SYNTHESIS OF VANADIUM CARBIDE BY TEMPERATURE-PROGRAMMED REACTION

Vanadium carbide powders are prepared with moderate surface areas of 6 0 m(2) g(-1) (particle size 17 mm) by a temperature programmed reactio n between solid vanadium pentoxide (19 m(2) g(-1)) and a methane-hydro gen mixture. The synthesis involves two steps. In the first step a sin gle suboxide intermediate, V2O3, is formed by reduction of V2O5 by hyd rogen at 800 K. In the second step the V2O3 is reduced and carburized by methane with production of CO at 1180 K. In the early stages, the s ynthesis is found to be limited by the activation of hydrogen as found from experiments with Pt/V2O5. The transformation is accompanied by r etention of external shape and size, and so is pseudomorphic, but does not conserve orientation of crystallographic planes, so is not topota ctic. The results are compared and contrasted to those of nitridation with ammonia and reduction by pure hydrogen. (C) 1995 Academic Press, Inc.