Mixed Catalyst SmMn 2 O 5 /Cu-SAPO34 for NH 3 -Selective Catalytic Oxidation.

Low-temperature selective catalytic oxidation (SCO) is crucial for removing the NH 3 slip from the upstream of NH 3 -selective catalytic reduction (NH 3 -SCR). Herein, combining zeolite Cu-SAPO34 and the active oxidant mullite SmMn 2 O 5 , we developed mixed-phase catalysts SmMn 2 O 5 /Cu-SAPO34 by grinding powder mixtures to achieve a low-temperature activity and a reasonable N 2 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 NH 3 oxidation activity showed that for 30 wt % SmMn 2 O 5 /Cu-SAPO34, 90% NH 3 conversion was at a temperature of 215 °C in the presence of 500 ppm NH 3 and 21% O 2 balanced with N 2 . The in situ DRIFTS spectra reveal the internal SCR mechanism (i-SCR), i.e., NH 3 oxidizing to NO x on mullite and NO x 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 NH 3 oxidation via synergistic utilization of the advantages of each individual catalyst.