Chemical state

About: Chemical state is a research topic. Over the lifetime, 2378 publications have been published within this topic receiving 78183 citations.

CuO/CeO2 catalysts: Redox features and catalytic behaviors

Abstract: The reduction and oxidation features of nanostructured CuO/CeO2 catalysts prepared by the deposition-precipitation method were extensively investigated by TPR, FIF-IR and in situ XPS techniques. Both the chemical states of copper and the reduction degree of ceria could be well controlled during the reduction with hydrogen by adjusting the temperature. Noticeably, the fully reduced Cu-0 could be further oxidized into Cu+ in hydrogen by increasing the reduction temperature through the interaction between Cu-0 and lattice oxygen of ceria immigrating to the surface. Structure-reactivity relationship was established between the structural features of CuO/CeO2 formed during the pre-reduction with hydrogen and its catalytic activities for CO oxidation. It was observed that reduction with hydrogen at 473-573 K, which leads to the full presence of metallic copper in the catalyst, gives rise to higher CO conversion. These phenomena were interpreted in terms of the reduction degrees of ceria, the changes of surface morphology and the chemical states of copper species. The interface oxygen activation as well as its transfer from the interface to the adsorbed reactant was found to play decisive roles in determining the reaction rate of CO oxidation. (c) 2005 Elsevier B.V. All rights reserved.

Chemical Distribution and Bonding of Lithium in Intercalated Graphite: Identification with Optimized Electron Energy Loss Spectroscopy

Abstract: Direct mapping of the lithium spatial distribution and the chemical state provides critical information on structure-correlated lithium transport in electrode materials for lithium batteries. Nevertheless, probing lithium, the lightest solid element in the periodic table, poses an extreme challenge with traditional X-ray or electron scattering techniques due to its weak scattering power and vulnerability to radiation damage. Here, we report nanoscale maps of the lithium spatial distribution in electrochemically lithiated graphite using electron energy loss spectroscopy in the transmission electron microscope under optimized experimental conditions. The electronic structure of the discharged graphite was obtained from the near-edge fine structure of the Li and C K-edges and ab initio calculations. A 2.7 eV chemical shift of the Li K-edge, along with changes in the density of states, reveals the ionic nature of the intercalated lithium with significant charge transfer to the graphene sheets. Direct mapping ...

Controlled Growth and Characterization of Tungsten Oxide Nanowires Using Thermal Evaporation of WO3 Powder

Abstract: Tungsten oxide (WO3) nanowires were prepared on a tungsten (W) substrate by thermal evaporation of WO3 powder at elevated temperature in a tube furnace. The morphology, structure, composition, and chemical state of the prepared nanowires were characterized by SEM, EDX, TEM, XRD, Raman spectroscopic, and XPS measurements. The nanowires grown using WO3 powder were found to have uniform morphology with a high density and a crystalline structure consistent with monoclinic WO3. The field-emission measurements showed that the prepared nanowires have a turn-on field of 4.8 V/μm. The role of WO3 powder in the growth of high-density nanowires has been discussed by comparing the above results with those of nanowires grown without using WO3 powder and also on a different substrate. Also, the effects of growth temperature on the chemical binding states and product morphology of the nanowires were investigated.