Preparation of Nitrogen-Enriched Activated Carbons from Brown Coal

Nitrogen-enriched activated carbons were prepared from a Polish brown coal. Nitrogen was introduced from urea at 350 °C in an oxidizing atmosphere both to carbonizates obtained at 500−700 °C and to activated carbons prepared from them. The activation was performed at 800 °C with KOH in argon. It has been observed that the carbonization temperature determines the amount of nitrogen that is incorporated (DC5U, 8.4 wt % Ndaf; DC6U, 6.3 wt % Ndaf; and DC7U, 5.4 wt % Ndaf). X-ray photoelectron spectroscopy (XPS) measurements have shown that nitrogen introduced both at the stage of carbonizates and at the stage of activated carbons occurs mainly as N-6, N-5, and imine, amine and amide groups. On the other hand, the activation of carbons enriched with nitrogen results in the formation of pyridonic nitrogen and N−Q. The introduction of nitrogen at the activated carbon stage leads to a slight decrease in surface area. It has been proven that the most effective way of preparing microporous activated carbons enriched with nitrogen to a considerable extent and having high surface area (∼3000 m2/g) is the following: carbonization → activation → reaction with urea.