Correlating hydrogenation activity with binding energies of hydrogen and cyclohexene on M/Pt(111) (M = Fe, Co, Ni, Cu) bimetallic surfaces

This study used a combination of density functional theory (DFT) and temperature-programmed desorption (TPD) to determine trends in the hydrogenation activity of cyclohexene on several bimetallic surfaces prepared by modifying Pt(111) with 3d transition metals (Fe, Co, Ni, and Cu). The hydrogen binding energy (HBE) on the subsurface Pt-3d-Pt(111) “sandwich” structures was significantly lower than that on the corresponding 3d-Pt-Pt(111) surface structures and monometallic parent metal surfaces. The binding of cyclohexene on these surfaces followed the same trend as that of HBE. The weaker binding energies of atomic hydrogen and cyclohexene on Pt-3d-Pt(111) led to a novel low-temperature hydrogenation pathway that did not occur on either 3d-Pt-Pt(111) or the corresponding parent metal surfaces. Pt-Ni-Pt(111) had the highest hydrogenation activity among the surfaces studied, with 0.030 molecules of cyclohexene converted to cyclohexane per surface metal atom. This activity was maximized on the Pt-Ni-Pt(111) surface, which had an intermediate cyclohexene binding energy, leading to a volcano-type relationship between hydrogenation activity and cyclohexene binding energy.