Self-Prevention of Well-Defined-Facet Fe2O3/MoO3 against Deposition of Ammonium Bisulfate in Low-Temperature NH3–SCR

Low-temperature selective catalytic reduction of NO by NH3 (NH3-SCR) is a promising technology for controlling NO emission from various industrial boilers, but it remains challenging because unavoidable deposition of ammonium bisulfates (ABS) in the stack gases containing both SO2 and H2O inevitably results in deactivation of catalysts. Here we developed a stable low-temperature NH3-SCR catalyst by supporting Fe2O3 cubes on surfaces of MoO3 nanobelts with NH4+-intercalatable interlayers, which enables Fe2O3/MoO3 to spontaneously prevent ABS from depositing on the surfaces. Using in situ synchrotron X-ray diffraction, 1H magic angle spinning nuclear magnetic resonance, and temperature-programmed decomposition procedure, the results demonstrate that NH4+ of ABS was initially intercalated in the interlayers of MoO3, leading to a NH4+-HSO4- cation-anion separation by conquering their strong electrostatic interactions, and subsequently the separated NH4+ was consumed by taking part in low-temperature NH3-SCR. Meanwhile, the surface HSO4- separated from ABS oxidized the reduced catalyst during the NH3-SCR redox cycle, concomitant with release of SO2 gas, thereby resulting in decomposition of ABS. This work assists the design of stable low-temperature NH3-SCR catalysts with strong resistance against deposition of ABS.