The structure of ethylene polymerisation catalysts. Part 1.—Fast-atom bombardment–secondary-ion mass spectrometry studies of chromium clusters

Abstract

Chromium(6+) oxide was supported on γ-alumina and silica by aqueous impregnation producing two series of samples (SiO₂, 1–18% Cr; Al₂O₃, 1–12% Cr) dried by vacuum desiccation at 25 °C and calcined in air at temperatures from 100 to 600 °C. Fast-atom bombardment–secondary-ion mass spectroscopy studies have revealed contrasting development of chromium oxide clusters, so that clusters on silica are thin and widely spread relative to clusters of uneven thickness on alumina. These surface models are explained in terms of the long-range chromium oxide–support interaction evident in alumina-supported material.