The selective oxidation of hydrocarbons is of great importance in the chemical industry. Nanocarbons have attracted intensive attention as metal-free catalysts in this field. Efforts have been made to reveal the crucial role of nanocarbons in the activation of C–H bonds and radical propagation in hydrocarbon oxidation, but it is still far from being understood. In this work, in situ Electron Paramagnetic Resonance (EPR) was conducted in the selective oxidation of cyclohexane (CyH) catalyzed by nitrogen-doped carbon nanotubes (N-CNTs) and multiwalled carbon nanotubes (MWCNTs) in the liquid phase. The interaction between the radicals and nanocarbons was disclosed. The unique role of N-CNTs as a catalyst in the selective oxidation of CyH for the production and propagation of C6H11˙ and O2˙ radicals was evidently confirmed. This work will provide new mechanistic insights into the oxidation of hydrocarbons in the liquid phase.

•A NiCuCaOCa12Al14O33 hybrid catalyst is effective for sorption-enhanced steam reforming of glycerol.•97% H2 with <30 ppm CO can be directly produced for fuel cell applications.•The catalyst performs stable for ten reaction–regeneration cycles.•Cu promoter adjusts the activity of Ni for low CO concentration without sacrificing H2 purity.The concentration of CO in the high-purity hydrogen from sorption-enhanced steam reforming (SESR) processes is usually too high to be directly used in fuel cells. Herein, we report a production of fuel-cell grade H2 with <30 ppm CO through SESR of glycerol (SESRG), a by-product of biodiesel manufacture. High purity H2 can be produced by employing a catalyst-sorbent hybrid material composed of Ni as catalyst, CaO as CO2 sorbent and Ca12Al14O33 as spacer. By introducing copper as promoter, the performance of the bi-functional catalyst could be modified to produce a 97.15 vol% purity of H2 with 28 ppm CO. With an optimized Ni/Cu ratio, the 7.5Ni–7.5Cu catalyst shows the excellent stability for producing about 97% H2 with <30 ppm CO for ten cycles. The characterizations and model reaction tests indicate that copper can affect CO, CO2 hydrogenation and water gas shift reaction to adjust the performance of SESRG reaction. The results presented here show the promise of tuning the catalyst composition for achieving high quality H2 through SESR processes.Download high-res image (373KB)Download full-size image

•Two-dimensional (2D) transition metal carbide Ti3C2 and a novel Ti3+ doped rutile TiO2/Ti3C2 composite was firstly fabricated.•The high active (111) facets of TiO2 was adjusted by the concentration of NH4F.•The percentage of Ti3C2 in composites was adjusted by hydrothermal duration.•The Ti3C2 for separating charges and Ti3+ dopant for narrowing band gap, the composite exhibited excellent photocatalytic activity under visible light.The rational design of interface is a key factor for improving the performance of photocatalysts. Herein, a nanocomposite comprised of Ti3+ doped rutile TiO2 octahedrons exposing active (111) facets and two-dimensional Ti3C2 sheets was synthesized by a hydrothermal oxidation route and subsequent hydrazine hydrate reduction. The crystallographic facet proportions of TiO2 can be controlled by NH4F as a facet controlling agent. The photocatalytic activity of the TiO2/Ti3C2 composite was maximized by completely exposing the active (111) surfaces. The interfacial microstructure between Ti3C2 and TiO2 can be tuned by the hydrothermal reaction duration. The charge kinetics was substantially steered by the hole trapping effect of 2D Ti3C2 terminated by OH groups. Through the reduction by hydrazine hydrate, Ti3+ was doped into the bulk of TiO2, thereby enabling the photocatalytic activity under visible light. This work opens a new window to the rational design of photocatalysts based on 2D MXene materials.Download high-res image (85KB)Download full-size image

