Molecular oxygen adsorbates at a Au/Ni(111) surface alloy and their role in catalytic CO oxidation at 70 - 250 K

Oxygen is observed to adsorb molecularly on 0.13 - 0.27 ML Au/Ni(1 111) surface alloys at 77 K, in stark contrast to dissociative adsorption on Ni and no adsorption on Au surfaces. Molecular 02 adsorbates on the Au/Ni(111) surface alloy are identified by their 0=0 vibrational modes at 790, 850 and 950 cm-', measured by electron energy loss spectroscopy. Possible Ni adsorption sites for the three types of molecularly adsorbed 02 are proposed. The dramatic change in Ni reactivity occurs within a narrow Au coverage range around 0.13 ML Au and arises from poorer overlap between the Ni d-band and the 02 LUMO as the Ni d-band shifts to lower energy with increasing Au content of the Au/Ni surface alloy. The amount of molecular adsorption as a function of Au coverage cannot be described by an analytical or simulated model based on Au atom proximity to Ni sites, suggesting the role of cooperative effects in 02 stabilization. Adsorbed molecular 02 dissociates between 110 to 150 K. No oxygen desorbs. At Au coverages greater than 0.27 ML, the energy of the Ni d-band is shifted sufficiently low to destabilize oxygen adsorption.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2006

Author dc:creator

• Lahr, David Louis

Advisor dc:contributor.advisor

• Sylvia T. Ceyer.

• Chemistry.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/36250

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/36250