(670b) Investigation of Surface Reaction Dynamics Using Imaging Ellipsometry

Ellipsomicroscopy for surface imaging (EMSI) is an optical based technique where image contrast is derived from local differences in the optical properties of the surface system. In heterogeneous catalytic systems, such variations are due to the presence of different adsorbates on the surface, making EMSI a valuable tool for the study of catalytic systems in real-time at arbitrary pressures. In this work, we employ EMSI to investigate dynamic behavior in both the CO oxidation reaction as well as the reduction of NO with ammonia on single and polycrystalline Pt surfaces. In both cases, EMSI allowed for the detection of spatio-temporal adsorbate patterns spontaneously formed due to reaction and diffusion of adsorbates. Also, because EMSI is operated at the Brewster angle, allowing for direct access to the catalyst surface, we have been able to go beyond the observation of patterning to selectively initiating dynamic behavior by locally dosing reactant onto the catalytic surface. Under these unique conditions, EMSI provided critical insight into the stability of reaction wave fronts and reaction induced surface memory effects. Collectively, these results have enhanced our understanding of the fundamental processes occurring on the surface of heterogeneous catalysts.