Amination and ammoxidation of activated carbons

Abstract

Four commercially available carbons were subjected to ammonia and ammonia/oxygen gas mixtures at temperatures between 200 and 420°C. The pore structure of the carbons, as determined by nitrogen porosimetry, was virtually unchanged after the treatments. The surface chemistry of aminated and ammoxidized carbons was found to differ from that of carbons treated with ammonia at high temperatures (600 to 900°C). Probably imide-, amide-, and lactam-type surface species are formed as indicated by FTIR, TPD-MS, acid/base-titration, and elemental analysis. The amide-lactam-imide ratio depends on the modification technique; these surface groups can be converted to aromatic nitrogen species by heat treatment above 600°C. Nitrogen contents and surface fractions are obtainable of 4.4 wt% and 0.14, respectively, for amination and of 3.2 wt% and 0.11 for ammoxidation. A high nitrogen incorporation efficiency on applied ammonia can be reached for ammoxidation (58%). The lactam, imide, and amide groups enhance the absorption of the graphitic plane at 1600 cm −1 in FTIR spectroscopy by induction. The intensity of this absorption is generally related to the amount of oxygen.