Proposal Title: NIRT: Tuning the Electronic and Molecular Structures of Catalytic Active Sites with Oxide Nanoligand
Proposal Number: CTS-0609018
Principal Investigator: Israel E. Wachs
Institution: Lehigh University
Analysis (rationale for decision):
This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 05-610, category NIRT. Heterogeneous catalysts are solid substances that accelerate chemical reactions at the surface, whereby the nanoscale and chemical features of the surface affect the activity, selectivity, and longevity of the catalyst. Nanoscale engineering of the catalyst offers tremendous potential for understanding more deeply the nature of the catalytic active surface site, and offers the opportunity to improve catalyst performance in environmental, energy, petrochemical, pharmaceutical and food industries, and more recently in homeland security. This proposal specifically describes a four-year research and teaching plan focused on tailoring the electronic and molecular structures of oxide nanoligands and their resulting impact on the catalytic performance of molecularly engineered supported metal oxide catalytic active sites.
This project will systematically examine the influence of the oxide substrate nanostructure in the critical 0.5-10 nm range for the catalytic active metal oxide-support interaction upon the resultant electronic structures, molecular structures and catalytic properties. A series of model supported catalysts will be molecularly engineered to allow for variation of the catalytic active sites and oxide nanoligands. The nanoligand dimension, electronic structure, molecular structure, composition (CeO2, TiO2, ZrO2, and their mixtures) and the catalytic active sites (acidic WOx, basic BaOx, redox VOx, and their mixtures) will be controlled to tune the catalytic activity/selectivity. These nano-supported catalysts will be synthesized in vivo within inert amorphous siliceous matrices to control the oxide nanoligand domain size and its distribution. These novel catalytic materials will be electronically, molecularly, and chemically characterized with the most advanced state-of-the-art molecular level in situ microscopic and spectroscopic techniques currently available, and under different reaction conditions, to determine their fundamental electronic/molecular structure-activity/selectivity relationships. These new insights will be employed to develop molecular level models that capture the influence of oxide nanoligand electronic and molecular characteristics on chemical properties of catalytic active sites anchored on such nanoligand substrates. The theoretical models will subsequently be used to guide the molecular design of advanced supported catalytic materials by tuning the electronic and molecular structures of catalytic active sites with the oxide nanoligands for several challenging catalytic applications of current industrial interest.
This fundamental information will allow the establishment of molecular level relationships between oxide nanoligand domain size and supported catalytic active site electronic and molecular structures for a range of important catalytic reactions. These molecular level relationships will lead to the development of new theoretical models for nano and conventional supported catalysts, as well as non-catalytic materials applications, of such multicomponent designed materials. The new insights will assist in the molecular design of 'next generation' supported catalysts where the oxide support nanoligand domain size is a critical factor in tailoring physical and chemical properties of supported catalytic active sites. The educational and outreach programs include undergraduate and graduate student training, high school teacher training, an annual site-rotating workshop, and state-of-the-art microscopy and spectroscopy schools. An industrial partner, BP, has agreed to pursue commercialization of promising advanced catalytic materials that will be discovered in the course of this research program.
The production of gasoline, chemicals, medicine, and plastics comes from a chemical process called catalysis. Catalysis involves the use of a nanostructured material that causes chemical reactions to happen that do not otherwise happen. In this Project, a new concept in catalysis was hypothesized and carefully scrutinized experimentally and computationally by focusing on two supported metal oxide catalysts: VOx/TiO2/SiO2 and WOx/TiO2/SiO2 in which the TiO2 active phase supported VOx (redox sites) and WOx (acid sites) molecular species; and WOx/ZrO2, in which the WOx acidity was controlled by its molecular/nano structure. For the former material, it was shown that the activity of VOx and WOx species could be controlled by the size of the TiO2 phase due to electronic delocalization via a quantum confinement effect. For WOx/ZrO2, electron microscopy images showed for the first time the presence of Zr-stabilized, ~1-nm WOx nanocrystals that were highly active to methanol oxidation and to the acid-demanding reaction of pentane isomerization. These basic research findings provide new, groundbreaking information on how current supported metal oxide catalysts can be improved, an important objective in the broad directive of energy research. This Project provided cutting-edge training in materials chemistry, computational modeling, spectroscopy, and microscopy techniques to undergraduate and graduate students across 3 different universities. Much of the science has been disseminated through peer-reviewed publications and student poster presentations, and at the top scientific meetings in the US and around the world. Important lessons in energy research, spectroscopy, microscopy, and nanotechnology were taught to high school teachers in coordination with an NSF-sponsored high school teacher training program, to scientists and engineers through short courses, and through a web site accessible by the public. Finally, in addition to the training of the work force, this Project resulted in several filed or issued patents, contributing to the technology innovation efforts in the US.
