LAUSR

Abstract It is important to develop new materials/methods to remove NO from gas streams to protect the environment. Use of porous materials to catalytically convert NO to NO2 may improve existing NOx control technologies. In this work, three porous materials (i.e., activated carbon fiber cloths (ACFCs), zeolites, and metal-organic frameworks (MOFs)) were evaluated as NO oxidation catalysts at 25 °C. Maximum included sphere diameter (Di) between 5.5 and 11.0 A is shown to result in higher steady-state NO conversion (23%−71.5 ± 2.5%) by providing appropriate channels/cages that accommodate and stabilize the first transition state (TS1) through van der Waals interactions. For all considered catalysts but MIL-53 (Al), steady-state NO conversion initially increases, then decreases, with increasing pore volume contributed by Di (5.5–11.0 A). Maximum free sphere diameter (Dmax) for the selected catalysts with steady-state NO conversion between 23% and 71 ± 2.5% is between 3.7 and 9.0 A, allowing transport of reactants and products. Extra-framework cations (H+, NH4+, and Na+) and coordinatively unsaturated sites (Cu2+, Fe3+, and Cr3+) increase steady-state NO conversion by providing TS1 stabilization through electrostatic and coordinative interactions, respectively. However, appropriate Di and Dmax values are identified as the most influential variables for steady-state NO conversion using these catalysts. For NO conversion in the presence of SO2, no impact is observed for steady-state NO conversion of a MOF sample, but decreases of 100% and 36% for ACFC and zeolite samples, respectively. These results provide direction for designing NO oxidation catalysts to improve steady-state NO conversion.