Reforming of Oxygenates for H₂ Production:  Correlating Reactivity of Ethylene Glycol and Ethanol on Pt(111) and Ni/Pt(111) with Surface d-Band Center

Abstract

The dehydrogenation and decarbonylation of ethylene glycol and ethanol were studied using temperature programmed desorption (TPD) on Pt(111) and Ni/Pt(111) bimetallic surfaces, as probe reactions for the reforming of oxygenates for the production of H2 for fuel cells. 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 CO, H2, CH4, C(ad), and O(ad). Surfaces prepared by deposition of a monolayer of Ni on Pt(111) at 300 K, designated Ni-Pt-Pt(111), displayed increased reforming activity compared to Pt(111), subsurface monolayer Pt-Ni-Pt(111), and thick Ni/Pt(111). Reforming activity was correlated with the d-band center of the surfaces and displayed a linear trend for both ethylene glycol and ethanol, with activity increasing as the surface d-band center moved closer to the Fermi level. This trend was opposite to that previously observed for hydrogenation reactions, where increased activity occurred on subsurface monolayers as the d-band center shifted away from the Fermi level. Extrapolation of the correlation between activity and the surface d-band center of bimetallic systems may provide useful predictions for the selection and rational design of bimetallic catalysts for the reforming of oxygenates.

Enhancing H2 and CO Production from Glycerol Using Bimetallic Surfaces

“…The TPD results obtained for glycerol were similar to previous experiments using ethylene glycol [7] and ethanol. [7] [a] O.…”

“…The objective of these experiments was to determine whether the chemistry of glycerol is sufficiently similar to that of smaller oxygenates to validate the use of smaller molecules as models in catalysis and surface science studies. We have previously investigated the reactivity of ethylene glycol, [7] ethanol, [7] and methanol [8] on Ni/PtA C H T U N G T R E N N U N G (111) bimetallic surfaces. These studies demonstrated that surfaces with a Ni monolayer on top of PtA C H T U N G T R E N N U N G (111), designated as Ni-Pt-PtA C H T U N G T R E N N U N G (111), display increased reforming activity as compared to either an unmodified PtA C H T U N G T R E N N U N G (111) surface or a PtA C H T U N G T R E N N U N G (111) surface containing a subsurface Ni monolayer, designated as Pt-Ni-PtA C H T U N G T R E N N U N G (111).…”

“…[7] [a] O. Skoplyak Figure 2 shows the H 2 and CO TPD spectra for these oxygenates on Ni-Pt-PtA C H T U N G T R E N N U N G (111), the surface with the highest reforming activity.…”

“…The TPD results were quantified by using a similar procedure to that described previously for other oxygenates. [7,8] The peak areas were converted into units of monolayers (ML) by calibration of saturation H 2 and CO coverages against literature values for PtA C H T U N G T R E N N U N G (111) [13,14] (0.45 ML H 2 and 0.68 ML CO). Blank experiments were carried out to determine the contributions from H 2 and CO adsorbed from the UHV background, and the final product yields were obtained by subtracting the contributions attributed to adsorption of these molecules from the chamber background.…”

“…[15] The surface d band center was calculated previously using DFT. [7] NiPt-PtA C H T U N G T R E N N U N G (111) displayed an increased reforming yield as compared to PtA C H T U N G T R E N N U N G (111), while Pt-Ni-PtA C H T U N G T R E N N U N G (111) exhibited a decreased reforming yield. The reactivity trend of glycerol on Ni/PtA C H T U N G T R E N N U N G (111) bimetallic surfaces was similar to previous results for ethylene glycol and ethanol, [7,8] with increasing reforming yield as the surface d band center shifts closer to the Fermi level.…”