Comparison of olefin metathesis by rhenium-containing γ-alumina or silica–aluminas and by some mesoporous analogues

Abstract

Oxide materials with rhenium(V) oxochloro complexes highly dispersed on the surface were prepared by grafting Re(V) alkoxochloro complexes onto γ-Al 2O 3, chlorinated alumina, 25 and 75 wt% SiO 2 silica–aluminas, mesoporous alumina with high specific surface area (685 m 2 g −1) and mesoporous silica–alumina (950 m 2 g −1). The activities of these catalysts for 1-octene metathesis at room temperature are compared in the presence of a promoter: Bu 4Sn or Ph 2SiH 2. Systems consisting of pure alumina and chlorinated alumina supports with rhenium species and Bu 4Sn lead to selective formation of 7-tetradecene and ethylene at 90–100% conversion. There is a dramatic change of selectivities with Bu 4Sn and silica–alumina or with Ph 2SiH 2 and aluminas. The difference is attributed to the formation of hydrido and carbene rhenium surface species which promote at the same time isomerization, self- and cross-metathesis. Mesostructured oxides do not show any clear advantage over commercial supports. Interestingly, modifying γ-alumina with hydrogen chloride increases the catalytic activity even at low rhenium loading (ca. 0.7 wt%).