Reduction of NO with NH3 over ferric oxide nanocrystals: the crystallographic facet-induced catalytic enhancement

Abstract

Different synthesis methods of a given material will lead to different mesoscopic architectures, which in turn would strongly influence the catalytic performance. Therefore, morphology control is thought to be helpful for creating high-performance catalysts. Here, a series of well-defined α-Fe₂O₃ crystals with different morphologies, including hexagon, rod, and diamond, have been prepared and investigated for the selective catalytic reduction (SCR) of NO with NH₃, which is of major environmental interest for air pollution control. We report that the {001} surface of the hexagon-shaped Fe₂O₃ catalyst is very active for NO removal. From temperature-programmed desorption measurements, we find that the NH₃ reactant adsorbed strongly on the {001} surface. In contrast, other high-index ferric oxide facets, including {012}, {−210}, {01−4}, {110}, and {1−10}, exhibit the weakly adsorbed state of NH₃. Density functional theory calculations show that the {001} surface has a high surface energy of 1.4 J m⁻², which should account for the observed SCR kinetics. A link between the experimentally observed activity trend and the exposed facets of ferric oxides has been established.