The effect of Cs and Cu on the physicochemical characteristics of zirconium oxide and the catalytic properties of the corresponding solids in the oxidation of toluene are studied. The influence of NOx as oxidizing agent is also investigated. Cu(II) species in Cs-x-Cu-y/ZrO2 catalysts correspond to dispersed Cu(II) and CuO crystallites in interaction with the alkali promoter. The low activity of Cs-x-Cu-y/ZrO2 with high amount of Cs is explained by the low specific area and to the presence of CuO crystallites. Moreover, NOx are strongly adsorbed in the form of nitrate species in Cs-x-Cu-y/ZrO2 with high amount of Cs, hindering the toluene conversion. Cs-x-Cu-y/ZrO2 catalysts with low Cs content are highly active in toluene oxidation and NOx acts in this case as an oxidizing agent. Dispersed Cu(II) species in interaction with Cs are both responsible of the catalytic activity and the transformation of NO into NO2 prior to the oxidation of toluene. (C) 2011 Elsevier B.V. All rights reserved.