Evolution and impact of acidic oxygen functional groups on activated carbon fiber cloth during NO oxidation

Fundamental studies describing the impact of carbon’s physical and chemical properties on NO oxidation allow for the development of catalysts tailored specifically for abating emissions of nitrogen oxides. Here, we show that acidic oxygen functional groups are developed on activated carbon fiber cloth during carbon-catalyzed NO oxidation. Reaction and thermal desorption cycle experiments demonstrate the continuous addition of oxygen to carbon as carbonyl and carboxyl functional groups. After four cycles, the oxygen content of carbon increased by 280%. There is also a 65% reduction in the time required to release NO2 from the carbon surface, allowing the reaction to achieve steady-state NO conversion 45% faster. The steady-state NO oxidation rate remains constant during the four cycles (48.5 ± 1.6 μmol/h), which is attributed to stable physical properties of carbon during the cycles. Oxygen groups added during the cycles, therefore, have no detectable impact on the overall conversion of NO over carbon, but control the pathway to achieving stable conditions. Carbon catalysts prepared with acidic oxygen functionalities are promising as NO oxidation catalysts, as confirmed with NO2 and nitric acid treatments. It is proposed that carbon’s chemical properties impact NO oxidation kinetics while carbon’s physical properties impact the steady-state NO oxidation rate.