The effect of calcination time on the activity of WO3/Al2O3/HY catalysts for the metathesis reaction between ethene and 2-butene

A series of WO3/Al2O3/HY catalysts were prepared by thermal spread method (i.e., calcination of physically mixed WO3, Al2O3 and HY zeolite) for the metathesis reaction between ethene and 2-butene to propene. The transformation of tungsten oxide species was studied by the characterization techniques of XRD, H-2-TPR, UV-Vis, UV Resonance Raman, NH3-TPD and N-2 adsorption-desorption techniques. The thermal spread effect during calcination results in the dispersion of bulk WO3 phase into microcrystallites on gamma-Al2O3 surface, followed by a chemical transformation to the monomeric surface tungstate species via the involvement of Bronsted acid sites of HY zeolite. These monomeric surface tungstate species, identified by a characteristic Raman band at 970 cm(-1), are crucial for the metathesis activity. We suggest such activity related species are tetrahedrally coordinated. Moreover, it is found that there is an optimal calcination time for the formation of these WO42- species and further calcination causes the condensation to the polytungstate clusters, which are less active for the metathesis reaction. The optimized catalyst shows superior catalytic activity of metathesis reaction between ethene and 2-butene to propene at 453 K with 2-butene conversion close to thermodynamic equilibrium value (similar to 64%). (C) 2007 Elsevier B.V. All rights reserved.