We propose that all A| "B"glas ses [where A (B) is a late (early) transition metal) are structurally isomorphic, chemically random alloys which store hydrogen in tetrahedral interstitial sites A4 "B"(indecreasing order n =4, 3, 2, . . . ). The maximum absorbed hydrogen-to-metal atomic ratio within each type of interstitial site is 1.9(")x"(1 -x)' " [('")=4!In!(4 n-)!] independent of alloy and temperature. The chemical potential as a function of hydrogen concentration within a single site type n is also independent of composition and temperature. The only nonuniversa1 feature is the dependence of the typical site energies E"ofthe type-n sites on the A and B atoms, which may, however, be estimated from crystalline hydride properties. This model agrees with our electrochemical measurements of hydrogen in Ni-Zr, Pd-Ti, and Ni-Ti, predicts total H/M ratios for Ni-Zr and Cu-Ti alloys in excellent agreement with literature gas-phase data over a wide range of compositions and thermodynamic conditions, and is consistent with literature H/M data on other alloys at isolated compositions. %e show theoretically that infinite near-neighbor hydrogenhydrogen interactions (blocking) in a glass dominated by fivefold rings of tetrahedral units predicts the observed x dependence of H/M with a prefactor of 1.9 -2. 1, in excellent agreement with the observed factor of 1.9. This result supports theoretical models of icosahedral ordering in glasses.
The results of a comprehensive study of the superconducting transition temperatures of Zrand Hf-based metallic glasses are reported. The microscopic origins of superconductivity in these glasses are discussed in terms of recent ultraviolet photoelectron spectroscopy (UPS) measurements and calculations based on the renormalized atom technique. These calculations accurately predict the UPS spectra and the results of low-temperature heatcapacity measurements.The complete description of the electronic structure afforded by these calculations allows, for the first time, a consistent picture of the variation of T, with X in the glasses Zr~» X» (X=3d or 4d transition metals). In addition, the dependence of T, with composition (y) can be understood in terms of the X d subband positions relative to E~. The results reported here support our recent contention that the strong depression of T, observed for X=Fe, Mn, Cr, and V glasses is related to the formation of localized magnetic moments and spin fluctuations. An alternate explanation for the low T, of X=V and Cr glasses based on the idea of an atomic-structure change is also discussed.
The sections in this article are Introduction Ammoxidation of Alkenes General Propene Ammoxidation to Acrylonitrile The SOHIO Acrylonitrile Process Key Catalytic Functionalities Role of Lattice Oxygen‐Catalyst as Redox Solid Generalized Mechanism of Alkene Ammoxidation Bifunctional Nature of Active Sites Ammoxidation Mechanism (Molybdates, Antimonates) Molybdate Catalysts Multicomponent Molybdates Role of Excess Molybdenum Commercial Molybdate Catalysts Antimonate Catalysts Role of Excess Antimony Commercial Antimony Catalysts Ammoxidation of Substituted Alkenes Isobutene Ammoxidation to Methacrylonitrile α‐Methylstyrene Ammoxidation to Atroponitrile Ammoxidation of Alkanes Structure of Mo VNb Te O Catalysts Symbiosis between M1 and M2 Phases Reaction Network and Mechanism Future Research Ammoxidation of Aromatics Toluene Ammoxidation to Benzonitrile Xylene Ammoxidation to Corresponding Mono‐ and Di‐nitriles Ammoxidation of Heteroaromatics 3‐Methylpyridine Ammoxidation to Nicotinonitrile Ammoxidation of 4‐Methylthiazole to 4‐Cyanothiazole Acknowledgments
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