Hydrogen intermetallic phases

Jaksic has tried to propose a predictive basis for the hydrogen reaction beyond the volcano curve. The idea is based on Brewer-Engel s theory [82] for bonding in metals and intermetallic phases. According to this theory, a maximum in bond strength and stability of the intermetallic phases is expected as a metal lying at the beginning of a transition period in the Periodic Table (e.g., Ti or Zr) is combined with... 

Fig. 4. Activity of various intermetallic phases of Ni and Zr for electrolytic hydrogen evolution. The phase diagram is also shown. From ref. 83, by permission of Elsevier Sequoia.

Steel phases have an influence on the rate of corrosion. Ferrite has a weak resistance to pitting. The presence of martensite can increase the hydrogen fragilization of steel. Intermetallic phases as Fe2Mo in high Ni content alloys can influence the corrosion resistance. The precipitate CuA12 in aluminum alloys the series 2000 is more noble than the matrix, with corrosion around the precipitate. The majority of case histories reported in the literature have involved austenitic stainless steels, aluminum alloys, and to a lesser degree, some ferritic stainless steels and nickel-based alloys.31... 

Unpublished results RUx nanoparticles synthesized in xylene has the tendency to coordinate easily with oxygen from air (a gentle treatment with hydrogen at RT releases the oxygen [95]). The EXAFS function x(k) damped quickly on these Ru O nanoparticles revealing that high disorder increases (nanoparticles become amorphous). P. Villars, L.D. Calvert, eds. Pearson s Handbook of Crystallographic Data for Intermetallic Phase, American Society for Materials Metals Park, OH 1985. 

A model for the nano-structural evolution of Raney-type nickel catalysts (widely used in hydrogenation reactions) from the constituent intermetallic phases present in nickel-aluminium precursor alloys is presented here. Nano-porous nickel catalysts are prepared via a caustic leaching process where the NiAl alloy powder (typically 50-50 at.%) is immersed in concentrated NaOH solution in order to leach away the aluminium present to leave a highly-porous nickel catalyst (often referred to as spongy nickel). 

The quantitative aspect of the EXAFS technique is also well known and the literature gives several studies where chemisorption and EXAFS measurements are compared (see for example We can illustrate this particular contribution of the spectroscopy by a study of rare earth transition metal catalysts prepared from intermetallic LaNij-type compounds. The three classical preparation steps are here skipped with a carbon monoxide hydrogenation reaction. The intermetallic phase is transformed into a rare earth oxide upon which the transition metal is left as metallic clusters which form the active species. This transformation has been followed as a function of the time reaction In Fig. 5 we plot the Fourier transforms of CeNij at the nickel edge before the reaction (a), after 10 hours (b) and after 27 hours (c) under the CO + H2 mixture. These are all compared to elemental nickel (d). The increase of the amplitude of the first peak and the growth of three new ones at greater distances are the consequence of the formation of nickel particles. A careful analysis of these four shells has allowed us quantitatively to estimate the fraction of extracted nickel during the reaction as 30% after 10 hours and 80% after 27 hours on a CO + flux at 350 °C. 

Hydrogenolysis of triphenylarsine (AsPh ) on alumina supported nickel (Ni/Al Oj) has been studied as model reaction for metallic catalyst poisoning. The hydrogenolysis of AsPh on Ni/Al Oj occurs at temperature ranging from 303 to 443 K under 12 bars of hydrogen and in n-heptane solution. It has been followed by kinetics analysis of the AsPh consumption and Benzene and cylohexane evolution as well as XRD measurements of the metallic and intermetallic phase(s). 

The rate of benzene hydrogenation on the various solids obtained by reaction of AsPh on Ni/AljOj was used as catalyst performance evaluation. It was found that benzene hydrogenation is already completely inhibited when the NiAs j intermetallic phase is formed. 

Jaksic MM (1989) Brewer intermetallic phases as synergetic electrocatalysts for hydrogen evolution. Mater Chem Phys 22 1-26... 

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