OH versus CH bond scission sequence in ethanol decomposition on Pd(111)

The low temperature reaction sequence of ethanol adsorption and decomposition on Pd(111) has been studied using temperature programmed desorption and high-resolution electron energy loss spectroscopy. The goal of these studies was to experimentally determine whether OH or CH bond scission occurs first. This was accomplished by examining the reaction of two partially deuterated ethanol molecules (only the fully deuterated version has been studied previously); a deuterium atom at the hydroxyl (CH3CH2OD) or two deuterium atoms at the α-carbon (CH3CD2OH). To support the experiment, density functional theory was used to calculate vibrational spectra for the respective adsorbed alcohols, alkoxides and hydroxyethyl intermediates. Based on the thermal evolution of vibrational spectra together with the sequence of desorption of D2O and H2O during TPD, we conclude that the decomposition of adsorbed ethanol proceeds directly to ethoxide (not hydroxyethyl) on Pd(111).