SO₂-Tolerant Selective Catalytic Reduction of NO_<i>x</i> over Meso-TiO₂@Fe₂O₃@Al₂O₃ Metal-Based Monolith Catalysts

Abstract

It is an intractable issue to improve the low-temperature SO₂-tolerant selective catalytic reduction (SCR) of NO _x with NH₃ because deposited sulfates are difficult to decompose below 300 °C. Herein, we established a low-temperature self-prevention mechanism of mesoporous-TiO₂@Fe₂O₃ core-shell composites against sulfate deposition using experiments and density functional theory. The mesoporous TiO₂-shell effectively restrained the deposition of FeSO₄ and NH₄HSO₄ because of weak SO₂ adsorption and promoted NH₄HSO₄ decomposition on the mesoporous-TiO₂. The electron transfer at the Fe₂O₃ (core)-TiO₂ (shell) interface accelerated the redox cycle, launching the "Fast SCR" reaction, which broadened the low-temperature window. Engineered from the nano- to macro-scale, we achieved one-pot self-installation of mesoporous-TiO₂@Fe₂O₃ composites on the self-tailored AlOOH@Al-mesh monoliths. After the thermal treatment, the mesoporous-TiO₂@Fe₂O₃@Al₂O₃ monolith catalyst delivered a broad window of 220-420 °C with NO conversion above 90% and had superior SO₂ tolerance at 260 °C. The effective heat removal of Al-mesh monolithcatalysts restrained NH₃ oxidation to NO and N₂O while suppressing the decomposition of NH₄NO₃ to N₂O, and this led to much better high-temperature activity and N₂ selectivity. This work supplies a new point for the development of low-temperature SO₂-tolerant monolithic SCR catalysts with high N₂ selectivity, which is of great significance for both academic interests and practical applications.