AVS 56th International Symposium & Exhibition
    Surface Science Tuesday Sessions
       Session SS3-TuA

Paper SS3-TuA8
In Situ Study of Heterogeneous Catalysis on Oxide Support: CO Oxidation on Au/TiO2 Catalysts

Tuesday, November 10, 2009, 4:20 pm, Room N

Session: Catalysis: Mechanisms & Morphology
Presenter: S. Porsgaard, Lawrence Berkeley National Lab and University of Aarhus, Denmark
Authors: S. Porsgaard, Lawrence Berkeley National Lab and University of Aarhus, Denmark
P. Jiang, Lawrence Berkeley National Lab
F. Borondics, Lawrence Berkeley National Lab
M. Köber, Lawrence Berkeley National Lab
S. Wendt, University of Aarhus, Denmark
H. Bluhm, Lawrence Berkeley National Lab
F. Besenbacher, University of Aarhus, Denmark
M. Salmeron, Lawrence Berkeley National Lab
Correspondent: Click to Email
It has been known for more than a decade that the system of gold nanoparticles on a TiO2 support (Au/TiO2) is an active catalyst for a variety of reactions even below room temperature.[1] However, there is still little agreement on several important questions such as the role of the substrate, the charge state of gold, and the role of oxygen vacancies, even for the simplest reaction of CO oxidation.

In this study we focus on the questions related to the electronic band structure of the substrate. We chose a model system of evaporated Au nanoparticles on a rutile TiO2(110) single crystal substrate. The morphology of the evaporated Au nanoparticles were studied by STM, and it turned out to be strongly dependent on the pre-treatment of the TiO2 surface.[2]

For traditional surface science, the pressure gap between the studies in ultra high vacuum (UHV) and the industrial relevant reaction conditions is an important challenge. To overcome this problem, we have used in situ X-ray Photoelectron Spectroscopy (in situ XPS)[3] to study the evolution of the adsorbed chemical species and the electronic band structure of the rutile TiO2(110) during the individual steps in the reaction under pressures up to 1 Torr.

However, XPS on semiconductor substrates is challenging especially in the presence of gases. We have designed novel samples and test experiments to overcome these drawbacks. These results show that most in situ experiments on semiconductor substrates require extraordinary precautions. Now, we are able to avoid the newly discovered pitfalls, and we are able to present decisive results on the previously debated problems, e.g. the ongoing discussion about the charge state of gold and the role of oxygen vacancies.

[1] M. Haruta, S. Tsubota, T. Kobayashi, H. Kageyama, J.M. Genet , and B. Delmon, “Low-Temperature Oxidation of CO over Gold Supported on TiO2, α-Fe2O3, and Co3O4,” Journal of Catalysis, vol. 144, Nov. 1993, pp. 175-192.

[2] D. Matthey, J. Wang, S. Wendt, J. Matthiesen, R. Schaub, E. Laegsgaard, B. Hammer, and F. Besenbacher, “Enhanced bonding of gold nanoparticles on oxidized TiO2(110),” SCIENCE, vol. 315, Mar. 2007, pp. 1692-1696.

[3] D. Ogletree, H. Bluhm, G. Lebedev, C. Fadley, Z. Hussain, and M. Salmeron, “A differentially pumped electrostatic lens system for photoemission studies in the millibar range,” REVIEW OF SCIENTIFIC INSTRUMENTS, vol. 73, Nov. 2002, pp. 3872-3877.