Chemical state

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

XRD and XPS Study of Cu−Ni Interactions on Reduced Copper−Nickel−Aluminum Oxide Solid Solution Catalysts

Abstract: Copper−nickel−aluminum oxide solid solutions were reduced in hydrogen to produce alumina-supported copper−nickel alloy catalysts. XRD patterns of reduced oxides showed that the type of active metals which emerged upon reduction were sensitive to the reduction temperature and the copper content. Variations from +0.8 to +1 eV were found in the experimental Ni 2p3/2 binding energy (BE) of nickel in the solid solutions compared to the experimental Ni 2p3/2 BE of bulk nickel, attributed to the Ni−Ni arrangements in the solid solution. Also, when the curve-fitted BE values of Ni 2p3/2 and Cu 2p3/2 of different reduced solid solutions were compared, it was found that copper and nickel were in different chemical states depending on reduction temperature and the amount of the copper. Changes in Ni 2p3/2 BE in the reduced solid solutions were also discussed in terms of the filling of nickel d-hole bands due to nickel−copper d−d band interactions. At both high copper content and reduction temperature, copper had a t...

In situ x-ray photoelectron spectroscopy studies of gas-solid interfaces at near-ambient conditions

Abstract: X-ray photoelectron spectroscopy (XPS) is a quantitative, chemically specific technique with a probing depth of a few angstroms to a few nanometers. It is therefore ideally suited to investigate the chemical nature of the surfaces of catalysts. Because of the scattering of electrons by gas molecules, XPS is generally performed under vacuum conditions. However, for thermodynamic and/or kinetic reasons, the catalyst's chemical state observed under vacuum reaction conditions is not necessarily the same as that of a catalyst under realistic operating pressures. Therefore, investigations of catalysts should ideally be performed under reaction conditions, that is, in the presence of a gas or gas mixtures. Using differentially pumped chambers separated by small apertures, XPS can operate at pressures of up to 1 Torr, and with a recently developed differentially pumped lens system, the pressure limit has been raised to about 10 Torr. Here, we describe the technical aspects of high-pressure XPS and discuss recent applications of this technique to oxidation and heterogeneous catalytic reactions on metal surfaces.

The influence of nonstoichiometry on LaMnO3 perovskite for catalytic NO oxidation

Abstract: A series of structural modified LaxMnO3 (x = 0.9, 0.95, 1, 1.05, 1.11) perovskites used for NO oxidation was synthesized by a sol–gel method and characterized by XRD, BET, XPS, EPR and H2-TPR. La0.9MnO3 sample exhibits superior activity, and a 50% NO conversion at 250 °C is obtained. XPS and EPR results reveal a higher Mn4+/Mn3+ ratio in Mn-rich samples, which induce more active oxygen bonding to Mn4+ due to the need for balancing the chemical states and stabilizing the structure. Easily regenerated oxygen associated with Mn4+ catalyzes the low-temperature NO oxidation. The constant activation energy (44.8 kJ/mol) obtained in the kinetics tests indicates the same mechanism of NO oxidation operated on all the samples.