Lanthanum(III) was immobilized on various zeolite supports by simple cation exchange. The resulting materials were tested in the disproportionation of H2O2 into singlet molecular oxygen (O-1(2)). The rate of H2O2 disproportionation and the reaction of the formed O-1(2) with citronellol as a typical olefinic substrate were strongly dependent on the zeolite topology and composition. Zeolites with a large crystal size, small pores, or a one-dimensional pore system showed low activity in the disproportionation of H2O2. In contrast, zeolites with a small crystal size or zeolites possessing large intersecting pores were active 102 generators. La supported on ultrastable Y zeolite (USY) and zeolite Beta were identified as the most active and efficient catalysts. Typically, within 24 h at 40 degrees C, 100 mol of citronellol hydroperoxides is produced per mol of La supported on USY zeolite. Within this time, 800 mol of H2O2 is disproportionated into O-1(2). In comparison with unsupported La-hydroxide, La-USY shows a significantly higher activity and a slightly more efficient use of H2O2. The heterogeneous nature of the catalysis by La-USY was verified by filtration tests, and its stability was proved by X-ray diffraction and recycle experiments. Finally, the catalyst was used in the peroxidation of various olefinic compounds. Compared with conventional molybdate catalysts, La-USY is particularly useful for the selective peroxidation of allylic alcohol derivatives, with very little competitive epoxidation and no alcohol oxidation being observed. (c) 2005 Elsevier Inc. All rights reserved.