Studies on Hydrogenation of Ni/C with PES and Molecular Beam Techniques

Formation of hydrocarbon out of CO and H₂ is one of the most frequently studied reaction systems in catalysis. But in our experiments, the dissociative chemisorption of CO was modelled prior to the reaction by preparing a deposit of reactive carbon on and in the Ni（poly） foil, where the Ni/C specimen was exposed to a molecular beam of H₂. A photoelectron spectroscopic in-situ analysis of kinetic surface intermediates of the hydrogenation of carbon on Ni（poly） foil was given by spectra taken during the running reaction in the temperature range from 90 to 575 K. Thermal desorption spectra of H₂ and CH₄were also observed in that temperature range. These experiments were proceeded in an UHV apparatus with molecular beam sources and various electron spectroscopies.
It was shown by experiments that of hydrogenation processes in forming CH₄, the forma tion of CH₂ out of CH is the slowest reaction while the generation of CH is the fastest reaction. Hence, formation of C₂H_x, and longer hydrocarbon chains as well starts by dimerization of CH. The barrier between CH and CH₂ is understood by consideration of the orbital hybridization ofthe adsorbed C₁ groups. The energies are dipicted by the electron binding energies of C 1s electron: the most significant difference is the one between CH and CH₂. It is also shown that the essential role of C as a co-catalyst which is able to chemisorb and to transfer H at temperature well above the desorption temperature of H from clean Ni is established.