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

Abstract

A CeO2-based catalytic microchannel reactor fixed-bed experiment was carried out to investigate the N2O formation in NOx-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 NOx), led to a stronger inhibition of N2O formation.