Steady State Isotopic Transient Kinetic Analysis of Ethanol Coupling Reaction Catalyzed by Magnesia

Although ethanol can be produced on a large scale by fermentation, its use as a
transportation fuel has several drawbacks. Ethanol can be coupled to form butanol, a more desirable fuel, over basic catalysts via the Guerbet reaction. In this work, the coupling of ethanol to butanol over a magnesia catalyst at 673 K and 1.29 atm has been studied in a fixed bed reactor using an isotopic transient method.
The transient method enabled surface coverages and the intrinsic rate of the
catalytic cycle to be measured. At 673 K, the fractional coverage of absorbed ethanol under steady state reaction conditions was 0.51 relative to the number of exposed MgO atom pairs on the surface, whereas the coverage of surface intermediates was less than 0.1, depending on the conversion in the reactor. The intrinsic rate at which the catalytic cycle turned over was found to be 0.04 s-1 at 673 K. These results suggest that only a small fraction of the MgO surface is involved in the coupling reaction, presumably through aldol condensation reactions, and that adsorbed ethanol present on the surface prevents multiple condensation events from deactivating the catalyst.