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  • 2000-2004  (23)
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  • 1
    Electronic Resource
    Electronic Resource
    A density functional theory study of hydroxyl and the intermediate in the water formation reaction on Pt (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 513-519 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Density functional theory has been used to study the adsorption of hydroxyl at low and high coverages and also to investigate the nature of the intermediate in the H2O formation reaction on Pt(111). At low coverages [1/9 of a monolayer (ML) to 1/3 ML] OH binds preferentially at bridge and top sites with a chemisorption energy of ∼2.25 eV. At high coverages (1/2 ML to 1 ML) H bonding between adjacent hydroxyls causes: (i) an enhancement in OH chemisorption energy by about 15%; (ii) a strong preference for OH adsorption at top sites; and (iii) the formation of OH networks. The activation energy for the diffusion of isolated OH groups along close packed rows of Pt atoms is 0.1 eV. This low barrier coupled with H bonding between neighboring OH groups indicates that hydroxyls are susceptible to island formation at low coverages. Pure OH as well as coadsorbed OH and H can be ruled out as the observed low temperature intermediate in the water formation reaction. Instead we suggest that the intermediate consists of a mixed OH+H2O overlayer with a macroscopic surface coverage of 3/4 ML in a 2:1 ratio of OH and H2O. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1328746
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  • 2
    Electronic Resource
    Electronic Resource
    A density functional theory study of CH2 and H adsorption on Ni(111) (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6006-6014 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio total energy calculations within the density functional theory framework have been used to study the adsorption of CH2 and H as well as the coadsorption of CH2 and H on Ni(111). H binds strongly at threefold hollow sites with calculated adsorption energies of 2.60 and 2.54 eV at the face-centered-cubic (fcc) and hexagonal-close-packed (hcp) hollow sites, respectively. Adsorption energies and H-Ni distances are found to agree well with both experimental and theoretical results. CH2 adsorbs strongly at all high symmetry sites with calculated adsorption energies of 3.26, 3.22, 3.14 and 2.36 eV at the fcc, hcp, bridge and top sites, respectively. Optimized structures are reported at all sites, and, in the most stable hollow sites there is considerable internal reorganization of the CH2 fragment. The CH2 molecule is tilted, the hydrogens are inequivalent and the C-H bonds are lengthened relative to the gas phase. In the CH2-H coadsorption systems the adsorbates have a tendency to move toward bridge sites. The bonding of all adsorbates to the surface is analyzed in detail. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481173
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  • 3
    Electronic Resource
    Electronic Resource
    A density functional theory study of CO oxidation on Ru(0001) at low coverage (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10564-10570 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have performed ab initio density functional theory calculations with the generalized gradient approximation to investigate CO oxidation on Ru(0001). Several reaction pathways and transition states are identified. A much higher reaction barrier compared to that on Pt(111) is determined, confirming that the Ru is very inactive for CO oxidation under UHV conditions. The origin of the reaction barrier was analyzed. It is found that in the transition state the chemisorbed O atom sits in an unfavorable bonding site and a significant competition for bonding with the same substrate atoms occurs between the CO and the chemisorbed O, resulting in the high barrier. Ab initio molecular dynamics calculations show that the activation of the chemisorbed O atom from the initial hcp hollow site (the most stable site) to the bridge site is the crucial step for the reaction. The CO oxidation on Ru(0001) via the Eley–Rideal mechanism has also been investigated. A comparison with previous theoretical work has been made. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481690
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  • 4
    Electronic Resource
    Electronic Resource
    A first principles study of CH3 dehydrogenation on Ni(111) (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 8120-8125 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Density functional theory with gradient corrections and spin polarization has been used to study the dehydrogenation of CH3 on Ni(111), a crucial step in many important catalytic reactions. The reaction, CH3(ads)→CH2(ads)+H(ads), is about 0.5 eV endothermic with an activation energy of more than 1 eV. The overall reaction pathway is rather intriguing. The C moiety translates from a hcp to a fcc site during the course of the reaction. The transition state of the reaction has been identified. The CH3 species is highly distorted, and both C and the active H are centered nearly on top of a row of Ni atoms with a long C–H bond length of 1.80 Å. The local density of states coupled with examination of the real space distribution of individual quantum states has been used to analyze the reaction pathway. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481412
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  • 5
    Electronic Resource
    Electronic Resource
