The formation of NOx during the combustion of model nitrogen-containing chars was investigated in a thermogravimetry-mass spectrometry system. The model chars were prepared from well-defined nitrogen compounds at different temperatures (460-800 degrees C) under argon and hydrogen pressure (5 MPa). After preparation, the nitrogen structures of the chars were determined by XPS. The purpose of this study was to examine how the primary nitrogen structure influences the nitrogen oxide emission. The formation of NO was correlated with distinguished nitrogen functionalities and with carbon oxides emission. No relationship was found between any of nitrogen structures (pyrrolic, pyridinic, quaternary nitrogen) and nitrogen oxide evolution. That indirectly proves that nitrogen oxide is a primary intermediate product of the combustion process leading to the final product of nitrogen burning that is molecular nitrogen, N-2.