MgO and MgO-modified with Na and Cs ions have been studied for the side-chain oxidative methylation of toluene with methane to C-8 fraction (ethylbenzene+styrene). The addition of two ions, rather than just only one, onto the magnesium oxide surface increases greatly the activity/productivity in this reaction and this improvement is directly connected with the high concentration of strong monoelectron-donor properties of 1% Na+ + 1% Cs+/MgO (4.6 [a.u. NB radical anion[/m(2)) studied by EPR. Chemical trapping has been a very useful technique to identify the adsorbed species on the catalyst surface under the reaction conditions. By this method, methyl and benzyl groups and epoxydating oxygen have been identified. The pre-oxidation of the surface is of paramount importance for the activation of methane and toluene. Chemical trapping and catalysts strong monoelectron-donor studies are very good experimental evidence of the radical mechanism in this reaction. (C) 2009 Elsevier B.V. All rights reserved.