4
06
LUO AND FALCONER
at room temperature. Similarly, acetaldehyde forms cro- of the surface. Acetaldehyde is more reactive than acetone
tonaldehyde by 400 K, which indicates that acetaldehyde for oligomer formation on each TiO2, and this is attributed
condensation products also form at relatively low temper- to the higher surface concentrations of acetaldehyde and
ature.
less steric hindrances with acetaldehyde and its condensa-
Since aromatics have much lower PCO rates than alco- tion products than with acetone and its condensation prod-
hols, aldehydes, or ketones (15), these condensation reac- ucts.
tions can cover the TiO2 surface with less reactive species
and poison PCO. This poisoning would be expected to be
more important at elevated temperature. Indeed, during ac-
ACKNOWLEDGMENTS
etaldehyde PCO on Degussa TiO2, the PCO rate reached
We gratefully acknowledge support by the National Science Founda-
a steady state at room temperature. At 363 K, however, tion, Grant CTS-9714403. We also thank Professor Mark A. Barteau of
the catalyst rapidly deactivated (13), presumably because the University of Delaware for providing us the TiO2 anatase sample and
his manuscripts prior to publication and for his valuable suggestions.
condensation products formed faster at 363 K than they
could be oxidized. Thus, for PCO of reaction mixtures that
contain acetone or acetaldehyde or contain reactants that
can form these as intermediates, condensation reactions at
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1
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1
the higher surface concentration of acetone and the higher
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Reductive coupling of acetaldehyde or acetone forms
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(
1991).
2
2
2
2
2
2
2
2
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