KINETICS, IN-SITU X-RAY-DIFFRACTION AND ENVIRONMENTAL SCANNING ELECTRON-MICROSCOPY OF ACTIVATED-CHARCOAL GASIFICATION CATALYZED BY VANADIUM-OXIDE, MOLYBDENUM OXIDE AND THEIR EUTECTIC ALLOY

Mechanisms of carbon oxidation catalyzed by vanadium pentaoxide (V2O5) and molybdenum trioxide (MoO3) have been a subject of controversy. Tw o complementary in situ techniques, X-ray diffraction (XRD) and enviro nmental scanning electron microscopy (ESEM), were used in this work to study the gasification of an activated charcoal catalyzed by the two metal oxides, their eutectic alloy and the binary mixture with the eut ectic composition. Gasification experiments were carried out at relati vely low temperatures (300-650 degrees C) in an XRD cell (1 atm) and E SEM (2.2 Torr) to monitor phase transformations and morphological chan ges of oxide catalysts, respectively. The experimental results showed that MoO3 and V2O5 particles in contact with active carbon surfaces ar e reduced to oxides with lower oxidation states, e.g. MoO2 and V6O13, respectively. The reduction of MoO3 to MoO2 on the carbon surface prev ents the sublimation of MoO3 which takes place readily on a quartz sur face under the same conditions. The formation of V6O13, on the other h and, causes more extensive spreading of the catalyst on carbon surface s, since V6O13 has a lower melting point than V2O5. Based on the XRD a nd ESEM observations, it is clear that phase transformations of metal oxides during gasification depend on their interactions with carbon su rfaces. The phase transformations of the metal oxides, play, in turn, a significant role in carbon gasification, as evident from the kinetic data obtained for the catalytic gasification of the activated charcoa l sample. The synergy observed between the components of the eutectic mixture is discussed, comparing the XRD and ESEM observations. (C) 199 8 Elsevier Science Ltd. All rights reserved.