Novel rhenium catalysts (chlorides and/or alkoxides dispersed on inorganic supports) for metathesis: A comparison with ammonium perrhenate precursors

Abstract

The trans-/cis- ratios in 9-octadecene, 2, monoester, 1, and dimethyl 9-octadecenedioate, 3, produced in the metathesis of methyl oleate, cis-1, are measured against time for a series of rhenium-supported precursors (ReO x /γ-alumina or ReO x /silica-alumina 25% SiO 2 and 75% SiO 2). These trans-/cis- ratios show a marked dependence on the nature of the support. An explanation is proposed in terms of specific support interactions. The effect of the precursors is also considered. Easily accessible inorganic chloro complexes such as potassium hexachlororhenate(IV), K 2ReCl 6], and/or lsrhenium pentachloriders (see text), Re 2Cl 10, are used to prepare bifunctional heterogeneous catalysts which catalyze both double bond isomerization and metathesis of 1-octene at room temperature. Activation of the catalysts can be achieved by thermal treatments in nitrogen, the final temperature being in the range 300–360°C. Several chemical species of rhenium are evidenced by XPS analysis for the active catalysts. It should be emphasized that the XPS spectral differences between the catalysts prepared with K 2[ReCl 6] and those obtained with Re 2Cl 10 on silica-alumina (75% SiO 2) are correlated with the different catalytic reactivities. These novel rhenium catalysts can be modified to generate ‘tailor-made catalysts’.