The low temperature solvent-free aerobic oxidation of cyclohexene to cyclohexane diol over highly active Au/Graphite and Au/Graphene catalysts

The selectivity and activity of gold-catalysts supported on graphite and graphene have been compared in the oxidation of cyclohexene. These catalysts were prepared via impregnation and sol immobilisation methods, and tested using solventless and radical initiator-free reaction conditions. The selectivity of these catalysts has been directed towards cyclohexene epoxide using WO3 as a co-catalyst and further to cyclohexane diol by the addition of water, achieving a maximum selectivity of 17% to the diol. The sol immobilisation catalysts were more reproducible and far more active, however, selectivity towards the diol was lower than for the impregnation catalyst. The results suggest that formation of cyclohexane diol through solventless oxidation of cyclohexene is limited by a number of factors, such as the formation of an allylic hydroperoxyl species as well as the amount of in situ generated water

The influence of teacher identities on teachers’ perspectives towards the incoming Dual Language Policy in Abu Dhabi secondary schools

As part of an extensive education reform programme, Abu Dhabi Education Council (ADEC) is currently introducing a Dual Language Policy (DLP) in which English, maths and science are to be taught fully through the medium of English while other subjects are taught through Arabic with the goal of producing biliterate school graduates. The DLP has already been implemented in Grades 1-6 and it is hoped that it will be migrated into secondary schools by 2015. The success of any major educational policy innovation is dependent on professional support at many levels, including that of teachers. For this reason it is important to explore teachers’ perspectives of the policy and how the policy might be in alignment or conflict with their professional identities. This study has adopted a discursive understanding of identity and a post structural theoretical framework. Using semi-structured interviews, observations and documentary analysis, this study sought firstly to explore the primary discourses which shape Emirati female secondary school maths teachers’ professional identities. It then identified their perspectives on the DLP before exploring how their identities explained these perspectives. The research found that the importance of childhood experiences in education, gendered roles, Islam, professional roles, relationships with students and their perspectives of society’s view of them as secondary maths teachers were key aspects of participants’ professional identities. It also found that teachers had fragmented identities resulting in mixed perspectives on the DLP. In some regard, this resulted in positivity towards the policy although simultaneously they felt their identities were threatened by it, causing them to view its implementation with caution. These threats were clustered around three main areas relating to pedagogic beliefs, their work ethic and linguistic and nationalistic discourses. A significant finding of this study was that the participants held differing views regarding the principles behind the DLP. Some teachers had accepted the policy ideologically, having adopted a position which assumed the neutrality of English, while others expressed strong views against the encroachment of English in education and society more generally. Nevertheless, there was agreement across the participants that while English was necessary in 21st century Abu Dhabi, it must remain a second language. While this is the stated intention of the DLP, teachers expressed limited awareness of how Arabic is being protected and promoted by ADEC, causing further animosity towards the policy. By adopting a post structural position, this research demonstrates the complexity of the situation as teachers find themselves caught in the intersection of multiple, and often conflicting, discourses. It shows that contrary to the prevailing belief, teachers are neither powerless nor passive but are exercising their power, at the micro level, through acts of negotiation, resistance and subversion. By drawing attention to these teachers’ discursive positionings, ‘framing discourses’, such as those related to patriarchy, Islam and linguistic imperialism, are highlighted. These are shown to both shut down and open up possibilities of being (Keddie, 2011), emphasizing the limited space these subjects have to manoeuvre in. By exploring the construct of teacher identities in the Emirati context and relating it to the practical aspect of policy implementation, this study aims to highlight its relevance to education reform and contribute to a gap in the field. It is hoped that through this, teacher identity will become a more significant part of the educational discourse in this region, disrupting the continued epistemic privilege of Western-informed views of education

The role of Mg(OH)2 in the so-called 'base-free' oxidation of glycerol with AuPd catalysts

Mg(OH)2 and Mg(OH)2 containing materials can provide excellent performance as supports for AuPd nanoparticles for oxidation of glycerol in the absence of base, which is considered to be a result of additional basic sites on the support's surface. However, its influence on the reaction solution is not generally discussed. In this paper, we examine, in detail, the relationship between the basic Mg(OH)2 support and AuPd nanoparticles using four types of catalyst, where the physical interaction between Mg(OH)2 and AuPd was adjusted. It was found that the activity of the AuPd nanoparticles increased with the amount of Mg(OH)2 added under base-free conditions, regardless of its interaction with the noble metals. In order to investigate how Mg(OH)2 affected glycerol oxidation, detailed information about the performance of AuPd/Mg(OH)2, physically mixed (AuPd/C+Mg(OH)2) and (AuPd/C+NaHCO3) was obtained and compared. Furthermore, NaOH and Mg(OH)2 were added during the reaction using AuPd/C. All these results indicate that the distinctive and outstanding performance of Mg(OH)2 supported catalysts in base-free condition is in fact directly related to its ability to affect the pH during the reaction and as such, assists with the initial activation of the primary alcohol which is considered to be the rate determining step in the reactionperformance of Mg(OH)2 supported catalysts in base-free condition could be correlated to its ability to affect the pH during the reaction

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

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

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

Recent advances in the catalytic oxidation of volatile organic compounds: a review based on pollutant sorts and sources

It is well known that urbanization and industrialization have resulted in the rapidly increasing emissions of volatile organic compounds (VOCs), which are a major contributor to the formation of secondary pollutants (e.g., tropospheric ozone, PAN (peroxyacetyl nitrate), and secondary organic aerosols) and photochemical smog. The emission of these pollutants has led to a large decline in air quality in numerous regions around the world, which has ultimately led to concerns regarding their impact on human health and general well-being. Catalytic oxidation is regarded as one of the most promising strategies for VOC removal from industrial waste streams. This Review systematically documents the progresses and developments made in the understanding and design of heterogeneous catalysts for VOC oxidation over the past two decades. It addresses in detail how catalytic performance is often drastically affected by the pollutant sources and reaction conditions. It also highlights the primary routes for catalyst deactivation and discusses protocols for their subsequent reactivation. Kinetic models and proposed oxidation mechanisms for representative VOCs are also provided. Typical catalytic reactors and oxidizers for industrial VOC destruction are further discussed. We believe that this Review will provide a great foundation and reference point for future design and development in this field

Low temperature solvent-free allylic oxidation of cyclohexene using graphitic oxide catalysts

A range of graphitic oxides have been utilised as metal free carbocatalysts for the low temperature oxidation of cyclohexene. The activity of the catalysts was correlated with the amount of surface oxygen on the graphitic oxide. In the case of cyclohexene oxidation, major selectivity is observed to allylic oxidation products. This is in contrast to the epoxide being the major product in linear alkene oxidation. This selectivity was maintained over long reaction times and at a conversion of above 50 %. Only small amounts of epoxide were observed, which eventually decreases at higher conversion due to hydrolysis to cyclohexane diol. The similarity between the non-catalysed and the catalysed product distribution suggests that these catalysts act as a solid initiator, and the role of the graphitic oxide is to decrease the lengthy induction period observed in the blank non-catalysed reaction

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