Rational selection of Fe2V4O13 over FeVO4 as a preferred active site on Sb-promoted TiO2 for catalytic NOX reduction with NH3

Abstract

FeVO₄ (Fe₁) is a particular class of metal vanadate that has recently been highly profiled as an active site to selectively reduce NO_X with NH₃ (NH₃-SCR). This primarily results from NO_X/NH₃-accessible VO₄³⁻ anions and an electronic inductive effect between the Fe and V species, leading to the formation of abundant catalytic defects available for NO_X turnover. Motivated by a structural inspection of the vanadates reported to date, this study detailed the use of Fe₂V₄O₁₃ (Fe₂) as a novel active site deposited on anatase (TiO₂) for NH₃-SCR. While providing the aforementioned structural benefits, Fe₂/TiO₂ also enhanced the redox character as well as the number of sites accessible to NO_X/NH₃ over Fe₁/TiO₂ because of the greater electronic inductive effect of Fe₂. Therefore, Fe₂/TiO₂ converted NO_X better than Fe₁/TiO₂ in the presence of H₂O. To further improve the NH₃-SCR performance of Fe₂/TiO₂, its catalytic surface was modified via two steps. The first step was to incorporate 1.9 wt% Sb into Fe₂/TiO₂. Sb could promote the redox feature of Fe₂/TiO₂ and help its surface to preferentially interact with NH₃/NO_X, thereby making the resulting Fe₂–Sb_1.9/TiO₂ outperform Fe₂/TiO₂ during NH₃-SCR in the presence of H₂O. The second step was to functionalize the Fe₂–Sb_1.9/TiO₂ surface with SO₃²⁻/SO₄²⁻ species. The resulting Fe₂–Sb_1.9/TiO₂ (S) was validated to further increase redox cycling of Fe₂–Sb_1.9/TiO₂, favor NO₂ production from NO oxidation for fast NH₃-SCR, and hamper surface interplay with SO₂. Fe₂–Sb_1.9/TiO₂ (S), therefore, showed higher NO_X conversions than a control simulating a commercial catalyst during NH₃-SCR feeding H₂O and SO₂. Fe₂–Sb_1.9/TiO₂ (S) also showed greater durability than the control because of its enhanced resistance to SO₂, ammonium (bi)sulfates, and alkali metals.