THE SURFACE-ACIDITY OF PURE AND MODIFIED ALUMINAS IN RE/AL2O3 METATHESIS CATALYSTS AS STUDIED BY H-1 MAS NMR-SPECTROSCOPY AND ITS IMPORTANCE IN THE ETHENOLYSIS OF 1,5-CYCLOOCTADIENE

In this work some very active low-loading metathesis catalysts are presented in which rhenium is directed to favourable sites on the surface of gamma-alumina. This was achieved by ion exchange of Cl-, F-, MoO42-, and some carboxylic acid anions on the surface prior to rhenium adsorption or by ion exchange of very small amounts of ReO4- (around 0.08 Re atoms/nm(2)). The results of catalyst tests for the ethenolysis of 1,5-cyclooctadiene are presented and the catalysts are characterised by solid state H-1 MAS NMR spectroscopy. Two distinct peaks are observed in H-1 MAS NMR spectra of dehydrated gamma-alumina and the catalysts. The peaks are assigned to the more basic and more acidic OH groups. They are used to describe the bonding of ion-exchanged anions to the surface. (C) 1994 Academic Press,Inc.