Unveiling the role of sodium ion in the conversion of amino acid intermediates and the formation mechanism of NOx precursors during kitchen waste pyrolysis

Incineration is an effective method to recover energy from kitchen waste. Na+ in kitchen waste affects the conversion of nitrogen compounds and the formation of NOx precurors during the pyrolysis stage of incineration. However, the catalytic mechanism of Na+ is still unclear. This work studies the conversion of compounds and the formation of NOx precursors during pyrolysis using 3-butanamide and 2-pyrrolidone as nitrogen-containing model compounds. The effect of Na+ on the conversion between 3-butanamide and 2-pyrrolidone, the main amino acid intermediate in the pyrolysis of kitchen waste, is theoretically investigated by density functional theory for the first time. Based on this work, Na+ has an inhibitory effect on cyclization of 3-butanamide but promotes ring-opening of 2-pyrrolidone. In most cases, Na+ negatively influences the formation of NOx precursors by forming a temporary bond with the transition state atom, thereby raising the energy barrier of the transition state. On the other hand, the energy barrier for the formation of NH3 and HCN is increased in the presence of Na+, which theoretically explains the negative effect of Na+ on their formation in the previous experiments. For HNCO, Na+ tends to promote its decomposition, making HNCO more difficult to be observed in experiments.