Effect of alkali metal ions on the formation mechanism of HCN as NOx precursor during pyrrole pyrolysis

Pyrrole is selected as the N-containing model compound for the investigation of the effect of alkali metal ions (Na+ ,K+ ) on NOx formation during coal thermal utilization process. Based on conventional non-catalytic mechanism studies,the density functional theory(DFT) method and B3LYP / 6-31+G(d,p) basis set are adopted to elucidate the pyrolysis mechanism and pathways of pyrrole. The calculation results indicate that both Na+ and K+ show significant effects on the internal hydrogen transfer,ring-opening and concerted decomposition reactions,while rarely influence the internal hydrogen isomerization reaction. It is found that the alkali metal ions(Na+ and K+ ) can promote the formation of HCN from pyrrole through decreasing the activation energy of the rate-determining step. In addition,Na+ exhibits a better catalytic activity than K+ .