Silica-alumina-supported, tungsten-based heterogeneous alkane metathesis catalyst: Is it closer to a silica- or an alumina-supported system?

Article abstract of DOI:10.1002/adsc.200600436

Grafting of [W(≡C-t-Bu)(CH₂-t-Bu)₃] (1) on silica-alumina partially dehydroxylated at 500°C generates a surface complex [(≡SiO)W(≡C-t-Bu)-(CH₂-t-Bu)₃] (2) as evidenced by mass balance analysis, IR, and NMR spectroscopy. Upon treatment of this species under H₂, a tungsten hydride derivative, [(≡SiO)(EO)W(H)_x] (3), (E=Si or Al), is formed. Both of these complexes are active as alkane metathesis catalysts. The activity of this hydride is similar to that observed for the tungsten hydride-supported on alumina and much greater than that obtained on silica. Noteworthy are the selectivities in higher alkane homologues, that is C_n+1>C _n+2, which are fully consistent with olefin metathesis being the key homologation process.