Effect of Ce and La dopants in Co3O4 nanorods on the catalytic activity of CO and C3H6 oxidation

Abstract

Ce and La doped Co₃O₄ nanorod catalysts were prepared and their catalytic activity for CO and C₃H₆ oxidation reactions was examined. XRD, TEM, XPS, TPR, TGA and in situ DRIFTS have been used to characterize structural properties, reducibility, mobility of adsorbed oxygen and lattice oxygen, and surface intermediates for both CO and C₃H₆ oxidation. When doping with either Ce or La, the cations occupy the Co²⁺ sites in Co₃O₄. XPS, TPR, and TGA characterization showed that the Ce dopant decreased the ratio of surface adsorbed oxygen to lattice oxygen, and facilitated the extraction of adsorbed oxygen and lattice oxygen with hydrogen from CeO₂–Co₃O₄ in comparison to Co₃O₄, while the La dopant caused the opposite effect. The light-off performance for both CO and C₃H₆ oxidations has been improved due to Ce doping on Co₃O₄, while the doping of La actually inhibited the oxidation activity of the Co₃O₄ catalyst. Similar catalytic activity facilitation and inhibition of Ce and La dopants were also observed for the simultaneous oxidation of CO, C₃H₆, and NO under the conditions of simulated diesel exhaust. The results of in situ DRIFTS suggested that bidentate carbonate species could be the key intermediates of CO oxidation, which would further react with CO to form CO₂. The results of DRIFTS showed that the mobility of lattice oxygen plays an important role in the C₃H₆ oxidation. A mechanism was proposed where the formate and acetate species could be the reaction intermediates of C₃H₆ oxidation, and these intermediates are more stable on La₂O₃–Co₃O₄ than on Co₃O₄ and CeO₂–Co₃O₄ catalysts.