•N-doped CNTs with residual growth catalysts performed worse than CNTs as supports of Pd for nitrobenzene hydrogenation.•Residual trace Fe deactivates Pd catalysts as contamination.•Most metal impurities, Co, Ni, Mn, Cr, Cu, Zn, Mo, Al and Mg, may significantly contaminate Pd catalyst.•The residual Fe effect can be avoided by coating CNTs with N-doped carbon shells.•3.85 fold activity improvement using N-doped carbon coated CNTs as support of Pd.Nitrogen-doped carbons can effectively stabilize noble metal particles to achieve high catalytic performances. However, the metallic impurities in carbon nanomaterials, e.g. the residual growth catalysts of carbon nanotubes (CNTs), have some unforeseen effects on the catalysis involving nanocarbons. Herein, we demonstrate that the residual growth catalysts of N-doped CNTs (NCNTs) may significantly deactivate Pd catalysts for the hydrogenation of nitrobenzene. Through high-resolution transmission electron microscopy and CO-stripping, it was determined that the N dopants improved the dispersion of Pd nanoparticles. However, the iron, at ppm level, in residual catalysts encapsulated inside NCNTs can transfer onto the surface of Pd to block active sites so that the activity of Pd/NCNTs was much lower than that of Pd/CNTs. The similar effect was observed for most of the common metallic impurities in carbon materials, including Co, Ni, Mn, Cr, Cu, Zn, Mo, Al and Mg. To exploit the N-doped carbons, we deposited N-doped carbon layers on purified CNTs through pyridine pyrolysis and then supported Pd nanoparticles. By this means, the activity of Pd for nitrobenzene hydrogenation was improved by 3.85 folds compared to conventional CNTs, emphasizing the importance of controlling impurities in N-doped carbon materials for high performance catalysts.Download high-res image (117KB)Download full-size image

Effectively harvesting light to generate long-lived charge carriers to suppress the recombination of electrons and holes is crucial for photocatalytic reactions. Exposing the highly active facets has been regarded as a powerful approach to high-performance photocatalysts. Herein, a hybrid comprised of {001} facets of TiO2 nanosheets and layered Ti3C2, an emerging 2D material, was synthesized by a facile hydrothermal partial oxidation of Ti3C2. The in situ growth of TiO2 nanosheets on Ti3C2 allows for the interface with minimized defects, which was demonstrated by high-resolution transmission electron microscopy and density functional theory calculations. The highly active {001} facets of TiO2 afford high-efficiency photogeneration of electron–hole pairs, meanwhile the carrier separation is substantially promoted by the hole trapping effect by the interfacial Schottky junction with 2D Ti3C2 acting as a reservoir of holes. The improved charge separation and exposed active facets dramatically boost the photocatalytic degradation of methyl orange dye, showing the promise of 2D transition metal carbide for fabricating functional catalytic materials.Keywords: (001) TiO2; hole trapping; layered Ti3C2; MXenes; Schottky junction

As an emerging catalyst based on earth-abundant metals, Co3O4 supported on carbon materials, derived from the pyrolysis of metal salts and nitrogen-containing ligands, shows excellent performance in hydrogenation, hydrogenated coupling, oxidative esterification and oxidation of amines. Herein, we unravel the real active sites of this catalyst through a combination of XRD, XPS, HRTEM, EELS and poisoning experiments with sulfur-containing compounds. The oxidative esterification of benzyl alcohol, hydrogenation of nitrobenzene and hydrogenated coupling of nitrobenzene with benzaldehyde were used as probe reactions. By comparing the catalytic performance before and after HCl washing, it was demonstrated that particulate Co3O4 has a marginal effect on the catalysis, and the highly dispersed CoNx on carbon nanotubes created during the pyrolysis is responsible for the activity. It was proposed that cobalt chelate complexes bonded to 2 to 3 nitrogens in the graphene lattice, probably like the pyridinic vacancy, might be responsible for the activity.

