POTASSIUM-CONTAINING COAL CHARS AS CATALYSTS FOR NOX REDUCTION IN THEPRESENCE OF OXYGEN

The use of inexpensive potassium-containing coal chars for NO, reducti on in a fuel-lean (oxygen-rich) environment has been investigated. Coa ls of different rank have been used as char precursors. Two types of e xperiments were performed to study the kinetics of the NOx/carbon reac tion: (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 identica l mixture. Two characteristic temperature regimes were identified: (i) At temperatures below 200 degrees C, NOx adsorption on the char surfa ce is the more important phenomenon. (ii) At temperatures above 200 de grees C, the true NOx reduction by carbons starts with N-2 and CO2 bei ng the main reaction products. A very active potassium-containing coal char has been prepared by using the following char preparation condit ions: pyrolysis at 900 degrees C and a KOH/coal ratio of 0.5/1.