Adsorption and oxidation of NO and N2O on soot surfaces: Evolution of functional groups

Co-firing ammonia with hydrocarbon fuel (such as methane) is an attractive method for reliable application of ammonia for power, and in this case the interaction of NOx (NO, N2O) and soot is possible. To reveal the interaction mechanism, the role of NO and N2O in adsorption and oxidation processes on soot surfaces was investigated in terms of the evolutions of functional groups by thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) technologies. During the adsorption and oxidation processes, the content of C-O groups on soot surfaces at NO and N2O atmosphere is larger than that in air. C-O accumulated in the adsorption stage is prone to be converted into C=O and O=C-O in the oxidation stage. In addition, the N-O bonds on soot surfaces remained stable in air but underwent significant changes in the presence of NOx. O atoms arise from air and N2O may be more likely to replace the H atom on methyl or methylene on soot surfaces, while NO can not only attack C–H groups but also be prone to break C=C on aromatic rings. This study offers novel insights into the fuel-NOx interactions with soot and is helpful for co-reducing soot and NOx emissions from NH3/hydrocarbon fuel combustion.