•Dual-metal oxide particles were homogeneously supported on graphene.•CoFe2O4 nanoparticles display superior electrochemical performance as LIB anodes.•Phase pure dual-metal oxide particles can be hollowed by applying Kirkendall effect.•Solid nanosized dual-metal oxides have superior capacity to the hollow spheres.Dual-transition-metal oxide (DTMO) nanostructures are emerging materials for lithium-ion battery (LIB) anodes with improved structural stability, electronic conductivity and electrochemical performance compared to their single-metal counterpart. Herein, composites of graphene with DTMOs (MFeO, M = Co, Mn, Zn) were controllably prepared by harnessing the synthesis atmospheres and the nanoscale diffusion couple. Their composition and morphology were characterized by TEM, EDS mappings, XRD and XPS. The NH3 treatment resulted in the formation of hollow DTMO nanoparticles on nitrogen-doped graphene, while H2 and Ar gave graphene-supported hollow and solid DTMO particles, respectively. Electrochemical tests were applied to compare the performance of these composites as LIB anodes. The superior anode performance DTMO electrodes was demonstrated to the corresponding iron oxide composite. CoFe2O/RGO composites exhibit excellent rate capability and high-rate cycling stability for lithium storage, due to its stable solid structure. However, the hollowing of DTMO particles cannot elevate the capacity and stability, due to the interfacial resistance and structural changes upon cycling.

Tuning the morphology of nanocatalysts has been regarded as a powerful approach to high-performance heterogeneous catalysts, since the highly active facets might be selectively exposed to reactants. Herein, we report how the shape effect significantly improves the performance of Ir/La2O2CO3 catalyst in the steam reforming of glycerol at high temperatures up to 650 °C toward a sustainable hydrogen production. La2O2CO3 nanorods (NRs) with different sizes and aspect ratios were synthesized for supporting Ir nanoparticles. Compared with conventional Ir/La2O2CO3, the NR catalysts considerably improved the activity, selectivity, and stability, allowing for a stable hydrogen production for 100 h without obvious deactivation. The role of the NRs was rationalized by XRD, XPS, TPR, TPD, and HRTEM analysis. The high performance of the NR catalyst is elucidated by the formation of hexagonal La2O2CO3 NRs with selectively exposed {110} facets under reaction conditions, which strongly interact with Ir catalysts, thereby preventing the tiny catalyst particles from sintering at 650 °C. A mechanistic insight is presented to understand the interaction based on the structure of the La2O2CO3 supports.Keywords: lanthanum dioxycarbonate; metal−support interaction; morphology effect; nanorod; steam reforming of glycerol

A new catalyst, cobalt carbonitride (CoCN) nanoparticles supported on nitrogen-doped graphenes (NG), was synthesized via a high temperature ammonia nitridation method. The catalyst has a core–shell structure with a highly active CoCN core and a protective cobalt oxide shell. Linear sweep voltammetry measurements show that the catalyst presents excellent activity in an oxygen reduction reaction compared to cobalt oxide supported on NG and commercial Pt/C catalysts, benefiting from the strong synergistic effect between CoCN and NG and the electronic modification of cobalt oxide by CoCN from within.

Carbon nanotubes (CNTs) and nitrogen-doped CNTs (NCNTs) as metal-free catalysts exhibited an excellent activity in the selective oxidation of α-pinene with molecular oxygen as the terminal oxidant. Two distinct pathways, i.e. epoxidation and allylic oxidation, were active in this reaction. Enhancement of epoxidation was observed over CNTs, yielding the highest epoxidation/allylic oxidation products ratio. Excellent activity was achieved over NCNTs, giving 54.5% α-pinene conversion and 272.4 mmol g−1 h−1 mass-normalized activity, which compete with that of the state-of-the-art metal catalysts. Allylic oxidation was enhanced over NCNTs, using which equimolar amounts of epoxide and allylic products were produced. Thus, N-doping boosted the overall conversion and the yields of both epoxidation and allylic oxidation products, which was supported by the results of theoretical simulation.

Carbon nanotubes (CNTs) and nitrogen-doped CNTs (NCNTs) were systematically investigated as metal-free catalysts in the selective allylic oxidation of cyclohexene using molecular oxygen as oxidant in the liquid phase. High cyclohexene conversion (up to 59.0%) and 620.1 mmol g–1 h–1 mass-normalized activity were obtained for NCNTs, competing with the state-of-the-art metal catalysts. The positive effect of nitrogen dopant on the performance of CNTs was demonstrated, with respect to the aspects of enhancing activity and increasing selectivity of 2-cyclohexen-1-one, allowing for a ketone/alcohol ratio of 3.7 at 59% conversion. The unique catalytic role of NCNTs was attributed to their capability to promote the radical chain propagation via stabilizing peroxyl and cycloxyl radicals, which boosted the further conversion of 2-cyclohexen-1-ol toward 2-cyclohexen-1-one as well.Keywords: aerobic oxidation; allylic oxidation; carbon nanotubes; cyclohexene; nitrogen

