Supercritical ion exchange synthesis and kinetic modeling ofselective catalytic reduction catalysts for diesel and hydrogenengine aftertreatment systems with engine control unitoriented implementation

This thesis investigates the synthesis, characterization, kinetic modeling, and control-oriented implementation of catalysts for selective catalytic reduction of NOx by ammonia (NH3-SCR) applications in advanced aftertreatment systems, including hydrogen internal combustion engines (H2-ICEs) and diesel engines. Various zeolite frameworks (SSZ-13, ZSM-5, and MOR) were ion exchanged with Copper(II)trifluoroacetylacetonate (Cu(tfa)2) using Supercritical and Aqueous Ion Exchange (SCIE and AIE) methods. Catalytic activity assessments revealed that Cu/MOR synthesized via SCIE exhibited superior NO conversion compared to AIE. Furthermore, SCIE enabled site-selective copper exchange, by varying synthesis temperature (40–80 °C) and Cu(tfa)2 concentration, tuning the distribution of ZCuOH and Z2Cu species located on the 8 membered-rings and 6 membered-rings of SSZ-13. Spectroscopic techniques (UV–Vis and ATR-FTIR) revealed that ZCuOH species dominated at high SCIE temperatures, while Z2Cu became more prevalent with increased Cu precursor concentration. The NH3-SCR performance of a commercial Cu/CHA catalyst was also evaluated under H2-ICE relevant conditions, including 175-760 ppm of NOx and NH3, 1–20% H2O, 1–14% O2, and 500 ppm H2 across 150–490 °C. NH3 uptake decreased by ~40% as H2O content increased from 1% to 20%. In Standard SCR conditions (NO/NOx=1), low-temperature NOx conversion decreased notably with increasing water content—dropping by up to 30% at 200 °C when H2O increased from 1% to 20%. However, at higher temperatures, water exerted a promoting effect: NOx conversion improved with increasing H2O and consistently exceeded 99% above 250 °C at 60,000 h⁻¹ gas hourly space velocity. In Fast SCR conditions (NO2/NOx=0.5), the impact of water was less pronounced, and high NOx conversion (>95%) was achieved even at 200 °C. Co-fed hydrogen (500 ppm) had minimal effect below 400 °C but slightly impacted high temperature NOx efficiency and N2 selectivity. To enable real-time application in Engine Control Units (ECUs), a Reduced Order Model (ROM) of the NH3-SCR process was developed. The model was calibrated using synthetic gas bench data and validated against dynamometer tests with 7.5 L (close coupled) and 41 L (underfloor) commercial SCR reactors. The ROM accurately predicted transient NO, NH3, and N2O behavior under World Harmonized Test Cycle (WHTC) conditions with less than 5% error as well as fluid/solid thermal behavior, offering a robust solution for ECU-integrated urea dosing strategies.