DECARBONYLATION AND DECOMPOSITION PATHWAYS OF ALCOHOLS ON PD(111)
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The reactions of methanol, ethanol, 1-propanol, and 2-propanol were examined on the clean Pd(111) surface using temperature programmed desorption (TPD). Methanol decomposed to CO and H2 while ethanol and 1-propanol underwent cleavage of the carbon-carbon bond to form CO, H2, and the hydrocarbons methane and ethylene, respectively. No selective dehydrogenation reactions of the primary alcohols to aldehyde products were detected on clean Pd(111). The elimination of CO to form a hydrocarbon one carbon atom shorter than the parent alcohol is essentially the reverse of steps proposed for higher alcohol synthesis on transition metals via CO insertion terminating hydrocarbon chain growth. In contrast to the primary alcohols, 2-propanol underwent selective dehydrogenation to acetone in addition to decomposition to methane, CO, and H2. A reaction scheme involving first dehydrogenation to alkoxides followed by formation of 2(O, C) aldehyde and ketone intermediates is proposed to account for this behavior. Decomposition of the higher alcohols was also found to deposit residual carbon on the surface of the Pd(111) crystal. For both ethanol and 2-propanol, C1 surface hydrocarbon species decomposed at 410 K to deposit residual surface carbon and evolve reaction-limited H2, whereas the C2 surface hydrocarbons from 1-propanol decomposed at 450 K. 1987 Elsevier Science Publishers B.V.
