The role of the support in acid-treated montmorillonite/copper(II) nitrate oxidation reagents has been examined in an attempt to identify structural features within the support which are important in conferring reactivity to the supported nitrate. Reactivity has been measured in the oxidation of benzyl alcohol to benzaldehyde using a series;of progressively acid-treated clay supports, with a range of salt loadings and following thermal activation at up to 180 degrees C. Optimum reactivity has been achieved with a salt loading of 2.7 mmol g(-1) support, and following thermal activation at 130 degrees C. The most effective support was montmorillonite clay which received only very short acid treatment. It is proposed that the oxidation by supported nitrate operates most effectively by a mechanism which involves acid sites on the support, and the optimum support combines a high surface area and a high concentration of acid sites.