FTIR STUDY OF THE ACTIVE ETHENE POLYMERIZATION CATALYST, ALUMINA-SUPPORTED C6H6CR(CO)(3)

IR spectra are reported for C6H6Cr(CO)(3) adsorbed on alumina which ha d been pretreated in vacuum at 500, 700 and 800 degrees C. Two dominan t modes of adsorption involved H-bonding of surface hydroxy groups to benzene nuclei and O-ligation of CO groups to Lewis acidic Al3+ surfac e sites. Displacement of both benzene and CO ligands occurred and led to adsorbed sub-carbonyl species. Ligand loss was enhanced by evacuati on at 25 degrees C, mild heating or contact with ethene. Sub-carbonyl surface species contained coordinatively unsaturated Cr sites which we re active for the polymerisation of ethene to give highly linear polye thene.