Gas Phase Atomic Hydrogen-Induced Hydrogenation of Cyclohexene on the Ni(100) Surface

Abstract

Gas phase hydrogen atoms add to adsorbed cyclohexene at 100 K on the Ni(100) surface, resulting in cyclohexane formation during subsequent TPR (temperature-programmed reaction) experiments. No C-C bond activation is observed after exposure to gas phase atomic hydrogen. Vibrational and isotope studies indicate that a cyclohexyl intermediate is formed by the addition of gas phase atomic hydrogen to adsorbed cyclohexene. This adsorbed cyclohexyl is hydrogenated primarily by surface hydrogen to form cyclohexane during subsequent heating. Cyclohexane yields increase with increasing atomic hydrogen exposure, and yields in the 90% range have been observed with large atomic hydrogen exposures. In the presence of only coadsorbed hydrogen, no significant hydrogen addition to adsorbed cyclohexene is observed, and cyclohexene desorption dominates during subsequent TPR experiments. Vibrational spectroscopy indicates that π-bonded cyclohexene with the CdC bond parallel to the surface is the dominant surface species in the presence of coadsorbed surface hydrogen. In contrast, di-σ-bonded cyclohexene is the dominant species in the absence of coadsorbed hydrogen. In the absence of coadsorbed hydrogen, dehydrogenation of the adsorbed cyclohexene results in benzene formation with increasing temperature. Adsorbed benzene formed by dehydrogenation has been identified after heating to 390 K in the absence of hydrogen using vibrational spectroscopy.

Ni/Pt(111) Bimetallic Surfaces: Unique Chemistry at Monolayer Ni Coverage

“…From the TPD, HREELS, and NEXAFS results presented above, it is clear that the monolayer Ni/Pt(111) surface is characterized by chemical properties that are distinctly different from those of either Pt(111) or the thick Ni(111) film. Our results of the reaction pathways of cyclohexene on Pt(111) and thick Ni(111) film are consistent with previous studies on Pt 6,9-14,29,30 ,, and Ni; − ,, in the remainder of the discussion we will focus on the unique chemistry on the monolayer Ni/Pt(111) surface.…”

Reactivity of Ethyl Groups on a Sn/Pt(111) Surface Alloy

“…The estimated cross section for hydrogen addition to ethylene on Cu(111) was 18 Å 2 [29]. Gas-phase H-atoms have also been shown to react with di-r-bonded cyclohexene to produce adsorbed cyclohexyl species on Ni(100) [46], even though pbonded alkenes should have larger cross sections for radical addition reactions than di-r-bonded alkenes. These H-radical addition reactions occur through an Eley-Rideal mechanism [4] utilizing 218 kJ/mol of potential energy per mole of H-atoms to induce reactions.…”

Hydrogenation of Benzene on Ni(111)A DFT Study

“…Even though heterogeneous hydrogenation of benzene over supported and unsupported Ni catalysts has been well studied for some time, − fundamental aspects of the reaction kinetics are still unresolved. The reported activation energies range from 25 to 94 kJ mol -1 (0.26−0.97 eV); the reaction order with respect to benzene is given in a range from 0 to 0.5, with respect to the hydrogen partial pressure from 0.5 to 3 …”