In the recent years a number of publications have appeared on Al2O3 as ozonation catalyst. The results, however, raise many controversies. Adsorption of ozone on a surface of the catalyst and subsequent decomposition of O-3 molecule leading to formation of OH radicals is one of the possible mechanism of catalytic activity of alumina. However such the activity sometimes is observed while in other reports alumina does not show an ability to generate the radicals. As formation of the radicals depends strongly on pH controversial effects observed in the published papers may result from the lack of proper pH control. Aluminas are contaminated with alkali metals and the contaminants may cause unwanted (unexpected) changes in pH of ozonated solutions. The pH is a key factor responsible for the process of ozone decomposition in water. Therefore the purity of Al2O3 must be considered as an important parameter that can influence the process of ozone decomposition. This paper aims at showing that in the processes of catalytic ozonation special attention should be given to precise pH control. Commercially available aluminum oxides, purified by an extraction do not show the abilities to decompose ozone in water. (c) 2013 Elsevier B.V. All rights reserved.