Development of Ultra-Stable Cu-SCR Aftertreatment System for Advanced Lean NOx Control

The integration of SCR catalyst into diesel-particulate filter (SDPF) may be one of most viable ways to meet upcoming stringent emission regulations with new test protocols such as Worldwide harmonized Light vehicles Test Cycles (WLTC) and Real Driving Emissions (RDE) requirements. The chabazite-structured SSZ-13-based catalysts enabled the wide implementation of urea-SCR technology for mobile applications due to their robust thermal stability up to 750°C compared to the thermally unstable ZSM-5-based technologies. However, the thermally stable Cu-SSZ-13 catalyst starts losing its initial activity with the increase of aging time at 850°C, where the SCR catalyst on SDPF can possibly be exposed during filter regeneration under a drop-to-idle (DTI) condition. Therefore, more durable SCR catalysts that survive under higher temperatures have been strongly desired in automotive industry. Recently, we found Cu-exchanged high silica LTA revealed an excellent hydrothermal stability. In this study, our work successfully demonstrated the hydrothermally ultra-stable Cu/LTA catalyst that can potentially become a good candidate for the next generation SDPF application that enables tighter real-world driving emission requirement. After hydrothermal aging at 900°C for 12h, the NOx reduction over the Cu/LTA catalyst is superior to those of the state-of-the-art Cu/SSZ-13 based commercial catalyst in the entire reaction temperature. Furthermore, the Cu/LTA catalyst can maintain remarkable high-temperature NOx conversion after lean/rich cyclic aging at 620°C, due to the low oxidation of NH₃ to NO. More stable NH₃ storage capacity of Cu/LTA upon hydrothermal aging compared to the case for Cu/SSZ-13 will provide an additional benefit in integrating the on-board urea dosing control for the maximum system performance. Finally, the performance of the Cu/LTA catalyst under the simulated dynamic WLTC mode test will be presented. We believe that these enhanced features will help improving the future lean NOx aftertreatment systems under the real-world driving conditions.