This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
Intellectual Merit - For heterogeneously catalyzed reactions with more than one key surface intermediate, it is likely that multiphase catalysts have a significant advantage over conventional monophase catalysts since each phase can potentially be adjusted independently to activate a key reaction step. At the same time, understanding of bifunctional multiphase systems is relatively poor. It is the objective of this proposed research program to significantly enhance molecular understanding of heterogeneous catalysis at the three-phase boundary (TPB) of a gas-phase, a reducible oxide surface, and a noble metal cluster. To enable this theoretical investigation of chemical reactions at the TPB, the PI and his students propose to develop and validate a highly efficient and accurate computational strategy for these systems. It is their firm belief that only with a more accurate computational multiscale strategy that permits the reliable investigation of reactions on strongly correlated reducible oxide surfaces and metal clusters, will it be possible to truly understand the nature of the active sites, the origin of catalytic activity, and the reaction mechanism at the TPB under reaction conditions. As a model system for computational study, they intend to investigate the water-gas-shift (WGS) reaction on titania and ceria supported mono- and bimetallic clusters of Au, Pt, and Pd. Their computational strategy and study of the nature of the active site at the TPB is not limited to the WGS reaction but is likely more general as it has been shown that reducible oxide supported noble metals are highly active for various reactions such as the selective hydrogenation and oxidation of unsaturated hydrocarbons. Their computational strategy involves state-of-the-art periodic slab calculations to build and validate a periodic electrostatic embedded cluster model that is used for the study of various reaction pathways. Unlike periodic slab models, the periodic cluster model permits the use of modern doublehybrid density functionals with significantly improved accuracy for modeling chemical reactions on reducible oxide surfaces and metal clusters. Having determined reasonably accurate reaction energies and barriers, they intend to develop a microkinetic reactor model based on data obtained only from first principles and absolute rate theory. With the help of the microkinetic model, they will be able to study the effect of temperature and chemical potential of the gas phase on the reaction mechanism and key reaction intermediates. Furthermore, they will be able to determine the origin of the activity of the active sites by analyzing how the electronic structure is altered with changes in noble metal cluster and reducible oxide and by using Nørskov's method to distinguish electronic effects from geometric or structural effects. Finally, it is noted that the computational models and methods outlined in this proposal have not been used previously in the study of heterogeneous catalysis and collaboration with experimentalists such as Dr. Amiridis and Dr. Chen at USC is proposed to validate and test the computational predictions.
Broader Impact, Science - The development of a more accurate computational strategy for studying reactions at the TPB of a gas-phase, a reducible oxide surface, and a noble metal cluster will significantly increase the reliability of theoretical investigations of these surprisingly catalytically active systems that are computationally very difficult to describe. Furthermore, understanding of the origin of the unique catalytic activity of these systems will likely aid the development of improved catalysts for various reactions that can be selectively activated by oxide supported noble metals.
Broader Impact, Education - The graduate and undergraduate students directly involved in the proposed research will be exposed to a comprehensive set of theoretical tools that will allow them to study most issues in catalysis and material science. In addition, the results of the proposed research will be integrated in a joint graduate and undergraduate course "Multiscale Modeling: From Electrons to Chemical Reactors" that is currently being developed by the PI.
Community Outreach - The graduate student involved in this research will spend one Fall semester in the Partners in Inquiry program at USC. She will assist a science teacher from a local middle school (82% African American or Hispanic origin) to integrate engineering and science content (including her research) and problem solving methods into the science curriculum. Finally, the PI is involved in the Enhanced Learning Experience (ELE) program at USC, in which high school students interested in chemical engineering are given a one day hands-on learning experience.
