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

Abstract

Nitrogen oxides (NOx) 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 NOx with NH3. The confined MnCeOx 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 (MnCeOx@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 MnCeOx@Z5 catalyst displayed enhanced water and SO2 resistance as compared to the MnCeOx supported on ZSM-5 (MnCeOx/Z5) and its precursor (MnCeOx@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 deNOx catalysts for air pollution control.