Catalytic NO Oxidation in the Presence of Moisture Using Porous Polymers and Activated Carbon.

Abstract

NO oxidation catalyzed by porous materials is difficult to implement under industrial conditions because moisture in combustion exhaust streams blocks oxidation sites, decreasing NO conversion. In this work, hydrophobic cross-linked polymers are tested as NO oxidation catalysts to overcome these negative impacts associated with moisture. Although activated carbons (ACs) outperform hyper-cross-linked polymers by >88% and low-cross-linked polymers by >463% under dry conditions, their NO conversion drops to 0% when 50% relative humidity is added. Performance of hyper-cross-linked and low-cross-linked polymers, however, decreases by only 19-35% and <6%, respectively, for NO conversion in the presence of moisture. NO conversion differences between materials are attributed to differences in the catalysts' initial hydrophilicity and their proclivity to react with generated NO2, which also increases hydrophilicity. While the initial hydrophobicity of the polymers contributes to their consistent performance, it is their intrinsic ability to resist NO2 reduction reactions, compared to AC, that makes them the more viable catalyst for industrial application. Results suggest that the polymer hyper-cross-linking process improves steady-state NO conversion but increases NO2 surface reactivity and hydrophilicity.