Chemical state

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

An experimental system for surface reaction studies in microwave plasma etching

Abstract: An experimental system for studying surface reactions in the process of microwave plasma etching has been developed. In the system, a surface etched in the microwave plasma can be analyzed with x‐ray photoemission spectroscopy (XPS) without exposure of the surface to room air. In addition, we have developed a procedure for calculating a thickness of a surface layer stoichiometrically different from the substrate material and densities of atoms in the layer. Chemical changes in etched Si and SiO2 surfaces caused by exposing these surfaces to room air are investigated with XPS to show the utility of the system. When the surfaces etched in SF6 microwave plasma are exposed to room air, the chemical states of the surfaces change rapidly. This is mainly due to surface oxidation and adsorption of hydrocarbon compounds to the surfaces. The rapid changes are more clearly shown from increases in surface layer thickness and the number of O and C atoms in the layer. It is clarified that exposure of etched surface to room air causes the serious disturbance, and that accurate information can not be obtained any longer. The present system which eliminates this disturbance allows accurate measurement of surfaces for detailed investigation of the surface reaction in microwave plasma etching.

Supported Binary Oxide Catalysts Containing CuO Coupled with Ga2O3 and SnO2

Abstract: Two series of binary oxide catalysts (CuGa/SA and CuSn/SA) containing CuO coupled with Ga2O3 or SnO2 were prepared by dispersing the metal phases onto a high surface area acidic silica−alumina (SA) support by an adsorption method. Similar total amounts of metals (about 1.6 atomMet·nm-2) were deposited onto the support, in different proportions, to obtain samples with weight percent of copper varying from 3.3 to 6.5% The SA support was first covered by the copper precursor, Cu(C2H3O2)2, and then gallium (Ga(NO3)3·H2O) or tin (SnCl4·5H2O) precursors were deposited on the dried Cu-containing sample. The calcined materials were characterized by surface techniques (N2 adsorption and XPS), to detect the surface morphology and chemical state of metal species, and by FT-IR and adsorption calorimetry after CO adsorption. Nanosized metal phases were observed in every case. Besides Cu(II), the surfaces contained Cu(I) as well as Cu(δ+) ions (with 1 < δ < 2) stabilized by the interaction with the acid centers of the ...

Behaviour of a cyanide-derived Fe/Al2O3 catalyst during Fischer-Tropsch synthesis

Abstract: The interaction of carbon monoxide and hydrogen with an alumina-supported iron catalyst has been studied at temperatures ranging from 300 to 523 K and at a pressure of 103 kPa. The species produced and adsorbed on the catalyst surface have been examined by infrared spectroscopy, while the chemical state of the iron within the catalyst was investigated by magnetization measurements and Mossbauer spectroscopy. At 300 K the main type of adsorbed species on the iron particle surface appeared to be molecular carbon monoxide and formate groups. The amount of the latter species increases considerably at elevated reaction temperatures up to 473 K. Changes in the infrared absorption bands of CO, and in the magnetization and Mossbauer data indicate that under the applied conditions the surface properties of the iron particles are affected by the synthesis gas, but that the bulk remains metallic. The increased Fischer-Tropsch activity at more elevated temperatures, viz. 473 and 523 K, is accompanied by significant changes in the in situ recorded infrared spectra. The formation of hydrocarbons is evident from the well developed absorption bands in the 3000-2800 cm−1 range, due to (a)symmetric stretching vibrations of CH2 and CH3 groups. Assignment of the various absorption bands in the 1700-1200 cm−1 wavenumber range is speculative due to (partial) coincidence of the bands and the gradual change in chemical composition of the catalyst particles. At higher temperatures the bulk of the iron particles reacts rapidly to a mixture of carbides. Initially the unstable e-Fe2C is formed which reacts to e′-Fe2.2C upon prolonged periods of time of reaction and/or increased reaction temperatures. These carbides appeared to be thermally unstable: upon heating in helium they are converted into a mixture of χ-Fe5C2 and metallic Fe. Interaction of the reduced iron catalysts with ethylene or methane at 523 K gives rise to absorption bands at 1555, 1345 and 1050 cm−1, which are assigned to CHx adsorbed species. Upon reaction with ethylene also a band at 2160 cm−1 was observed, which was assigned to an ethylidyne species.

Unravelling the Role of Structural Geometry and Chemical State of Well-Defined Oxygen Vacancies on Pristine CeO2 for H2O2 Activation.

Abstract: Although H2O2 has been often employed as a green oxidant for many CeO2-catalyzed reactions, the underlying principle of its activation by surface oxygen vacancy (Vo) is still elusive due to the irreversible removal of postgenerated Vo by water (or H2O2). The metastable Vo (ms-Vo) naturally preserved on pristine CeO2 surfaces was adopted herein for an in-depth study of their interplay with H2O2. Their well-defined local structures and chemical states were found facet-dependent affecting both the adsorption and subsequent activation of H2O2. It is concluded that a strong adsorption of H2O2 on ms-Vo may not guarantee its subsequent activation. The ms-Vo can be only free for the next catalytic cycle when the electron density of surface Ce is high enough to reduce/break the O-O bond of adsorbed H2O2. This explains the 211.8 and 35.8 times enhancement in H2O2 reactivity when the CeO2 surface is changed from (111) and (110) to (100).

Electron spectroscopic investigation of Sn coatings on glasses.

Abstract: Float glasses of different thicknesses and a conducting tin oxide glass have been investigated using Photo and Auger Electron Spectroscopy induced by AlKalpha X-rays. On the basis of measured chemical XPS shifts in the binding energies the chemical state of Sn (+2 or +4) incorporated on the float glasses could not be assigned. The use of the Auger parameter allows to separate relaxation and chemical contributions. The derived true chemical shifts of Sn on float-glasses are larger than those of SnO and/or SnO(2) due to the larger ionic environment of the glass matrix. Ar(+) or HF etching reveals that the concentration of Sn decreases exponentially as a function of depth from the surface.