Polyoxometalate clusters supported on functionalized graphene sheets as nanohybrids for the catalytic combustion of liquid fuels

Catalyzing the combustion of liquid fuels offers interesting prospects for further improvement of the fuel economy and the performance of engines, in particular for jets and advanced propulsion systems. Polyoxometalates are well-known oxidation catalysts which are expected to also catalyze combustion reactions. However, their polarity makes their dispersion in fuels particularly challenging. Herein, functionalized graphene sheets were used as a support due to their high surface area as well as their compatibility with the target reaction. In order to further improve the dispersion of the catalyst in fuels, alkyl chains were grafted to the sheets' surface. An innovative grafting technique was developed to attach alkyls at a variety of oxygen-containing functionalities already present on reduced graphene oxide, such as hydroxyl and epoxy groups. A phase transfer to the organic phase was observed when dispersing the dry powder in water:toluene mixtures. In addition, the dry alkyl chain-modified graphene sheets readily dispersed in common organic solvents without the assistance of sonication. Polyoxometalates (H₃PMo ₁₂O₄₀ and H₄PMo₁₁VO₄₀) were dispersed on the modified sheets as discrete clusters even at a relatively high loading (20 wt.%). The catalytic activity of these nanostructured materials was demonstrated for the combustion of methylcylcohexane, tested here as a model fuel.