    N2O and NO2 formation on Pt(111): A density functional theory study (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2902-2908 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Catalytic formation of N2O and NO2 were studied employing density functional theory with generalized gradient approximations, in order to investigate the microscopic reaction pathways of these catalytic processes on a Pt(111) surface. Transition states and reaction barriers for the addition of chemisorbed N or chemisorbed O to NO(ads) producing N2O and NO2, respectively, were calculated. The N2O transition state involves bond formation across the hcp hollow site with an associated reaction barrier of 1.78 eV. NO2 formation favors a fcc hollow site transition state with a barrier of 1.52 eV. The mechanisms for both reactions are compared to CO oxidation on the same surface. The activation of the chemisorbed NO and the chemisorbed N or O from the energetically stable initial state to the transition state are both significant contributors to the overall reaction barrier Ea, in contrast to CO oxidation in which the activation of the O(ads) is much greater than CO(ads) activation. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1490338
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  • 6
    Electronic Resource
    Electronic Resource
    Stepwise addition reactions in ammonia synthesis: A first principles study (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 609-611 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Catalytic ammonia synthesis is believed to proceed via dissociation of N2 and H2 with subsequent stepwise addition reactions from an adsorbed nitrogen atom to NH3. The first step, N2 dissociation, has been thoroughly studied. However, little is known about the microscopic details of the stepwise addition reactions. To shed light on these stepwise addition reactions, density functional theory calculations with the generalized gradient approximation are employed to investigate NHx (x=1,3) formation on Ru(0001). Transition states and reaction barriers are determined in each elementary step. It is found that the reaction barriers for stepwise addition reactions are rather high, for example, the barrier for NH hydrogenation is calculated to be 1.28 eV, which is comparable with that of N2 dissociation. In addition, one of the stepwise addition reactions on a stepped surface is also considered. The reaction barrier is found to be much higher than that of N2 dissociation on the same stepped surface, which indicates the importance of stepwise addition reactions in ammonia synthesis. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1384008
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  • 7
    Electronic Resource
    Electronic Resource
    A first principles study of methanol decomposition on Pd(111): Mechanisms for O–H bond scission and C–O bond scission (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 7182-7186 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: There is some dispute as to whether methanol decomposition occurs by O–H bond scission or C–O bond scission. By carrying out density functional theory calculations, we investigate both scenario of the reaction pathways of methanol decomposition on a Pd(111) surface. It is shown that the O–H bond scission pathway is much more energetically favorable than the C–O bond scission pathway. The high reaction barrier in the latter case is found to be due to the poor bonding abilities of CH3 and OH with the surface at the reaction sites. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1405157
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  • 8
    Electronic Resource
    Electronic Resource
    Mechanism for the high reactivity of CO oxidation on a ruthenium–oxide (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 5956-5957 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A long-standing puzzle in heterogeneous catalysis, CO oxidation on a Ru(0001) surface under high oxygen pressure, was clarified recently by Over et al. [Science 287, 1474 (2000)], who obtained experimental evidence that the active phase is RuO2(110) when the reaction is operated at an elevated temperature. To find microscopic details of the reaction and to understand the high reactivity of RuO2(110), we performed density functional theory calculations for CO oxidation on RuO2(110). The transition state is located and the reaction barrier is determined to be 1.15 eV, being considerably lower than that on Ru(0001). The high reactivity of RuO2(110) for CO oxidation is analyzed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1353584
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  • 9
    Electronic Resource
    Electronic Resource
    Insight into why the Langmuir–Hinshelwood mechanism is generally preferred (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 4379-4381 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In heterogeneous catalysis, the two main reaction mechanisms which have been proposed are the Langmuir–Hinshelwood and the Eley–Rideal. For the vast majority of surface catalytic reactions, it has been accepted that the Langmuir–Hinshelwood mechanism is preferred. In this study, we investigate catalytic CO oxidation on Pt(111). It is found that reaction barriers for Langmuir–Hinshelwood mechanisms actually tend to be higher than those for Eley–Rideal ones. An explanation is presented as to why it is still more probable for the reaction to proceed via the Langmuir–Hinshelwood mechanism, despite its higher reaction barrier. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1458938
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  • 10
    Electronic Resource
    Electronic Resource
    Methane transformation to carbon and hydrogen on Pd(100): Pathways and energetics from density functional theory calculations (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 322-327 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Density functional theory with gradient corrections has been employed to study the reaction pathways and the reaction energetics for the transformations of CH4 to C and H on a Pd(100) surface. On examination of transition state structures identified in each elementary reaction, a clear relationship between the valencies of the CHx fragments and the locations of the transition states emerges. The higher the valency of the CHx fragment, the higher the coordination number of the CHx with the surface atoms. The calculated reaction energetics are in good agreement with the experiments. In addition, calculation results are also used to illustrate an interesting issue concerning the CH3 stability on Pd surfaces. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1423663
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