Insight into the Alkali Resistance Mechanism of FeMoTiOx Catalysts for NH3 Selective Catalytic Reduction of NO: Self-Defense Effects of MoOx for Alkali Capture

Abstract

The deactivation of selective catalytic reduction (SCR) catalysts caused by alkali metal poisoning remains an insurmountable challenge. In this study, we examined the impact of Na poisoning on the performance of Fe and Mo co-doped TiO₂ (Fe_aMo_bTiO_x) catalysts in the SCR reaction and revealed the related alkali resistance mechanism. On the obtained Fe₁Mo_2.6TiO_x catalyst, the synergistic catalytic effect of uniformly dispersed FeO_x and MoO_x species leads to remarkable catalytic activity, with over 90% NO conversion achieved in a wide temperature range of 210-410 °C. During the Na poisoning process, Na ions predominantly adsorb on the MoO_x species, which exhibit stronger alkali resistance, effectively safeguarding the FeO_x species. This preferential adsorption minimizes the negative effect of Na poisoning on Fe₁Mo_2.6TiO_x. Moreover, Na poisoning has little influence on the Eley-Rideal reaction pathway involving adsorbed NH_x reacting with gaseous NO_x. After Na poisoning, the Lewis acid sites were deteriorated, while the abundant Brønsted acid sites ensured sufficient NH_x adsorption. As a benefit from the self-defense effects of active MoO_x species for alkali capture, Fe_aMo_bTiO_x exhibits exceptional alkali resistance in the SCR reaction. This research provides valuable insights for the design of highly efficient and alkali-resistant SCR catalysts.

Keywords: acid sites; alkali resistance; nitrogen oxides; reaction mechanism; selective catalytic reduction.