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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Langmuir 10 (1994), S. 4530-4533 
    ISSN: 1520-5827
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7031-7036 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spatial distributions of NO, N2, and N2O desorbing from Pd(211), Pd(S)-[3(111)×(100)], in temperature programmed desorption (TPD) and that of N2 produced in the temperature programmed reaction (TPR) of NO+H2 have been studied. The spatial distribution of N2 desorbing at 510 K in the TPD had a maximum intensity at θ=−25–−30 deg (down the steps) in the [1 1¯ 1¯] direction, which is almost normal to the (100) steps, and is described by 2.4 cos12(θ+26 deg). Taking account of the fact that NO molecules are preferentially adsorbed on the (111) terraces of a Pd(211) surface at low coverage, it is deduced that the NO adsorbed on the (111) terraces undergoes migration to the (100) steps, where N2 is produced. An isotopically labeled angle-resolved TPD experiment showed that N2 was produced by the NO+N reaction. On the other hand, the desorption of NO is normal to the crystal surface. This phenomenon indicates that NO desorbs via a predesorption state, where NO molecules forget their memory of the previous adsorption sites. In contrast, the spatial distribution of N2 given by the catalytic reaction in a flow of NO+H2 at 650 K, was completely different from that of N2 produced by NO+N reaction at around 500 K. It is concluded that the spatial distribution reflects the reaction or desorption mechanisms, especially the reaction coordinate on the surface. © 1999 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1650-1654 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The p(2×3) Ni(110)-N surface structure was produced by the reaction of NO with highly excess H2 (1:150) on a Ni(110) surface at 650 K. The N atoms on Ni(110) surface were inactive for the hydrogenation with H2. They, however, reacted with H atoms in the presence of H2, and the formation of NH species was detected by high resolution electron energy loss spectroscopy (HREELS). In the temperature range between 300 K and 450 K, the amount of N on Ni(110) surface decreased by reacting with H atoms in the zero order kinetics with respect to the amount of N and the decreasing rate did not depend on the temperature. When the temperature is higher than a critical temperature of 500 K, however, the amount of N on the Ni(110) surface does not decrease even if the surface is exposed to H atoms. This critical temperature corresponds to the decomposition temperature of the NH species on Ni(110) surface determined by the HREELS. One one hand, the NH species were produced by the reaction, hydrogenation, of N with H atoms on the Ni(110) suface. On the other hand, it was reported that NH2 species were preferentially formed by the decomposition, dehydrogenation, of NH3 on the Ni(110) surface. Taking these facts into account, it was deduced that there is a rather high activation barrier in an elementary reaction path from NH to NH2 on the Ni(110) surface. © 1995 American Institute of Physics.
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The availability of cloned cDNAs encoding the four subunits of the Torpedo acetylcholine receptor, which can be expressed to make functional receptors in Xenopus oocytes, has made possible a detailed investigation of the functions of the different structural components of the receptor. The ...
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of solid state electrochemistry 1 (1997), S. 187-193 
    ISSN: 1433-0768
    Keywords: Key words Crystal habit ; fcc metal ; Icosahedron ; Decahedron ; Multiply twinned particles ; Electrode potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The crystal habit of fcc metal particles formed on an amorphous carbon film electrode in solution at different electrode potentials is discussed. The fcc metal particles have different crystallographic habits depending on applied electrode potential; that is, icosahedral and/or decahedral particles are formed at lower potentials, and fcc single-crystalline or polycrystalline particles at higher potentials. It was found that decahedra and icosahedra of Cu-Au alloy particles are formed in the potential region of underpotential deposition (UPD) of Cu at which only fcc Au single-crystalline particles and Au polycrystalline particles appear. This is attributed to the charge transfer from the UPD Cu ions to the Au overlayer of Cu-Au alloy particles. The formation of decahedral and icosahedral Cu-Au alloy particles depends on the composition of the Cu-Au alloy. On the basis of these results it was deduced that the contraction of the surface lattice of the growing particles is responsible for the formation of icosahedral and decahedral particles.
