AN ENVIRONMENTAL SCANNING ELECTRON-MICROSCOPY STUDY OF ACTIVATED-CHARCOAL GASIFICATION CATALYZED BY MOO3 IN AIR AND IN OXYGEN AND BY A EUTECTIC ALLAY OF MOO3 AND V2O5 IN AIR

An environmental scanning electron microscope (ESEM) was used to study the gasification of an activated carbon catalyzed by MoO3 in air and oxygen atmospheres and by a eutectic mixture and alloy of MoO3 and V2O 5. In an air atmosphere, the melting of MoO3 starts at 630 degrees C a nd the reaction occurs by preferential gasification on the edges of ca rbon particles. In an O-2 atmosphere, however, homogeneous gasificatio n is observed in all directions. This difference can be explained by m ore extensive oxidation of the carbon surface in an oxygen atmosphere and the more effective spreading of the catalysts on charcoal surfaces . The ESEM experiments showed that some particles of the eutectic allo y of MoO3 and V2O5 had higher melting points than those of the single oxides. The analysis of alloy particles by EDS and by electron micropr obe indicated that large areas of single oxides are segregated and enc apsulated by the other oxide in some alloy particles. It is proposed t hat the encapsulation of either oxide (MoO3 or V2O5) inhibits the init ial contact of the catalyst with the carbon surface and leads to diffe rent reactions than those which take place on carbon surfaces. A lower activity of the ''eutectic'' alloy, compared to that of the binary mi xture with the eutectic composition, is, thus, ascribed to the heterog eneous composition of alloy particles which can give rise to the forma tion of different oxide phases with higher melting points than those o f the single oxides.