Theoretical insights into the poisoning effect of Na and K on α-Fe2O3 catalyst for selective catalytic reduction of NO with NH3

The poisoning effect of potassium (K) and sodium (Na) on the α-Fe2O3 catalyst in the ammonia-selective catalytic reduction (NH3-SCR) for the NO reduction was investigated by the density functional theory calculation. The results show that, in the presence of alkali metals, the strength of the Lewis acid site on the surface is not affected, while the strength of the Brønsted acid site is significantly inhibited, which thus decreases the de-NOx performance of the α-Fe2O3 catalyst. Both K and Na enhance the NOx (NO and NO2) adsorption capacity and inhibit the O2 adsorption capacity of the α-Fe2O3 catalyst. These data indicate that NO and NH3 form competitive adsorption, and the 'Fast-SCR' reaction is inhibited in the alkali metal poisoned systems. In addition, the alkali metals don't affect the dehydrogenation of NH3, but inhibit the formation of H2O which is the rate determination step of NH3-SCR for α-Fe2O3 catalyst.