| Abstract
| - The size and shape of pores is a key factor in the successful deployment of mesoporous silicas as supportsfor high-activity catalytic nanoparticles. Critical concerns are the accessibility of catalyst particles to reactantspecies, the effect of the particle−support interaction on catalytic activity, and the stability of the systemwith respect to degradation or sintering. In the present work, high-angle annular dark field scanning transmissionelectron microscopy (HAADF−STEM) tomography has provided quantitative three-dimensional informationabout the location of bimetallic nanoparticles supported on and within disordered mesoporous silica (GraceDavison 634-type). The surface of the pore network was found to be fractal in nature (fractal dimension Ds∼ 2.4) with implications for the selectivity of the catalyst−support system. By measuring the location ofcatalyst particles as a function of the local curvature of the support, particle adsorption sites were classified.The distribution of nanoparticles within the interior of the support showed preferential adsorption on anticlastic(“saddle-shaped”) surfaces, whereas nanoparticles adsorbed on the exterior surfaces of the support structurealso demonstrated a strong preference for concave (“cup-like”) regions. These results highlight the criticalimportance of three-dimensional characterization for quantitative evaluation of porous media and catalyticsupports.
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