Novel shielding and synergy effects of Mn-Ce oxides confined in mesoporous zeolite for low temperature selective catalytic reduction of NO_x with enhanced SO₂/H₂O tolerance

Nitrogen oxides (NO_x) are a primary source of air pollutants from combustion of fossil fuels. Though Mn-Ce based catalysts exhibit superior low temperature activities, their water and SO₂ tolerance is inferior to other metal oxide catalysts, due to their strong water adsorption and sulfate species formation tendency at low reaction temperatures. Herein, a confinement strategy was adopted to design and synthesize a novel Mn-Ce based catalyst for selective catalytic reduction of NO_x with NH₃. The confined MnCeO_x catalyst was assembled with a simple one pot method, using a mesoporous zeolite (ZSM-5) as the shell and Mn-Ce oxides as the active core (MnCeO_x@Z5). Owing to the zeolite shell's shielding effect and the synergy between the alumina-silica zeolite shell's acidic properties and the mixed oxide cores’ redox properties, the novel MnCeO_x@Z5 catalyst displayed enhanced water and SO₂ resistance as compared to the MnCeO_x supported on ZSM-5 (MnCeO_x/Z5) and its precursor (MnCeO_x@Al-SiO₂). Evidently, the zeolite sheath hinders sulfate species formation, and this phenomenon was further investigated by in situ diffuse reflectance infrared Fourier transform spectroscopy (In situ DRIFTS). The novel shielding and acid-redox synergy effect/strategy adopted in this work can be applied to design other high performance deNO_x catalysts for air pollution control.