Mixed Catalyst SmMn2O5/Cu-SAPO34 for NH3-Selective Catalytic Oxidation.

Abstract

Low-temperature selective catalytic oxidation (SCO) is crucial for removing the NH3 slip from the upstream of NH3-selective catalytic reduction (NH3-SCR). Herein, combining zeolite Cu-SAPO34 and the active oxidant mullite SmMn2O5, we developed mixed-phase catalysts SmMn2O5/Cu-SAPO34 by grinding powder mixtures to achieve a low-temperature activity and a reasonable N2 selectivity. The physicochemical properties of the catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The evaluation of NH3 oxidation activity showed that for 30 wt % SmMn2O5/Cu-SAPO34, 90% NH3 conversion was at a temperature of 215 °C in the presence of 500 ppm NH3 and 21% O2 balanced with N2. The in situ DRIFTS spectra reveal the internal SCR mechanism (i-SCR), i.e., NH3 oxidizing to NOx on mullite and NOx subsequently to proceed with SCR reactions, leading to higher conversion and selectivity over the mixed catalysts. This work provides a strategy to design the compound catalyst to achieve low-temperature NH3 oxidation via synergistic utilization of the advantages of each individual catalyst.