Coke formation on WO3/SiO2 metathesis catalysts

An appreciable amount of coke forms over an 8 wt% WO3/SiO2 during the metathesis of 1-alkenes to internal alkenes. Catalyst activity is maintained despite the high coke levels (49 wt%). To understand this phenomenon, the coked catalyst was characterized by thermogravimetric analysis (TGA), BET and energy filtered transmission electron microscopy (EFTEM). Even at high coke levels, carbon maps show that the coke is dispersed over the support rather than covering the tungsten oxide. This observation may explain why the high activity of the catalyst is maintained and gives an indication that the location of coke laydown is more important than the amount deposited, in determining catalyst activity. Trace quantities of water, butanol and 2-pentanone were introduced into the feed stream and this resulted in the inhibition of coke formation without a significant loss in catalyst activity. 2-Pentanone was found to be the most effective inhibitor. Coking profiles indicated that the internal alkenes coked more rapidly than the 1-alkene feed.

An appreciable amount of coke (49 wt%) forms over an 8 wt% WO3/SiO2 catalyst during the metathesis of 1-alkenes to internal alkenes. Catalyst activity is maintained despite these high coke levels. To understand this phenomenon, the coked catalyst was characterized by energy filtered transmission electron microscopy (EFTEM). Trace amounts of oxygenated compounds were shown to dramatically reduce coke levels. Figure optionsDownload as PowerPoint slide