SO2-Tolerant Selective Catalytic Reduction of NOx over Meso-TiO2@Fe2O3@Al2O3 Metal-Based Monolith Catalysts

It is an intractable issue to improve the low-temperature SO 2 -tolerant selective catalytic reduction (SCR) of NO x with NH 3 because deposited sulfates are difficult to decompose below 300 °C. Herein, we established a low-temperature self-prevention mechanism of mesoporous-TiO 2 @Fe 2 O 3 core–shell composites against sulfate deposition using experiments and density functional theory. The mesoporous TiO 2 -shell effectively restrained the deposition of FeSO 4 and NH 4 HSO 4 because of weak SO 2 adsorption and promoted NH 4 HSO 4 decomposition on the mesoporous-TiO 2 . The electron transfer at the Fe 2 O 3 (core)-TiO 2 (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-TiO 2 @Fe 2 O 3 composites on the self-tailored AlOOH@Al-mesh monoliths. After the thermal treatment, the mesoporous-TiO 2 @Fe 2 O 3 @Al 2 O 3 monolith catalyst delivered a broad window of 220–420 °C with NO conversion above 90% and had superior SO 2 tolerance at 260 °C. The effective heat removal of Al-mesh monolithcatalysts restrained NH 3 oxidation to NO and N 2 O while suppressing the decomposition of NH 4 NO 3 to N 2 O, and this led to much better high-temperature activity and N 2 selectivity. This work supplies a new point for the development of low-temperature SO 2 -tolerant monolithic SCR catalysts with high N 2 selectivity, which is of great significance for both academic interests and practical applications.