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    Title: Ab Initio Study of the Reaction Mechanisms of NiO and NiS with H2
    Authors: 黃德彥;Hwang, Der-yan;Mebel, Alexander M.
    Contributors: 淡江大學化學學系
    Date: 2002-01-24
    Issue Date: 2009-12-01
    Publisher: Washington: American Chemical Society (ACS)
    Abstract: Singlet and triplet potential energy surfaces for the NiO + H2 → Ni + H2O and NiS + H2 → Ni + H2S reactions have been investigated by density functional calculations at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G** level as well as by ab initio CCSD(T), CASSCF, and MRCI calculations for some of the key species. The singlet−triplet intersystem crossing is shown to play a crucial role for both reactions. The reaction of nickel oxide with molecular hydrogen starts from the formation of a t-ONi−H2 complex bound by 3.7 kcal/mol relative to NiO(3Σ-) and H2. This is followed by an intersystem crossing (the spin−orbit coupling computed at a representative point CI1 of the singlet−triplet intersection is 86 cm-1) and the system proceeds via a barrier of 13.3 kcal/mol (transition state s-TS1) in singlet electronic state to form a HNiOH intermediate in singlet or triplet states. t-HNiOH, 9.1 kcal/mol more stable than s-HNiOH, lies 44.8 kcal/mol below the reactants. The HNiOH molecule rearranges to a triplet t-Ni−OH2 molecular complex via transition state s-TS2 on the singlet potential energy surface and via singlet−triplet transitions, whereas the spin−orbit coupling for a crossing point CI2 in the transition state vicinity is evaluated as 27 cm-1. On the last reaction step the complex bound by 3.8 kcal/mol dissociates to Ni(3F) + H2O without an exit barrier. For the reverse reaction, Ni(3F) + H2O → t-HNiOH, the barrier, which occurs at s-TS2 in singlet electronic state, is 12.1 and 4.9 kcal/mol at the B3LYP/6-311+G(3df,2p) and CCSD(T)/6-311+G(3df,2p) levels, respectively. The NiS + H2 reaction begins on the triplet potential energy surface and proceeds via a barrier [transition state t-TS1(S)] of 19.1 kcal/mol relative to NiS(3Σ-) + H2 to produce the global minimuma triplet HNiSH molecule, 18.2 kcal/mol below the reactants. This intermediate dissociates to the triplet Ni atom and H2S via s-TS2(S) and a s-Ni−SH2 complex involving singlet−triplet intersections. The Ni(3F) + H2S reaction is predicted to rapidly produce the HNiSH molecule, which, in turn, can dissociate to NiS + H2 overcoming a barrier of 13 kcal/mol with respect to the reactants. Since the highest barriers along the NiO + H2 → Ni + H2O and NiS + H2 → Ni + H2S reaction pathways are 13 and 19 kcal/mol, molecular hydrogen is expected to reduce nickel oxide and NiS to atomic nickel at elevated temperatures.
    Relation: Journal of physical chemistry A 106(3), pp.520-528
    DOI: 10.1021/jp012650a
    Appears in Collections:[化學學系暨研究所] 期刊論文

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