Insight into the N2O formation mechanism on the β-MnO2 (1 1 0) during low-temperature NH3-SCR: Reaction pathway and electronic analysis of different intermediates

Abstract

Nitrous oxide (N2O) is a harmful pollutant to the atmosphere. The prepared β-MnO2 catalysts can produce significant amounts of N2O at 180 ∼ 240 °C during the deNOx. Here, the N2O formation mechanism on the β-MnO2 surface was clarified by experimental and DFT studies. (i) A small quantity of N2O can be produced from a single NO catalyzed by β-MnO2 at 60 ∼ 240 °C, mainly due to the decomposition of adsorbed Tran- or cis- N2O2 dimers. One of the cis-N2O2 dimers possesses the lowest energy barrier to dissociate into N2O. (ii) When the reaction gases only contain NH3 and NO, the amount of N2O produced increases considerably at 180 ∼ 240 °C, mainly due to the easy decomposition of *NH2NO and the *NH3 deep oxidation by Olattice. (iii) In the standard NH3-SCR environment of 180 ∼ 240 °C, *NH3 can easily form *NH4NO3 with nitrite species, and the dissociation of *NH4NO3 to form N2O can produce *NH2NO2 intermediates. This reaction is difficult and *NH3 + *HNO3 → *NH2 + *NO2 + H2O is the rate-limiting step. Therefore, the newly formed *NH4NO3 can poison catalysts and limit the production of N2O. These results can be used to develop deNOx catalysts with the power of controlling N2O production.