Methane activation by cobalt cluster cations, Co-n(+) (n=2-16): Reaction mechanisms and thermochemistry of cluster-CHx (x=0-3) complexes

Citir M., Liu F., Armentrout P. B.

JOURNAL OF CHEMICAL PHYSICS, cilt.130, sa.5, 2009 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 130 Sayı: 5
  • Basım Tarihi: 2009
  • Doi Numarası: 10.1063/1.3073886
  • Dergi Adı: JOURNAL OF CHEMICAL PHYSICS
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Abdullah Gül Üniversitesi Adresli: Hayır

Özet

The kinetic energy dependences of the reactions of Co-n(+) (n=2-16) with CD4 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0-10 eV. The main products are hydride formation, ConD+, dehydrogenation to form ConCD2+, and double dehydrogenation yielding ConC+. These primary products decompose to form secondary and higher order products, ConCD+, Con-1D+, Con-1C+, Con-1CD+, and Con-1CD2+ at higher energies. Adduct formation of ConCD4+ is also observed for the largest cluster cations, n >= 10. In general, the efficiencies of the single and double dehydrogenation processes increase with cluster size, although the hexamer cation shows a reduced reactivity compared to its neighbors. All reactions exhibit thresholds, and cross sections for the various primary and secondary reactions are analyzed to yield reaction thresholds from which bond energies for cobalt cluster cations to D, C, CD, CD2, and CD3 are determined. The relative magnitudes of these bond energies are consistent with simple bond order considerations. Bond energies for larger clusters rapidly reach relatively constant values, which are used to estimate the chemisorption energies of the C, CD, CD2, and CD3 molecular fragments to cobalt surfaces.

The kinetic energy dependences of the reactions of Co+nCon (n=2–16)n216 with CD4CD4 are studied in a guided ion beam tandem mass spectrometer over the energy range of 0–10 eV. The main products are hydride formation,ConD+ConD, dehydrogenation to form ConCD+2ConCD2, and double dehydrogenation yielding ConC+ConC. These primary products decompose to form secondary and higher order products, ConCD+ConCD, Con−1D+Con1D, Con−1C+Con1C, Con−1CD+Con1CD, and Con−1CD+2Con1CD2 at higher energies. Adduct formation of ConCD+4ConCD4 is also observed for the largest cluster cations, n≥10n10. In general, the efficiencies of the single and double dehydrogenation processes increase with cluster size, although the hexamer cation shows a reduced reactivity compared to its neighbors. All reactions exhibit thresholds, and cross sections for the various primary and secondary reactions are analyzed to yield reaction thresholds from which bond energies for cobalt cluster cations to D, C, CD, CD2CD2, and CD3CD3 are determined. The relative magnitudes of these bond energies are consistent with simple bond order considerations. Bond energies for larger clusters rapidly reach relatively constant values, which are used to estimate the chemisorption energies of the C, CD, CD2CD2, and CD3CD3 molecular fragments to cobalt surfaces.