Helen Edström

Doctoral candidate

Lund University
Department of Physics
Synchrotron Radiation Research
Box 118, SE 221 00 Lund


Doctoral project

Alloy Systems in Catalytic Reactions

In this project, I look at the structural changes on the surfaces of model catalysts during oxidation reactions. I am particularly interested in so-called single atom alloy catalysts, consisting of single atoms of a catalytically active metal embedded in the surface of a more inert metal. The catalytic atoms will then form weaker bonds to the surrounding inert atoms, and thus stronger bonds to the adsorbates. However, for easier preparation, alloy single crystals are used to study the same effect in this project.

I am involved in a project about PtRh(100) with DESY. We performed CO oxidation over a Pt25Rh75(100) single crystal and investigated the structural surface changes with high-energy surface X-ray diffraction (HESXRD). Under oxidizing conditions, we found a couple of familiar structures, namely a (3×1) reconstruction with chemisorbed oxygen and a c(8×2) surface oxide. Under reducing conditions, however, we found a new structure, c(2×2). On both Pt(100) and Rh(100), CO adsorbs in this structure, so there are two alternatives for the occurrence of c(2×2) on PtRh(100): either it originates from CO adsorption, or the adsorbed CO molecules make the Pt and Rh atoms rearrange into an ordered alloy surface.

In collaboration with DESY, I will try to find out whether the observed c(2×2) structure indicates just CO adsorption or a CO induced ordered alloy surface. To do that, I will learn to perform a quantitative analysis of CTRs and surface rods visible in the X-ray diffraction images. That is my goal with the HELIOS project.