An 8% WO3/SiO2 catalyst was used for a metathesis reaction of 1-octene in the presence of different additives. These additives represents the possible components in an industrial 1-heptene feed stream that might have an influence on the performance of a WO3/SiO2 metathesis catalyst. The reaction conditions for the metathesis reaction in a once-through mode reactor were 460degreesC and aLiquid Hour Space Velocity (LHSV) of 5 h(-1). The operating conditions for the recycle reactor were 460 degreesC, LHSV = 16 h(-1) and a feed to recycle ratio of 1:5.6. The oxygenates used for the poison testing were 2-pentanone, hexanal, acetic acid, butanol and water. Both Bronsted acids and Lewis bases used, slows the reaction rate down if the amount of oxygenates are more than 500 ppm. The reaction was unstable with more than 500 ppm of oxygenates present in the feed, but this resulted in a product with a clearer colour (more colourless). Changing the feed back to pure feed resulted in reactivation of the catalyst. The catalyst was thereafter more selective and active towards the primary metathesis products, indication a permanent change in morphology of the catalyst. (C) 2003 Elsevier B.V. All rights reserved.