Effect of pretreatment gases on the performance of WO3/SiO2 catalysts in the metathesis of 1-butene and ethene to propene

Different gases were employed to pretreat WO3/SiO2 for the metathesis of 1-butene and ethene to propene. Air-pretreated WO3/SiO2 was inactive, whereas N2-, N2/H2-, and H2-pretreated WO3/SiO2 exhibited high 1-butene conversion and propene selectivity. Tetragonal WO3 and partially reduced WO2.92 were found to be the active phases/species, whereas monoclinic WO3 was inactive. N2/H2- and H2-pretreated WO3/SiO2 contained both W6+ and W5+ species (i.e., nonstoichiometric WO3−x). Air- and N2-pretreated WO3/SiO2 only contained monoclinic W6+ species (WO3) before the reaction. However, the used N2-pretreated WO3/SiO2 contained both W6+ and W5+ species, suggesting that the N2 pretreatment can facilitate the formation of some W5+ species during the reaction. This in situ partial reduction can activate the N2-pretreated WO3/SiO2 for the metathesis.