Collaborative Research: Development of New Heterogeneous Catalysts for NOx Storage and Reduction (NSR)

迈克尔·哈罗德0730824目前最大的挑战之一是有效和公平地消耗化石燃料。需要保护有限的石油资源的后果之一是过渡到更有效的柴油发动机和稀燃汽油发动机。与向这些贫燃发动机的转换相关联的是，由于高度氧化的条件，NOx减少的难度增加，这导致需要改进传统的三效排气催化剂。NOx储存还原（NSR）催化剂已经成为解决这个问题的最成功的方法。这些系统需要在两种不同的制度下运行。在氧化条件下，NO在贵金属组分（通常为Pt）上反应形成NO2，其随后可以吸附在存储剂（通常为氧化钡）上。然后，在第二个较短的循环期间，发生还原剂（例如H2、CO、C3H6）的注入，并且由催化剂释放的NOx反应以产生N2。虽然丰田已经将这种方法商业化，但仍有几个关键的科学问题尚未解决，需要进一步改进。本研究将研究开发涉及双金属的新型多相催化剂的策略，预计将改善低温（冷启动）NOx储存并更有效地使用还原剂。据推测，催化剂的主要作用之一是在不使用氢气的情况下将还原剂转化为氢气。氢气又可以有效地还原由催化剂释放的NOx，更重要的是，通过还原任何累积的含硫表面物质来再生存储部件。由于其他还原剂比氢气更容易在NSR系统中实施，因此从CO和H2O水煤气变换（WGS）反应或通过重整从烃类有效生产氢气对于NSR催化剂的性能至关重要。因此，除了Pt之外，将使用第二金属如Cu（以促进WGS）或Ru（以促进HC重整和低温NO氧化）的存在。此外，将Pd和Pd钯合金与Pt和Pt合金催化剂进行比较，因为最近的证据表明Pd对于低温氧化以及改进的对N2（与N2O相反）的选择性是上级的。知识价值这项工作的重要性是双重的。首先，这项工作的目的是获得一个非常复杂的，但可访问的催化剂系统中所涉及的催化机制的基本理解。由此获得的信息可用于涉及加氢催化剂的各种其它应用中。第二，新的改进催化剂的开发对于更省油的稀燃发动机的环境性能至关重要。这项工作将利用多种技术在实验和理论之间进行合作。将合成双金属合金催化剂，并使用EXAFS，XPS和IR光谱进行广泛表征。在其表征之后，将在实际操作条件下使用传统的微型反应器和TAP反应器对催化剂进行测试，以识别重要的中间体，从而提高对机理的理解，从而有助于设计新的催化剂。密度泛函理论的计算将有助于提供一个完整的反应机制，并确定在氧化和还原化学的限速步骤。新的加氢裂化催化剂将在一个迭代过程中开发，该过程将联合收割机所需的特性结合起来，以满足在各种条件和环境下相互矛盾的性能要求。新型NSR催化剂的开发可以对稀燃车辆的商业部署产生重大影响，并具有明显的环境和社会效益。从教育的角度来看，这项研究的跨学科性质将用于培养未来的科学家和研究人员，使其具备采用多方面方法进行催化剂设计所需的技能。该项目将为参与研究的学生提供一个独特的机会，因为他们不仅学习了超出自己实验室能力的各种技术，而且还将接触其他机构的研究环境。这三个机构都是主要研究型大学中少数民族入学人数不足的领导者，我们打算使用REU补充材料，使少数民族本科生接触研究生涯。这项研究将通过期刊出版物和会议记录传播。

Michael P. Harold0730824One of the great challenges of at this time is the efficient and equitable consumption of fossil fuels. One of the consequences of the need to conserve finite petroleum resources is a transition to more efficient diesel engines and lean burning gasoline engines. Associated with the switch to these lean burning engines is an increased difficulty of NOx abatement due to the highly oxidizing conditions which results in a need to improve conventional three-way exhaust catalysts. The NOx storage reduction (NSR) catalysts have emerged as the most successful approach to combat this problem. These systems are required to operate under two distinct regimes. Under oxidizing conditions, NO reacts over a noble metal component (usually Pt) to form NO2 which can subsequently adsorb on the storage agent (usually barium oxide). Then, during a second shorter cycle, an injection of a reducing agent (e.g. H2, CO, C3H6) takes place and NOx released by the catalyst reacts to produce N2. Although this approach has been already commercialized by Toyota, several key scientific issues remain unresolved and the need exists for further improvement. This research will examine strategies to develop new heterogeneous catalysts involving bimetallics, expected to improve the low temperature (cold start) NOx storage and to more efficiently use the reducing agent. It has been speculated that one of the primary roles of the catalyst is the conversion of the reducing agent to hydrogen in cases where hydrogen is not used. Hydrogen in turn can effectively reduce the NOx released by the catalyst and more importantly, regenerate the storage component by reducing any accumulated sulfur containing surface species. Since, other reducing agents are easier to implement in NSR systems then hydrogen, the efficient production of hydrogen either from CO and H2O Water-Gas Shift (WGS) reaction or from hydrocarbons by reforming is essential to the performance of the NSR catalyst. Therefore, the presence of a second metal such as Cu (to promote WGS) or Ru (to promote HC reforming and low termperature NO oxidation), in addition to Pt, will be used. Furthermore, Pd and Pd bimetallic alloys will be compared to Pt and Pt alloy catalysts as recent evidence shows that Pd is superior for low temperature oxidation as well as improved selectivity to N2 (as opposed to N2O). Intellectual Merit The importance of this work is two-fold. First, this work is aimed at obtaining a fundamental understanding of the catalytic mechanisms involved in very complex but accessible bimetallic systems. Information thus obtained may be used in a variety of other applications where bimetallic catalysts are involved. Second, the development of new improved catalysts is critical to the environmental performance of more fuel efficient lean burning engines. The work will be performed in a collaborative effort between experiment and theory utilizing multiple techniques. Bimetallic alloy catalysts will be synthesized, and extensively characterized using EXAFS, XPS, and IR spectroscopies. Following their characterization the catalyst will be tested under realistic operating conditions using both a traditional microreactor and a TAP reactor for identification of important intermediates so as to improve understanding of the mechanism and thereby aid in the design of new catalysts. Density functional theory calculations will aid in providing a complete picture of the reaction mechanism and identify the rate limiting steps in both the oxidation and reduction chemistry. New bimetallic catalysts will be developed in an iterative process which combine the desired features to meet the conflicting demands of performance over a wide range of conditions and environments. Broader Impact The development of novel NSR catalysts can have a substantial impact on the commercial deployment of lean-burn vehicles with apparent environmental and societal benefits. From an educational standpoint, the interdisciplinary nature of this research will be used to train future scientists and researchers with skills necessary to employ a multi-faceted approach to catalyst design. This project will provide a unique opportunity for the graduate students involved as they learn about not only a variety of techniques beyond their capabilities of their own lab but will have exposure to research environment of other institutions All three institutions are among the leaders in the enrollment of underrepresented minorities among major research universities and we intend to use REU supplements for the purpose of exposing minority undergraduates to research careers. This research will be disseminated through journal publications and conference proceedings.