Isotopic study of ethanol dehydrogenation over a palladium membrane

Dehydrogenation of ethanol and the subsequent permeation of hydrogen throug h a 25-mum-thick palladium membrane has been studied. At 350 degreesC, adso rbed ethanol will decompose on the surface. Initially, released hydrogen ca n permeate the membrane. In a continuous ethanol supply a carbonaceous laye r will grow on the membrane surface, and eventually quench further permeati on. If, however, oxygen is added to the ethanol supply, continuous oxidatio n of the decomposition products will occur, and the growth of the carbonace ous layer is suppressed. In this way a steady hydrogen permeation rate can be maintained. Experiments using isotopically labeled ethanol, CH3CH2OH, CH 3CH2OD, CH3CD2OH, and CD3CH2OH, show that methyl hydrogen preferentially fo rms methane, and the hydroxyl hydrogen forms water, while it is the methyle ne hydrogen that is most likely to permeate the membrane. (C) 2000 Academic Press.