Effect of ammoxidation of activated carbons obtained from sub-bituminous coal on their NO2 sorption capacity under dry conditions

The paper presents results of a study on obtaining N-enriched activated carbons from Polish sub-bituminous coal and their effectiveness as adsorbents for removal of pollution from gas phase. The crushed precursor was subjected to pyrolysis at 500, 600 and 700 °C followed by activation with KOH at 800 °C. The carbonaceous adsorbents were further subjected to the ammoxidation at 350 °C, by a mixture of ammonia and air at the ratio of 1:3. Adsorption of NO2 was carried out from dry air. The surface structure and chemistry of the initial and exhausted adsorbents were analysed using the method based on adsorption of nitrogen, Boehm method, elemental analysis. The results have shown that the process of ammoxidation results in the introduction of new nitrogen functional groups in the structure of the activated carbon but also changes the acid–base character of their surface and deteriorates their textural parameters. Introduction of nitrogen into the structure of activated carbons improves their sorption capacity towards NO2 of the majority of the samples. The best sorption capacity in both unmodified and nitrogen-enriched activated carbons obtained from sub-bituminous coal was obtained for the activated carbon pyrolysed at 600 °C, with respective values of 33.8 and 66.8 mg/g, respectively.