Nitrogen-, phosphorous- and boron-doped carbon nanotubes (N-CNTs, P-CNTs and B-CNTs) were prepared by a chemical vapor deposition method using xylene as carbon source and aniline-NH3, triphenyl phosphine and triethyl borate as nitrogen, phosphorous and boron precursors, respectively. By tailoring the composition of reactants and reaction atmosphere, N-CNTs with nitrogen contents from 0% to 4.36% and P-CNTs with phosphorous contents from 0.55% to 5.14% were synthesized. N- and P-CNTs are active for the oxidation of cyclohexane in the liquid phase with molecular oxygen as oxidant. The highest mass-normalized activity, 761 mmol g−1 h−1, was achieved over N-CNTs synthesized from aniline in an NH3 atmosphere, while the highest surface-area-normalized activity, 28 mmol m−2 h−1, was observed over P-CNTs. B-doping does not improve the activity of CNTs. The effect of the number of nitrogen functionalities and defects was investigated to reveal the structure–activity relationship of the doped CNTs. By using the work function as an indicator of the electron donation of carbon, an exponential dependence of specific activity on work function was discovered for N- and P-CNTs, suggesting that the electron transfer on the surfaces of CNTs plays a central role in the CNT-catalyzed oxidation of cyclohexane.

The catalytic properties of sp2- and sp3-hybridized carbons, represented by graphene and diamond, in the selective oxidation of cyclohexane were investigated to understand the structure dependence of carbon materials in the reaction. sp2 carbons showed the higher activity than sp3 carbons. The highest activity was obtained over mesoporous graphene, a representative sp2-hybridized carbon, yielding a weight-normalized activity of 162.6 mmol g−1 h−1. The excellent performance of sp2 carbons was rationalized by their ability to catalyze the decomposition of peroxide intermediates, such as cyclohexyl hydroperoxide, which promoted the oxidative reaction to produce cyclohexanol and cyclohexanone.

Two types of flow distributors, that is, a jet-flow-splitter and a simplified constructal distributor, were designed to equalize the gaseous reagents in the inlet of a microreformer packed with catalyst supported on ceramic foam. The effects of type and geometry of distributors on flow, temperature distributions, and reaction performance over the catalyst during the autothermal reforming of ethanol were investigated experimentally and computationally. It was found that the jet flow splitter in the shape of cone or hemisphere can effectively equalize the flow distribution on the lower surface of catalyst, thereby improving the temperature distribution and performance of the microreformer. A microreformer with a hemisphere jet-flow-splitter in optimal geometry can convert 91% of ethanol with a selectivity to hydrogen of 74%, equivalent to yielding 3.3 mol of hydrogen per mol ethanol. Such a distribution device can be used to fabricate an efficient microreformer with simple structure for the hydrogen production orienting the portable fuel cell application.

Porous hollow iron oxide nanoparticles (PHNPs) supported on carbon nanotubes (CNTs) were facilely synthesized by etching Fe@FexOy/CNT with dilute nitric acid aqueous solution at ambient temperature without the assistance of any surfactants and ligands. The mean diameter of hollow iron oxide nanoparticles was about 17 nm, with a wall thickness of about 4 nm. The formation mechanism of PHNPs is discussed based on the characterization results from TEM, XRD and H2-TPR. The combination of nanoscale Kirkendall effect and selective acid etching is proposed to be responsible for the formation of CNT supported PHNPs, through a transformation from core/void/shell structures to hollow nanoparticles.Highlights► Facile synthesis of porous hollow iron oxide nanoparticles supported on carbon nanotubes. ► Organic reagent-free synthesis at ambient temperature. ► Formation of Fe@FexOy core/shell structures by Kirkendall effect. ► Selectively etching of Fe cores by HNO3.

