Potassium-containing coal chars as catalysts for NO_x reduction in the presence of oxygen

The use of inexpensive potassium-containing coal chars for NO_x reduction in a fuel-lean (oxygen-rich) environment has been investigated. Coals of different rank have been used as char precursors. Two types of experiments were performed to study the kinetics of the NO_x/carbon reaction: (i) temperature-programmed reaction in a ¹⁵NO(0.5%)/O₂(5%)/He mixture and (ii) isothermal reaction at 300 and 350°C. NO_x adsorption at room temperature was also carried out using an identical mixture. Two characteristic temperature regimes were identified: (i) At temperatures below 200°C, NO_x adsorption on the char surface is the more important phenomenon, (ii) At temperatures above 200°C, the true NO_x reduction by carbons starts with N₂ and CO₂ being the main reaction products. A very active potassium-containing coal char has been prepared by using the following char preparation conditions: pyrolysis at 900°C and a KOH/coal ratio of 0.5/1.