Nanoscale Cobalt–Manganese Oxide Catalyst Supported on Shape-Controlled Cerium Oxide: Effect of Nanointerface Configuration on Structural, Redox, and Catalytic Properties

Understanding the role of nanointerface structures in supported bimetallic nanoparticles is vital for the rational design of novel high-performance catalysts. This study reports the synthesis, characterization, and the catalytic application of Co–Mn oxide nanoparticles supported on CeO₂ nanocubes with the specific aim of investigating the effect of nanointerfaces in tuning structure–activity properties. High-resolution transmission electron microscopy analysis reveals the formation of different types of Co–Mn nanoalloys with a range of 6 ± 0.5 to 14 ± 0.5 nm on the surface of CeO₂ nanocubes, which are in the range of 15 ± 1.5 to 25 ± 1.5 nm. High concentration of Ce³⁺ species are found in Co–Mn/CeO₂ (23.34%) compared with that in Mn/CeO₂ (21.41%), Co/CeO₂ (15.63%), and CeO₂ (11.06%), as evidenced by X-ray photoelectron spectroscopy (XPS) analysis. Nanoscale electron energy loss spectroscopy analysis in combination with XPS studies shows the transformation of Co²⁺ to Co³⁺ and simultaneously Mn^4+/3+ to Mn²⁺. The Co–Mn/CeO₂ catalyst exhibits the best performance in solvent-free oxidation of benzylamine (89.7% benzylamine conversion) compared with the Co/CeO₂ (29.2% benzylamine conversion) and Mn/CeO₂ (82.6% benzylamine conversion) catalysts for 3 h at 120 °C using air as the oxidant. Irrespective of the catalysts employed, a high selectivity toward the dibenzylimine product (97–98%) was found compared with the benzonitrile product (2–3%). The interplay of redox chemistry of Mn and Co at the nanointerface sites between Co–Mn nanoparticles and CeO₂ nanocubes as well as the abundant structural defects in cerium oxide plays a key role in the efficiency of the Co–Mn/CeO₂ catalyst for the aerobic oxidation of benzylamine

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 Fe₂O₃ (7.3 ± 0.5 nm) particles on the surface of CeO₂ nanorods (diameter is 8.5 ± 2 nm and length within 16–89 nm). In addition to diffraction peaks of CuO and Fe₂O₃ nanocrystallites, X-ray diffraction (XRD) studies reveal doping of Cu²⁺ and Fe³⁺ ions into the fluorite lattice of CeO₂, hence abundant oxygen vacancies in the Cu/CeO₂ and Fe/CeO₂ nanorods, as evidenced by Raman spectroscopy studies. XRD and Raman spectroscopy studies further show substantial perturbations in Cu/CeO₂ rods, resulting in an improved reducibility of bulk cerium oxide and formation of abundant Lewis acid sites, as investigated by H₂-temperature-programmed reduction and pyridine-adsorbed Fourier transform infrared studies, respectively. The Cu/CeO₂ rods catalyze the soot oxidation reaction at the lowest temperatures under both tight contact (Cu/CeO₂; T50 = 358 °C, temperature at which 50% soot conversion is achieved, followed by Fe/CeO₂; T50 = 368 °C and CeO₂; T50 = 433 °C) and loose contact conditions (Cu/CeO₂; T50 = 419 °C and Fe/CeO₂; T50 = 435 °C). A possible mechanism based on the synergetic effect of redox and acid properties of Cu/CeO₂ 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

Controlling Core/Shell Formation of Nanocubic <i>p</i>‑Cu₂O/<i>n</i>‑ZnO Toward Enhanced Photocatalytic Performance

p-Type Cu₂O/n-type ZnO core/shell photocatalysts has been demonstrated to be an efficient photocatalyst as a result of their interfacial structure tendency to reduce the recombination rate of photogenerated electron–hole pairs. Monodispersed Cu₂O nanocubes were synthesized and functioned as the core, on which ZnO nanoparticles were coated as the shells having varying morphologies. The evenly distributed ZnO decoration as well as assembled nanospheres of ZnO were carried out by changing the molar concentration ratio of Zn/Cu. The results indicate that the photocatalytic performance is initially increased, owing to formation of small ZnO nanoparticles and production of efficient p–n junction heterostructures. However, with increasing Zn concentration, the decorated ZnO nanoparticles tend to form large spherical assemblies resulting in decreased photocatalytic activity due to the interparticle recombination between the agglomerated ZnO nanoparticles. Therefore, photocatalytic activity of Cu₂O/ZnO heterostructures can be optimized by controlling the assembly and morphology of the ZnO shell

Designing CuO_<i>x</i> Nanoparticle-Decorated CeO₂ Nanocubes for Catalytic Soot Oxidation: Role of the Nanointerface in the Catalytic Performance of Heterostructured Nanomaterials

This work investigates the structure–activity properties of CuO_<i>x</i>-decorated CeO₂ nanocubes with a meticulous scrutiny on the role of the CuO_<i>x</i>/CeO₂ nanointerface in the catalytic oxidation of diesel soot, a critical environmental problem all over the world. For this, a systematic characterization of the materials has been undertaken using transmission electron microscopy (TEM), transmission electron microscopy–energy-dispersive X-ray spectroscopy (TEM–EDS), high-angle annular dark-field–scanning transmission electron microscopy (HAADF–STEM), scanning transmission electron microscopy–electron energy loss spectroscopy (STEM–EELS), X-ray diffraction (XRD), Raman, N₂ adsorption–desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The TEM images show the formation of nanosized CeO₂ cubes (∼25 nm) and CuO_<i>x</i> nanoparticles (∼8.5 nm). The TEM–EDS elemental mapping images reveal the uniform decoration of CuO_<i>x</i> nanoparticles on CeO₂ nanocubes. The XPS and Raman studies show that the decoration of CuO_<i>x</i> on CeO₂ nanocubes leads to improved structural defects, such as higher concentrations of Ce³⁺ ions and abundant oxygen vacancies. It was found that CuO_<i>x</i>-decorated CeO₂ nanocubes efficiently catalyze soot oxidation at a much lower temperature (<i>T</i>₅₀ = 646 K, temperature at which 50% soot conversion is achieved) compared to that of pristine CeO₂ nanocubes (<i>T</i>₅₀ = 725 K) under tight contact conditions. Similarly, a huge 91 K difference in the <i>T</i>₅₀ values of CuO_<i>x</i>/CeO₂ (<i>T</i>₅₀ = 744 K) and pristine CeO₂ (<i>T</i>₅₀ = 835 K) was found in the loose-contact soot oxidation studies. The superior catalytic performance of CuO_<i>x</i>-decorated CeO₂ nanocubes is mainly attributed to the improved redox efficiency of CeO₂ at the nanointerface sites of CuO_<i>x</i>–CeO₂, as evidenced by Ce M_5,4 EELS analysis, supported by XRD, Raman, and XPS studies, a clear proof for the role of nanointerfaces in the performance of heterostructured nanocatalysts