A carbon-nanotube-supported RuO2 nanocatalyst encapsulated in thin silica layer was successfully synthesized. The prior formation of silica over RuO2 nanoparticles effectively hindered catalyst aggregation at high temperatures. The significant improvement of the resistance to sintering and the catalytic selectivity were demonstrated in competitive oxidation of n-butanol and i-butanol and methanol oxidative dehydrogenation.

A thermodynamic analysis of the steam reforming of representative oxygenate fuels, including methanol, ethanol, n-propanol, n-butanol, n-hexanol, ethylene glycol, glycerol, glucose, acetic acid, and acetone, was carried out with the Gibbs free-energy minimization method. The operational regime, energy efficiency, and reformate composition of reforming various oxygenate fuels were studied. It was revealed that the critical steam/carbon ratio, by which there is free carbon deposition in the reforming product, decreases with an increasing oxygen/carbon ratio in oxygenate fuels. The appropriate operating temperature range for steam reforming of oxygenate fuels is within 600–700 °C. Fuels with a higher hydrogen/carbon ratio have wider operational windows. The results would offer a guideline toward a rational selection of raw materials for a renewable reformer proton-exchange membrane fuel cell system based on understanding features of oxygenate fuels in the steam-reforming process.

The activity of RuO2·xH2O/CNT for benzyl alcoholoxidation can be predicted by the specific capacitance (SC) of RuO2, suggesting that highly active RuO2 nanocatalysts are also good supercapacitor materials with SC high up to 1500 F gRuO2−1.

Highly dispersed ruthenium oxide clusters were synthesized on carbon nanotubes (CNTs) to form RuO2·xH2O/CNT catalyst by a homogeneous oxidation precipitation method. Methanol oxidation was carried out on RuO2·xH2O/CNT at low temperatures for the production of diverse oxygenous products, such as methyl formate (MF) and dimethoxymethane (DMM). Unprecedented conversion rate of methanol, high up to 545 molMeOH (mol Rusurface)−1 h−1, was observed at 120 °C. The effect of structural water in RuO2 domains on the performances of the methanol oxidation reaction was investigated by annealing them in N2 at elevated temperatures. The dehydration of RuO2 clusters decreased the oxidation ability and changed the selectivity patterns. It was suggested that the behaviors of RuO2 during the annealing process may be strongly influenced by the interaction between RuO2 and CNTs.

Hydrogen was produced over noble metal (Ir, Ru, Rh, Pd) catalysts supported on various oxides, including γ-Al2O3, CeO2, ZrO2 and La2O3, via the autothermal reforming reaction of ethanol (ATRE) and oxidative reforming reaction of ethanol (OSRE). The conversion of ethanol and selectivites for hydrogen and byproducts such as methane, ethylene and acetaldehyde were studied. It was found that lanthana alone possessed considerable activity for the ATRE reaction, which could be used as a functional support for ATRE catalysts. It was demonstrated that Ir/La2O3 prevented the formation of methane, and Rh/La2O3 encumbered the production of ethylene and acetaldehyde. ATRE reaction was carried out over La2O3-supported catalysts (Ir/La2O3) with good stability on stream, high conversion, and excellent hydrogen selectivity approaching thermodynamic limit under autothermal condition. Typically, 3.4 H2 molecules can be extracted from a pair of ethanol and water molecules over Ir(5wt%)/La2O3. The results presented in this paper indicate that Ir/La2O3 can be used as a promising catalyst for hydrogen production via ATRE reaction from renewable ethanol.

The effects of additives containing iron or nickel during chemical vapor deposition (CVD) on the growth of carbon nanotubes (CNTs) by methane decomposition on Mo/MgO catalyst were investigated. Ferrocene and nickel nitrate were introduced as deactivation inhibitors by in-situ evaporation during CVD. The precisely controlled in-situ introduction of these inhibitors increased the surface renewal of catalyst, and therefore prevented the catalyst from deactivation. Using this method, aligned multi-walled CNTs with parallel mesopores can be produced on a large scale.

