(337b) Reforming of Oxygenates for H2 Production: Reactivity of Ethylene Glycol and Ethanol on 3d-Pt(111) Bimetallic Surfaces

Production of hydrogen for use in fuel cells can be achieved by selective reforming of oxygenates. The oxygenates may be derived from renewable biomass and offer advantages such as low toxicity, low reactivity and compatibility with the current infrastructure for transportation and storage. Platinum has been identified as one of the most promising catalysts for the reforming of oxygenates[1]. Nickel catalysts have shown high activity, but also displayed decreased hydrogen selectivity[1]. In this study[2], the reactions of oxygenates, such as ethylene glycol and ethanol, were investigated on 3d-Pt(111) bimetallic surfaces using temperature-programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), and Density Functional Theory calculations (DFT). The formation of bimetallic surfaces often alters the physical and chemical properties of the parent metals, in some cases producing novel catalytic properties not seen for either of the parent metals[3,4]. The bimetallic surfaces in this work were prepared by physical vapor deposition (PVD) of the desired second metal onto Pt(111), using Auger electron spectroscopy (AES) to monitor surface compositions. Ethylene glycol reacted via dehydrogenation to form CO and H2, corresponding to the desired reforming reaction, and via total decomposition to produce C(ad), O(ad), and H2. Ethanol reacted by three reaction pathways, dehydrogenation, decarbonylation, and total decomposition, producing H2, CO, CH4, C(ad), and O(ad). Surfaces prepared by deposition of a monolayer of Ni on Pt(111) at 300 K, designated as Ni-Pt-Pt(111), displayed increased reforming activity compared to Pt(111), subsurface monolayer Pt-Ni-Pt(111), and thick Ni/Pt(111). The experimentally measured reforming activity was correlated with the d-band center of the surfaces from DFT and displayed a linear trend for both ethylene glycol and ethanol. The reforming activity increased as the surface d-band center moved closer to the Fermi level, opposite to the trend previously observed for hydrogenation reactions. DFT was also used to determine the binding energy of ethanol on 3d-Pt-Pt(111) bimetallic surfaces with other 3d metals as the surface monolayer. The modeling results indicate that the binding energy should increase as the d-band center of the bimetallic surface moves closer to the Fermi level, which can be achieved by choosing 3d metals from the left side of the periodic table as the surface monolayer. Further studies are underway to investigate oxygenate reforming on other 3d-Pt-Pt(111) bimetallic surfaces.

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