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Re-activation of a passivated Au/α-MoC catalyst found Au clusters dispersed to smaller species that were simultaneously coated by newly-formed carbide thin layers, substantially extending the Au-MoC interfacial perimeter length.

The effect of water on CO oxidation over a Au/Fe2O3 catalyst, fabricated by dispersing 2.3 nm Au particles on a rod-shaped Fe2O3, was examined comprehensively. Under the dry gas condition (a CO/O2 ...

We report the in-situ sol-gel synthesis of TiO2–carbon composites (black TiO2) by carbonization of the gel. With ultra-fine anatase TiO2 nanoparticles dispersed homogeneously on amorphous carbon, the as-prepared black TiO2 possesses a BET surface area as high as 145.4 m2/g. Due to the synergy effect of adsorption and photocatalysis, the as-synthesized black TiO2 is demonstrated to exhibit enhanced photocatalytic activity. The gas sensing properties of black TiO2 have been rigorously investigated with and without UV illumination at room temperature. It is found that increased adsorption of gas molecules can effectively improve the sensor response. The mechanism of the adsorption-enhanced gas sensing performance of black TiO2 has been detailedly discussed.

The geometrical structure of the Au-Fe2 O3 interfacial perimeter, which is generally considered as the active sites for low-temperature oxidation of CO, was examined. It was found that the activity of the Au/Fe2 O3 catalysts not only depends on the number of the gold atoms at the interfacial perimeter but also strongly depends on the geometrical structure of these gold atoms, which is determined by the size of the gold particle. Aberration-corrected scanning transmission electron microscopy images unambiguously suggested that the gold particles, transformed from a two-dimensional flat shape to a well-faceted truncated octahedron when the size slightly enlarged from 2.2 to 3.5 nm. Such a size-induced shape evolution altered the chemical bonding environments of the gold atoms at the interfacial perimeters and consequently their catalytic activity. For Au particles with a mean size of 2.2 nm, the interfacial perimeter gold atoms possessed a higher degree of unsaturated coordination environment while for Au particles with a mean size of 3.5 nm the perimeter gold atoms mainly followed the atomic arrangements of Au {111} and {100} facets. Kinetic study, with respect to the reaction rate and the turnover frequency on the interfacial perimeter gold atom, found that the low-coordinated perimeter gold atoms were intrinsically more active for CO oxidation. 18 O isotopic titration and Infrared spectroscopy experiments verified that CO oxidation at room temperature occurred at the Au-Fe2 O3 interfacial perimeter, involving the participation of the lattice oxygen of Fe2 O3 for activating O2 and the gold atoms for CO adsorption and activation.

The geometrical and electronic properties of the active sites on the surface of metal nanoparticles and their structure evolution and dynamic behavior during catalysis, consitute the core issue of heterogeneous catalysis. Metal nanoparticles are characterized by the highly reduced size, in a typical range of 1–10 nm, and the significantly enhanced catalytic performance; but they are subject to structural and chemical changes under the reaction conditions, primarily induced by the reactive gases at elevated temperatures. In situ characterization techniques, like environmental transmission electron microscopy and X-ray absorption spectroscopy, allow to directly visualize the structural variations at nano and atomic scales and simultaneously probe the chemical variations of the metal nanoparticles at functionalities. This review article summarizes the most recent advances on the structure evolution and dynamic behavior of metal nanoparticles, including late transition metals and IB metals, during their activation and reaction processing. Analyses on the correlation between the dynamic nanostructures observed under or close to reaction conditions and the catalytic performance shed profound insights into the fundamental understanding of the structure-reactivity relationship of metal nanoparticles.

An effective and facile strategy to synthesize spherical Li(Ni0.83-xCo0.10Mn0.07Aly)O2 with a metal concentration gradient is presented. Spherical-shaped Ni0.83Co0.10Mn0.07(OH)2 with hierarchical microstructure is used as the precursor. Al3+ inserts into Ni0.83Co0.10Mn0.07(OH)2 by replacing Ni2+ in Ni0.83Co0.10Mn0.07(OH)2 microspheres, resulting in a gradient distribution of Al and Ni within the microspheres. The Ni concentration decreases linearly, whereas the Al concentration increases linearly from the center to the outer layer of each particle. However, the distribution of Mn and Co is nearly uniform throughout the whole particle. This result is verified by using energy-dispersive X-ray mapping, line scanning, and inductively-coupled plasma spectrometry. Electrochemical tests are carried out by using the as-synthesized samples as positive-electrode materials in lithium-ion batteries. Results show that the discharge capacity, cyclability, and rate performance of these samples are clearly enhanced with respect to those of the untreated sample. The specific discharge capacity of the obtained sample at a discharge current of 0.1 C reaches 203.4 mAh g−1, whereas the modified material depicts a much higher specific capacity of 141.7 mAh g−1 during the 30th cycle, compared with only 80.8 mAh g−1 for the untreated sample. In addition, a series of materials with different Ni/Al ratios are synthesized by using this approach, for which the adjusted reaction parameters also affect their electrochemical properties. This simple synthetic strategy may be extended to construct nano-/microsized particles with concentration gradients, offering new opportunities to study the composition-dependent phenomena at the nano-/microscale, as well as to provide a way of tuning the chemical/physical properties.

Cu/CeO2 catalysts are highly active for the low-temperature water–gas shift—a core reaction in syngas chemistry for tuning the H2/CO/CO2 proportions in feed streams—but the direct identification and quantitative description of the active sites remain challenging. Here we report that the active copper clusters consist of a bottom layer of mainly Cu+ atoms bonded on the oxygen vacancies (Ov) of ceria, in a form of Cu+–Ov–Ce3+, and a top layer of Cu0 atoms coordinated with the underlying Cu+ atoms. This atomic structure model is based on directly observing copper clusters dispersed on ceria by a combination of scanning transmission electron microscopy and electron energy loss spectroscopy, in situ probing of the interfacial copper–ceria bonding environment by infrared spectroscopy and rationalization by density functional theory calculations. These results, together with reaction kinetics, reveal that the reaction occurs at the copper–ceria interfacial perimeter via a site cooperation mechanism: the Cu+ site chemically adsorbs CO whereas the neighboring Ov–Ce3+ site dissociatively activates H2O.