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  • 6
    ISSN: 1572-879X
    Keywords: Pt(110) ; Pt(100) ; Rh/Pt(110) ; Rh/Pt(100) ; activity ; structure sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The catalytic activity of the Pt(110) surface for the reaction of NO + H2 was much less than that of the Pt(100) surface. However, the catalytic activity of the Rh deposited Pt(1l0) surface was almost equal to that of the Rh deposited Pt(100) surface. That is, the catalytic reaction of NO + H2 on Pt(110) and Pt(100) surfaces is highly structure sensitive, but it changes to structure insensitive by the deposition of Rh atoms. These results are rationalized by formation of an active overlayer on the Pt(110) and Pt(100) surfaces, which is very analogous to the Rh-O/Pt-layer formed on Rh/Pt(100), Pt/Rh(100) and Pt-Rh(100) alloy surfaces during catalysis. The formation of the common overlayer of Rh-O/Pt-layer during catalysis is responsible for the structure insensitive catalysis of Rh deposited Pt-based catalysts, which is an important role of Rh in a three way catalyst.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis surveys from Japan 3 (1999), S. 81-93 
    ISSN: 1572-8803
    Keywords: intermediates ; olefin metathesis ; NO reduction ; activation of catalyst ; active sites ; Pt–Rh catalyst ; alloy single crystal ; bimetallic single crystal ; quasi-compound ; reconstruction ; surface segregation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Why can solid surfaces promote a variety of chemical reactions? We supposed that active sites or active compounds are formed over the catalyst surface during catalysis or in pretreatment. Three topics are discussed from this viewpoint in this review. The first topic is an activation of inactive MoOx film to super-active olefin metathesis catalyst, where Mo=CHR sites are prepared on MoOx. A total mechanism for the productive and the cross metathesis of propene was firstly established on an activated catalyst by using deuterium labeled olefins. In the second topic, a new concept of quasi-compounds is discussed by using scanning tunneling microscopy (STM), and it is shown that the reaction of quasi-compounds yields (Cu)6 cluster and (–Cu–O–) strings on Ag(110). In the third topic, a self-activation of Pt–Rh alloy and Pt/Rh bimetallic surfaces during the reaction of NO + H2 is discussed by using single crystal surfaces. STM image showed that a Pt–Rh(100) surface is activated by reacting with oxygen where a specific array of Pt and Rh atoms is established. Formation of similar active sites on the other crystallographic surfaces is responsible for structure insensitive catalysis of Pt/Rh bimetallic surfaces.
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  • 8
    ISSN: 1572-879X
    Keywords: platinum ; rhodium ; alloy ; surface composition ; nitrogen ; oxygen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two kinds of adsorbed N atoms exist on a Pt0.25Rh0.75(100) surface. One desorbs at 490 K and the other desorbs at 650 K. The former reacts with H2 at 400 K, but the latter does not. It is supposed that the adsorption of these two N atoms is responsible of the surface composition, ratio of Pt and Rh.
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  • 9
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A super active catalyst (T.F. = 0.2 ∼ 0.3) for alkene metathesis reaction was prepared by coordinating CH2 radicals onto sublimed molybdenum oxide films, where the radicals were prepared by the reaction of CH2I2 with Al or Mg metals deposited near the oxide film.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 12 (1992), S. 1-6 
    ISSN: 1572-879X
    Keywords: Surface carbide ; surface nitride ; intermediates ; NO + H2 reaction ; methanation reaction ; catalysis on single crystal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A key intermediate of the methanation reaction on nickel catalyst is a carbidic carbon. Accumulated carbidic intermediates on Ni(100) gives a p(2×2) p4g structure, whereas that on Ni(111) is too complex to be solved. A single domain carbide layer accidentally on Ni(111) allowed us to solve the structure explicitly. Comparison of the carbide layer on Ni(100) and that on Ni(111) showed that the carbon atoms are arranged by forming the same ordered structure. The carbide layers prepared on Ni(100), Ni(111) and Ni(110) have almost equal decomposition temperatures. Consequently, we can conclude that the same overlayer compound is formed on the three surfaces. Furthermore, the hydrogenation of the p4g carbide on Ni(100) occurs at almost equal rate to the turnover frequency of the catalytic methanation reaction. The structure insensitive methanation reaction on Ni(100), Ni(111) and Ni(110) is responsible for the same intermediate compound on these surfaces. The same strategy was applied to the reaction of NO with H2 on Pd(100), Rh(100) and Pt-Rh(100) surfaces, and ac(2×2)-N overlayer was isolated on each of these. The hydrogenation of the isolatedc(2×2)-N produced predominantly NH species, which indicates slow NH species hydrogenation.
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