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

最近的研究表明，高硅沸石上的Brønsted酸位（Si-OH-Al）在550°C以上的温度下会热分解产生氢。该反应导致沸石骨架的正式氧化，其中一些氧原子将氧化态从2-变为1-。观察到Brønsted酸位的均匀分解是一个非常意想不到的结果，它开启了一种可能性，即沸石中高温下的酸催化实际上是氧化还原化学。本提案的目的是确定这种氧化还原化学是否确实对沸石中高温下碳氢化合物反应的选择性和产率有影响，并阐明这些氧化还原位点的分子和电子结构。智力优势：该项目将使用质谱-程序化温度反应技术研究惰性和氧化条件下Brønsted酸位的分解，以确定导致Brønsted酸位氧化分解的条件。分解后的样品将使用x射线吸收光谱、高场27Al MAS NMR光谱、非弹性中子散射和多种光谱学技术进行研究，以阐明其分子和电子结构。简单烷烃的瞬态动力学研究将用于评价这些氧化还原位点对烃裂解的影响。这项研究计划的成功完成将为研究沸石的化学性质打开一扇新的窗口。这些发现可能会对重要的催化过程产生影响，例如流化催化裂化和在Rh/沸石催化剂上增强燃料重整。此外，预期的结果也可能有助于阐明在石英和其他几十年来一直无法解释的矿物中观察到的类似氧化还原过程。广泛影响：本文给出了三种机制，以接触到小学和初中学生以及代表性不足的群体，以增强他们对科学和工程的理解，并诱使他们将工程视为一种职业未来。首先，在校园和当地学校，将针对小学和初中学生进行简短的演讲，以非专业的方式交流沸石对我们生活的影响。本讲座将作为特拉华大学工程学院外展活动的一部分，每年准备和讲授几次。第二，每年邀请1 ~ 2名教师到自己的实验室，参加由首尔大学主办的以高中科学、数学教师为对象的暑期实践研究项目“教师研究体验”。最后，他计划与林肯大学化学系的教职员工合作，林肯大学是一所以非裔美国人为主的机构，靠近特拉华大学，让他们的一些大四本科生参与他实验室拟议的项目和其他正在进行的研究项目。他计划利用这些特拉华大学和林肯大学的合作研究活动，吸引学生在完成本科学位后继续进行研究生研究。除了用一个丰富而复杂的科学问题来教育一名研究生外，PI还将让两名本科生参与本文所述的研究。这将通过大学科学与工程学者计划来完成，这是UDEL本科生研究计划的标志之一，本科生与个别教师一起连续两个夏天进行特定的研究项目。这些学生中的许多人最终在大四的时候开始攻读研究论文。

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.