Digging into the Mechanism for Carbon Monoxide Catalysis

27 March 2006

Researchers from the Chinese Academy of Sciences (CAS) have worked with scientists from The Queen’s University of Belfast to explore the process of carbon monoxide (CO) oxidation in an effort to further reduce tailpipe emissions.

In a study published online in the Journal of the American Chemical Society, the researchers found that a composite material composed of gold and titanium oxides can trigger the catalytic reaction at an indoor temperature and that water plays a special role in maintaining the reaction to the end.

Using density functional theory, the researchers found that:

• Water that can dissociate readily into OH groups can facilitate O₂ adsorption on TiO₂;

• the effect of OH group on the O₂ adsorption is surprisingly long-ranged;

• O₂ can also diffuse along the channel of Ti (5c) atoms on TiO₂(110), and this may well be the rate-limiting step for the CO oxidation.

The team found direct evidence that O₂ is supplied by O₂ adsorption on TiO₂ in the presence of OH and can diffuse to the interface of Au/TiO₂ to participate in CO oxidation.

Furthermore, they identified the physical origin of the water effects on Au (gold) catalysis electronic structure analyses: there is a charge transfer from TiO₂ in the presence of OH to O₂, and the O₂ adsorption energy depends linearly on the O₂ charge.

The transfer of oxygen molecules and water’s constructive role are thus closely related to one another. The water is dissociated to OH and enables the TiO₂ surface to absorb oxygen molecules while O₂ is able to diffuse freely on the surface.

The research was supported by China’s National 973 Program and the CAS Foundation for Studying Abroad.

Resources:

• “Identifying an O₂Supply Pathway in CO Oxidation on Au/TiO₂(110): A Density Functional Theory Study on the Intrinsic Role of Water”; L. M. Liu, B. McAllister, H. Q. Ye, and P. Hu; J. Am. Chem. Soc., 128 (12), 4017 -4022, 2006. 10.1021/ja056801p S0002-7863(05)06801-0