II International Symposium on Carbon for Catalysis ABSTRACTS

PP-I-11
THE FORMATION AND PHYSICAL-CHEMICAL PROPERTIES OF
CONDENSATION PRODUCTS – THE SELECTIVE CATALYSTS OF OXIDATIVE
DEHYDROGENATION OF LIGHTS ALKANES
Danilova I.G., Paukshtis E.A., Chuvilin A. L., Litvak G. S.
Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia
Е-mail: danig@catalysis.nsk.su
It is known, that the carbon materials could exhibited high catalytic activity and
selectivity in the oxidative reactions of various hydrocarbons. Oxidative condensation
products (OCP), which are formed and accumulated in the course of reaction on acid
catalysts, were identified as an active component in the ammoxidation of toluene [1] and in
the oxidative dehydrogenation of alkylbenzenes [2]. The polycyclic compounds containing O,
S, or N atoms with a developed system of conjugated bonds and a high concentration of
paramagnetic centers are catalytically active OCP.
It was found that the OCP exhibited high catalytic activity in the oxidative
dehydrogenation of propane by SО 2 . The carbonization of silica (surface area 40 m 2 /g) from 0
to ~40 wt % in course of the reaction was accompanied by an increase of propylene yield
from 3.4 to 46 mol % (640 O C; C 3 H 8 :SО 2 :Не = 10:10:80 vol %) [3]. The formation and nature
of active and deactivated condensation products on some Al-Si oxides was studied by
DRIFTS, UV-VIS, EPR, XPS, thermal and chemical analysis, and electron microscopy.
The initial stage of formation of a carbon coating was accompanied by a the relatively
sharp decrease in the concentrations of basic and strong acid sites of oxides. The further
carbonization of the catalyst causes the complete blocking of the oxides surface. We observed
transformation of OCP during its formation: the weakly condensed aromatic (probably,
polyphenyl) compounds with branched alkyl substituents → the condensed polycyclic
aromatic structures → the polyaromatic rings of highly condensed coke (Fig. 1).
It was found that catalytic activity of OCP in oxidation dehydrogenation of propane by
sulfur dioxide depends on the C/H ratio of the соkе. Structural changes of OCP in the course
of their accumulation or high temperature pretreatment were detected in rising of coke
condensation. The OCP with a maximum exothermic effect of coke burning (T max ) at 823-
853 K were highest selective catalysts. The accumulation of highly condensed OCP with T max
at 908-993 K decreased selectivity to propylene. The carbon-like coke (with T max at 993 K)
close to sibunit are nonselective catalysts.
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