275231 Theoretical Investigation of the Three-Phase Boundary of Ceria (111) Supported Platinum Clusters for the Water-Gas Shift Reaction

Wednesday, October 31, 2012
Hall B (Convention Center )
Sara Aranifard, Salai C. Ammal and Andreas Heyden, Department of Chemical Engineering, University of South Carolina, Columbia, SC

This work is focused on the investigation of the water-gas shift (WGS) activity of the three-phase boundary (TPB) of Pt10 supported CeO2(111) model catalysts. We find that under WGS reaction conditions oxygen vacancies and vacancy clusters are thermodynamically stable while oxygen adatoms are not stable on the Pt cluster. Pt-atoms that are not in contact with the ceria surface are susceptible to be covered by CO molecules. These adsorbed CO molecules increase the hydrogen adsorption energy and decrease the CO adsorption energy at the Pt atoms at the TPB. At the same time, H atoms adsorb strongly on the ceria (111) surface. Presence of these H adatoms can considerably change the redox behavior of the ceria surface in a reducing environment by destabilizing the oxygen vacancy clusters at relatively low temperatures (400-700 K). However, presence of co-adsorbed CO molecules on the Pt cluster likely compensate for this destabilization effect. After these thermodynamic studies, we investigated different reaction pathways at the boundary sites of Pt10/CeO2(111) and developed a micro-kinetic model that permits comparing the turnover frequencies, apparent activation barriers, and reaction orders for the redox, associative carboxyl and carboxyl pathway with redox regeneration at various reaction conditions.

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