Effect of MgO on WO₃/SiO₂-catalyzed light olefin metathesis using different feedstocks

Different feedstocks were adopted to undergo reactions catalyzed by WO₃/SiO₂ and WO₃/SiO₂-MgO catalysts to better understand the effect of MgO on the process. The results of 1-butene self-metathesis show that, although the isomerization of 1-butene was clearly enhanced by MgO, the propylene selectivity was not improved because of insufficient 1-butene or ethylene. The main route to produce propylene in this system is through cross-metathesis of 1-butene and 2-butene. When propylene was used as the feed, more 2-butene, which was produced from propylene self-metathesis, was transformed into 1-butene by the addition of MgO, resulting in an improved metathesis performance between 1-butene and propylene. The cross-metathesis of 2-butene and ethylene, however, did not show an significant enhancement by MgO. In addition, the analysis on n-butene isomers distribution reveals that the presence of MgO is helpful in keeping the isomers at their theoretical values, leading to the good stability of the reactions. Lastly, a further comparison for the reactions between trans-2-butene and cis-2-butene demonstrates that there is little difference in their metathesis reactivity.