Effects of calcination and pretreatment temperatures on the catalytic activity and stability of H2-treated WO3/SiO2 catalysts in metathesis of ethylene and 2-butene

Abstract

The effects of calcination and pretreatment temperatures of the H₂-treated WO₃/SiO₂ catalysts in metathesis of ethylene and 2-butene to propylene were investigated. The results showed that pretreatment with pure hydrogen over the non-calcined catalysts resulted in higher activity and stability than the calcined catalysts, and the hydrogen pretreatment temperature at 650 °C offered the highest 2-butene conversion and propylene selectivity. The calcination of the catalyst before hydrogen pretreatment was proved to be unnecessary. As revealed by various characterization results from N₂ physisorption, XRD, TEM, UV-Vis, Raman, in situ H₂-TPR, in situ NH₃-DRIFTS and in situ NH₃-TPD techniques, activity of the metathesis of ethylene and 2-butene to propylene was related to tungsten dispersion on the support, WO_2.83 and WO₂ phase composition, and isolated surface tetrahedral tungsten oxide species. The stability of the metathesis reaction was also related to the total acidity and the acid sites of both Brønsted and Lewis acid sites.