Hydrogen Dissociation on Pd₄ S Surfaces

Journal Article · Thu Oct 29 04:00:00 EDT 2009 · Journal of Physical Chemistry. C

DOI:https://doi.org/10.1021/jp906694k· OSTI ID:1015126

Miller, James B. ^[1]; Alfonso, Dominic R. ^[1]; Howard, Bret H. ^[1]; O’Brien, Casey P. ^[1]; Morreale, Bryan D. ^[1]

---

1. National Energy Technology Lab. (NETL), Pittsburgh, PA, (United States)

Exposure of Pd-based hydrogen purification membranes to H₂S, a common contaminant in coal gasification streams, can cause membrane performance to deteriorate, either by deactivating surface sites required for dissociative H₂ adsorption or by forming a low-permeability sulfide scale. In this work, the composition, structure, and catalytic activity of Pd₄S, a surface scale commonly observed in Pd-membrane separation of hydrogen from sulfur-containing gas streams, were examined using a combination of experimental characterization and density functional theory (DFT) calculations. A Pd₄S sample was prepared by exposing a 100 μm Pd foil to H₂S at 908 K. Both X-ray photoemission depth profiling and low energy ion scattering spectroscopic (LEISS) analysis reveal slight sulfur-enrichment of the top surface of the sample. This view is consistent with the predictions of DFT atomistic thermodynamic calculations, which identified S-terminated Pd4S surfaces as energetically favored over corresponding Pd-terminated surfaces. Activation barriers for H₂ dissociation on the Pd₄S surfaces were calculated. Although barriers are higher than on Pd(111), transition state theory analysis identified reaction pathways on the S-terminated surfaces for which hydrogen dissociation rates are high enough to sustain the separation process at conditions relevant to gasification applications.

• Research Organization: National Energy Technology Laboratory (NETL), Pittsburgh, PA, Morgantown, WV, and Albany, OR (United States)
• Sponsoring Organization: USDOE Assistant Secretary for Fossil Energy (FE)
• OSTI ID: 1015126
• Report Number(s): NETL-TPR--2637
• Journal Information: Journal of Physical Chemistry. C, Journal Name: Journal of Physical Chemistry. C Journal Issue: 43 Vol. 113; ISSN 1932-7447
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
96 KNOWLEDGE MANAGEMENT AND PRESERVATION
99 GENERAL AND MISCELLANEOUS