, which provides in depth understandings on the mechanism and structure-function relations in carbon catalyzed redox reactions.

Atomically precise subnanometer catalysts are of significant interest because of their remarkable efficiency in a variety of catalytic reactions. However, the dynamic changes of active sites under reaction conditions, in particular, the transition of cluster-oxide interface structure have not yet been well-elucidated, lacking in situ measurements. By using multiple state-of-the-art in situ characterizations, here we show a dynamic interplay between copper tetramers and iron oxides in a single-size Cu-4/Fe2O3 catalyst, yielding an enrichment of surface Cu-4-Fe2+ species under reaction conditions that boosts CO2 hydrogenation at near-atmospheric pressures. During reaction, Cu-4 clusters facilitate the reduction of Fe2O3 producing surface-rich Fe2+ species in the proximate sites. The as-formed Fe2+ species in return promotes CO2 activation and transformation over Cu4 cluster, resulting in strikingly high methanol synthesis at low temperatures and C-1/C-3 hydrocarbon production in a high-temperature regime. The discovery of highly active Cu-4-Fe2+ sites thus provides new insights for the atomic-level design of copper catalyst toward high-efficiency CO2 conversion under mild conditions.

A new synthetic strategy was developed for the fabrication of polydopamine modified carbon nanotube catalysts via in situ polymerization and subsequent thermal treatment process. The hybrid nonmetallic catalysts exhibited superior apparent and intrinsic activity than undoped or nitrogen doped carbon nanotube materials in ethylbenzene dehydrogenation reactions. The relatively high catalytic activity could be attributed to the electron transfer from polydopamine to nanocarbon matrix. The immediate result is that the improved nucleophilicity enhanced the hydrogen abstraction activity of nanocarbon catalysts, which is recognized as the rate determining step in alkane dehydrogenation reactions.

CNTs produced from chemical vapor deposition usually accompany with various impurities such as carbonaceous species and metal residues. In this work, the influence of graphitization and oxidation on the catalytic activity of the CNTs is investigated by using of acrolein oxidation reaction (ACR) as a probe reaction. The results suggest that the presence of amorphous carbon is detrimental to the catalytic performance because of the loss and reproducing from those of unstable functional groups on the surface. Kinetic measurements also reveal that the coverage of amorphous carbon attached on the carbon surface hampers the in-situ formation of active oxygen groups expoxy/lactone, reactant diffusion and ACR reaction. Our work provides valuable information on the design of modified carbon materials with more excellent properties and gives an alternative way for oxidation of aldehyde from an industrial point of view.

A metal-free catalytic system combining oxidized carbon nanotubes (oCNTs) and ionic liquids (ILs) is presented for the oxidation of aromatic thiophene compounds with H2O2 as an oxidant. The oCNTs exhibit impressively high activity and stability in the system, which show an even better performance than those of some reported metal catalysts. The ILs are proved to have indispensable influence on the enhanced catalytic performance of the oCNTs. Detailed characterization by TG-MS and XPS demonstrates that the carbonyl groups are the active sites for the oxidation process, which is further supported by the deactivation and the model catalysts experiments. The quantitative analysis of different oxygen groups in oCNTs could be achieved by an isothermal temperature programmed TG-MS method. The concentration of carbonyl groups is 1.46 mmol per 1 g oCNTs and the turnover frequency of oCNTs could also be obtained (10.7 h(-1) in the presence of OmimPF(6)). H2O2 decomposition experiments combined with the EPR results reveal that the presence of OmimPF(6) can avoid the intermediate HO center dot to form O-2 and then improve the catalytic performance of oCNTs for the oxidation of dibenzothiophene. (c) 2018 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Nitrogen (N)-doped nanocarbons (NDN) as metal-free catalysts have elicited considerable attention toward selective oxidation of alcohols with easily oxidizable groups to aldehydes in the past few years. However, finding a new NDN catalytic material that can meet the requirement of the feasibility on the aerobic catalytics for other complicated alcohols is a big challenge. The real active sites and the corresponding mechanisms on NDN are still unambiguous because of inevitable coexistence of diverse edge sites and N species based on recently reported doping methods. Here, four NDN catalysts with enriched pyridinic N species and without any graphitic N species are simply fabricated via a chemical-vapor-deposition-like method. The results of X-ray photoelectron spectroscopy and X-ray absorption near-edge structure spectra suggest that the dominating N species on NDN are pyridinic N. It is demonstrated that NDN catalysts perform impressive reactivity for aerobic oxidation of complicated alcohols at an atmospheric pressure. Eleven kinds of aromatic molecules with single N species and tunable π conjugation systems are used as model catalysts to experimentally identify the actual role of each N species at a real molecular level. It is suggested that pyridinic N species play an unexpected role in catalytic reactions. Neighboring carbon atoms in pyridinic N species are responsible for facilitating the rate-determining step process clarified by kinetic isotope effects, in situ nuclear magnetic resonance, in situ attenuated total reflectance infrared, and theoretical calculation. Moreover, NDN catalysts exhibit a good catalytic feasibility on the synthesis of important natural products (e.g., intermediates of vitamin E and K3) from phenol oxidation.

Supported gold nanoparticles with sizes below 5 nm display attractive catalytic activities for heterogeneous reactions, particularly those promoted by secondary metal (e.g., Cu) because of the well-defined synergy between metal compositions. However, the specific atomic structure at interfaces is less interpreted systematically. In this work, various bimetallic Au-CuOx catalysts with specific surface structures were synthesized and explored by aberration-corrected scanning transmission electron microscopy (AC-STEM), temperature-programmed experiments and in situ DRIFT experiments. Results suggest that the atomic structure and interfaces between gold and CuOx are determined by the nucleation behaviors of the nanoparticles and result in subsequently the distinctive ability for CO activation. Bimetallic CuO*/Au sample formatted by gold particles surrounded with CuOx nanoclusters have rough surface with prominently exposed low-coordinated Au step defects. Whereas the bimetallic Au@CuO sample formatted by copper precursor in the presence of gold nanoparticles have core-shell structure with relatively smooth surface. The former structure of CuO*/Au displays much accelerated properties for CO adsorption and activation with 90% CO converted to CO2 at 90 °C and nice stability with time on stream. The results clearly determine from atomic scale the significance of exposed gold step sites and intrinsic formation of defected surface by different nucleation. The above properties are directly responsible for the induced variation in chemical composition and the catalytic activity.

Developing economic, effective and stable bifunctional electrocatalysts to achieve sustainable hydrogen production is highly desired. Herein, C-coated CoP hollow microporous nanocages (C-CoP-1/12) are synthesized by calcination of a Prussian blue analog precursor and subsequent phosphorization treatment. Under alkaline condition, the C-CoP-1/12 exhibit splendid electrocatalytic performance with a low overpotential of 173 mV for hydrogen evolution reaction (HER) and 333 mV for oxygen evolution reaction (OER) at a current density of 10 mA cm-2. The C-CoP-1/12 show high electrocatalytic performance for overall water splitting at a low potential of only 1.650 V for the driving current density of 10 mA cm-2, and they exhibit remarkable stability for at least 24 h. The engineering of phosphating is the critical step for the synthesis of pure-phase CoP with hollow nanoarchitecture. Compared with Co2P, CoP possesses lower water dissociation barrier and favorable ΔGH* value according to theoretical calculations, resulting in superior electrocatalytic performance. Such impressive water splitting performance is mainly attributed to the collective effects of metal phosphide with unique electronic structure, the shortened electron transport paths, and the conductive C coating. This strategy is believed to provide a basis for the development of electrode materials with highly efficient electrocatalytic water-splitting capability.