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

The use of inexpensive potassium-containing coal chars for NO, 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 NOx/carbon reaction: (i) temperature-programmed reaction in a (NO)-N-15(0.5%)/O-2(5%)/He mixture and (ii) isothermal reaction at 300 and 350 degrees C. NO, adsorption at room temperature was also carried out using an identical mixture. Two characteristic temperature regimes were identified: (i) At temperatures below 200 degrees C, NOx adsorption on the char surface is the more important phenomenon. (ii) At temperatures above 200 degrees C, the true NOx reduction by carbons starts with N-2 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 degrees C and a KOH/coal ratio of 0.5/1.