Reaction of molecular and atomic deuterium with methanol on Pd(111)

Multiplexed thermal desorption spectroscopy was used to study the influence of preadsorbed and postadsorbed deuterium on a methanol monolayer on Pd(111). In particular, the effect of atomic deuterium exposure on the reaction products was examined in detail. Preadsorbed deuterium hinders the formation of chemisorbed methanol and favors physisorption of methanol. This leads to a strong reduction of methanol dehydrogenation during sample heating. Postadsorption of molecular deuterium also changes partially chemisorbed to physisorbed methanol. No deuteration of methanol is found under these conditions. With atomic deuterium exposure, however, significant amounts of deuterated methanol, from methanol-D1 through methanol-D4, can be produced. In addition, D exposure also causes an increased dehydrogenation probability during sample heating. The probabilities for methanol deuteration, for methanol dehydrogenation, and for D-atom bulk absorption have been determined quantitatively.