II International Symposium on Carbon for Catalysis ABSTRACTS

KL-7
O- containing carbons provides more effective formation of O • 2 superoxide-anions - reactive
intermediate species of oxidation process in surface layer.
To confirm this approach we studied the process of oxygen reduction in the original
electrochemical cell with separate electrode spaces [1]. It was found that carbons containing
1,5-2,5% of N- and 4-6% of O- in position pyrrolic and furanic type really have highest
reductive ability (highest current of O 2 reduction).
It is well known that oxidized carbons contain the surface functional groups of carboxyl
and phenol types with mobile proton.
Having applied the potentiometric to determine the acidity of surface groups in
carboxylic cationites and oxidized carbons of various types we have shown that the acidity of
such groups in carbons, produced from fruit shells far exceeds (pK~ 2) the acidity of
carboxylic cationites (pK 2.5). It is likely due to the fact that π -electrons of oxygen atoms,
forming the surface groups in carbon, are very much delocated by the π -conjugated system of
the graphite-like planes. It reduced the effective negative charge on oxygen and, as a result,
the mobility of proton increases and, therefore, -OH and -COOH groups become more acidic.
It is worth to be noted that in the case of synthetic oxidized carbons, which possess much
more perfect ( almost without defects) structure of π -conjugation in the system of graphitic
planes, the acidity of surface group even more (pK~1) as far as in this case the delocalization
of electrons (π -electrons of oxygen) is mostly expressed.
To understand the general principles of catalysis by oxidized carbons in reactions of
esterification we studied in details kinetics and mechanism of synthesis of buthyl acetate in
gaseous phase in the wide range of temperatures (150-450 o C) using the H + modifications of
oxidized carbons, as well as reaction of hydrolysis for some ethers and lipids.
Thus, introduction of N- and O- heteroatoms into carbon matrix essentially influences on
their catalytic activity in the electron transfer reactions. On the other hand, π-conjugation in
oxidized carbons provides the increase of proton mobility with the raise of oxidation degree.
The last factor yields the growth of catalytic activity in the proton transfer reactions.
Reference
1 Strelko V.V., Kartel N.T., Dukhno I.N. // Surface Sci. 548, 281 (2004).
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