Ethanol and ethylene glycol on Ni/Pt(1 1 1) bimetallic surfaces: A DFT and HREELS study

Abstract

The reactions of ethanol and ethylene glycol have been studied on Ni/Pt(1 1 1) 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(1 1 1) 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(1 1 1) designated Ni–Pt–Pt(1 1 1), and the other with the Ni atoms diffusing into the subsurface region, designated Pt–Ni–Pt(1 1 1). At 120 K ethanol adsorbs molecularly with the O–H bond intact on Pt(1 1 1) and Pt–Ni–Pt(1 1 1), while dissociative adsorption is observed on Ni–Pt–Pt(1 1 1) and Ni(1 1 1) film surfaces. Ethylene glycol adsorbs molecularly with the O–H bond intact on all four surfaces at 200 K, and desorbs reversibly from Pt(1 1 1) and Pt–Ni–Pt(1 1 1). In contrast, ethylene glycol undergoes decomposition on Ni–Pt–Pt(1 1 1) and Ni(1 1 1) film surfaces through O–H bond cleavage, forming an ethylenedioxy (–OCH 2CH 2O–) 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(1 1 1) > Ni(1 1 1) film > Pt(1 1 1) > Pt–Ni–Pt(1 1 1).