Final Report of a CRADA Between Pacific Northwest National Laboratory and Cummins, Incorporated (CRADA No.PNNL/283): “Enhanced High and Low Temperature Performance of NO x Reduction Catalyst Materials”
The NO x Storage-Reduction (NSR, also known as lean-NO x trap – LNT), is based upon the concept of storing NO x as nitrates over storage components, typically barium species, during a lean-burn operation cycle and then reducing the stored nitrates to N 2 during fuel-rich conditions over a precious metal catalyst [1]. NO x Selective Catalytic Reduction (SCR), on the other hand, is accomplished by deliberately introducing reductant urea into the engine exhaust to reduce NO x with the aid of a Cu(Fe)/zeolite catalyst [2]. These two technologies have been recognized as the most promising approaches for meeting stringent NO x emission standards for diesel vehicles within the Environmental Protection Agency’s (EPA’s) 2007/2010 mandated limits. For NSR, problems arising from either or both thermal and SO 2 deactivation must be addressed to meet durability standards. For SCR, SO 2 deactivation is less of an issue, but hydrothermal deactivation of the zeolite catalysts must be addressed. With continuing R&D efforts in advanced powertrains, highly novel operating modes for internal combustion engines (ICEs) are being researched in order to meet the very stringent new demands for fuel efficiency (e.g., U.S. ‘‘CAFE’’ standards for average miles/gallon are scheduled to increase dramatically over the next 10–15 years). These new ICE engine operation modes, while highly fuel-efficient, result in much lower exhaust temperatures than current engines; temperatures so low that it is hard to imagine how the current catalytic emission control technologies will be able to function. For example, while steady-state operation of the NO x reduction technology at 150 °C may be required, current ‘‘light-off’’ temperatures for CHA-based zeolite catalysts are closer to 200 °C. Therefore, understanding low-temperature limitations in NO x reduction has become one of the most daunting challenges in R&D on new catalyst materials and processes that can effectively eliminate emissions at these quite low exhaust temperatures. This project has two clear focuses: (1) development of potassium-based high-temperature NSR materials, and studying their key causes of deactivation and methods of regeneration. By comparing results obtained on ‘Simple Model’ Pt-K/Al 2 O 3 with ‘Enhanced Model’ Pt-K/ MgAlO x and Pt-K/TiO 2 materials, we have developed an understanding of the role of various additives on the deactivation and regeneration processes. Studies have also been performed on the real commercial samples being used in a Dodge Ram truck with a Cummins diesel emission control system. However, the results about these ‘commercial samples’ will not be covered in this report. Following a brief description of our experimental approach, we will present a few highlights from some of the work performed in this CRADA with more details about these results provided in publications/reports/presentations lists presented at the end of the report. (2) for the Cu and Fe/Chabazite SCR catalysts, since these are so newly developed and references from open literature and industry are nearly absent, our work started from zeolite synthesis and catalyst synthesis methodology development, before research on their low- and high-temperature performance, deactivation, regeneration, etc. was conducted. Again, most work reported here is based on our “model” catalysts synthesized in-house. Work done on the ‘commercial samples’ will not be covered in this report.