II International Symposium on Carbon for Catalysis ABSTRACTS

OP-I-19
explore the role of CNF surface oxygen complexes in catalyzing ODP. TPD and TPSR runs
were carried out on Autochem <strong>II</strong> 2920 (Micromeritics, USA) and the outgoing gas was
diverted to a quadrupole mass spectrometer (Questor, ABB Extrel, USA) to be analyzed.
Results and discussion
HRTEM images show that CNF used in this work is a fish-bone CNF. Except for the
samples being severely oxidized in air, the physical properties of all the samples are close.
Only CO, CO 2 and C 3 H 6 are detected as TPSR products. It’s found that the amount of
TPSR products increases along with the amount of carbonyl-like groups. Especially, when the
surface oxygen complexes are totally removed by H 2 treatment at 900 o C or TPD up to
1000 o C, no product was detected, which implies that carbonyl-like groups could be the active
sites for catalyzing ODP. Desorption of some surface oxygen complexes from samples
without heat treatment at 1700 o C could be ascertained by material balance, which indicates
that optimizing the surface oxygen complexes by heat treatment is necessary from the point of
view of structure stability. The propene selectivity in TPSR runs decreases when increasing of
the surface oxygen complexes. So, optimizing the surface oxygen complexes could restrain
the direct over-oxidation of propane, which is testified by the fact that the initial propene
selectivity in catalytic test decreases along with increase of the surface oxygen complexes.
The propene TPSR results show that carbonyl-like groups could also be active sites for
propene combustion. The propene turnover frequency is lower over the sample experienced
liquid phase oxidation than that of air oxidation sample. The possible reasons are that trace
amount of Ni or Fe ion are removed or other heteroatom groups are introduced. The results of
a propene TPSR run successively after TPD run show that free active sites on CNF produced
by surface oxygen complexes desorption could lead propene cracking. But these sites are not
responsible for propane conversion.
The sample without heat treatment has lower structure stability when tested as catalyst for
ODP. One reason is that surface oxygen groups are facile to desorb, which has been
mentioned above. The other one could be that CNF gasification is initialized by coking
produced through CO disproportionation catalyzed by CNF itself. CO disproportation is
suppressed after CNF being heat treated at 1700 o C.
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