Morphology and Structure of CuO_x/CeO₂ Nanocomposite Catalysts Produced by Inert Gas Condensation:  An HREM, EFTEM, XPS, and High-Energy Diffraction Study

Abstract

Inert gas condensation (IGC) has been employed to produce nanoparticles of the low-temperature combustion catalyst CuO x /CeO2. For the first time we have used a multiple heating crucible setup to tailor various morphologies over the whole compositional range (2−98% Cu). The factors that control the growth, structure, and morphology of the nanocomposite have been studied. A powerful combination of complementary characterization methods has been used to elucidate the catalytic synergistics of this material. Investigations by high-resolution transmission electron microscopy (HRTEM) and energy-filtered TEM (EFTEM) are supported by X-ray photoelectron spectroscopy (XPS) and high-energy diffraction (HED) measurements. The nonstoichiometric CuO x /CeO2 composite displays an amorphous character consisting of aggregated CeO2 (ceria) nanocrystallites over which amorphous copper clusters (or a thin film of a solid solution) are finely dispersed. In the range 6∼20% Cu, copper is predominantly located at the surface, which can give the material optimum catalytic properties. Development of crust structures, for example, core−shells, are formed in the 30∼70% Cu concentration range and is attributable to a sequential oxidation of Ce followed by Cu and an ideal proportion of lattice expansion for the oxides. We suggest a model that illustrates the formation of the crust structure and may explain the observed extreme dispersion of copper on ceria. The helium gas pressure during the thermalization controls the crystal size and the degree of crystallite aggregation. Rounded particle shapes consisting of epitaxially interfaced nanocrystallites exhibit an X-ray amorphous character, while block-shaped crystals displaying sharp edges and distinct flat surfaces give rise to a higher X-ray crystallinity. Bulk CuO crystals were detected by high-energy diffraction above a 30% Cu content. However, the extreme copper dispersion is preserved even for higher copper contents, showing no limit of surface saturation.

Protein adsorption and cellular uptake of cerium oxide nanoparticles as a function of zeta potential

“…The {1 1 0} and {0 0 1} planes are less stable compared to the {1 1 1} planes. Therefore {1 1 1} planes are inherently less reactive [20][21][22]. Yang et al [23] found that adsorption of CO on {1 1 1} is weak, whereas there are both weak and strong adsorptions on the {1 1 0} plane.…”

Facile preparation of 3D ordered mesoporous CuOx–CeO2 with notably enhanced efficiency for the low temperature oxidation of heteroatom-containing volatile organic compounds

“…[12][13][14] For instance, Huang et al have reported that a CuO modified USY zeolite possessed good activity and high selectivity for Cl-VOC decomposition. 15 Adding ceria as a promoter to copper oxide has many advantages for catalytic performance: 1) it stabilizes the dispersion of the active Cu phase; 16 2) it acts as an oxygen storing phase (Ce 3+ /Ce 4+ ) and strongly affects the copper redox properties; [17][18][19][20] and 3) it creates structural defects and improves the oxygen storage capacity and diffusivity. 19,21,22 However, studies concerning the low-temperature catalytic combustion of HCVOCs using CuO-CeO 2 have seldom been reported, despite the material being proven to have excellent catalytic activities for the oxidation of many VOC pollutants.…”

Electrochemical bulk synthesis and characterisation of hexagonal-shaped CuO nanoparticles

“…Furthermore, CuO exhibits high mechanical strength, high-temperature durability, giant magnetoresistance and piezoelectricity. Apart from being an excellent catalytic material for CO oxidation, it has been widely used in indoor air cleaning and automotive exhaust treatment [33].…”