•Synthetic methods drastically affect Pt electronic structure.•Synthetic methods affect the interaction between Pt and nitrogen sites on NCNTs.•The Pt4f7/2(0) binding energy decreases in the order: Pt/NCNTs(H2) > Pt/NCNTs(EG) > Pt/NCNTs(NaBH4).•The electron-enriched Pt NPs are in favor of the electro-oxidation reactions.•The electron-deficient Pt NPs are in favor of ammonia borane hydrolysis.The influence of catalyst synthesis strategy, including ethylene glycol (EG) reduction, sodium borohydride reduction and impregnation-H2-reduction, on the metal-support-interaction of Pt on nitrogen-doped carbon nanotubes (Pt/NCNTs) was systematically investigated and summarized. The catalytic performances were explored in the electro-oxidation reactions of glycerol, formic acid and CO, and the hydrolysis of ammonia borane (AB). Through X-ray photoelectron spectroscopy (XPS), density functional theory calculations and CO stripping technique, it was revealed that the synthesis methods drastically affected the electronic property of Pt nanoparticles (NPs). Pt NPs preferentially interacted with graphitic nitrogen in EG reduction method due to the electron donating property of graphitic nitrogen, while preferentially interacted with pyridinic nitrogen and defects in the impregnation-H2-reduction method due to the vacancies containing NP favoring the charged metal ion adsorption. The catalytic activity strongly depended on the electronic property of Pt NPs, which can be ascribed by the binding energy of Pt4f7/2(0) from XPS. The higher catalytic activity was obtained over electron-enriched Pt NPs for the electro-oxidation reactions. On the other hand, electron-deficient Pt NPs had better intrinsic activity in AB hydrolysis. The results herein suggested that appropriate synthesis method should be rationally applied to maximize the activities of Pt for targeting reactions benefited from electron-enriched or electron-deficient metal NPs.Download high-res image (171KB)Download full-size image

•Solvents affect the oxidation of cyclohexene catalyzed by N-doped CNTs.•The higher polarity is beneficial for the activity in aliphatic solvents.•Aromatic solvents are less reactive due to the competitive adsorption.•A modest solvent basicity is required for high reactivity.•2-cyclohexen-1-one selectivity slightly increases with solvent polarity.A wide spectrum of, up to 22, organic solvents, including aprotic/protic aliphatics/aromatics, was studied to achieve a comprehensive understanding to the solvent effect on the cyclohexene oxidation. It was found that the catalytic activity was significantly influenced by the viscosity, polarity and basicity of solvents in this reaction. Among these solvents, the polar aprotic aliphatic solvents displayed higher catalytic reactivities than other types of solvents. A volcano curve was found describing the dependence of activity on solvent basicity because of the suitable stability of intermediates. Among the solvents investigated, acetonitrile afforded the highest activity and selectivity of 2-cyclohexen-1-one, because of a good compromise between strong polarity and moderate basicity.Download high-res image (64KB)Download full-size image

La2O3-supported Ir catalyst was prepared by wetness impregnation method for the oxidative steam reforming of ethanol (OSRE). Fresh, reduced, and used catalysts were characterized by N2 adsorption, H2 chemisorption, XRD, FT-IR, TEM, and XPS. La2O3 would transform into hexagonal La2O2CO3 during OSRE, which suppress coking effectively. Reduced Ir metal can interplay with La2O2CO3 to form Ir-doped La2O2CO3. It dynamically forms and decomposes to release active Ir nanoparticles, thereby preventing the catalyst from sintering and affording high dispersion of Ir/La2O3 catalysts at elevated temperatures. By introducing ultrasonic-assisted impregnation method during the preparation of a catalyst, the surface Ir concentration was significantly improved, while the in situ dispersion effect inhibited Ir from sintering. The Ir/La2O3 catalyst prepared by the ultrasonic-assisted impregnation method is highly active and stable for the OSRE reaction, in which the Ir crystallite size was maintained at 3.2 nm after 100 h on stream at 650 °C and metal loading was high up to 9 wt%.Ir nanoparticles are in situ formed and dispersed over La2O2CO3-II through the strong interaction between metal and support during the course of oxidative steam reforming of ethanol.Download high-res image (101KB)Download full-size image

