Closing the Loop
24 January 2012
Increasing production of sulphur-free diesel fuel from natural gas and biomass will create a glut of low value C7-C12 alkanes. The Cardiff Catalysis Institute (CCI) has been investigating catalytic routes for upgrading this stream of by-products into much more useful chemicals. The catalytic chemistry is fraught with difficulty arising from the tendency of these hydrocarbons to over-dehydrogenate or to combust, depending on whether oxygen is absent or present during the reaction. In an article published in the February edition of Nature Chemistry, the CCI team directed by Professor Graham Hutchings report the discovery that a typical long-chain hydrocarbon can be partially oxidised to a range of oxygenated aromatics using a mixed-metal oxide catalyst.
The breakthrough came when the CCI team fed decane and air, as a gas mixture, through an iron molybdate catalyst. At higher temperatures, where the catalyst is known to function by providing oxide ions from its lattice, the major pathway was oxidative dehydrogenation to form decene. At lower temperatures, however, the reaction took a different route to produce oxygenated aromatic molecules such as phthalic anhydride and coumarin. The significance of this discovery that decane can be transformed directly into oxygenated aromatics lies in the implication that electrophilic oxygen is involved. It overturns the widely-held view in heterogeneous catalysis that this type of oxygen is too labile to form anything other than CO and CO2 when it reacts with hydrocarbons.
S. Pradhan, J.K. Bartley, D. Bethell, A. F. Carley, M. Conte, S. Golunski, M.P. House, R.L. Jenkins, R. Lloyd and G.J. Hutchings, ‘Non-lattice surface oxygen species implicated in the catalytic partial oxidation of decane to oxygenated aromatics’, Nature Chemistry 4 (2012) 134-139.