Center for Functional Nanomaterials Seminar
"Surface Chemistry over Model Catalysts: from the Atomic-Scale under UHV"
Presented by Ashleigh Baber
Thursday, March 29, 2012, 10:00 am — CFN, Building 735, conf. rm. B
Using model catalysts, we have studied the fundamentals of surface and adsorbate structure and identity. Bimetallic alloys play a central role in a wide variety of industrial catalytic reactions. Scanning tunneling microscopy (STM) was used to investigate the atomic-scale electronic and geometric structure of Pd/Au(111) and Pd/Cu(111) bimetallic model catalysts, as well as their interaction with hydrogen, a vital component in alcohol synthesis and water-gas shift reactions. We demonstrate that individual, isolated Pd atoms in an inert Cu matrix are active for the dissociation of hydrogen and subsequent spillover onto Cu sites, but no H was found under the same H2 flux on a Pd/Au samples with identical atomic composition and geometry. In the case of Au, larger ensembles of Pd were required to activate H2 dissociation.1 These results demonstrate the powerful effect of the substrate on the catalytic activation of Pd atoms supported within or on its surface.2 Hydrogen, along with carbon monoxide, is used in the catalytic production of methanol. Fundamentally, methanol represents the simplest alcohol for understanding hydrogen-bonded networks. STM was used to investigate the stability and structure of methanol3 and formic acid on model systems. Similarly, formic acid has great importance for its use as a liquid fuel in direct formic acid fuel cells, and formates are considered important intermediates in several key catalytic reactions including the water-gas shift, alcohol synthesis and decomposition, and the hydrogenation of oxygenates. To obtain a full picture of the morphological and chemical changes during model catalytic studies, X-ray photoelectron spectroscopy (XPS) experiments, from UHV to near-ambient pressure (NAP) conditions, are presented to provide insight into the correlation between adsorbate identity and model catalysts structure.
Hosted by: Peter Sutter
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