Ethene production by oxidative dehydrogenation of ethane at short contact times over Pt-Sn coated monoliths

The oxidative dehydrogenation of ethane to ethene was studied in a monolithic reactor at short contact times using a Pt-Sn/Al2O3 catalyst. The catalyst was characterised by Temperature Programmed Reduction (TPR). Scanning Transmission Electron Microscopy as well as H-2 and CO chemisorption. Three different preparation methods were used for the Pt-Sn catalyst; two-step impregnation where Pt was impregnated first, two-step impregnation where Sn was impregnated first and co-impregnation. The results from the oxidative dehydrogenation of ethane show that the two-step impregnated catalyst with Sn first gave lower ethene selectivity compared to the other impregnation procedures. TPR results indicate that this could be due to a weaker interaction between Pt and Sn in the catalyst. The Pt-Sn catalyst was also compared to LaMnO3, another catalyst which has been reported to be active for oxidative dehydrogenation of ethane. In these experiments Pt-Sn was found to give superior performance when H2 was added to the feed. Pt-Sn was clearly more active towards the oxidation of hydrogen compared to LaMnO3 which was active towards total combustion of hydrocarbons, even when relatively large amounts of hydrogen were present. It seems that ethene is produced mainly in the gas-phase and that the catalyst is important for the oxidation of hydrogen on the surface thus providing heat to the dehydrogenation reactions. However, the results also indicate that there is some ethene production on the Pt-Sn catalyst, either directly or indirectly. (C) 2010 Elsevier B.V. All rights reserved.