Competition between C-O and 1-C-H bond scission during deoxygenation : the reactions of 1-propanol on Mo(110)

The reactions of 1-propanol on Mo(110) were investigated using temperature programmed reaction and high resolution electron energy loss and X-ray photoelectron spectroscopies. 1-propanol forms 1-propoxide upon adsorption on Mo(110) at 120K. An intensity analysis of the vibrational data indicates that the C--O bond vector is nearly perpendicular to the surface. Vibrational data also suggest that the C--O bond is weakened in 1 propoxide relative to 1-propanol. The 1-propoxide intermediate is stable up to 375K, at which point it decomposes via three competing pathways: deoxygenation and dehydrogenation to form propene, the major hydrocarbon product; C--O bond hydrogenolysis to afford propane; and nonselective decomposition to gaseous dihydrogen, surface carbon, and surface oxygen. The reaction of isotopically-labeled 1-propanol shows that only the C--H bond at the two position ( gamma to the metal and beta to the O) in 1-propoxide is broken during propene formation. C--O bond scission is proposed to limit the rate of propene elimination. Conversely, dehydrogenation at the 1-C of 1-propoxide is proposed to limit the rate of nonselective decomposition. At the maximum coverage of 1-propoxide, approx 60% of the adsorbed 1-propoxide forms hydrocarbons, whereas approx 40% nonselectively decomposes. The reactions of 1-propanol are compared with 2-propanol and 1-propanethiol in an effort to delineate the controlling factors in deoxygenation kinetics.