From support to carbocatalyst: the aerobic and solvent free epoxidation of dec-1-ene using graphitic oxide as a catalyst

The solvent-free selective epoxidation of dec-1-ene has been achieved under mild conditions and using atmospheric oxygen as the sole oxidant. Furthermore this has been conducted in the absence of radical initiators which is a first for such an oxidation to the best of our knowledge. The selective epoxidation of alkenes typically requires the use of supported active metals such as gold or silver. These have been studied for the epoxidation of dec-1-ene however they were found to be inactive in the absence of radical initiators. Alternatively, this transformation has been achieved using a graphitic oxide catalyst which harbours no active metal species. This is yet another remarkable example of the potential of carbocatalysis for green chemistry. The commonly raised issues when using carbocatalysts such as identification of active species and presence of impurities are addressed. A range of graphitic oxides have been produced using modified Hofmann and Hummers methods with attention given to the effect of amount of oxidant used compared to commonly employed literature standards. We conclude that the popular highly oxidised Hummers materials used in the bulk production of graphene may not be the optimum material for all applications and that specification of graphitic oxides may be required to suit each application. An investigation of activity in the epoxidation of dec-1-ene partnered with a full characterisation of the surface suggests that an optimum level of oxidation is required along with the need for a surface free of potential poisons such as sulphur. We also evaluate the current methods used in the preparation and separation of these materials and suggest that for applications such as epoxidation alternative techniques may be required in order to realise its potential as a carbocatalyst. This work provides the basis for the development of an efficient catalyst for the selective epoxidation of α-alkenes, eradicating the need for expensive stoichiometric reagents or toxic radical initiators

Cinnamyl alcohol oxidation using supported bimetallic Au-Pd nanoparticles: An optimization of metal ratio and investigation of the deactivation mechanism under autoxidation conditions

The aerobic oxidation of cinnamyl alcohol in toluene under autoxidation conditions has been studied using a range of 1 wt% Au–Pd/TiO2 catalysts. The catalysts have been studied to determine the effect of preparation method (impregnation and sol immobilisation) and metal ratio on the conversion of cinnamyl alcohol and the selectivity to cinnamaldehyde. The catalysts prepared by sol-immobilisation demonstrate higher selectivity to the desired aldehyde than the analogous impregnation materials. The most active catalyst was found to be 0.75 wt% Au–0.25 wt% Pd/TiO2 prepared by sol-immobilisation and this demonstrates the importance of metal ratio optimisation in this catalytic process. Furthermore, this metal ratio was found to be most stable under the reactions conditions with little change observed over multiple uses

Tuning graphitic oxide for initiator- and metal-free aerobic epoxidation of linear alkenes

Graphitic oxide has potential as a carbocatalyst for a wide range of reactions. Interest in this material has risen enormously due to it being a precursor to graphene via the chemical oxidation of graphite. Despite some studies suggesting that the chosen method of graphite oxidation can influence the physical properties of the graphitic oxide, the preparation method and extent of oxidation remain unresolved for catalytic applications. Here we show that tuning the graphitic oxide surface can be achieved by varying the amount and type of oxidant. The resulting materials differ in level of oxidation, surface oxygen content and functionality. Most importantly, we show that these graphitic oxide materials are active as unique carbocatalysts for low-temperature aerobic epoxidation of linear alkenes in the absence of initiator or metal. An optimum level of oxidation is necessary and materials produced via conventional permanganate-based methods are far from optimal

Highly regioselective di-tert-amylation of naphthalene over reusable H-mordenite zeolite

Highly regioselective di-tert-amylation of naphthalene using different alcohols can be achieved over a H-mordenite (HM) zeolite. For example, the tert-amylation of naphthalene using tert-amyl alcohol in cyclohexane over HM (Si/Al = 10) zeolite has been optimised to give a 70% yield of 2,6-dialkylnaphthalenes, of which 2,6-di-tert-amylnaphthalene was produced in 46% yield along with 2-tert-amyl-6-tert-butylnaphthalene (23%) and 2,6-di-tert-butylnaphthalene (1%). This has been achieved by varying the reaction time, temperature, pressure and amounts of tert-amyl alcohol and zeolite. No 2,7-dialkylnaphthalenes were seen under the conditions tried. The zeolites can be easily regenerated by heating and then reused

Oxidative carboxylation of 1-decene to 1,2-decylene carbonate

Cyclic carbonates are valuable chemicals for the chemical industry and thus, their efficient synthesis is essential. Commonly, cyclic carbonates are synthesised in a two-step process involving the epoxidation of an alkene and a subsequent carboxylation to the cyclic carbonate. To couple both steps into a direct oxidative carboxylation reaction would be desired from an economical view point since additional work-up procedures can be avoided. Furthermore, the efficient sequestration of CO2, a major greenhouse gas, would also be highly desirable. In this work, the oxidative carboxylation of 1-decene is investigated using supported gold catalysts for the epoxidation step and tetrabutylammonium bromide in combination with zinc bromide for the cycloaddition of carbon dioxide in the second step. The compatibility of the catalysts for both steps is explored and a detailed study of catalyst deactivation using X-ray photoelectron spectroscopy and scanning electron microscopy is reported. Promising selectivity of the 1,2-decylene carbonate is observed using a one-pot two-step approach

Facile synthesis of a porous 3D g-C3N4 photocatalyst for the degradation of organics in shale gas brines

