Oxygen-Functionalized Few-Layer Graphene Sheets as Active Catalysts for Oxidative Dehydrogenation Reactions

Nanostructured graphitic forms of carbons have shown intersting potential for catalysis research and are ideal candidates to substitute the conventional metal-oxide catalysts because they can be easily disposed, which enables a greener, more sustainable catalytic process. Few-layer graphene and its functionalized form offer the opportunity to investigate the nature of graphitic active sites for oxidation reactions in well-defined carbon-based catalysts. In this paper, we report the utilization of oxygen-functionalized few-layer graphene sheets containing variable amounts of oxygen in the heterogeneous catalytic oxidative dehydrogenation (ODH) reaction of isobutane at 400oC. Interestingly, there is poor correlation between oxygen content and catalytic performance. Carbonyl groups were found to be highly stable, and graphene that had higher sp(2) character, the lowest oxygen content, and fewer edge sites presented the lowest specific rate of isobutane reaction, although the isobutene selectivity remained high. The reoxidation of the graphene surface occurred at the same rate as the ODH reaction suggesting a Mars-van Krevelen type of mechanism, similar to that which takes place on oxide surfaces. These results appear to suggest that a higher fraction of exposed edges where oxygen active sites can be formed and exchanged should lead to more active catalysts for ODH reactions.