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

University Of Illinois At Chicago, Chicago IL

Investigators

Abstract

Randall Meyer 0730937 One 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.