Combined in situ attenuated total reflection infrared and UV-vis spectroscopic study of alcohol oxidation over Pd/Al2O3

In situ attenuated total reflection (ATR) infrared and UV-vis spectroscopy are combined to yield simultaneous time-resolved information on dissolved reaction products, adsorbed species, and the catalyst during the oxidation of ethanol and 2-propanol on a 5% Pd/Al2O3 catalyst. The oxidation is initiated by change from hydrogen- to oxygen-saturated solvent flow. 2-Propanol oxidation is observed only in the transient period, whereas ethanol oxidation is also observed in the steady state. This may be ascribed to overoxidation of the catalyst in the former case. In a mixture of the two alcohols the same thing is observed. Competitive adsorption in the steady state may explain this behavior. For ethanol oxidation ethyl acetate is also observed during the transient period. The UV-vis spectra reveal a fast reversible change of the catalyst with switching between hydrogen and oxygen and a slow irreversible change during ethanol oxidation. The latter is ascribed to the change in Pd particle structure, which hardly affects, however, catalyst activity on the time scale of about 1 h.