Effects of calcination and pretreatment temperatures on the catalytic activity and stability of H 2 -treated WO 3 /SiO 2 catalysts in metathesis of ethylene and 2-butene.

The effects of calcination and pretreatment temperatures of the H 2 -treated WO 3 /SiO 2 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 N 2 physisorption, XRD, TEM, UV-Vis, Raman, in situ H 2 -TPR, in situ NH 3 -DRIFTS and in situ NH 3 -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 WO 2 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.