Heterostructured Copper-Ceria and Iron-Ceria Nanorods: Role of Morphology, Redox, and Acid Properties in Catalytic Diesel Soot Combustion.

This work reports the synthesis of heterostructured copper-ceria and iron-ceria nanorods and the role of their morphology, redox, and acid properties in catalytic diesel soot combustion. Microscopy images show the presence of nanocrystalline CuO (9.5 ± 0.5 nm) and FeO (7.3 ± 0.5 nm) particles on the surface of CeO nanorods (diameter is 8.5 ± 2 nm and length within 16-89 nm). In addition to diffraction peaks of CuO and FeO nanocrystallites, X-ray diffraction (XRD) studies reveal doping of Cu and Fe ions into the fluorite lattice of CeO, hence abundant oxygen vacancies in the Cu/CeO and Fe/CeO nanorods, as evidenced by Raman spectroscopy studies. XRD and Raman spectroscopy studies further show substantial perturbations in Cu/CeO rods, resulting in an improved reducibility of bulk cerium oxide and formation of abundant Lewis acid sites, as investigated by H-temperature-programmed reduction and pyridine-adsorbed Fourier transform infrared studies, respectively. The Cu/CeO rods catalyze the soot oxidation reaction at the lowest temperatures under both tight contact (Cu/CeO; T50 = 358 °C, temperature at which 50% soot conversion is achieved, followed by Fe/CeO; T50 = 368 °C and CeO; T50 = 433 °C) and loose contact conditions (Cu/CeO; T50 = 419 °C and Fe/CeO; T50 = 435 °C). A possible mechanism based on the synergetic effect of redox and acid properties of Cu/CeO nanorods was proposed: acid sites can activate soot particles to form reactive carbon species, which are oxidized by gaseous oxygen/lattice oxygen activated in the oxygen vacancies (redox sites) of ceria rods.