Effects of ammonia addition on soot and precursors formation in 1-butene pyrolysis: View from solid particles

Ammonia, a zero-carbon and hydrogen-rich fuel, has the potential to regulate the emission of soot particulates. In this work, soot nanostructure and related reactivity evolution in 1-butene/ammonia co-pyrolysis at various gas flow rates were investigated. Transmission electron microscopy and Raman spectroscopy were adopted to characterize soot morphology and its nanostructure, thermogravimetric analysis was used to evaluate soot reactivity, and X-ray photoelectron spectroscopy and elemental analysis were employed to investigate soot chemical composition. Results revealed that increasing gas flow rate and ammonia content both led to a decrease in primary particle diameter, whose fringe length was negatively correlated with the gas flow rate, while blending NH₃ had no obvious impact on structural parameters. Rising gas flow rate enhanced the soot oxidation reactivity by reducing its residence time in the high-temperature reaction region, where it did not undergo sufficient carbonization. The introduction of nitrogen-containing species depleted available carbon source for soot formation, and deactivated the reaction sites by binding with the defective carbon in the carbon layer, thus inhibiting the surface growth of soot. Nitrogen atoms embedded in the soot particles were predominantly found in the form of pyridines. The inhibitory effect of added ammonia on soot reactivity depended on adequate gas residence time. The coupling relationship of gaseous soot precursors and solid particles formation with ammonia addition has been further developed in conjunction with the previous work.