Potassium-modified ordered mesoporous carbon materials (K-CMK-3): Highly efficient adsorbents for NO adsorption at low temperatures

Abstract

To improve the removal capacity of (NO ​+ ​O2) effectively, the K-CMK-3(x) (KNO3: CMK-3 mass ratio (x) ​= ​10–20 ​wt%, in which CMK-3 is an abbreviation of the ordered mesoporous carbon) samples were prepared, and their physical properties and (NO ​+ ​O2) adsorption performance were determined by means of analytical techniques, such as XRD, TEM, BET, TG, TPD, and DRIFTS. The ordered mesostructures were retained and specific surface areas and pore volumes of the K-CMK-3(x) samples increased after doping of K. Moreover, the doped K species were uniformly distributed on the surface of CMK-3, and K doping increased the amount of the basic sites in the sample. The structure and amount of the basic sites were the main factors influencing the (NO ​+ ​O2) adsorption on the sample. The sequence in (NO ​+ ​O2) adsorption performance was as follows: K-CMK-3(15) (143.8 ​mg/g) ​> ​K-CMK-3(20) (127.6 ​mg/g) ​> ​K-CMK-3(10) (103.6 ​mg/g) ​> ​CMK-3 (88.8 ​mg/g), with the K-CMK-3(15) sample possessing the best adsorption performance. There were two main adsorption pathways during the process of (NO ​+ ​O2) adsorption: one pathway was the conversion of NO and O2 to a large number of NO2, in which part of NO2 was weakly adsorbed on the surface hydroxyl groups, and the other part of NO2 was disproportionated to NO, NO2−, and NO3−; and the other pathway was first the direct oxidization of NO to NO2− by the oxygen functional groups in carbon and then some of the formed NO2− species were converted to NO3−.