Graphene supported CoO nanoparticles as an advanced catalyst for aerobic oxidation of cyclohexane

Transition metals are commonly employed as catalysts for the oxidation of cyclohexane.

Bio-reduction of Graphene Oxide: Catalytic Applications of (Reduced) GO in Organic Synthesis

This work is based on various bio-reduction of graphene oxide into reduced graphene oxide and their applications in organic synthesis and group transformations. Graphene oxide, with abundant oxygencontaining functional groups on its basal plane, provides potential advantages, including excellent dispersibility in solvents and the good heterogeneous catalyst. This manuscript reviews various methods of synthesis of graphene and graphene oxide and a comparative study on their advantages and disadvantages, how to overcome disadvantages and covers extensive relevant literature review. In the last few years, investigation based on replacing the chemical reduction methods by some bio-compatible, chemical/impurity-free rGO including flash photo reductions, hydrothermal dehydration, solvothermal reduction, electrochemical approach, microwave-assisted reductions, light and radiation-induced reductions has been reported. Particularly, plant extracts have been applied significantly as an efficient reducing agent due to their huge bioavailability and low cost for bio-reduction of graphene oxide. These plant extracts mainly contain polyphenolic compounds, which readily get oxidized to the corresponding unreactive quinone form, which are the driving force for choosing them as bio-compatible catalyst. Currently, efforts are being made to develop biocompatible methods for the reduction of graphene oxide. The reduction abilities of such phytochemicals have been reported in the synthesis and stabilization of various nanoparticles viz. Ag, Au, Fe and Pd. Various part of plant extract has been applied for the green reduction of graphene oxide. Furthermore, the manuscript describes the catalytic applications of graphene oxide and reduced graphene oxide nanosheets as efficient carbo-catalysts for valuable organic transformations. Herein, important works dedicated to exploring graphene-based materials as carbocatalysts, including GO and rGO for organic synthesis including various functional group transformations, oxidation, reduction, coupling reaction and a wide number of multicomponent reactions have been highlighted. Finally, the aim of this study is to provide an outlook on future trends and perspectives for graphene-based materials in metal-free carbo-catalysis in green synthesis of various pharmaceutically important moieties.

Selective Catalytic Oxidation of Benzyl Alcohol to Benzaldehyde by Nitrates

In this paper, ferric nitrate was used to oxidize benzyl alcohol in a mild condition and demonstrated its better performance compared to HNO₃. In the reaction, the conversion rate and product selectivity could be both as high as 95% in N₂ atmosphere, while the benzaldehyde yield also reached 85% in air. Similar to Fe(NO₃)₃·9H₂O, the other metallic nitrates such as Al(NO₃)₃·9H₂O and Cu(NO₃)₂·3H₂O could also oxidize the benzyl alcohol with high activity. The applicability of Fe(NO₃)₃·9H₂O for other benzylic alcohol was also investigated, and the reaction condition was optimized at the same time. The results showed the Fe(NO₃)₃·9H₂O would be more conducive in oxidizing benzyl alcohol under the anaerobic condition. The experiments in N₂ or O₂ atmospheres were conducted separately to study the catalytic mechanism of Fe(NO₃)₃. The results showed the co-existence of Fe³⁺ and NO3- will generate high activity, while either was with negligible oxidation property. The cyclic transformation of Fe³⁺ and Fe²⁺ provided the catalytic action to the benzyl alcohol oxidation. The role of NO3- was also an oxidant, by providing HNO₂ in anaerobic condition, while NO3- would be regenerated from NO in aerobic condition. O₂ did not oxidize the benzyl alcohol conversion directly, while it could still be beneficial to the procedure by eliminating the unwelcome NO and simultaneously reinforcing the circulation of Fe²⁺ and Fe³⁺, which therefore forms a green cyclic oxidation. Hence, the benzyl alcohol oxidation was suggested in an air atmosphere for efficiency and the need of green synthesis.

Cerium Oxide Nanoparticles Inside Carbon Nanoreactors for Selective Allylic Oxidation of Cyclohexene

The confinement of cerium oxide (CeO₂) nanoparticles within hollow carbon nanostructures has been achieved and harnessed to control the oxidation of cyclohexene. Graphitized carbon nanofibers (GNF) have been used as the nanoscale tubular host and filled by sublimation of the Ce(tmhd)₄ complex (where tmhd = tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)) into the internal cavity, followed by a subsequent thermal decomposition to yield the hybrid nanostructure CeO₂@GNF, where nanoparticles are preferentially immobilized at the internal graphitic step-edges of the GNF. Control over the size of the CeO₂ nanoparticles has been demonstrated within the range of about 4-9 nm by varying the mass ratio of the Ce(tmhd)₄ precursor to GNF during the synthesis. CeO₂@GNF was effective in promoting the allylic oxidation of cyclohexene in high yield with time-dependent control of product selectivity at a comparatively low loading of CeO₂ of 0.13 mol %. Unlike many of the reports to date where ceria catalyzes such organic transformations, we found the encapsulated CeO₂ to play the key role of radical initiator due to the presence of Ce³⁺ included in the structure, with the nanotube acting as both a host, preserving the high performance of the CeO₂ nanoparticles anchored at the GNF step-edges over multiple uses, and an electron reservoir, maintaining the balance of Ce³⁺ and Ce⁴⁺ centers. Spatial confinement effects ensure excellent stability and recyclability of CeO₂@GNF nanoreactors.

Trace amounts of Cu(OAc)2 boost the efficiency of cumene oxidation catalyzed by carbon nanotubes washed with HCl

Trace amounts of Cu(OAc)₂ significantly improve the activity and selectivity of cumene oxidation catalyzed by HCl-washed carbon nanotubes.

Generalized reactivity descriptor of defective carbon catalysts for acetylene hydrochlorination: the ratio of sp2 : sp3 hybridization

Surface engineering of sp² and sp³ oriented carbons with optimized hybridization configuration makes excellent metal free catalysts for acetylene hydrochlorination

Unravelling the radical transition during the carbon-catalyzed oxidation of cyclohexane by in situ electron paramagnetic resonance in the liquid phase

The selective oxidation of hydrocarbons is of great importance in the chemical industry.

Nickel-oxide multiwall carbon-nanotube/reduced graphene oxide a ternary composite for enzyme-free glucose sensing

We report a solvent-free method of preparation for a NiO–carbon nanotube/graphene ternary composite using nickel formate as a green precursor via a thermal decomposition method.

Aerobic oxidation of α-pinene catalyzed by carbon nanotubes

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.

Decomposition of Cyclohexane on Ni₃Al Thin Foil Intermetallic Catalyst

Micro-grained thin foils made of Ni₃Al intermetallic alloy were fabricated, according to a previously described procedure, and tested as catalyst for decomposition of cyclohexane. The conversion efficiency of the catalyst was evaluated in a synthetic air atmosphere, and found to be as high as 98.7% ± 1.0% at 600 °C and 86.7% ± 3.6% at 500 °C. During the reaction, the growth of carbon nanofibers on the catalysts surface was observed. The chemical and phase composition of the nanofibers was investigated with scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD), finding them to be made of graphitic carbon. Additionally, nanoparticles of nickel appear to be incorporated in the fibers. The obtained material is promising for large scale fabrication in industrial applications because of its high efficiency in the hydrocarbon decomposition, the simple fabrication procedure, and the form of self-supporting foils with the presence of additional carbon nanofibers that increase its efficiency.

Preparation and characterization of MTiX for the catalytic oxidation of cyclohexane

Conversion of the cyclohexane oxidation reaction with TBHP catalyzed by VTiX in different solvents.