The absolute energy positions of conduction and valence band edges were compiled for about 50 each semiconducting metal oxide and metal sulfide minerals. The relationships between energy levels at mineral semiconductor-electrolyte interfaces and the activities of these minerals as a catalyst or photocatalyst in aqueous redox reactions are reviewed. The compilation of band edge energies is based on experimental flatband potential data and complementary empirical calculations from electronegativities of constituent elements. Whereas most metal oxide semiconductors have valence band edges 1 to 3 eV below the H2O oxidation potential (relative to absolute vacuum scale), energies for conduction band edges are close to, or lower than, the H2O reduction potential. These oxide minerals are strong photo-oxidation catalysts in aqueous solutions, but are limited in their reducing power. Non-transition metal sulfides generally have higher conduction and valence band edge energies than metal oxides; therefore, valence band holes in non-transition metal sulfides are less oxidizing, but conduction band electrons are exceedingly reducing. Most transition-metal sulfides, however, are characterized by small band gaps (<1 eV) and band edges situated within or close to the H2O stability potentials. Hence, both the oxidizing power of the valence band holes and the reducing power of the conduction band electrons are lower than those of non-transition metal sulfides.

The absolute energy positions of conduction and valence bands of selected semiconducting minerals

Steam Reforming and Graphite Formation on Ni Catalysts

Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Steam reforming reactions will play a key role in new applications of synthesis gas and in a future hydrogen economy. The aim of this review is to provide a coherent description of the catalysis of the reforming reactions. The review is not comprehensive. The first section deals with the applications of synthesis gas and hydrogen and the various synthesis gas technologies. The optimum choice of technology depends on the requirements of the gas composition and the scale of operation. Two examples are included for illustration: synthesis gas for gas-to-liquid plants and hydrogen for fuel cells. The steam reforming process is described in the second section with emphasis on the role of the catalyst and problems related to carbon formation. The third section is a summary of the empirical evidence of the catalysis of the reforming reactions. The methods of characterization are discussed, and data representing sintering, activity trends, and promotion are summarized. The fourth section is a description of the mechanism based on a combination of empirical knowledge with recent data from studies of well-defined surfaces, in-situ high-resolution electron microscopy, and calculations based on density functional theory. The central concept is the role of surface defects as the source of reactivity and the nucleation centers for whisker carbon formation.

Hydrogen and Synthesis gas by Steam- and CO2 reforming

Ordered anion adlayers on metal electrode surfaces.

The structures of sulphur on Pd(111) studied by X-ray standing wavefield absorption and surface EXAFS

The band structure of lead sulphide has been investigated using angle-resolved photoemission, with synchrotron radiation in the photon energy range 25-95 eV as the excitation source. Many spectral features originate from direct transitions, while others are due to 'density of state' features, i.e. they arise from electrons scattered into the observation direction. Good agreement was found between the experimental spectra and transitions expected on the basis of the calculated linearized muffin-tin-orbital (LMTO) band structure and free electron final states. Partial yield spectra at the Pb O4,5 edge are also reported, from which it is concluded that the exciton energy in lead chalcogenides is not anomalously large, in contradiction to previous work.

http://iopscience.iop.org/article/10.1088/0953-8984/4/32/012/pdf

Band structure of lead sulphide

The 3d surface core-level shifts of the clean Ge(100)(2\ifmmode\times\else\texttimes\fi{}1) surface have been investigated at 300 K by photoemission. A previously unobserved (to our knowledge) shifted component at about +0.19 eV relative to the bulk emission has been clearly identified and associated with dimer down-atom emission. The binding energy difference of 0.72 eV between dimer down-atom and dimer up-atom 3d core levels, consistent with a charge transfer similar to that occurring in the Si(100)-(2\ifmmode\times\else\texttimes\fi{}1) surface, supports the so-called ionic model of the Ge(100)-(2\ifmmode\times\else\texttimes\fi{}1) buckled-dimer reconstruction. \textcopyright{} 1996 The American Physical Society.

A. Santoni

Papers

The structures of sulphur on Pd(111) studied by X-ray standing wavefield absorption and surface EXAFS

Band structure of lead sulphide

Evidence for three surface components in the 3d core-level photoemission spectra of Ge(100)-(2 x 1) surface.

Co dissociation and recombination reactions on Ni(100)

Photoemission and photoabsorption study of the high-temperature phases of the Ge(111) surface