Unveiling the Catalytic Conversion Pathways of Ammonia on α-MnO2 Nanowires: Experimental and First-Principles Studies

Abstract

In this study, catalytic NH3 oxidation and reduction reactions were carried out to investigate conversion pathways on α-MnO2 nanowires with different facets. Moreover, the active oxygen atoms of α-MnO2 facets were quantitatively analyzed by NH3 temperature-programmed surface reduction (TPSR) to predict the NH3 conversion pathways. Meanwhile, the mechanism was revealed using in situ DRIFTS and DFT calculations. It was found that NH3 conversion followed different pathways on the three α-MnO2 facets. Based on DFT calculations, it was demonstrated that the degree of difficulty in breaking the N-H bonds in NH3 varied greatly on the different α-MnO2 facets, leading to NOx formation on the (3 1 0) facet, N2O formation on the (1 1 0) facet and selective catalytic reduction (SCR) of NOx on the (1 0 0) facet. This study provides theoretical guidance for the design of catalysts for the catalytic ammonia oxidation and the selective catalytic reduction of NOx.

Keywords: α-MnO2, NH3-SCO, NH3-SCR, Facet engineering