Two-Photon Photoemission Spectroscopy Study of 1,3-Butadiene on Cu(111):  Electronic Structures and Excitation Mechanism

Abstract

The characteristics of 1,3-butadiene (C(4)H(6)) adsorbed on Cu(111) were investigated with temperature-programmed desorption (TPD) and two-photon photoemission spectroscopy (2PPE). Dosed at 90 K, the work function drops by 0.4 eV and TPD provides no evidence for dissociation, but there are four coverage-dependent local maxima located at 195, 135, 121, and 115 K. From the 2PPE spectra, three unoccupied electronic states of the C(4)H(6)-Cu(111) system were identified: the LUMO (pi(1)*, 2a(u)), LUMO + 1 (pi(2)*, 2b(g)), and LUMO + 2 (sigma*, 7b(u)), lying 1.3, 3.4, and 4.8 eV above the Fermi level, respectively. Although the excitation mechanisms for the LUMO and LUMO + 1 are substrate mediated, the excitation of the LUMO + 2 is attributed to intramolecular excitation.

Carbon-Supported Copper for Gas-Phase Hydrogenation Catalysis

“…A possible cause for the activity onset above 100 °C is the recovery of the metallic Cu surface under reaction conditions. [256][257][258][259][260] The presence of trace amounts of O2 (~50 ppm) in the reaction gas mixture may lead to Cu surface oxidation and catalyst inactivity. 217,237,261 We compared the activity during two consecutive heating ramps for the 7_Cu/C catalyst, either after in situ H2 reduction or after N2 pretreatment (Figure 6.…”