Ethanol and ethylene glycol on Ni/Pt(111) bimetallic surfaces: A DFT and HREELS study

The reactions of ethanol and ethylene glycol have been studied on Ni/Pt(111) bimetallic surfaces using density functional theory (DFT) and high resolution electron energy loss spectroscopy (HREELS). A linear correlation has been observed between the binding energies of ethanol, ethoxy, and ethylene glycol species and the surface d-band center, with increasing binding energy as the d-band center shifts closer to the Fermi level. HREELS measurements have identified the bond scission sequence of ethanol and ethylene glycol on Ni/Pt(111) bimetallic surfaces. Two bimetallic surfaces can be formed that possess very different chemical properties: one with a monolayer of Ni atoms on top of Pt(111) designated Ni-PtPt(111), and the other with the Ni atoms diffusing into the subsurface region, designated Pt-Ni-Pt(111). At 120 K ethanol adsorbs molecularly with the O-H bond intact on Pt(111) and Pt-NiPt(111), while dissociative adsorption is observed on Ni-Pt-Pt(111) and Ni(111) film surfaces. Ethylene glycol adsorbs molecularly with the O-H bond intact on all four surfaces at 200 K, and desorbs reversibly from Pt(111) and Pt-Ni-Pt(111). In contrast, ethylene glycol undergoes decomposition on Ni-PtPt(111) and Ni(111) film surfaces through O-H bond cleavage, forming an ethylenedioxy (-OCH2CH2O-) intermediate. This intermediate reacts by further dehydrogenation and C-C bond scission to eventually form CO. Overall, the HREELS results are consistent with TPD studies that show the reforming activities of ethanol and ethylene glycol follow the trend Ni-Pt-Pt(111) > Ni(111) film > Pt(111) > Pt-Ni-Pt(111). (C) 2008 Elsevier B.V. All rights reserved.