#1258715 - Fabio Ribeiro #1258690 - William Schneider #1258717 - Jean-Sabin McEwen
The lack of a practical and cost-effective lean NOx aftertreatment is the major obstacle to the widespread adoption of fuel-efficient diesel and lean-burn gasoline engines for transportation. Increasingly stringent NOx emissions standards demand that NOx conversion to N2 reach or exceed 90% averaged over standard drive cycles, and even higher instantaneous conversions to compensate for cold startup and transient operation. These high conversions are very difficult to achieve under lean conditions, in which NOx must compete with an overwhelming excess of O2 for a limited amount of reductant. Lean NOx traps can achieve the necessary NOx conversion efficiencies, but have many operational and cost issues in their current forms. NOx selective catalytic reduction (SCR) provides a much more satisfactory solution to lean NOx aftertreatment. In this approach the usual converter catalyst is replaced with a catalyst that promotes reaction of NOx with a reductant, such as urea, NH3, or hydrocarbons, to produce N2 selectively over the competing reactions of reductant with O2.
The selective catalytic reduction with ammonia on Cu-exchanged chabazite zeolites is the state-of-the-art for lean NOx reduction and enables access to the fuel efficiency of lean burn engines. Although these materials are used commercially in a small segment of the transportation market, their structure and catalytic behavior changes in unpredictable ways as they respond to varying SCR conditions and in particular as they accumulate deactivating sulfur species. Real-world application of these catalysts at Cummins reveals that their performance at low temperatures is diminished in ways not explained by previously published aging mechanisms. The primary obstacle to the rational improvement and effective application of NOx SCR catalysts is the lack of a firm fundamental understanding of the underlying catalyst structure and catalytic chemistry.
An approach to filling this knowledge gap to lead to maximum SCR catalyst performance has been proposed in response to the joint National Science Foundation and Department of Energy solicitation on Advanced Combustion Engines. The joint Agency award is made through the NSF Chemical, Bioengineering, Environmental and Transport Systems Division and its Catalysis & Biocatalysis Program to a multi-disciplined team made up of Professors Fabio H. Ribeiro, W. Nicholas Delgass, and Rajamani Gounder at Purdue University; Prof. Jean-Sabin McEwen at Washington State University; and Prof. William F. Schneider at University of Notre Dame; Dr. Jeffrey T. Miller, Argonne National Laboratory; Dr. Charles H. F. Peden, Pacific Northwest National Laboratory; and Dr. Aleksey Yezerets, Cummins Inc. NSF GOALI support is also provided to this team that has many years of combined industrial, National Laboratory and academic experience in NOx catalysis and catalysis science and a proven record of successful collaboration.
To dramatically improve the present catalyst materials, to optimize engine efficiency within emission constraints, and to circumvent deactivation, an atomic and molecularly detailed model of catalyst performance under all operating conditions and throughout the life cycle is essential. This team brings world-class excellence in the variety of experimental and theoretical disciplines that must be combined to reach the atomic-level understanding of the dynamic chemical and catalytic properties of this reaction system, which will form the basis of a predictive model for this SCR catalyst system and for further catalyst system improvements. Though the students working on this project will specialize in particular aspects of the research, frequent teleconferences with the entire team and groups traveling to the National Labs to do specialized experiments will provide broad experience and direct exposure to the importance of the interplay between various experiments and molecular theory at the frontier of catalysis research. Thus, this multi-institutional and diverse team will prepare graduate students and postdocs to operate at the highest levels in application of catalysis to the solution of energy efficiency and environmental problems. It will also provide career-defining educational opportunities to high school and undergraduate students. For high school students and educators, Purdue has already developed a hands-on presentation to interest students in science and engineering. The PIs intend to add the molecular view of this work to that presentation and deliver lectures to high schools across Indiana and to bring this view to the many science and engineering camps that run at Purdue and Notre Dame during the summer. Undergraduates working in the university research groups and in industrial internships at Cummins will also benefit from the breadth of scientific exposure and the unique approach that connects detailed fundamental understanding to the solution of important practical problems.
