Unraveling the anti-poisoning mechanism of highly dispersed Ni atoms enhanced porous MnOx catalysts in the selective reduction of NOx by NH3

Abstract

Rationally designing catalysts suitable for flue gas purification at low temperatures and unraveling the anti-poisoning mechanism at the atomic level remain challenges. Here, a highly dispersed Ni-doped MnO_x catalyst (Ni_0.1Mn_0.9O_x) was constructed and applied for selective catalytic reduction (SCR) of nitrogen oxides (NO_x). The long-term stability of Ni_0.1Mn_0.9O_x is up to 80% (180 °C) after 18 h under SO₂ and H₂O conditions. This is due to the fact that the highly dispersed Ni atoms enhance the redox and surface acidity of MnO_x, and modulate the electronic structure of the active Mn sites. The denitrification reaction on Ni_0.1Mn_0.9O_x mainly follows the Eley-Rideal mechanism. The anti-poisoning mechanism is that the introduction of Ni weakens the electron transfer between the Mn site and SO₂, thereby inhibiting the adsorption of SO₂. In particular, the H₂O adsorbed on the Ni sites is decomposed to replenish the depleted Brønsted acid sites, which facilitates the adsorption of NH₃. However, an excess of H₂O can have an inhibitory effect. In addition, the mesoporous structure may increase the mass transfer rate and reduce the accumulation of harmful substances. This study provides viable insights for the design of SCR catalysts with excellent anti-poisoning ability.