Abstract
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.
Highlights
In recent decades, the impact of chemistry on society has largely been influenced by its capacity to make new molecules in an environmentally considerate and sustainable way
This study shows the high activity of Au catalysts supported on graphite or graphene for cyclohexene oxidation
This study highlights the effect that a WO3 co-catalyst can have on the selectivity, to the epoxide, but subsequently to the diol, which was not presented in previous work by Ovoshchnikov et al The results from this work have shown that a catalyst prepared via sol-immobilisation can be highly active for cyclohexene oxidation, most likely because of the narrow size distribution and high dispersion, as shown by transmission electron electron microscopy microscopy (TEM) imaging
Summary
The impact of chemistry on society has largely been influenced by its capacity to make new molecules in an environmentally considerate and sustainable way. This has led to the development of catalysts with increasing efficiency and selectivity, which, when combined with the improvements in reaction engineering and purification methods, leads to greater atom economies and energy efficiencies [1]. The resulting product mixture of cyclohexanol and cyclohexanone, known as KA oil, is oxidised by nitric acid to adipic acid [2,3]. The process for producing adipic acid from KA oil via nitric acid oxidation historically produced 400,000 metric tons of N2 O globally. Recent catalytic and thermal abatement of these emissions within both adipic acid and nitric acid processes has resulted in very significant reductions in attendant N2 O emissions, and of their environmental significance
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