Study of the N2O formation mechanism in NOx-assisted heterogeneous catalytic combustion of soot in CeO2-based catalytic microchannel reactor

A CeO₂-based catalytic microchannel reactor fixed-bed experiment was carried out to investigate the N₂O formation in NO_x-assisted catalytic combustion with fresh and hydrothermally aging catalysts during NOx-assisted heterogeneous catalytic combustion of soot. An evolved NOx-assisted soot catalytic combustion reaction mechanism was built to investigate N₂O formation and key reaction pathways based on in situ Fourier Transform Infrared Spectroscopy (FTIR) diagnostics and destiny functional theory (DFT) computations. It was found that the temperature range of N₂O formation was the same as the initiation temperature of soot catalytic combustion, while the significant catalytic activity of CeO₂ catalyst induced a decrease in the temperature range of N₂O formation. The CeO₂ catalyst inhibited N₂O formations from NOx-assisted soot catalytic combustion, while its inhibition effect was gradually weakened with the decrease of catalyst activities. The inhibitory effect of CeO₂ on N₂O was revealed in the reduction of CN formation rate in high temperatures. Fresh CeO₂ catalyst increased the dominance in the CN formation reaction, reduced the CN production rate, and contributed to the decrease in the reaction rate of CNO oxidation by NO and NO₂. The increase in the ratio of NOx to soot (β) was more sensitive to N₂O formation than the ratio α (NO₂ to NOx) and γ (O₂ to NO_x), led to a stronger inhibition of N₂O formation.