Formation, Structure and Reactivity of Redox Sites in High-Silica H-Zeolites

点击翻译按钮获取中文摘要

0931059LoboRecent studies from the PI's group have shown that Brønsted acid sites (Si-OH-Al) on high-silica zeolites decompose thermally at temperatures above 550°C producing hydrogen. This reaction leads to a formal oxidation of the zeolite framework where some oxygen atoms change oxidation state from 2- to 1-. The observation of this homolytic decomposition of Brønsted acid sites is a very unexpected result and opens the possibility that some of what is believed to be acid catalysis at high temperatures in zeolites is in fact redox chemistry. The aim of this proposal is to establish if this redox chemistry can indeed have an effect on the selectivity and yield of hydrocarbon reactions in zeolites at high temperatures and to elucidate the molecular and electronic structure of these redox sites.Intellectual Merit: The PI will investigate the decomposition of Brønsted acid sites under inert and oxidative conditions using Mass-Spectrometry-Temperature-Programmed- Reaction techniques to determine the conditions that lead to the oxidative decomposition of the Brønsted acid sites. After decomposition, the samples will be investigated using X-ray absorption spectroscopy, high-field 27Al MAS NMR spectroscopy, inelastic neutron scattering and a number of optical spectroscopy techniques to clarify their molecular and electronic structure. Transient kinetic studies of simple alkanes will be used to evaluate the effect of these redox sites on hydrocarbon cracking. The successful completion of the proposed research program will open a new window of inquiry into the chemistry of zeolites. These findings could have implications for important catalytic processes such as fluidized catalytic cracking and enhanced fuel reforming on Rh/zeolite catalysts. Furthermore, the expected results could also help elucidate similar redox processes observed in quartz and other minerals that have remained unexplained for decades.Broad Impact: Three mechanisms are given to reach out to elementary and junior high-school students and to underrepresented groups to enhance their understanding of science and engineering and entice them to think about engineering as a professional future. First, on campus and at local schools a short talk will be given directed to elementary and junior-high school students communicating in lay terms the impact that zeolites have on our lives. This talk will be prepared and delivered several times a year as part of the outreach activities of the College of Engineering at UD. Second, the PI plans to participate in the Research Experiences for Teachers program organized by the college, a hands-on summer research program for high-school science and math teachers, by hosting one or two of these teachers in his laboratory each year. Finally, he plans to work with faculty in the department of Chemistry at Lincoln University, a predominantly African American institution located closely to the University of Delaware, to bring some of their senior undergraduate students to participate in the proposed project and other on-going research programs in his laboratory. He plans to use these collaborative Delaware-Lincoln research activities to lure students into the benefits of pursuing graduate research after the completion of their undergraduate degree.In addition to educating one graduate student using a rich and complex scientific problem, the PI will also involve two undergraduate students in the research described here. This will be done through the University Science and Engineering Scholars Program, one of the hallmarks of Undergraduate Research Program at UDEL where undergraduates work with individual faculty for two consecutive summers on a specific research project. Many of these students end up pursuing research thesis during their senior year.