Effect of pretreatment atmosphere of WO x /SiO 2 catalysts on metathesis of ethylene and 2-butene to propylene.

The effect of a gas pretreatment atmosphere (pure N 2 , pure H 2 and mixed H 2 /N 2 ) on the metathesis reaction between ethylene and 2-butene to propylene over calcined and non-calcined WO 3 /SiO 2 catalysts was investigated. The non-calcined catalysts exhibited higher activity than the calcined catalysts under different gas pretreatment atmospheres. The non-calcined catalyst with the use of pure H 2 pretreatment showed the highest catalytic performances. As revealed by various characterization results from N 2 physisorption, XRD, XPS, TEM, SEM-EDX, UV-Vis, Raman, H 2 -TPR, and NH 3 -TPD techniques, the WO 2.83 phase occurring from the H 2 pretreatment of the non-calcined catalyst played an important role on the high activity of the catalyst. In addition, better tungsten dispersion, higher isolated surface tetrahedral tungsten oxide species, and W 5+ species were obtained on the H 2 -treated non-calcined WO 3 /SiO 2 catalyst.