ANALYSIS AND DESIGN OF STRUCTURED MULTI-FUNCTIONAL TRAPPING CATALYSTS FOR CONVERSION OF HYDROCARBONS AND NOX FROM DIESEL AND ADVANCED COMBUSTION ENGINES

Multifunctional automotive catalysts can help abate harmful emissions, such as NOx (x=1, 2), CO, and hydrocarbons (HCs) and provide a potential solution to meet the need of increasingly stringent vehicle fuel economy standards and emissions regulations. The proposed LHCNT (lean hydrocarbon NOx trap) concept involves the combination of NOx trapping with HC trapping and oxidation for conversion of NOx, HC, and CO during sustained, low-temperature exhaust drive cycles and engine cold-start. In the first part of the work, we focus on NOx uptake and release features on Pd-exchanged SSZ-13 (PNA- Passive NOx Adsorber) catalyst to trap NOx in the absence and presence of several diesel exhaust components (CO, C2H4, H2, C7H8, and C12H26). We identified two prospective mechanistic schemes which are consistent with the uptake/release and DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) data. Second, we focused on DOC (Diesel Oxidation Catalyst) which is an essential component of modern vehicle emissions control systems. A new Pd-Cu alloy catalyst ((Pd+Cu/SiO2-Al2O3), prepared in-house, exhibited higher resilience to increased light-off temperature, resultant of mutual inhibition between the various pollutants, in comparison with the commercial DOC (Pt+Pd/Al2O3-CeO2). The benefit of eliminating the inhibition effect of NO on CO oxidation is clearly demonstrated in the juxtaposition of the two catalyst and reactor configurations using a CO and NO containing feed. Next, we investigate the spatiotemporal features of a multifunctional monolith lean hydrocarbon NOx trap (LHCNT) for eliminating NOx and C2H4 in simulated diesel exhaust. Spatially-resolved mass spectrometry (SpaciMS) is used to measure the temporal species concentration profiles spanning the sequentially- positioned PNA (Pd/SSZ-13), HCT (Hydrocarbon Trap; Pd/BEA) and DOC (Pt/Al2O3-CeO2) zones. The working concept of the LHCNT is demonstrated through measured integral trapping efficiency profiles, which show NO and C2H4 trapping followed by delayed NO release along with NO and ethylene oxidation during the simulated warmup. Finally, we utilized the same sequential configuration system to identify the impact of CO on NO trapping. Conditions are identified which lead to CO induced deactivation. We conclude our study with the scope of future work based on our results and observations.