Bis-aryloxyalkylaluminium complexes, previously involved in the synthesis of aryloxyaluminium perrhenate complexes that are active in olefin metathesis in homogeneous phase, are able to increase the activity of the supported Re2O7/Al2O3 metathesis catalyst. They are also able to make active an otherwise inactive low temperature-treated Re2O7/Al2O3 catalyst. They can be used to regenerate, for the first time at room temperature, a previously deactivated catalyst. Until now, a high temperature calcination treatment was essential for the regeneration. These properties are attributed to the strong Lewis acidic character of these aluminium complexes due to the low coordination state of the aluminium, protected by the aryloxy ligands. (C) 2002 Elsevier Science B.V. All rights reserved.