Part I. n-Butane dehydrogenation on unsupported carbon modified MoO3 (MoOxCy): effect of steam on the catalyst stability

MoO3 activated under butane and hydrogen mixture at 623 K was tested for th e reactions of simultaneous isomerization and dehydrogenation of n-butane a t 823 K. The active phase, a mixture of oxycarbide and oxide of molybdenum, was active but unstable under the reaction conditions, i.e. high temperatu res and a reducing environment, leading to the formation of a superficial c arbide layer and carbon-rich oxycarbide which were active but completely un selective, i.e. 100% selectivity towards methane. The introduction of steam into the feed largely stabilized the catalyst selectivity at around 80% by avoiding the extensive carburization. However, the introduction of steam o r oxygen led to a lower dehydrogenation activity by favoring the active pha se sintering. Along with sintering an additional deactivation due to coke f ormation was also observed. This latter deactivation process becomes more p ronounced as the hydrogen to hydrocarbon molar ratio decreased. However, th e deactivated catalyst can be totally recovered by applying a short oxidati ve regeneration process at the same reaction temperature. (C) 1999 Elsevier Science B.V. All rights reserved.