Alkali-Poisoning-Resistant Fe₂O₃/MoO₃/TiO₂ Catalyst for the Selective Reduction of NO by NH₃: The Role of the MoO₃ Safety Buffer in Protecting Surface Active Sites

The exhaust gas contains harmful products, including fuel-additive elements such as compounds of sodium, which cause dramatic catalyst deactivation of catalysts during selective catalytic reduction (SCR) of NO with NH₃. There is an increasing demand to synthesize alkali-poisoning-resistant catalysts for industrial NH₃-SCR applications. In this study, the as-synthesized Fe₂O₃/MoO₃/TiO₂ exhibits a high degree of resistance toward Na₂SO₄ poisoning during the NH₃-SCR reaction. With 500 μmol g^-1 Na⁺ poisoning, Fe₂O₃/MoO₃/TiO₂ showed approximately 95% (or more) of its original activity throughout the entire temperature rage. Even with 700 μmol g^-1 Na⁺ poisoning, Fe₂O₃/MoO₃/TiO₂ still performed well. The 500 and 700 μmol g^-1 Na⁺ loadings dictate that, on average, SCR catalysts could be exposed to alkali-rich and highly dusty environments for more than 14 000 and 20 000 h, respectively. The layered MoO₃ building block is used as a binding buffer and sandwiched between the active phase and TiO₂ support to provide sufficiently stable binding sites for Na₂SO₄ poison and to present alkali blocking of the surface active phase. Our findings provide useful information regarding the use of MoO₃ as a safety buffer for developing functional NH₃-SCR catalysts with enhanced alkali-poisoning-resistant performance and long lifetimes.