LaMnO3, LaFeO3, LaCoO3 and LaNiO3 perovskite oxides were prepared using combustion method for autothermal reforming of ethanol (ATRE). Fresh, reduced and used catalysts were characterized by XRD, TEM, ethanol-TPD, and H2-TPR. The perovskite-type oxides exhibit moderate activities in the ATRE reaction. Well dispersed Ni particles on lanthanum oxide species were obtained by reducing the LaNiO3 sample. It favors the dehydrogenation, decomposition of ethanol/acetaldehyde, methane reforming and water gas shift reactions, thus leads to good activity and H2 selectivity in ATRE reaction. Typically, 3.2 H2 molecules per ethanol molecule were produced at EtOH:H2O:O2 = 1:2:0.98 and GHSV = 4 × 105 h−1. A comparison between LaNiO3 derived and impregnated Ni/La2O3 shows that the LaNiO3 derived sample favored the dispersion of Ni, which increased the activity and the resistance to coke deposition.

As an emerging catalyst based on earth-abundant metals, Co3O4 supported on carbon materials, derived from the pyrolysis of metal salts and nitrogen-containing ligands, shows excellent performance in hydrogenation, hydrogenated coupling, oxidative esterification and oxidation of amines. Herein, we unravel the real active sites of this catalyst through a combination of XRD, XPS, HRTEM, EELS and poisoning experiments with sulfur-containing compounds. The oxidative esterification of benzyl alcohol, hydrogenation of nitrobenzene and hydrogenated coupling of nitrobenzene with benzaldehyde were used as probe reactions. By comparing the catalytic performance before and after HCl washing, it was demonstrated that particulate Co3O4 has a marginal effect on the catalysis, and the highly dispersed CoNx on carbon nanotubes created during the pyrolysis is responsible for the activity. It was proposed that cobalt chelate complexes bonded to 2 to 3 nitrogens in the graphene lattice, probably like the pyridinic vacancy, might be responsible for the activity.

A new catalyst, cobalt carbonitride (CoCN) nanoparticles supported on nitrogen-doped graphenes (NG), was synthesized via a high temperature ammonia nitridation method. The catalyst has a core–shell structure with a highly active CoCN core and a protective cobalt oxide shell. Linear sweep voltammetry measurements show that the catalyst presents excellent activity in an oxygen reduction reaction compared to cobalt oxide supported on NG and commercial Pt/C catalysts, benefiting from the strong synergistic effect between CoCN and NG and the electronic modification of cobalt oxide by CoCN from within.

The activity of RuO2·xH2O/CNT for benzyl alcoholoxidation can be predicted by the specific capacitance (SC) of RuO2, suggesting that highly active RuO2 nanocatalysts are also good supercapacitor materials with SC high up to 1500 F gRuO2−1.

Carbon nanotubes (CNTs) and nitrogen-doped CNTs (NCNTs) as metal-free catalysts exhibited an excellent activity in the selective oxidation of α-pinene with molecular oxygen as the terminal oxidant. Two distinct pathways, i.e. epoxidation and allylic oxidation, were active in this reaction. Enhancement of epoxidation was observed over CNTs, yielding the highest epoxidation/allylic oxidation products ratio. Excellent activity was achieved over NCNTs, giving 54.5% α-pinene conversion and 272.4 mmol g−1 h−1 mass-normalized activity, which compete with that of the state-of-the-art metal catalysts. Allylic oxidation was enhanced over NCNTs, using which equimolar amounts of epoxide and allylic products were produced. Thus, N-doping boosted the overall conversion and the yields of both epoxidation and allylic oxidation products, which was supported by the results of theoretical simulation.

The catalytic properties of sp2- and sp3-hybridized carbons, represented by graphene and diamond, in the selective oxidation of cyclohexane were investigated to understand the structure dependence of carbon materials in the reaction. sp2 carbons showed the higher activity than sp3 carbons. The highest activity was obtained over mesoporous graphene, a representative sp2-hybridized carbon, yielding a weight-normalized activity of 162.6 mmol g−1 h−1. The excellent performance of sp2 carbons was rationalized by their ability to catalyze the decomposition of peroxide intermediates, such as cyclohexyl hydroperoxide, which promoted the oxidative reaction to produce cyclohexanol and cyclohexanone.