NO oxidation in dry and humid conditions using hyper-cross-linked polymers: Impact of surface chemistry on catalytic conversion efficiency

Microporous and hydrophobic polymers were synthesized and tested as NO oxidation catalysts to overcome water co-adsorption in combustion flue gas streams. The self-cross-linked 4,4′-bis(chloromethyl)-1,1′-biphenyl polymer (PBCMBP), with micropore volume of 0.38 cm³/g and surface area of 1430 m²/g, provided 62% NO oxidation efficiency at 25 °C in dry conditions but its performance dropped to 50% in the presence of 1.6 vol% moisture (wet conditions). To decrease performance loss, PBCMBP was modified with benzene (PBCMBP-BZ) to remove pendant chloromethyl groups, improving resistance to surface reactions with NO₂ that add hydrophilicity. In wet conditions, PBCMBP-BZ has 59% NO oxidation efficiency, an 18% increase compared to PBCMBP at 25 °C. PBCMBP was also functionalized with dimethylamine (PBCMBP-DMA) to increase surface basicity, increasing NO oxidation by 11% in dry conditions, but decreasing NO oxidation in wet conditions by 30% due to increased proclivity to react with NO₂. The combined impact of temperature and humidity was measured up to 100 °C, showing that moisture's impact decreases with increasing temperature and that PBCMBP-DMA outperforms other catalysts at higher temperatures. Findings suggest that catalyst surface chemistry can be manipulated to further improve NO oxidation performance, especially in the presence of moisture.