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 Fe 2 O 3 (7.3 ± 0.5 nm) particles on the surface of CeO 2 nanorods (diameter is 8.5 ± 2 nm and length within 16–89 nm). In addition to diffraction peaks of CuO and Fe 2 O 3 nanocrystallites, X-ray diffraction (XRD) studies reveal doping of Cu 2+ and Fe 3+ ions into the fluorite lattice of CeO 2, hence abundant oxygen vacancies in the Cu/CeO 2 and Fe/CeO 2 nanorods, as evidenced by Raman spectroscopy studies. XRD and Raman spectroscopy studies further show substantial perturbations in Cu/CeO 2 rods, resulting in an improved reducibility of bulk cerium oxide and formation of abundant Lewis acid sites, as investigated by H 2 -temperature-programmed reduction and pyridine-adsorbed Fourier transform infrared studies, respectively. The Cu/CeO 2 rods catalyze the soot oxidation reaction at the lowest temperatures under both tight contact (Cu/CeO 2; T50 = 358 °C, temperature at which 50% soot conversion is achieved, followed by Fe/CeO 2; T50 = 368 °C and CeO 2; T50 = 433 °C) and loose contact conditions (Cu/CeO 2; T50 = 419 °C and Fe/CeO 2; T50 = 435 °C). A possible mechanism based on the synergetic effect of redox and acid properties of Cu/CeO 2 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.