Selective acetylene removal from ethylene-rich feed by cross-metathesis over supported WO3 catalysts

Acetylene in ethylene-rich feed can be removed via acetylene/ethylene cross-metathesis over WO3-supported catalysts at 450 degrees C, yielding 1,3-butadiene with cyclohexene as a minor product. The catalyst must be treated with ethylene at 600 degrees C to generate a genuinely active site of tungsten (IV) alkylidene species (W=CH2). The H2 treatment decreases surface W--O concentration, and hence the activity. Raman spectroscopy shows that active single-site WO3 species, including mono oxo-WO3 ((O=)W(O-Si)3 and (O=)W(O-Si)4) and dioxo-WO3 species (O=)2W(O-Si)2) were generated in 2%WO3/SiO2, while the WO3 cluster and bulk WO3 exist in 3-5%WO3/SiO2 and 7%WO3/SiO2, respectively. The 5%WO3/NaX and 5%WO3/NaY provide lower activity due to coke forma-tion over the acid sites. With high surface area and confined surface silanol of 5%WO3/MCM-41% and 5%WO3/ SBA-15, in situ TR-EXAFS evidences the formation of only O--W(O-Si)3. This species provides an isolated W=CH2 site with relatively higher activity and is less prone to coke formation than the WO3 cluster in 5%WO3/SiO2.