Isotopic Study of Ethanol Dehydrogenation over a Palladium Membrane

Dehydrogenation of ethanol and the subsequent permeation of hydrogen through a 25-μm-thick palladium membrane has been studied. At 350°C, adsorbed ethanol will decompose on the surface. Initially, released hydrogen can permeate the membrane. In a continuous ethanol supply a carbonaceous layer will grow on the membrane surface, and eventually quench further permeation. If, however, oxygen is added to the ethanol supply, continuous oxidation of the decomposition products will occur, and the growth of the carbonaceous layer is suppressed. In this way a steady hydrogen permeation rate can be maintained. Experiments using isotopically labeled ethanol, CH3CH2OH, CH3CH2OD, CH3CD2OH, and CD3CH2OH, show that methyl hydrogen preferentially forms methane, and the hydroxyl hydrogen forms water, while it is the methylene hydrogen that is most likely to permeate the membrane.