Selective oxidation of benzene to phenol in the liquid phase over copper-substituted LaFeO3 perovskite oxide as catalyst

Abstract Selective oxidation of benzene to phenol is done in the liquid phase over copper-substituted LaFeO3 perovskite oxides as catalyst using H2O2 as oxidant under mild reaction conditions. Among the different copper-substituted perovskite catalysts synthesized by a novel solution combustion method, the LaFe0.90Cu0.10O3 catalyst showed highest activity (∼56 % with 100 % selectivity of phenol) and also gives better activity than the corresponding catalyst made via incipient wetness impregnation of 10 at % Cu over combustion-synthesized LaFeO3. XRD analysis revealed formation of the perovskite phase as the predominant one. The greater activity of the combustion-made catalyst has been attributed to the occurrence of a peculiar poorly-defined structure having substitutional copper ion sites on top of the LaFeO3 particle as observed in HRTEM analysis. Much less occurrence of this phase in the impregnated catalyst, where copper is primarily present as dispersed CuO crystallites, explains its comparatively lower activity in the oxidation reaction. The effect of catalyst recycling shows negligible change of activity for the combustion-made catalyst whereas the analogous impregnated catalyst shows considerable decrease in activity in recycling. This explained to be due to the essentially intact poorly-defined structure in the former and leaching of the finely dispersed CuO crystallites from the latter catalyst during cycling.