The influence of H2S on surface segregation patterns in a polycrystalline Pd70Cu30 hydrogen separation membrane

COLL 504

James B. Miller, jbmiller@andrew.cmu.edu1, Christopher Matranga, matranga@netl.doe.gov2, Bryan D. Morreale, bryan.morreale@netl.doe.gov3, and Andrew J. Gellman, gellman@cmu.edu1. (1) Department of Chemical Engineering, Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, PA 15213, (2) National Energy Technology Laboratory, U. S. Department of Energy, P.O. Box 10940, Pittsburgh, PA 15236, (3) National Energy Technology Laboratory, United States Department of Energy, 626 Cochrans Mill Road, Pittsburgh, PA 15236
Palladium-based alloys have received significant attention as hydrogen purification membranes for gasification applications because of their ability to perform in hot, corrosive environments. Surface segregation—a composition difference between the bulk material and its surface—is common in alloys and can affect important surface properties. In this work, Low Energy Ion Scattering Spectroscopy (LEISS) and X-ray Photoelectron Spectroscopy (XPS) are used to examine the impact of adsorbed H2S on segregation patterns in a polycrystalline Pd70Cu30 separation membrane.

The clean alloy presents a top layer that is Cu-rich relative to the bulk, but an XPS-accessible near-surface region that is Cu-depleted. High temperature annealing causes the surface to undergo an order-disorder transition that is reflected in its interactions with both H2 and CO. Upon exposure to H2S, segregation patterns change significantly; Cu retreats from both the top layer and the near-surface, leaving a top layer that presents only Pd and S atoms.

 

Advanced Materials for Conversions and Separations in Energy Applications
8:30 AM-11:55 AM, Thursday, August 23, 2007 BCEC -- 153C, Oral

Division of Colloid & Surface Chemistry

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007