Adsorbed Hydrogen Effect on the Adsorption and Reactivity of N2 Molecules on Ru/MgO and Ru–Cs+/MgO: Hydrogen Dipole Effect Enhanced by Doped Cs+

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Abstract
The effects of adsorbed hydrogen on the N2 adsorption and N2 isotope displacement rate on Ru/MgO and Ru–Cs+/MgO were investigated by FTIR. The H2 was found to be adsorbed dissociatively on on-top sites [1880w(sh), 1801w(sh), and 1717s cm−1], bridging sites [1550w and 1330w cm−1], and threefold sites [1120m and 933m cm−1] on Ru/MgO, and similarly on three kinds of adsorption sites on Ru–Cs+/MgO. The bridging hydrogen on Ru/MgO was thermally more stable than the other two. Molecular N2 could be adsorbed as an on-top form on Ru. By the small amount of preadsorbed H(a) [H(a)/Rusurf = 14%], the N2 isotope displacement rate 15N2(a) → 14N2(a) in 14N2 on Ru/MgO was largely reduced to 12%, and the reduction on Ru–Cs+/MgO was more serious (to 4%). The main factors of these reductions were interpreted as direct repulsion of H(a) and N2 on Ru/MgO and Ru-hydride dipole effect enhanced by doped Cs+ on Ru–Cs+/MgO. The common factors in N2 displacement reaction and the catalysis from N2 are discussed in terms of the hydrogen effect.

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