Treatment and subsequent re-use of wastewater from shale gas extraction is a feasible strategy to ensure sustainability and reduce the environmental impact of the process. Here we demonstrate the photocatalytic benefits of improved three-dimensional graphitic carbon nitride (3D g-C3N4) during the degradation of organic contaminants. We show that precursor ratio (melamine to cyanuric acid) affects both the properties of 3D g-C3N4 as well as catalytic performance. When optimized, 3D g-C3N4 displayed the highest organics removal rate in brine-free solutions, achieving 99% conversion within 240 min. Significantly, the 3D g-C3N4 materials improved photocatalytic activity even in simulated shale gas brine solutions

Oxidative carboxylation of 1-Decene to 1,2-Decylene carbonate

© 2018 The Author(s) Cyclic carbonates are valuable chemicals for the chemical industry and thus, their efficient synthesis is essential. Commonly, cyclic carbonates are synthesised in a two-step process involving the epoxidation of an alkene and a subsequent carboxylation to the cyclic carbonate. To couple both steps into a direct oxidative carboxylation reaction would be desired from an economical view point since additional work-up procedures can be avoided. Furthermore, the efficient sequestration of CO 2 , a major greenhouse gas, would also be highly desirable. In this work, the oxidative carboxylation of 1-decene is investigated using supported gold catalysts for the epoxidation step and tetrabutylammonium bromide in combination with zinc bromide for the cycloaddition of carbon dioxide in the second step. The compatibility of the catalysts for both steps is explored and a detailed study of catalyst deactivation using X-ray photoelectron spectroscopy and scanning electron microscopy is reported. Promising selectivity of the 1,2-decylene carbonate is observed using a one-pot two-step approach

Microwave synthesis of ZnIn2S4/WS2 composites for photocatalytic hydrogen production and hexavalent chromium reduction

A rapid microwave synthesis route for the fabrication of ZnIn2S4 powder and ZnIn2S4/WS2 composites is presented. Firstly, the effects of different sulfur sources – thioacetamide and L-cysteine – on the physicochemical properties and photocatalytic H2 production of the synthesized ZnIn2S4 were investigated. It was found that well-defined flower-like ZnIn2S4 microspheres obtained from L-cysteine facilitated a relatively higher H2 production rate. Then, different loadings of WS2 were introduced into the well-defined flower-like ZnIn2S4 microspheres aiming to improve its photocatalytic H2 production. Compared to pure ZnIn2S4 and WS2, all ZnIn2S4/WS2 composite photocatalysts exhibited enhanced photocatalytic H2 production in the presence of Na2S/Na2SO3 as sacrificial reagents under UV-visible irradiation, where the ZnIn2S4/WS2-40% wt composite had the highest photocatalytic activity. For this material, 293.3 and 76.6 μmol h−1 g−1 of H2 gas were produced under UV-visible and visible light irradiation, respectively. In addition, the photoreduction activity of hexavalent chromium (Cr(VI)) by ZnIn2S4/WS2-40% wt was also investigated under visible light irradiation and it was observed that 98.5% of Cr(VI) was reduced within 90 min at pH 4

Enhanced visible-light-driven photocatalytic H2 production and Cr(vi) reduction of a ZnIn2S4/MoS2 heterojunction synthesized by the biomolecule-assisted microwave heating method

In this work, the biomolecule-assisted microwave heating synthesis of ZnIn2S4, along with the ZnIn2S4/MoS2 composites and their photocatalytic applications, were studied. Well-defined flower-like ZnIn2S4 microspheres synthesized at microwave heating time of 1 h provided the highest surface area and total pore volume, which offered the highest H2 production rate (111.6 μmol h−1 g−1). Different amounts of MoS2 were loaded into the ZnIn2S4 microspheres to form ZnIn2S4/MoS2 composites aiming to improve the H2 production rate. Among the fabricated ZnIn2S4/MoS2 composites, the ZnIn2S4/MoS2-40% wt composite exhibited the highest H2 production rate (200.1 μmol h−1 g−1) under UV-visible light irradiation. In addition, for the first time, this composite was applied for the photoreduction reaction of Cr(VI) ion under visible light irradiation. It provided higher photoreduction efficiency than the single components, where the efficiency was improved in the acidic solutions over the levels recorded in the basic solution. The charge transfer pathway and photocatalytic mechanisms of the ZnIn2S4/MoS2-40% wt photocatalyst have been proposed based on the results obtained from UV-visible diffuse reflectance spectroscopy, photoluminescence spectroscopy, electrochemical impedance spectroscopy, Mott–Schottky measurements and the silver photo-deposition experiment

Effect of the preparation method of LaSrCoFeOx perovskites on the activity of N2O decomposition

N2O remains a major greenhouse gas and contributor to global warming, therefore developing a catalyst that can decompose N2O at low temperatures is of global importance. We have investigated the use of LaSrCoFeOx perovskites for N2O decomposition and the effect of surface area, A and B site elements, Co–O bond strength, redox capabilities and oxygen mobility have been studied. It was found that by using a citric acid preparation method, perovskites with strong redox capabilities and weak Co–O bonds can be formed at relatively low calcination temperatures (550 °C) resulting in highly active catalysts. The enhanced activity is related to the presence of highly mobile oxygen species. Oxygen recombination on the catalyst surface is understood to be a prominent rate limiting step for N2O decomposition. Here the reduced strength of Co–O bonds and mobile lattice oxygen species suggest that the surface oxygen species have enhanced mobility, aiding recombination, and subsequent regeneration of the active sites. La0.75Sr0.25Co0.81Fe0.19Ox prepared by citric acid method converted 50% of the N2O in the feed (T50) at 448 °C