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43980-G5
Atomically Resolved Reaction Dynamics Involving Catalytically Active, Surface Supported Clusters
A great deal of interest lies in uncovering active sites, rate limiting steps, and reaction intermediates for heterogeneously catalyzed processes as a function of surface morphology, electronic structure, and nanoscale effects such as confinement and quantization. The motivation behind such an approach is based on the insights gained from fundamental examinations of how surfaces, interfaces, and tailored thin films direct adsorbed molecule behavior and interadsorbate interactions en route to overlayer organization and reactivity. The focus of our project efforts is uncovering, through the use of high spatial resolution microscopy, nanoscale influences on heterogeneous catalytic activity for reactions associated with energy production and storage. These include efficacious routes to production of hydrogen as well as recycling of carbon dioxide for the synthesis of simple alcohols.
There are two key ways in which the funds from the ACS-Petroleum Research Foundation Type G award have been used to achieve project goals. The first has been to purchase key equipment, supplies, and materials for positioning experiments to be conducted in this next year. An electron beam evaporator for the controlled deposition of various metals on metallic oxides in ultra-high vacuum has been purchased and will be delivered in Fall 2007. This piece of equipment will be added to our existing UHV-STM system with possible use in our future UHV-STM/AFM which is currently under construction. Clusters of varying size of key catalytically active metals including Pt and Cu, from isolated adatoms to large, nanometer sized, multilayer facets, will be deposited onto catalytic supports such as graphite (0001) and metallic oxide thin films such as alumina and barium oxide. Single crystalline alloy samples like NiAl(110) and Ag(111) have likewise been acquired using this award. Summer support for the PI has been used during year 1 to support project goals as well as expand to other heterogeneous catalytic systems. Funds from this award have also been used to purchase chemical reagents and liquid cryogen for operating low and variable temperature scanning probe microscopes.
The second use of the funding for this project has been to leverage pursuit of further external support from the National Science Foundation and the Department of Energy. Both single investigator and multi-PI proposals have been submitted over the past year to continue work on selective and tuned catalytic interfaces. Of particular note is the burgeoning collaboration with a computational group at NCSU led by Marco Buongiorno Nardelli. Preliminary calculations suggest utilizing low dimensional materials for selective catalysis, where the role of size and surface defect type and composition is significant in the catalytic production of hydrogen via the dissociation of water as well as methanol production from carbon dioxide.
Hydrogen production is clearly a targeted energy resource area, and exploration of efficient, low barrier routes especially using an abundant precursor such as water are extraordinarly critical. High resolution microscopy and spectroscopy experiments involving the dissociation of water over graphite for hydrogen synthesis are currently slated in our group. We will attempt to uncover the key active sites on the surfaces of both planar graphene as well as curved surfaces such as carbon based nanotubes.
With the use of high performance simulations and predictions in concert with scanning tunneling microscopy we are additionally focusing on avenues of promoting the adsorption and subsequent cracking of carbon dioxide over nanostructured and electronically tuned metal catalysts. Specifically, heterogeneous catalysis for methanol synthesis from carbon dioxide hydrogenation will be studied as a function of the reactivity for single copper and platinum adatoms and islands grown on a metallic oxide such as barium oxide grown on Ag(111). The properties of a thin metal films, metal clusters, and atomic chains have substantially different electronic and therefore chemical bonding attributes compared to their bulk counterpart. As a means of tuning the available electronic density of states at the catalytically active surface, we will proceed to the study of full copper and platinum layers grown on a ferroelectric crystal, e.g. strontium titanate grown on Ag(111). In both of these cases, initial calculations that are presented in this proposal have shown that the sticking probability and therefore cross section for dissociation of carbon dioxide is greatly enhanced. Modeling of novel materials for environmentally relevant remediation and recycling reactions, in this case the management of carbon dioxide, will serve to promote the development of functional catalytic surfaces and interfaces.
Our group focuses on the use of low temperature STM and AFM and we believe that the next period of activity will push the frontier in the exploration of nanoscale behavior with dividends that impact the development of new generations of selective, efficient heterogeneous catalytic systems as well as other chemically selective materials. A deeper understanding of the native properties of these complex surfaces has far reaching implications in the advancement of tailoring selective surfaces for driving surface chemical reactions with high efficiency and specificity.
