AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM2
Suppression of NO Dissociation by Adsorbed Gold on Pt(335)

Wednesday, October 4, 2000, 8:40 am, Room 208

Session: Chemical Interactions and Surface Reactivity
Presenter: D.C. Skelton, Michigan State University / General Motors
Authors: D.C. Skelton, Michigan State University / General Motors
R.G. Tobin, Tufts University
C.L. DiMaggio, Delphi Automotive Research Labs
D.K. Lambert, Delphi Automotive Research Labs
G.B. Fisher, Delphi Automotive Research Labs
Correspondent: Click to Email
We have conducted a temperature programmed desorption study to compare the dissociation probabilities of oxygen and NO on a partially gold-covered stepped Pt(335) surface. NO dissociation takes place almost exclusively at step sites. It apparently requires either multiple adjacent open step sites, or special sites such as kinks, and is therefore unusually sensitive to modification of steps and defects. A gold coverage of 0.15 ML reduces NO dissociation by a factor of five compared to bare Pt, and increasing the gold coverage to 0.3 ML further reduces it to an undetectable level. Oxygen dissociation also occurs preferentially at step sites, but is far less sensitive to step blockage: At 0.3 ML gold, the saturation oxygen coverage is only 20% lower than on bare Pt. These results help explain the operation of a recently developed electrochemical NO@sub x@ sensor.@footnote 1@ An effective NO@sub x@ sensor is vital for pollution control in fuel-efficient lean-burn gasoline and diesel engines. The electrochemical sensor uses a platinum-gold alloy electrode in a pumping cell to remove oxygen from the exhaust gas without dissociating NO. For effective sensor operation, the electrode must be ~10@super 3@ more effective at dissociating oxygen than at dissociating NO. Our experiments suggest that a platinum-gold alloy electrode has this remarkable selectivity because gold blocks special sites that are needed for NO dissociation but not for oxygen dissociation. @FootnoteText@ @footnote 1@ N. Kato, Y. Hamada and H. Kurachi, SAE Paper 970858 (1997).