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Aerobic oxidation of hydrocarbons yielding corresponding oxygenated products is one of the most important chemical processes. In current work, carbon nanotubes supported encapsulated cobalt nanoparticles with carbon layers (Co@C/CNTs) were synthesized and utilized as catalysts in the oxidation of ethylbenzene (EB) in the liquid phase, exhibiting high catalytic performance. The synergistic effect between Co@C and CNTs played the vital role on facilitating the decomposition of peroxides to enhance the overall activity. The inadequate covered Co@C on CNTs surface were considered as catalytic sites. Density functional theory revealed that the exist of Co nanoparticles could improve the interaction between the catalyst and intermediate free radicals, which were significant for EB oxidation. Last but not least, the electron transfer on carbon surface was enhanced by the incorporation of Co@C nanoparticles, which greatly improved the catalytic performance on EB oxidation. This study provides a new insight into the Co‐based catalysts in the aerobic oxidation of hydrocarbons. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have excellent catalytic activity in liquid phase reaction, especially in aerobic oxidation of cumene. In previous work, the conversion of cumene was 41.8% and the selectivity of cumene hydroperoxide was 71.5%, which was catalyzed by CNTs. But a small amount of impurity Zn2+ totally blocked up the aerobic oxidation of cumene that catalyzed by CNTs, which is an unexpected discovery. By analyzing the catalytic mechanism of CNTs, the inhibition effect of Zn2+ is locked on the abstraction of H atom from cumene. The inhibition of Zn2+ is confirmed in two effects by density functional theory calculations. First, due to the strongly coordination of active oxygen species (ROS) by Zn2+, the energy barrier of initial reaction increases to 1.90 eV, which is nearly 4 times higher than that of the only ROS promoted‐process. Second, the interaction of Zn2+ and RO· or ROO· to inhibits the chain propagation reaction of free radicals. This work precisely demonstrates that the inhibition effect of Zn2+ on initial reaction of cumene. The most significant thing is that the effect of metallic heteroatoms is not negligible in organic oxidation reaction. [ABSTRACT FROM AUTHOR]

Selective aerobic oxidation of hydrocarbons undergoes a free‐radical chain reaction to yield corresponding value‐added products is the significant process in the chemical industry. Nanocarbons with heteroatoms doping as free‐metal catalysts have been proved to be excellent alternatives in various fields of reactions. In this work, nitrogen doped carbon nanotubes (NCNTs) were applied for the aerobic oxidation of ethylbenzene (EB) in the liquid‐phase. The catalytic performance was unexpectedly suppressed, even lower than the control experiment, which is totally different from earlier publications. Mechanistic studies demonstrated that N doping would inhibit the abstraction of α‐H from EB molecule and end the radical propagation, thus suppressing the overall activity. Addition of TBHP would be helpful for the α‐H abstraction and forming alkyl radicals, which start the Franck‐Rabinowitch cage reaction and promote radical propagation in the presence of carbon catalysts. Herein, a higher catalytic efficiency with 46 % EB conversion and 72 % AcPO selectivity were obtained over NCNTs with O2 and TBHP as dual‐oxidants. [ABSTRACT FROM AUTHOR]

Cyclo[18]carbon (C18) as a special molecular allotrope of carbon composed of two‐coordinate carbon atoms has recently been manufactured and characterized by atomic manipulation. Herein, we analyze the electrochemical reduction characteristics of carbon dioxide (CO2) on typical carbon materials (graphene, C60, carbon nanotubes and C18) using density functional calculations. Encouragingly, C18 shows excellent CO2 reduction activity compared to other carbon materials. [ABSTRACT FROM AUTHOR]

Abstract: A HNO3-promoted benzyl alcohol catalytic oxidation system was developed in the presence of carbon nanotubes (CNTs), using molecular oxygen as the terminal oxidant under the mild reaction conditions. The effects of solvent, reaction temperature, amount of HNO3, catalyst loading and surface structure of CNTs on the catalytic performances have been investigated. The CNTs showed excellent catalytic activity exhibiting benzyl alcohol conversion of 96.2% and benzaldehyde selectivity of 88.3% under optimal conditions. In particular, it had remarkable reusability without a significant loss in its activity and selectivity after six consecutive usages. The carbon catalysts were characterized by N2 adsorption–desorption, FT-IR (Fourier transform infrared spectroscopy), Raman, SEM (scanning electron microscopy) and TEM (transmission electron microscopy) techniques. A possible reaction pathway has been proposed, it is clarified that HNO2 attacks benzyl alcohol to generate benzyl nitrite, which is decomposed to benzaldehyde over the HNO3-promoted CNTs-catalyzed system, and electron transfer in graphene sheets plays an important role in the decomposition of benzyl nitrite. These results not only provide an attractive metal-free alternative to noble-metal-catalyzed systems but also come up with a better understanding of the mechanism of CNTs as a metal-free catalyst for the liquid-phase oxidation of benzyl alcohol. [Copyright &y& Elsevier]

[Display omitted] • MnO 2 /CNTs catalysts for cumene oxidation is prepared. • Synergistic effect between MnO 2 and CNTs facilitating CHP decomposition is observed. • Kinetic modelling of 7 elementary steps is established. • MnO 2 /CNTs mainly accelerates the initial and terminal steps. • Enhanced k 80 and reduced E a are obtained over MnO 2 /CNTs. Synergistic effects between the carbon materials and metal oxides usually are considered as the significant factor in the selective oxidation of hydrocarbons. In current study, MnO 2 /CNTs catalysts were prepared under mild condition and applied in the cumene oxidation. As high as 73.44% cumene conversion with 59.06% selectivity of 2-phenyl-2-propanol(PP) was obtained over 21.23-MnO 2 /CNTs, which is much higher than those of CNTs-catalysis and MnO 2 -catalysis systems. The decomposition of cumene hydroperoxide (CHP), a key step for cumene oxidation, was proved to be facilitated by the interaction between MnO 2 nanoparticles and CNTs, which also confirmed from the DFT calculations. These results demonstrated that the synergistic effect between MnO 2 nanoparticles and CNTs would greatly enhance the activity and tune the distribution of products selectivity. The kinetic modeling study in this work further revealed that the interactions between MnO 2 nanoparticles and CNTs would accelerate all the elementary steps, especially, the homolytic cleavage of CHP. The reaction rate constant (k 80 = 9 h−1) for 21.23-MnO 2 /CNTs is 450-folds of CNTs (k 80 = 0.02 h−1). Moreover, the concentration distributions of acetophenone (AP) and PP were well illustrated from the kinetic study. [ABSTRACT FROM AUTHOR]

Abstract: The oxygen reduction reaction (ORR) has been investigated on fish-bone carbon nanotubes (F-CNTs) and parallel carbon nanotubes (P-CNTs). The results showed that the F-CNTs exhibited much higher activity than P-CNTs, which originated from the higher fraction of edge carbon atoms. The dependence of ORR peak potential on the fraction of edge carbon atoms was determined quantitatively for the first time. The density functional theory calculations clearly unveiled the mechanism of edge carbon atoms facilitating the ORR performance. [Copyright &y& Elsevier]