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

Abstract

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 Cn+1>C n+2, which are fully consistent with olefin metathesis being the key homologation process. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.